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Announcements & News => SHOW US YOURS.... (pics of installed systems) => Topic started by: Outtasight on August 21, 2009, 04:12:58 PM



Title: Cobbled together PV in W.Sussex
Post by: Outtasight on August 21, 2009, 04:12:58 PM
Hiya everyone!

Here's where I'm at today after just over a year of playing with some solar panels in my back garden.

It all started because I got turfed out of my company office and they said I had to work at home (no biggie as I work in IT and just need my laptop and a internet connection to earn my crust).  Besides, I can work in my pyjamas at noon and nobody is none the wiser  whistle

I baulked at providing the electricity to run my work laptop at home and there was a sale on of cheap amorphous panels at Maplins, so I thought, "How hard could it be to run my laptop from solar power?"...

(http://i29.tinypic.com/sncgsg.jpg)

From the top left there's:
1x BP 3160S 160Wp (35.1Vmp)
2x Sharp NE-80 80Wp (17.3Vmp) in a series pair

From the bottom left there's:
6x TopRay 15Wp amorphous (17.5Vmp) grouped in 3 parallel pairs
8x TopRay 12Wp amorphous (17.5Vmp) grouped in 4 parallel pairs

There's more on the garage too...  :D

(http://i25.tinypic.com/2je3b01.jpg)

From the near end there's:
2x Kyocera KC40 40Wp (16.9Vmp) in a pair
2x Sharp ND170E1F 170Wp (23.2Vmp) in a pair
6x TopRay 15Wp amorphous (17.5Vmp) grouped in 3 parallel pairs

The big 170Wp Sharps are on one Morningstar 15A MPPT controller and the rest are on a second identical controller that parallel charge 4x 110Ah 12V leisure batteries (yeah, I know, but they were really cheap) wired for 220Ah at 24V.  The noxious gasses get piped outside by fish tank tube that fits into the common vent holes on these batteries... Lucky, as they bubble noisily like a witches cauldron when it's really sunny  :-X

(http://i42.tinypic.com/ng3a4l.jpg)

(http://i31.tinypic.com/dnde2w.jpg)

I've got some DMMs that read battery charge Amps on embedded shunts (made by just sticking pins into the 10mmsq feed wires at measured distances) and a SmartGauge (see http://www.smartgauge.co.uk/smartgauge.html (http://www.smartgauge.co.uk/smartgauge.html)) to accurately read the bank state of charge in %.  A small variable lab PSU, that has been wired to work from the 24V supply rather than mains, powers an assortment of bits and bobs with any voltage between 3V and 15V (mostly an AA/AAA battery charger and a car phone charger - the DMMs run on rechargeable AAA cells).  These particular DMMs are often on sale at Maplins for just £7 and run for weeks on a charged set of AAAs even when turned on 24x7.

I've got a couple of 12V LED lights in the room with the solar gubbins but the rest of the house runs off a Cotek SK1000 24V 1kW pure sine inverter with a remote control and load / battery monitor in the living room. I also have a home-made wireless remote (fashioned from a cheap wireless doorbell!) upstairs so we can turn the power (and so the lights) on without having to stumble downstairs to the inverter controls.  You can tell if the switch is working because it still goes "bing-bong"  ::)

Another embedded shunt on the inverter provides info about net battery charge / drain with a little mental arithmetic from the other two meters.  The batteries and inverter are all wired up with 35mmsq truck jump-start cable.  It was really hard to solder... had to use a PipeMaster plumbing soldering iron.

Finally, a pair of cheap plug-in kWh meters measure yield and Winter charge from a grid charger to stop the batteries rotting. It's only a 3A 24V electric bike charger that I bought at a car boot sale for £2, but it does the job and I haven't had to use it since February :D.

(http://i44.tinypic.com/qs860k.jpg)

My system is still pure off-grid but with the house lighting circuits switch-able between grid and solar by a change-over socket. The grid socket (right) is just fed from one of the old 6A lighting breakers and the solar socket is plumbed into the inverter via the plug-in kWh yield meter and a RCD breaker.  The two lighting rings are just paralleled in the fuse box and go to the 13A plug to select the power source.  I've not had to run the house lights on grid since February  8)

(http://i38.tinypic.com/216735.jpg)

The rest of my solar appliances run on a completely separate "ring main" that consists of some semi-permanent trailing sockets round my living room, into the kitchen for some low watt appliances and upstairs to the computer room.

Back in June I broke 100kWh offset from the grid and in July I broke 5% lifetime offset as a percentage of all electricity I've used since starting measurements on December 8th. In June/July my weekly offset averages were 9.9% of all electricity consumed (solar plus grid). On a daily basis I might get up to about 15% or 2kWh.

My goal is to be able to run the computer room 24x7 off-grid. I work at home so the internet router, wireless, and mail/firewall/browser/file&print PC is a challenge.

I'm also thinking about converting half my array (the 35V one) to run on a SunnyBoy 1100LV grid tie inverter but I'm not sure what implications that will have for my metering and whether I have to contact the utility company or whatever.  It seems easy enough to install - just plugs into a grid AC socket and I'd just have to swap the DC wires over from my existing battery charge controller but I've got one of those digital (LCD) utility meters and I don't know if it will read right if I export power through it.  Some meters run forwards even when power is going out of the house and that won't do  :(.

For those interested in the gory details of the past year of tinkering to get to this point you can see it at another forum I hang out in.

http://www.mrsharkey.com/forum/vwtp.php?t=542 (http://www.mrsharkey.com/forum/vwtp.php?t=542)

My family are all solar mad...  My in-laws in Japan have "proper" grid tied solar systems.  My sister-in-law has a 3kWp system

(http://i35.tinypic.com/2crknro.jpg)

(http://i37.tinypic.com/27wu6oj.jpg)

(http://i33.tinypic.com/24ovqpz.jpg)

(http://i38.tinypic.com/2wh0chy.jpg)

My father-in-law has a 5kWp system

(http://i36.tinypic.com/a17d5e.jpg)

(http://i34.tinypic.com/2gvu1a9.jpg)

He's also got a air-water heat exchanger called a Sanyo EcoCute ("Cute" being a play on the English word "cute" and the Japanese word for hot water "yu").  It uses a reverse air conditioner to suck heat out of the hot and humid air outside the house and pump it into a big insulated water tank.  It uses electric but much less than if you used a traditional resistive heater.

(http://i34.tinypic.com/2zjmki0.jpg)


Title: Re: Cobbled together PV in W.Sussex
Post by: Justme on August 21, 2009, 09:57:15 PM
Sweet.

Tell me more about how you make a shunt by sticking two pins in a cable?

You must be getting over 5kwh per day with that lot of panels if not more on a good sunny day (remember them?)

Justme


Title: Re: Cobbled together PV in W.Sussex
Post by: wookey on August 21, 2009, 10:43:02 PM
That's a fine array of random pannelage. Do you know how much the whole system as cost so far?


Title: Re: Cobbled together PV in W.Sussex
Post by: EccentricAnomaly on August 22, 2009, 01:00:59 PM
Well, I'm impressed.

Any comments on is the relative performance of amorphous and crystalline panels in bright and diffuse sunshine?


Title: Re: Cobbled together PV in W.Sussex
Post by: Outtasight on August 23, 2009, 03:34:17 AM
As for cost... I was keeping tabs on this but it's kinda evaded me in the last few months.

The amorphous stuff I bought new but at various discounts.  Whenever Maplins were doing a special on the panels I'd buy one or two.  I started with some single 12Wp ones that they were doing for £40-£50 (but I get these discount vouchers they send out so if I spent more than £50 I usually got £3 off one or £7 off two together).  The 15W ones came from 60W kits that they sell but I'd wait until they discounted them to £200 and then use a £15 discount voucher so they cost me £185.  So in all I spent about £1,070 originally.  But some kits came with 4A controllers and some came with 10A controllers.  Some kits came with batteries and LED lamps as well and I sold these on eBay separately and then sold the first four I bought (that had diodes in them so weren't so good for 24V series use) at a car boot sale.  So in the end they maybe cost me about £800.  Not so great for 276Wp of power.

Then I got serious...  facepalm

I bought the new pair of Sharp ND-170's and that cost £1,250 (with the 13m MC3 extension leads) plus about £100 to build the aluminium mounting frame (although I bought too much aluminium so there's stuff left over for other projects).  The Morningstar controllers (that replaced one of the cheapo 10A controllers) cost £186 each (and another £100 for the battery temperature probes and the serial interface to programme them).

The batteries were £296 inc. quick release wiring posts.

The wiring was mostly left-overs in my garage but the truck jump start cable set was £30 from Halfords.  Seemed the cheapest way to get red/black flexible 35mmsq cable in my town as they were 5m long each.  I'm still using the off cuts on the spare 1kW inverter as those bits are about 2m long and still have the massive crock clips on them.

The pure sine inverter was £540 (inc. the remote panel) but I ended up buying two as the first was 12V and then a few months later (when I'd got too much PV for the Morningstars to handle at 12V), I decided to up the ante and go 24V.  I've still got the 12V inverter set and was playing with it this week to see if I could run my fridge-freezer from it to up the utilisation of the PV array (which often tops off the batteries by lunchtime and then lots of power just gets wasted).  Here's my hairbrain idea for running the fridge-freezer from an auxiliary inverter (because the inrush surge is too big for a 1kW inverter to handle on it's own when also running about 200W of continuous load):

(http://i31.tinypic.com/2mnmxog.jpg)

The SmartGauge was another £150.

Then I ran out of space in the garden for amouphous panels (they take up lots of space for quite low power outputs) and started buying used good quality panels from eBay.  I decided to do this on the results of the first 8-9 months of using cheap Chinese panels... don't do it.  Amorphous as a technology is ok if you've got lots of space and you buy good ones.  The thing with amorphous panels is that they have to be rated after "running in".  In the first few months of exposure to light they degrade in output but stabilise at a value and then they degrade at the same rate as traditional poly/mono cells.  An unscrupulous manufacturer ( whistle ) might quote the panels as 12Wp or 15Wp but this is on the day you buy them and then after a few months in the sun, gradually they degrade to their stabilised value which seems to be 65-70% of name-plate in this case (hence why in the diagram I only rate the 35V array at 600Wp).

The Sharp ND-170's quite happily outperform the amorphous panels in all light conditions, even though they are traditional poly panels.  They have more cells so their norminal Vmp is 23.2V with a Voc of over 29V so in series they kick out 46.2Vmp into the MPPT controller (this is a must or else you'll waste lots of power) and I often see them putting out 340-365W into the battery.  That's between 100% and 107% of name plate even after losses through the wiring and MPPT controller.

Good panels (BP, Sharp, Kyocera) are more expensive for a reason.  They put out their name plate power and they are built to last 25 years.  I bought one used unbranded (read cheap Chinese) 40W mono panel from someone on eBay but it's a very low voltage one (Voc ~19.5V) and I've never seen it put out more than 32W.  Luckily it was only £65 and it does lonely duty topping up some of my spare batteries but nothing else.  It has the typical paper thin aluminium frame and waterproofing that looks like it was done by a bathroom fitter with a hangover.

The Sharp panels don't use any silicone bath goo to keep the water out (because even in a bathroom it rots within 5-10 years) and they use frames made of sturdy stuff (with anti-torsion beams and such to aid rigidity).  But watch out kids, there are some fakes out there claiming to be used "quality" panels because they know that used quality brand panels fetch the same prices as new cheap Chinese ones and are much sought after by the likes of me...

Fakes can perform poorly and even catch fire under partial shade (one I saw had tiny 3A bypass diodes fitted to what claimed to be a 175Wp panel with a 5A nominal output).

At the moment the going rate for used quality panels is about £100 per 40W (so I paid £200 for my pair of Kyoceras and £375 for my BP 160W panel and £455 for my pair of Sharp 80W panels - ok I got carried away on the bidding on the last one  ::) ).  The Kyoceras are the oldest ones I have, being about 4 years old so plenty of life left in them yet.

My father-in-law has Sanyo HIT hybrid mono/amorphous panels on his roof and they probably are better than regular mono panels.  My sister-in-law has regular Sharp poly panels.

The amorphous panels I have do put out a lot of voltage in low light (but not much current).  The Sharp ND-170s easily match them in low light as they have such a high nominal voltage that they also work in overcast conditions.  In full sun, the whole array can put about 28A into the battery bank (actually the 35V array has overloaded the Morningstar controller it's on and on clear days it sits pegged at 14.9A as the controller has current limiting protection). In overcast (but not threatening to rain darkness) the whole array can muster about 3-5A.  The 35V array wins at the moment because it has (in theory) 676Wp installed but in reality under cloudy conditions, the Sharp ND-170 pair aren't far behind (I might see 2A from the Sharps when the 35V array is doing 3-4A).

As for the "embedded shunts"... it's very easy.  I just cut off the test probes from the cheap DMM leads and soldered them to brass drawing pins.  Then I pushed one into the cable (these are 10mmsq or 35mmsq so the pin can go right in and not come out the other side).  Then I pass a known current through the cable (with another DMM Ammeter in series) and just poke the other drawing pin into the cable a bit further down until the mV reading on the new "Ammeter" is equal to the known current.  You might have to have a couple of goes to find the right length from the first pin but the holes are small and you'll cover them up with electrical tape soon anyway.  The DMMs all can read DC Volts down to 0.1mV on their 200mV range. It's not hugely accurate as I just calibrate the new meter to read 1mV per Ampere (giving a resolution of 0.1A). On the fat 35mmsq wire, I calibrated for 0.1mV per Ampere (giving a resolution of 1A for the inverter that can run at 46A at full tilt so I don't care about anything less than 1A accuracy).  The latter meter reads with the decimal point in the wrong place (0.1 = 1A and 1.0 = 10A) but that's not a problem.

Why didn't I just calibrate the 35mmsq cable the same as the 10mmsq cable and have it read 0.1A to 200A (as the DMM can read to 200mV)?  Simple... the voltage drop on a 35mmsq cable is very low and the pins are about 20cm apart to read 0.1mV/A so to get 1mV/A I'd need the pins 200cm apart and the inverter wires are only 90cm long!

This method has two advantages... it's cheap.  And it means I don't have to cut the wire and insert a commercial shunt that would mean contact resistances and more joins.  I usually solder the probe wires on to the pin when it's sticking in the fat wire as this melts the plastic insulation around the pin and so makes an air tight seal.  Then I just use electrical insulation tape to cover up the heads of the pins (you can see the inverter shunt on my battery pic as two bits of black insulation tape on the positive cable going to the inverter with grey wires going off to the DMM on the wall above.  The wires to the DMM can be tiny as they carry next to no current (just measuring Volts). It's ok to do this kind of embedded metering at 24V but don't try it on a 600V DC feed or the mains output of the inverter or else bad things are gonna happen. 
sh*tfan:





Title: Re: Cobbled together PV in W.Sussex
Post by: kristen on August 23, 2009, 07:39:27 AM
"I can work in my pyjamas at noon and nobody is none the wiser"

I work from home too, but it never occurred to me to dress for work!

Great account, and thanks for posting.  Have an Applaud!

Do the panels on the garage roof shade the ones behind them (particularly in December)?

"I baulked at providing the electricity to run my work laptop at home and there was a sale on of cheap amorphous panels at Maplins, so ..."

So the panels cost you less than the electricity would have?  ;D

Now then ... I am self employed. I wonder if my company could buy panels for the house instead of paying for the electricity. (I know the answer to that, its based on area-of-house-used-as-office, but that's no use to me). I'll have a word with my accountant about the disproportionate amount of use the PCs and Servers use, whereas for Light and Heat I'm stuffed by the area-used-as-office proportion.


Title: Re: Cobbled together PV in W.Sussex
Post by: sjaglin on August 23, 2009, 08:55:33 AM
Hi,

Really detailed and exciting post! I found the Japanese houses very nice too, it seems that PV is quite developed there then?

Do you keep a tracker of your production?

Stef


Title: Re: Cobbled together PV in W.Sussex
Post by: stephend on August 23, 2009, 10:07:33 AM
Really detailed and exciting post! I found the Japanese houses very nice too, it seems that PV is quite developed there then?

Second only to Germany for installed PV: http://en.wikipedia.org/wiki/Photovoltaics#Worldwide_installed_totals


Title: Re: Cobbled together PV in W.Sussex
Post by: Justme on August 23, 2009, 10:38:39 AM

 I'll have a word with my accountant about the disproportionate amount of use the PCs and Servers use, whereas for Light and Heat I'm stuffed by the area-used-as-office proportion.


You need a better accountant. Whilst there are accepted "norms" for what you can claim, in fact you can claim what you like as long as when / if you get an inspection you can justify / convince the inspector your right. With your heating for instance, If you was at work the heating would not be on at all. As you are at home you need the heating on, If you dont have any zone controls its all on. Thats all business use (just the same as they dont make you claim 1/5 the mileage on a car cos the other 4 seats are empty & so not in business use) . Same with lights & elec. When we had a VAT inspection as long as I could justify what I had claimed for they were fine. Our fuel costs % of biss to personal use were much much higher (like 80+% biss) than normal for the industry I was in. But as I could show them how far & how often I went places it was fine.

Justme


Title: Re: Cobbled together PV in W.Sussex
Post by: dhaslam on August 23, 2009, 11:38:32 AM
If the solar panels are only used to power office equipment then they would qualify as being "wholly and exclusively" for business use.   In the longer term PV will be less expensive so the house portion would be less expensive if done later.     PV gets very interesting at  one euro, or less,  per watt  and this sort of price may be commonplace within five years. 


Title: Re: Cobbled together PV in W.Sussex
Post by: EccentricAnomaly on August 23, 2009, 06:46:55 PM
Thanks for the remarks on amorphous vs crystalline.  Having now read your Mr Sharkey thread I see you touched on the matter there but didn't really make a specific comparison.  Pity the whole matter is confused by the overrating of the cheap amorphous panels but it's also interesting what you say about using them at high voltages.  I think amorphous are traditionally used at higher voltages so maybe that's part of the reason people think they work better at low light levels.

Does anybody know of a source of reputable/properly rated amorphous panels?

My thinking is that crystalline is probably better for any sort of retrofit because of their smaller area/watt but on a new build where you can design for suitable space on and around the building the lower cost per watt and supposed somewhat better low-light performance of amorphous is attractive.

It's interesting that you use a number of charge controllers.  I worry about that from a number of points of view: that the charge controllers will trip over each other in controlling the charging process and also that they tend to throttle back the output of the PV array when the batteries are charged rather than putting the power to better use.  Does anybody know of an MPPT which isn't a charge controller: that is, one which just throws as much power at the battery as it can for whatever the battery voltage is at that moment?  I imagine that chargers like the Morningstars can be programmed to do that just by setting the various cut-off voltages high but it seems a pity to pay for and have potential unreliability from functionality which is not being used.


Title: Re: Cobbled together PV in W.Sussex
Post by: stephend on August 23, 2009, 07:03:38 PM
Does anybody know of a source of reputable/properly rated amorphous panels?

All of the below have the required IEC61646 certification.  Some are guaranteed to 80% at 25 years, others 20 years.
  • Kaneka k60 or GEA60 about 2 euro/watt (they also have a new hybrid panel which looks very interesting but could be pricey)
  • Sulfurcell www.sulfurcell.de
  • QS Solar 1.67 euro/watt, although there were recent announcements that they've dropped further
  • solartechnics www.solartechnics.de 1.4 euro/watt just a few months ago, these seem to be rebranded QS Solar panels
  • Inventux: www.inventux.com don't know much about these.

Reasonably priced suppliers:
  • www.b5-solar.de
  • www.nature-solar.de
  • www.ibc-solar.com
  • Solartechnics sell direct


Title: Re: Cobbled together PV in W.Sussex
Post by: Justme on August 23, 2009, 08:41:41 PM

It's interesting that you use a number of charge controllers.  I worry about that from a number of points of view: that the charge controllers will trip over each other in controlling the charging process and also that they tend to throttle back the output of the PV array when the batteries are charged rather than putting the power to better use.  Does anybody know of an MPPT which isn't a charge controller: that is, one which just throws as much power at the battery as it can for whatever the battery voltage is at that moment?  I imagine that chargers like the Morningstars can be programmed to do that just by setting the various cut-off voltages high but it seems a pity to pay for and have potential unreliability from functionality which is not being used.

Each controller will work on its own relative to the settings it using. You need sep controllers where the Vmp's dont match very well.

All chargers throttle back as the battery fills. Its that or over charge the bats. The thing to do is have a system that monitors the charging & when that stage is met to turn loads on to use the excess power. You can do this with a FM80 Outback controller or an controller with a suitable system. You could even set the inverter to do it with a Victron unit (virtual switch). I think its been mentioned in here about using every electron if not try the Outback forum.

Oh & its the battery that controls how much charge is accepted not the controller. Power is drawn not pushed.


Title: Re: Cobbled together PV in W.Sussex
Post by: kristen on August 23, 2009, 09:13:45 PM
"You need a better accountant. Whilst there are accepted "norms" for what you can claim, in fact you can claim what you like as long as when / if you get an inspection you can justify / convince the inspector your right. With your heating for instance, If you was at work the heating would not be on at all. As you are at home you need the heating on, If you dont have any zone controls its all on. Thats all business use (just the same as they dont make you claim 1/5 the mileage on a car cos the other 4 seats are empty & so not in business use) . Same with lights & elec. When we had a VAT inspection as long as I could justify what I had claimed for they were fine. Our fuel costs % of biss to personal use were much much higher (like 80+% biss) than normal for the industry I was in. But as I could show them how far & how often I went places it was fine."

My Accountant has agreed with the revenue a number of things that surprise me, but are justified on the basis that "You need to have that resource available to be able to do such-and-such when you need to, so although you only use 10% its OK to claim 50% [say]", so I reckon he is on the right tack generally. There are issues about capital gains on the property, which will be based on the proportion of office-as-business claimed, which I am keen not to over-egg.

However, I have not had a specific discussion with him about how the fact that Electricity use is disproportionate [between home and office] and how that might impact payment for Wind/PV installation, and I'll be interested to see what he can agree with HMR&C


Title: Re: Cobbled together PV in W.Sussex
Post by: Justme on August 23, 2009, 10:02:41 PM
Yes the CGT is a big issue now for home workers.


Title: Re: Cobbled together PV in W.Sussex
Post by: EccentricAnomaly on August 23, 2009, 11:00:36 PM
All of the below have the required IEC61646 certification.  ....

Excellent.  Thanks for passing on your research.

Each controller will work on its own relative to the settings it using. You need sep controllers where the Vmp's dont match very well.

Yes.  It's also useful to have separate chargers from the point of view of redundancy and also for mixed technology like solar/wind/hydro.  I don't know but I also suspect that a number of small chargers will be cheaper than one big one.

Quote
All chargers throttle back as the battery fills. Its that or over charge the bats.

Not necessarily, as you say in the next sentence:

Quote
The thing to do is have a system that monitors the charging & when that stage is met to turn loads on to use the excess power. You can do this with a FM80 Outback controller or an controller with a suitable system.

That's really my point; the "suitable system" turning on loads can usefully be separate from the power source (ie., the MPPT voltage/current converter) particularly if it knows how to make good use of the energy around the house and is part of the house's general control system anyway dealing with matters like not starting the freezer while the microwave is running or turning off the car charger while the freezer does start.

Quote
Oh & its the battery that controls how much charge is accepted not the controller. Power is drawn not pushed.

I suspect that's, at best, a confusing way of looking at it.


Title: Re: Cobbled together PV in W.Sussex
Post by: Justme on August 23, 2009, 11:15:43 PM

I suspect that's, at best, a confusing way of looking at it.

Ok look at it this way.

If it was the charger controlling it doubling the charger amps would half the charge time (and we all know it does not) PLUS a 100 amp charger would actually do 100amps for the full cycle & not tail off as the battery fills. Even simple car type non stage chargers do this.
 

My comments re chargers throttling back still stands. Even stupid chargers will up the power if a load is added cos the battery DOES NOT supply any loads whilst charging till the total available power from the charge source is used up first. Thats why with solar you want all your static loads on during your peak production. You save on charging losses.

Yes you could get a bunch of small chargers for the price of one good one (mine was over £500). But you also get less features & settings so like most things you pays your money & make your choices. For me the smaller ones could not do the high volts (over 100vdc) I wanted & would not be upgradeable to a much larger system when I go to 48v.


Title: Re: Cobbled together PV in W.Sussex
Post by: Outtasight on August 24, 2009, 02:39:43 AM
Thanks guys!

Here's my generating tally.  The first one shows total energy use.

(http://i30.tinypic.com/33dldz7.jpg)

This one focuses in on solar as a proportion of total electric use.

(http://i26.tinypic.com/213eueq.jpg)

This last one shows actual solar generation on its own plus the lifetime offset from the grid.

(http://i27.tinypic.com/28je8if.jpg)

The really big 4kWh spike a couple of days ago was me running the fridge-freezer for 24 hours on battery / solar only.  Drained the bank to about 80% DoD so won't be doing that often...

In my case, the system evolved and grew out of a simple 4A on-off controller to a 10A on-off controller and then one 15A Morningstar at 12V and then another Morningstar at 12V and then both converted to 24V to allow more PV power to be used as they are limited to 15A at 12V or 24V.  And yes, the main reason now for two controllers is both capacity and mis-matched arrays with very different Vmp ratings that could not be optimised on a single controller.

The MPPT-15 can do load diversion to the load terminals but only up to 15A current limited and has to be programmed by the serial port to do this non-standard behaviour. 

I'm waiting to see what the new Morningstar Tristar MPPT is like.  This will do 60A at 48V and can take arrays of up to 150Voc.  But I'd rather keep the DC side at under 60V as it makes DC wiring less problematic (cheaper) and I tried running the amorphous array in triplets for a max Voc of 75V (capped to about 68V with some bodging to protect the controllers that only go up to 75Voc).  It didn't really work out so I went back to 35V.

Various bits of the arrays get shaded by the roof eves, trees, and even the overhead wire to the garage at times of the day and I found overall yield was better at 35V because when you have a triplet part shaded it effectively takes the whole triplet out of the array.  If you have one of a pair part shaded then you only lose a pair in the array.  My amorphous panels are quite shading resistant as the cells are long strips that run the length of the panel so a spot shadow (like a leaf) doesn't shade a whole cell (like it does on the traditional panels).

Apart from buying a more capacious charge controller (or a SunnyBoy 1100LV) I might redeploy the excess amorphous panels so that some are partly oriented for early morning light and others are oriented for late afternoon light.  That way, I can create a passive tracked system.  I can't use the peak output of all the panels but I can extend the generating day...  The big Sharp panels probably will obscure the direct winter sun on the little Kyocera panels but I only installed them this summer so it hasn't been a problem yet.  The frames that they are on point them almost straight up anyway so they mostly work off of either direct overhead summer sun or diffused light from clouds.  This gives me some variability in collection as the big Sharps point at the the February solar altitude for maximum output on rare clear days but the others are all at a lower angle for either summer sun or diffused light collection.  Playing with a few panels in different weather it soon became clear that on a cloudy day the best power is from the panel facing the bulk of the sky rather than the invisible sun.  The wall mounted ones can be adjusted as they are mounted using brass hinges so by changing the stays (screwing the stay hinges to different positions on the wooden stay) I can change the panel angles.  But I liked the idea of the big BP one being a sort of roof for my patio door.

I don't expect any real output between November and January as the sky is mostly very dark and the direct sunlight at 15 degrees elevation in mid December is so weak as to be mostly useless (over 65% atmospheric absorption).  The graphs are a little mis-leading though as during the time from December to July, progressively more and more PV came on-line.  So this winter will be marginally better than last.

I'm not really that bothered about return on investment... I'm just doing this for fun.  In my view it actually has cost me nothing because I don't have to drive 50 miles a day to my old office.  That saved me about £200 a month in petrol so all I did was invest my petro-dollars in renewables rather than blow it on booze and holidays  :angel:

I manually load optimise at the moment... I let the bank charge on priority in the morning and when one or more of the chargers starts blinking that it's in absorption mode, I go and switch the computer room over from grid to solar power by swapping the input plug on the UPS.  I toyed with doing this automatically (I might still try) as the Morningstars do have a data logging and realtime output that the PC could read and with a bit of Visual Basic and a USB relay driver from Maplins I could get the PC to manage its own load by selecting the UPS input.  As Sharkey pointed out to me though, you need to be careful switching the AC to big inductive loads (the UPS is line interactive and has a big transformer) as a mis-matched phase on a change-over relay will cause a kick-back that can blow up stuff.  You need to let the transformer rest for a second (to let its magnetic field decay) before connecting the mis-matched phase.

If you use two relays programmed with a delay you then also need to consider relay failure modes (welded contacts) that could allow both AC sources to meet and BANG!..

The new Tristar is especially interesting as it will have a direct Ethernet interface (rather than serial) so with a wi-fi transmitter, I can have the PC talk to it without running any more wires around the house.  Wi-fi transmitters usually run off of 12V DC so it's easy to power them from the solar system directly.

I'm toying with the idea of using a 3kVA site tool transformer to step the 230VAC to 110VAC and feed that by a change-over socket to the immersion heater upstairs.  Again, it's because I've only got a 1kW inverter.  The immersion heater is a regular 3kW type so it's too big as a load for my system but if you run it at 110V it only consumes about 600W so would make a good diversion load on sunny days.  That would pre-heat the water before the main heating cycle at night, saving some of the 5kWh grid power it takes to heat 100L of water.
There's plenty more toys in the box...  bike:

The Japanese have been going solar for decades.  My wife's nan's house has the bones of a solar water heater on the roof and I've even seen a monks house at a temple with one on it.  PV is taking off now as well but you see loads of water systems all over the place when you travel by train.  I even saw a PV bus shelter that powers a hotel hot spa complex and astro observatory.

(http://i35.tinypic.com/20gl7ar.jpg)

(http://i36.tinypic.com/5x3hut.jpg)



Title: Re: Cobbled together PV in W.Sussex
Post by: kristen on August 24, 2009, 08:03:37 AM
Yes the CGT is a big issue now for home workers.
I'll tell Gordon & Darling that they are welcome to the CGT on a couple of sq.feet that the 6MW turbine's mast will sit on!!


Title: Re: Cobbled together PV in W.Sussex
Post by: kristen on August 24, 2009, 08:13:26 AM
"In my view it actually has cost me nothing because I don't have to drive 50 miles a day to my old office.  That saved me about £200 a month in petrol so all I did was invest my petro-dollars in renewables rather than blow it on booze and holidays"

Excellent concept.  Maybe employers could with some sort of pound-for-pound encouragement of green home improvements for home-workers, based on their petrol savings.

"you see loads of water systems all over the place when you travel by train."

When I lived in Japan (70's) the house had a solar thingie on the roof.  Filled with water in the morning, drained down into the "tub" in the evening, and then a fire lit under it for the bath.  So any gain from solar contributed.  Given that starting point getting the populous to move on to more sophisticated Solar can't have been all that hard :)


Title: Re: Cobbled together PV in W.Sussex
Post by: StBarnabas on August 24, 2009, 08:26:02 AM
Really nice thread must read it in more detail soon. Apologies for being busy recently.....


Title: Re: Cobbled together PV in W.Sussex
Post by: fizzy on August 24, 2009, 09:05:58 AM
All looks good but whats the crime like around your way? They are starting to get nicked all over the place and yours look 'liftable'. Sorry to be a downer but 20 years in steel and scrap metal have left me rather less than sanguine about crime prevention issues.


Title: Re: Cobbled together PV in W.Sussex
Post by: Justme on August 24, 2009, 09:23:23 AM

I'll tell Gordon & Darling that they are welcome to the CGT on a couple of sq.feet that the 6MW turbine's mast will sit on!!

It might be more than you think  :P

Garden would be less tha £1 per sq.ft & prime developement land poss £1000's.


Title: Re: Cobbled together PV in W.Sussex
Post by: kristen on August 24, 2009, 09:26:21 AM
I'll be thrilled if its £1,000 per sq.ft - there are several acres of it, and I'll swap Gordon a sq.foot for the business giving me free leccy until they carry me out of here in a box!


Title: Re: Cobbled together PV in W.Sussex
Post by: Outtasight on August 24, 2009, 12:00:11 PM
All looks good but whats the crime like around your way? They are starting to get nicked all over the place and yours look 'liftable'. Sorry to be a downer but 20 years in steel and scrap metal have left me rather less than sanguine about crime prevention issues.

Yeah I worry about that too.  We've had a few cases of people lifting lead from school roofs and so on round here too.  As solar gets more popular it's bound to become more of a target for the crimmos. At least my "patio roof" ones are quite high up (needs a proper roof ladder to get access to the wall bolts).  I'm gonna start checking into what insurance cover you can get for them.

You can't let fear of crime stop you though (unless it's really bad in your area!).  It's no different to having tools in your garage/shed or nice garden furniture.

Ideally, I'll put the big ones up on the house roof where they'd get less shading from trees but it was a stretch to get them on the garage roof (took four of us as I'd pre-assembled the whole thing on the ground).  I've got an IP CCTV camera on the garage area that records to the comms PC upstairs (to keep an eye out for the kids that drink / smoke and light camp fires on my drive) so hopefully that will help.  As I work at home and my wife is always at home (life of luxury  ::) ) they'd have to steal the things from practically under our noses.

I think I'll Dremmel my name and post code into the frames...

Right now I'm more worried about the big pair flying off the roof by itself.  It weighs 32kg and maybe another 15kg for the frame and then is weighed down with bricks and is tethered by a steel cable to a roof joist girder but I'm gonna tether it to a second joist at the front to make sure... The first of the autumn storms is coming this week (if you believe the Met office).  I might even get round to grounding the frames in case they get struck by lightning  whistle



Title: Re: Cobbled together PV in W.Sussex
Post by: Outtasight on August 24, 2009, 12:23:06 PM
Bummer... insurance companies are making new exclusions for turbines and solar panels... theft, damage from high winds / hail.  Why do we even bother paying these criminals their policy fees? 

http://www.allianz.co.uk/retailebroker/assets/pdfs/new/may09/ACPER1202-6%20Home%20Comforts%20Customer%20Newsletter%20May%2009.pdf (http://www.allianz.co.uk/retailebroker/assets/pdfs/new/may09/ACPER1202-6%20Home%20Comforts%20Customer%20Newsletter%20May%2009.pdf)


Title: Re: Cobbled together PV in W.Sussex
Post by: Ivan on September 01, 2009, 10:38:10 PM
Kristen, The taxman can't stop your company investing in some backup power (especially if it's imperative that your servers stay online all the time)....and he should be congratulating you on spending over the odds on a renewable form of power. He doesn't need to know that a grid-tie inverter stops producing power when the grid fails. The only downside is that any revenue generated would be taxable and belong to the business, although it could be handed over to you in lieu of the power consumed by your servers (again, taxman won't know how much they do consume).

Outasight:  Insurance - stop paying the premiums, and put the money into a savings account and use that to pay yourself in the event of a claim. These days, insurance companies consider 100% of your premium to be their profit. If you make a claim, they will surcharge your insurance in future years to reclaim that money, and as they all operate in a cartel these days, you can't go somewhere else and get a cheaper deal (you have to declare any previous claims). It's immoral and uneconomical


Title: Re: Cobbled together PV in W.Sussex
Post by: Brandon on September 01, 2009, 11:07:03 PM
I couldn't agree more Ivan, have a pat on the back!


Title: Re: Cobbled together PV in W.Sussex
Post by: Outtasight on September 13, 2009, 09:59:55 PM
Still pondering the next stage of my solar system...

Installing a grid tie inverter seems pretty easy but there's all the red tape that seems pretty troublesome.  I got a quote for the SunnyBoy 1100LV or rather a quote for a modified WindyBoy 1100LV...

Talked to some suppliers (including a certain Navitron bunch  ;) ) but all said "Nope, the SunnyBoy 1100LV is discontinued".  Then I tried the UK distributor for SMA and they said actually the WindyBoy 1100LV is identical to the SunnyBoy except that it says Windy on the front and has even the same firmware but it runs in turbine mode instead of PV MPPT mode!  The daft part is that the setting isn't user programmable (but for £50 they can oblige...)

Now the price of this 1kW grid tie inverter is about the same as a 3kW pure sine off-grid inverter and if I persisted with off-grid, it would mean I could run the fridge-freezer and a washing machine and a regular kettle off of solar power... but I'd need LOTS more battery capacity.  And batteries are expensive.

I've seen an eBay ad for some very cheap industrial 2V 1600Ah cells (like £65 each) but I'd need 12 of them - about 2 pallets worth!!!  Oh and they weigh 100kg each, so that's 1200kg of batteries.... in a three bed-semi living room........ Not even I'm that stoopid.  wackoold

They can go in the old coal-shed.  We just keep junk and stuff in there and it was originally designed as a facility for storing household energy  whistle


Title: Re: Cobbled together PV in W.Sussex
Post by: AndyB on September 14, 2009, 07:49:58 AM
Hi Outtasight, great to read you post and to see the pics. I'm like you my system is always in pieces and is being rebuilt. In some ways its better in doesn't run 100% as then there is no challenge.

As another take on this, we all must have very understanding partners with all these wires and bits around our houses. My wife went away for the weekend and the first thing she said to me when she walked through the door was " not another ******wire" I had promised the data wire that ran through the house to my laptop for the last 5 months would be removed but alas i added another..........

Maybe an applaud should go to our long suffering partners

Andy


Title: Re: Cobbled together PV in W.Sussex
Post by: Outtasight on September 28, 2009, 02:27:32 PM
Having seen Davebodgers excellent tracker assembly, I felt compelled to make more use of my spare 35W panel that I use for topping up the spare battery in the garage...

Behold my twin axis tracker!  To the untrained eye it might just look like a plastic garden table with a panel propped up precariously on a wicker basket and mandraulically turned round as the day progresses but I assure you that at least 10 minutes of effort went into it's design and it keeps the output at a nearly steady 1.8A for a good part of the day.

(http://i34.tinypic.com/f1ccio.jpg)

The elevation angle of the panel is changed by turning it from the long edge to the short edge rather than by selecting a different sized basket, in case you're wondering.

 bike:


Title: Re: Cobbled together PV in W.Sussex
Post by: talisman on September 28, 2009, 03:40:19 PM
Hmmm

Got me thinking, why not

Mount the panel on a very large battery clock face.

Panel charges battery, which turns the clock, which gets panel to face sun, which charges the battery, which turns ...

I think I have too much time on my hands  :laugh:


Title: Re: Cobbled together PV in W.Sussex
Post by: Outtasight on September 29, 2009, 04:13:12 PM
I've been pondering what to do with the excess power that my solar arrays make on very sunny days.  It gets to about lunchtime and the battery bank is about 75% full and so the charge controllers start to throttle back to their absorption power levels.  Good for the batteries but a waste of lots of solar power that can't be shoe-horned into them any faster.

Up until now I've gone upstairs and switched the computer room over to solar power.  But on a good day there's still power left over.  So I wired another extension to my wife's study and she then runs her laptop and desk lamps for craft work on solar power... but there's still power left over (who'd have thought you could have too much solar power 8)  )

So, I started looking at the big loads that I'd discounted in the past as "difficult" to run on solar power.

First up was the fridge freezer.  Uses about 1.5kWh per day and presents a fairly manageable load when running - about 125W.  Better than that, it only comes on for about half the time and consumes about 5W when idle, so it's really a 60W load when averaged out over a long time. 

The reason why it's a "difficult" load is that you have to watch it like a hawk because if the power fails (dead battery) all your food will defrost.  Also, fridge compressors take HUGE amounts of start-up power (maybe 10x the running power) so despite being a 125W nominal load, you need at least a 1kW inverter to get the thing going.

My main solar system has a 24V bank of batteries and the 1kW pure sine inverter that feeds my work laptop, the house lights, etc.

With the usual suspects turned on, the main system inverter sits around about 200W output constant load. I once tried running the fridge-freezer on it with nothing else plugged in and it just about worked. It overloaded for about half a second (more than 1150W on the power display) and it beeped. But after that it sat at at the bottom of the scale. I gave up on it because the inrush current meant that I couldn't risk running anything else at the same time.

Then, one especially sunny day, I decided to see if I could run the fridge-freezer and the other loads at the same time.

I had a few spare bits kicking around: A really old 100Ah battery (that just refuses to die even though I often neglect it in the garage for months), the spare 1kW pure sine inverter (left over from when my main system was 12V) and the 30A variable lab PSU that I use for charging batteries, starting small cars, blowing stuff up  whistle

Here's what I did:
(http://i31.tinypic.com/2mnmxog.jpg)

The fridge-freezer only needs 125W when running, so the main solar inverter can deliver this with the other constant loads it has to supply. The fridge-freezer only needs the 1-2kW surge for a fraction of a second and the 1kW inverter can deliver a 2kW surge. So I used the spare inverter and battery as a buffer. The 12V battery is only there to act as a big capacitor. In fact, I considered trying one of those 1 Farad car hi-fi capacitors instead of the battery (but I happened to have a battery kicking around).

Once the fridge-freezer is running, the 30A PSU runs the load from the house solar mains (drawing about 9-11A @ 13.8V, so it can recharge the 12V battery at the same time). I'm using an old deep cycle battery but a car battery would do fine as it only has to deliver a "starting" current before going back to bed... floating to 13.8V after a couple of minutes recovering from the "start".

(http://i36.tinypic.com/s486ed.jpg)

Obviously, the wife wasn't too happy about a big boat battery next to the fridge in the kitchen but it was just an experiment for a day.  whistle

One thing I discovered was that if the inverter can't muster the power for the surge then the compressor can fail to start and I did have this happen once (while doing the dishes in the evening).  The charger was sitting at 15A and the fridge was doing nothing.  The compressor had stalled on start-up, drawing 180W while not moving (hope nothing was damaged). I cycled the power and the fridge started up as normal after a couple of minutes.

It almost made it though the night on its dedicated battery (quite a feat for the 12 year old & often neglected battery).  After sun-down, it ran on the house bank via the charger and then at about midnight I turned off the house inverter (with the bank depleted to 60% DoD).

At about 4am, I woke up and had a look at it... still working. The compressor was running.  About 6am I woke again and this time the battery had died with the inverter locked out on a low voltage alarm.  I fired up the house inverter and the charger sat pegged at 30A for about 30 minutes (with the compressor running) but I had to stop it as the house bank was now drained down to 80% DoD.  The fridge carried on with its own battery and I let the sun start to charge the house bank.

So I managed to run the fridge off-grid for a whole 24 hours but the inefficient conversions meant I killed all the batteries.

Next time on this thread... The water heater.


Title: Re: Cobbled together PV in W.Sussex
Post by: desperate on September 29, 2009, 10:42:53 PM
Ya should have known, feng-shuae calls for big boat batterie, nex to oven , no wonder she wasn't happy facepalm

Desperate


Title: Re: Cobbled together PV in W.Sussex
Post by: Outtasight on September 30, 2009, 12:42:55 PM
Yay! Shopping days are here again! (to the tune of "Happy Days Are Here Again").

Just picked up another 2x Sharp 80W panels on eBay last night!  Last minute outbid fight but I secured two of the three panels on offer.  It's quite a ways to go and get them... Bradford!  Still, I paid under the odds for them at £340 for the pair.  The last two I bought cost me £460.

As a rule, I try not to spend more than £100 per 40Wp.

Just means I might have to put on hold my plan to buy a new 3kW off grid inverter. I've given up on the idea grid tie for now - seems like too much red tape to deal with and my array is made up of too much random panelage to create a high voltage string (being all geared to 24V battery charging).

I'll probably sell off some of my cheap Chinese plastic framed amorphous panels.  I sold four at a car boot a few weeks ago.  Alternatively, they might find use as part of my idea for passive tracking (i.e. bolt them flat on the wall at the East side of the house where they'd get hit for an hour or so at sunrise).


Title: Re: Cobbled together PV in W.Sussex
Post by: StBarnabas on September 30, 2009, 09:28:29 PM
Hi Outta
it is so much more doing it yourself. Grid tie is not so bad really. Don't let my saga put you off! 


Title: Re: Cobbled together PV in W.Sussex
Post by: Outtasight on September 30, 2009, 11:24:47 PM
There was some scaremongering in the news the other day about there being generating shortfalls in the next few years so more blackouts and so on.  If that comes to pass then having some off-grid backup would at least keep the lights, radiators and TV on even if the grid goes on the blink.

I can use gas to heat the water and the house but you still need some electric to run the circulating pump and the boiler electronics.


Title: Re: Cobbled together PV in W.Sussex
Post by: StBarnabas on September 30, 2009, 11:33:51 PM
Outta
yes the big downside of grid tie is if the mains power goes off, under G83/1 the grid tie inverter has to shut down within about a second. You are right stand alone had its advantages!


Title: Re: Cobbled together PV in W.Sussex
Post by: davebodger on October 03, 2009, 12:10:54 AM
Outta
yes the big downside of grid tie is if the mains power goes off, under G83/1 the grid tie inverter has to shut down within about a second. You are right stand alone had its advantages!

Hmmm, there are ways around this.....
My Soladin was quite happy feeding into the output of my 1400VA UPS whilst the UPS was running my computer (and not plugged into the mains).
The PV could help keep things running longer during a daytime blackout, but not much use at night.
And if the load is less than you are generating then fuses blow.  :(
Batteries do have their uses.  :)


Title: Re: Cobbled together PV in W.Sussex
Post by: Outtasight on October 03, 2009, 01:12:11 AM
Difficult Loads Part II - The Water Heater

So next there's the water heater problem...  Uses about 4kWh per day heating up a tank of water from 22'C to 60'C for our bath.

The solar system makes lots of spare power in the afternoons but I've only got a 1kW inverter and besides, the array only makes about 1kW with all other loads off... remember we want to just find a use for excess power.

Some charge controllers use dump loads for diversion regulation but that would require a separate tank to the normal one upstairs and a special 24V heater element.  The standard immersion heater element in the tank is 230V 3kW.

It would seem there's no easy way of getting the spare power into that water tank.

One way to solve the problem is to throttle the power to the 3kW heater - effectively using a "dimmer" on it like a light bulb.  Only you can't get 3kW dimmers.  So I thought about the supply side.  If I were to reduce the voltage to the heater to 115V, it would reduce the power drawn by the heater.  The heater has a cold resistance of about 20 Ohms and so at 115V it will only draw 5.75A (or 660W).  Perfect!

I thought about running a separate wire up to the heater so that I could feed it 115V AC.  Trouble is, that would mean running a special 115V inverter as well as the 230V one.

Then at a car boot sale the other weekend I saw this:

(http://i36.tinypic.com/24eopk9.jpg)

A 4kVA tool transformer.  Very rusty and neglected but the guy sold it to me for £15 (assuring me it hadn't been used for scuba diving).

(http://i36.tinypic.com/35klk60.jpg)

Inside it wasn't so bad and worked ok.  The transformer itself is potted in cement of some kind.  Made it very heavy but at least it's quiet - doesn't even hum noticeably.  

These things are usually a regulation bright yellow colour to denote they are 110/115V (230V isolation transformers are blue).  I didn't plan on selling it or using it on a building site so there was no need for it to be restored to it's former colour so I sanded the outside down and gave it a generous helping of black Hammerite (wot I bought half price at a supermarket clear-out a few months ago - 'cos "It'll come in handy sometime later").

(http://i36.tinypic.com/qs5j78.jpg)

I couldn't find anyone locally that sold 32A "commando" plugs (most transformers and extensions come with 16A plugs/sockets these days) and I actually needed a regular 13A 230V socket for the heater so I just drilled a hole in the thing and connected up a spare extension lead (through a cable grip grommet).

And here she is... Incredibly, it fits in the airing cupboard. Fired up, you can see it powering the water heater with about 630W.  Don't mind that water heater normally plugged into a plug-in timer, plugged into a three-way cube, plugged into a wall socket... It was like that when I moved in... Honest, guv'!  whistle

(http://i36.tinypic.com/34t305g.jpg)

Today, it was on for 1hr15 and used 0.76kWh and raised the tank temperature from 28.4'C to 34.0'C.  I gouged out a hole in the foam insulation and stuck the outdoor sensor of one of those "in/out" digital thermometers against the tank wall (about 1/3rd the way down from the top of the tank) so I can monitor the thing.  After glueing the sensor in place I repacked the hole with foam and even found a short bit of pipe insulation to snap over the hot water pipe that exits the top of the tank.

Being a 4kVA transformer, it can handle running at 650W indefinitely and didn't even get warm doing so.  I was worried that it might overload the inverter with its inrush current but it doesn't seem any worse than my hi-fi amp with its massive toroidal transformer that makes the house lights "blink"...

Now all I need is a way to make the solar charge controller automatically and wirelessly remote control the transformer so that when the sun goes behind some clouds, the dump load is disconnected... That and I need my new 3kW inverter that is out of stock for a couple of weeks.  With the dump load running we can't put the kettle on at the same time on my 1kW inverter or it overloads and trips out.


Title: Re: Cobbled together PV in W.Sussex
Post by: Justme on October 03, 2009, 09:11:16 AM
If you had an Outback solar charge controller or a Victron inverter they both have software switches that can control anything via a relay. So you could set it to turn on a mains device when say the V hits the EQ or absorb level (the outback can also be used as a MPPT charge controller for a wind turbine that way or just wire the turbine direct & use the Outback to control the solar as normal but set the switch to dump the excess wind power in to your loads). If you combined both Outback & the Victron you could set one higher than the other to give a stepped loading.


Title: Re: Cobbled together PV in W.Sussex
Post by: Alan on October 03, 2009, 10:48:43 AM
Not sure from your picture if the extension lead is fully unwound or not.

Running a 13 amp load off a coiled up extension lead will cause it to catch fire.
 
You should get away with a 600 watt load, but best practice says best not to do it.

Regards

Alan


Title: Re: Cobbled together PV in W.Sussex
Post by: Justme on October 03, 2009, 12:30:15 PM

And if the load is less than you are generating then fuses blow.  :(


That does not sound right.

The fuse should only see the current used by the device. You cant "push" the current in, its pulled out by the device. You can fit a 1 amp device & fuse to your 13amp socket & the 1amp fuse does not blow.


Title: Re: Cobbled together PV in W.Sussex
Post by: davebodger on October 03, 2009, 09:00:52 PM

And if the load is less than you are generating then fuses blow.  :(


That does not sound right.

The fuse should only see the current used by the device. You cant "push" the current in, its pulled out by the device. You can fit a 1 amp device & fuse to your 13amp socket & the 1amp fuse does not blow.

Sorry Justme, I was not clear with my statement.
The fuses I was talking about are in the UPS.
If the power output of the Solar Inverter is greater than the load is drawing and I am using the UPS to produce the "mains" (without the UPS being plugged into the real mains) then the excess power has to be absorbed in the output transformer of the UPS, which will cause it to overheat and, if the power being pushed into the UPS is great enough, something will blow.  sh*tfan:

OK, if you're lucky the inverter and/or the UPS will shut down with an "overvoltage" fault first.

Really this kind of electrical sillyness should only be performed with a large UPS that can take a bit of punishment, or a weedy solar PV system that can't put out much power. ;D
I was doing it knowing that my load (500W measured) was definitely larger than my PV generation and with a UPS (1400VA) bigger than my PV (400Wp); and with a few clouds in the sky for good measure.
I was just trying to test my PC interface and software without connecting an uncertified PV system to the (real) mains. whistle






Title: Re: Cobbled together PV in W.Sussex
Post by: Justme on October 03, 2009, 10:43:24 PM
Ah cos your back feeding the power into the output of the UPS.

Cos if it went in to the input the UPS would shut down thinking the mains was on & then the inverter would shut down too as it has no signal to sync to.


Title: Re: Cobbled together PV in W.Sussex
Post by: Outtasight on October 05, 2009, 12:48:17 AM
Not sure from your picture if the extension lead is fully unwound or not.

Running a 13 amp load off a coiled up extension lead will cause it to catch fire.
 
You should get away with a 600 watt load, but best practice says best not to do it.

Good spot and you're right but it's only a 10m extension and it's half unwound so it was ok.  This was just the test rig.  There's a solar power line running over the door frame going towards my wife's study.  As I've proved it works, I'll just put in a junction box on that line and drop a permanent solar feed to the transformer and avoid the trip hazard of the reel cable laying on the landing floor to the computer room.

I'm thinking to cook up an automatic transfer switch for the water heater.   Today, it was pretty sunny again and I put 1.37kWh into the tank (raising it from 28.3'C to 37.6'C) but then after sunset, I forgot to plug it back into the mains for the timed heating cycle and now we're waiting for the tank to come up to 60'C.

I've got a 230V coil double pole change-over relay that I was going to use for something else but it can select mains priority on the heater.  The timer is off most of the day, except for a couple of hours in the early evening.  If I put the relay coil on the mains after the timer switch it will "sense" the mains coming on and flip the change-over relay to select "230V mains" instead of "115V solar" as the input to the heater...  I might also get round to plumbing in a proper immersion heater timer rather than that suspicious plug-in one  whistle

I think I might be able to rig something with the SmartGauge as it has a programmable relay that works on voltage or SoC % alarms. I can arrange it so that if the battery is below 80% charged then the water heater will be locked out to give the battery priority on bulk charging.  A net current sensor on the battery would also allow me to lock out the heater if excessive net drain was detected once the battery is over 80% charged.

I need a bigger solar controller but I'm holding out for the new Morningstar Tristar MPPT 60A due out in November.  That's IP enabled so could open up a load of possibilities.

 bike:


Title: Re: Cobbled together PV in W.Sussex
Post by: Outtasight on October 06, 2009, 01:21:53 AM
This last weekend has seen probably the last of the really sunny days of the year here.  Today it was so dark and rainy all day that the battery bank ran right down.  So, it's probably just as well that I got me another huge haul of PV and batteries at the weekend!  ;D

Another eBay job.  This guy was selling three of the same Sharp 80W panels as I bought a couple of months back.  I won two of them in a last minute (literally) bidding battle but even so they were very cheap at only £340 for the pair (I paid £455 for the last pair).

When I arranged to pick them up (from some 250 miles away!) the guy asked if I be interested in some other kit (namely another four unbranded 80W monocrystalline panels and 16 deep cycle batteries!).  I told him I'd take a look - it'd be rude not to   ;)

Got there and the Sharp panels were ok but somehow he'd managed to put big dents in both the frames - still they were very cheap.  The unbranded ones were not bad (a bit flimsy frames but the output is fine).  And because they were unbranded he only wanted £150 each for them so I said I'd take two.  Even the super cheap Chinese ones that you see on eBay now are about £200+delivery each so two for £300 was a good deal.

Then he showed me the batteries... WOW!!  What a find!  They were Deka 8GGC2 180Ah 6V gel batts - proper solar ones.  These are rated for 1000 cycles at 50%.  

http://www.eastpenn-deka.com/assets/base/0919.pdf (http://www.eastpenn-deka.com/assets/base/0919.pdf)

Most were dated 2008 but I managed to dig out four that were almost new (just five months old, May 2009).  I gave them a load test with a 60W lamp and my voltmeter to see what they were like open circuit and then with the load on... Read 6.50 / 6.46V - These things really don't self discharge much!  He let me have them for just £50 each, pretty good considering they go for $250 each (about £150) new.

So, here are the new panels, washed down and sitting propped up on the plastic chairs... another 320Wp added to the pot.  

(http://i34.tinypic.com/scgcqw.jpg)

It's getting a bit crowded in the patio area  whistle

(http://i34.tinypic.com/1116l5d.jpg)

The solar controller was already pegged at 14.8A so I couldn't get any more through it so I just wired these panels into a 24V nominal 2x2 series parallel string and wired that into the terminal blocks for the mains charger - direct to the battery.  With that, I could make about 34A of solar power in the afternoon sun - enough to run the new 640W dump load and still have almost 6A charge current left over to finish topping the battery or run some of the computer gear.

Just need some chunky links for the new batteries now.

(http://i35.tinypic.com/2uo1mj5.jpg)

The terminals aren't particularly well placed for a 24V bank but if you arrange them in a circle you can use short links and the output terminals can be any two adjoining (+) and (-) posts.

(http://i34.tinypic.com/fv8umu.jpg)

180Ah is a bit smaller than my notional 220Ah pack now but the cheap flooded leisure batteries are showing their weakness after being cycled to 50% every day for over a year now.  They're probably only rated for 200 cycles at 50% but these Dekas are rated for 450 cycles to 100% discharge and 600 cycles to 80% discharge.

That, combined with the higher charge acceptance of these batteries should make the whole system more efficient.  Flooded cells take about 130% charge to complete (you have to put 130Ah in to get a 100Ah charge stored) whereas these gel cells are supposed to only take 110% charge to complete.  They charge at a lower voltage (2.35V per cell) and don't need (or rather are damaged by) the EQ charging that flooded cells do.

The very low rate of self-discharge should also help, as flooded cells can lose 10% per week doing nothing at all whereas the gel cells lose a claimed 2% per month.  That's an extra 21Ah (0.5kWh) a week you can use for AC generation rather than battery maintenance!

Now all I need is for it to stop bloody raining and let's see that golden globe in the sky again!!!!


Title: Re: Cobbled together PV in W.Sussex
Post by: Stuart on October 06, 2009, 01:53:19 AM
I think you want to start putting them on the roof  ;D its fun honest!


Title: Re: Cobbled together PV in W.Sussex
Post by: Outtasight on October 06, 2009, 12:35:34 PM
That's partly why I'm not buying panels bigger than 80W any more. I can just about man-handle a 80W panel on a ladder but the massive 170W Sharps were just too big and heavy for that kind of high-wire act.

I'm sure at some point I'll get the building approval to install some under-concrete tile-brackety-thingies and some strut to get six 80W panels up on me roof. ;D 

The alternative plan is a sort of paved area at the bottom of the garden for a bench to sit on and a "plant trainer" structure over it.  Just four posts in the ground and an open grid/cross brace timber frame at the top to hold it together, like those rose trainer thingies you see at formal gardens where the roses grow up the posts and over the top in a sort of "roof".  Instead of roses, I'd "train" solar panels over the framework. That way I don't have to mess with the house (a good thing given my potential for building bodgery) and the panels will be clear of the trees next to the garage.


Title: Re: Cobbled together PV in W.Sussex
Post by: Alan on October 06, 2009, 06:59:03 PM
Quote “ I'm thinking to cook up an automatic transfer switch for the water heater. “

If your house / ring mains do not use an earth leakage trip the relay will switch between supplies at 13 amps without problem.

If you have a whole house earth leakage trip, or the heater is fed from its own earth leakage trip it could be problematic with spurious trips. When switching the live and neutral the earth leakage trips get a bit confused with the relay mechanical contact bounce and are prone to nuisance tripping. Here the ring mains are switched between Economy ten and normal supply. The switching here is done before the earth leakage trips on each ring main and works without problem. The Megaflow water heaters are also switched between the grid and wind turbine supplies.

Regards

Alan


Title: Re: Cobbled together PV in W.Sussex
Post by: Outtasight on October 06, 2009, 09:25:31 PM
No fear of such earth leakage tripping here... I had a look at the relay I had spare and it's only rated at 10A so it's not quite big enough for the job.

We've got an Economy xx relay in our utility cupboard as well (but I'm on a single rate tariff).  It makes a "CHUNK!!!" sound that you can hear from the other side of the house!

We do have a RCD main breaker in the consumer unit and it does randomly trip when turning on the lights in the garage.  They're old 8ft and 6ft tubes (six in all) and sometimes the breaker trips when turning them on (like the instant I flick the switch).  Annoying.  It's not even condensation - it can do it on a warm bone dry afternoon.  They're switched from a water heater type switch and when you turn them off, the neon stays on for a few seconds from the residual power in the capacitors in the fittings.  I wonder if the wiring insulation has broken down a bit (it's some old twin & earth cable) and there's too much capacitance in the wires or the fittings (if the big capacitors in the fittings are leaking a bit to their outer cans or something).  Anyway, I rigged up a much smaller tube light that I got at a car boot sale and that doesn't trip the breaker and at 18W it's fine for rummaging around in the garage.  The six big tubes take up 550W!! - Great for working on the car or mad inventing in the workshop but not so good for my leccy bill.

The meter has been counting up much more than usual today... After two of the darkest days imaginable (almost like night at times today), I had to give in and switch the house lights, all the computers and the TV over to grid and turn off the inverter to prioritise what meagre solar power there was for battery charging. They'd drained right down to 29% by this morning and by teatime they'd only recovered to 32% so on went the grid charger too.  I'd already killed my old 12V reserve battery yesterday evening (when it's full I use the old 12V inverter to power the 3A 24V charger to "prop up" the main bank for a couple of hours).  The 12V battery can be charged from my spare 40W panel (that can't be used on the main array) and if the main bank is full, I can use the 30A 12V charger to fill up the reserve battery - for a rainy day (but not two).

And so ends this year's uninterrupted run of solar powered house lighting since the end of February... The dark days are truly here now.   :(

If I had space for them, I'd tie the new gel battery bank into the old flooded one for more autonomy but the problem is that the charging voltages are very different for the two types of battery and their discharge profiles are different too so the flooded cells will drag down the gel ones as the gels hold up their voltage better than flooded.


Title: Re: Cobbled together PV in W.Sussex
Post by: Outtasight on October 12, 2009, 11:52:59 PM
A few weeks go I was pondering whether to stick with off-grid or go for a grid-tie inverter.  Small ones like the Mastervolt Soladin 600 are quite cheap now (about £450) and can work at lowish voltages (unlike the normal grid tie stuff that works at 400-600V).  But it only puts out 600W so would be overloaded as I've already got ~1kWp of PV on the 35V array - oh, and the Soladin needs more than 35V to work.

Then I seriously considered the SMA SB/WB 1100LV but it's only a 1.1kW inverter so wouldn't have left much scope for expansion.  For a bit less money I could upgrade my off-grid inverter to a 3kW one and have lots of expansion capacity... Shhh!  Don't tell 'er indoors  ;)

With the state of under-investment in UK generating capacity, I figured it was more useful to have a backup supply of power.  In recent rain storms (and not very severe ones, just very wet, not even thunder or windy) we had quite a lot of brown-outs that caused the computer room UPS to cut in.

So, with my new haul of PV and batteries, I decided to stick with my off-grid route and called the Antares guys again for a 3kW inverter.  They were out of stock for a month  :(.

Then this week, on my last day before a weeks leave from work, I happened to be working in Reading (near their store) and decided to give them a call to see if they'd got any stock yet.  I got lucky and they had one!

And so here it is:

(http://i38.tinypic.com/2lien2t.jpg)

And installed...

(http://i33.tinypic.com/xlff5z.jpg)

It was quite easy as the technician calculated that my short (90cm) 35mmsq power leads would still be up to the job.  I had thought I might have to double up to 70mmsq (as it mentions this in the manual) but he said it was ok as the manual assumed up to 3m long connections.  So I was able to just connect it straight up using the existing 8mm bolt rings.  This model has nut and bolt fixings rather than 8mm machine screws that allows tighter clamping of the ring terminals - handy when the full rated DC current is 138A.  I uprated the three in-line fuses from 30A to 40A each (the original fuses I had for the 12V inverter).  Should be plenty for now but if I can find 60A fuses, I'll put those in.  The manual recommended a 200A fuse in the DC circuit.

The remote panel is common to all the 24V models and so all I had to do was plug it in.  The LED power display on the panel reads % power output so it automatically adjusts to each model.  Now each step on the ladder is just 300W load instead of 100W load.

In this picture I was just testing the install.  Since then I've re-wired the output using the hardwire terminals inside the front panel.  You just undo four screws and the output panel comes away, revealing the terminal block and earth bonding post.  I used 1.5mmsq (good for 16A) cable as far as the distribution block (via the RCD and generation meter) and then re-wired the extension to the kitchen with 1.25mmsq cable (good for 13A).  By the fridge, I upgraded the worktop single socket to a twin (it was getting annoying having to swap the toaster and kettle plugs all the time). I'll probably run another socket down to near the fridge power point so I can run the fridge on solar on good days.  Now I don't need my wacky power buffer system any more :). This inverter has more than enough muscle to start a compressor (up to 6kW surge and 3.3kW for 3 minutes).

The original battery bank isn't powerful enough to run a 3kW load for more than a couple of minutes and even at 2kW (our usual kettle, not the solar one) the battery bank sank to 23.2V when delivering 90A.

This inverter has a higher threshold for when the fan comes on.  Up to about 150W load it doesn't use them at all.  Above that but below about 250W one fan comes on.  Above that, both come on.

Now I've got two spare 1kW inverters... The 12V one is doing duty running the 24V battery charger from the old 12V battery for emergencies when the main bank is getting dangerously low.  I suppose I could try to sell the spare 24V one but it's also maybe useful to keep around as a spare in case the main one develops a fault.

If the 3kW inverter idle load of 1.5A is too much to bear in the depths of Winter (1.5A x 24hrs is 36Ah of battery!!) then I might have to use the small inverter as a Winter converter (it only draws 0.65A x 24hrs = 15.6Ah).

You can never have too many inverters, that's what I say   bike:


Title: Re: Cobbled together PV in W.Sussex
Post by: jango on October 13, 2009, 12:01:20 AM
Outta
yes the big downside of grid tie is if the mains power goes off, under G83/1 the grid tie inverter has to shut down within about a second. You are right stand alone had its advantages!
You could use sma backup inverter if grid goes off.


Title: Re: Cobbled together PV in W.Sussex
Post by: Outtasight on October 14, 2009, 11:18:19 PM
The gods of cheap Chinese solar panels intervened yesterday.  I was pondering where to put my two latest 80W Sharp panels and then noticed that the array output was a bit off for such a sunny day...  Time to get busy with the test meter (again).

One of the 15W panels on the patio was stone dead (again).  So I was 30W short even though the other panel in the pair was fine. 

So that settled it, the whole lot came out and I made up a couple of wooden rails for the Sharps to go on and screwed the tops to the wall (to prevent any wind toppling disasters).  I've left the bottom loose so I can change the angle.  At the moment it's on its Winter setting and in the Summer I can put a couple of blocks under the feet to raise them up, making the panel angle lower.

(http://i36.tinypic.com/ketc8n.jpg)

It takes up a lot less space and puts out much more power.

I still need to figure out where to put the other two new panels and what to do with the 15W ones that still work.  Maybe time for another car boot sale.  Luckily, two of the sets are still in warranty so I can get the dead one replaced but these are pretty unreliable panels so it may be best to get shot of them as fast as possible.  The aluminium framed 12W panels (from the same maker) are still going though, so it must be something about the ABS plastic frames of the 15W ones (water ingress?) that makes them fail quite often.

I could replace those eight 12W panels with the other 80W pair.  That would give me a net increase of 64W from the same space.  Then again, I haven't tested the other six 15W panels on the garage roof to see if they're still alive... Time for the big ladder tomorrow.

I'll also need to look into burying that overhead cable as it casts a line shadow on the panels below it.

More projects...   ::)


Title: Re: Cobbled together PV in W.Sussex
Post by: desperate on October 15, 2009, 01:24:08 PM
Outtasight,

I don't know doodlysquit about PV but it sure looks impressive, how do you get PP from 'er indoors, also leave us a bit of sunlight, I can see a big shadow to the south of cactusville ;D

Desperate


Title: Re: Cobbled together PV in W.Sussex
Post by: Outtasight on October 16, 2009, 12:53:45 AM
...how do you get PP from 'er indoors, also leave us a bit of sunlight, I can see a big shadow to the south of cactusville ;D

Simple, I don't have a plan so I don't need permission  whistle

I just say "It's temporary... I'm just testing it..." or summat like that  ;)

Today was really sunny and I got all the batts charged up.  By 2 o'clock the main bank and even the old faithful 12V battery I use for propping up the main bank and my fridge experiment were full.  There was even power spare to run the water heater for 45 minutes. 

I've finished making up the 35mmsq battery links for the gel bank and even bought some silver alloy solder to make the joints with the rings lower resistance.  I've done my usual trick of making one link long enough to make it a current metering shunt (reads 0.1mV per Amp).  Being in the middle of the bank it measures net current (charge / discharge). 

I ran the first real load test on the new 24V bank yesterday.  Ran it down a bit by connecting to the spare inverter and then the 24V battery charger on the main bank.  It held the 4.2A load for about 5 hours (about c/43 rate), only falling to 24.9V and then after an overnight rest, recovered to 25.6V.  No more than 0.02V difference on any 6V block in the bank so it seems in rude health.  I charged it up today using the spare pair of 80W panels.  I didn't bother with a controller as it only puts out 4A and I needed to put about 22Ah back so there was no chance of it over charging today (I kept an eye on the volts but it only reached 27.7V).  The sides of the blocks bulged out slightly by the end of the charge but the Deka manual says this is normal for their gel batteries when on charge (they say that deeply discharged ones can look a  bit "sucked in")


Title: Re: Cobbled together PV in W.Sussex
Post by: billi on October 16, 2009, 01:23:09 AM
Quote
You could use sma backup inverter if grid goes off.

 ;D

Jango you are right and others  have that as well , some have that soon ...

Question is only for what  event spent that extra cash ? for a few minutes ?  (i can buy a small off grid idea for that price)


 but saying this we should find an answer to this , cause its a niche  

Billi



Title: Re: Cobbled together PV in W.Sussex
Post by: Outtasight on October 23, 2009, 09:49:53 PM
I was sitting in the restaurant last night enjoying my expenses (it's ok, I'm not an MP) and the wife phoned me...

"All the lights have gone off in our road!"

"But not in our house?"

"No, but what should I do about the fridge?"

"Plug it into the solar socket in the kitchen and keep an eye on the red display by the solar batteries.  If it goes down to 30 before the mains comes back on, give up and plug the fridge back into the normal socket."

"ok, bye!"


The power cut in our street lasted about an hour and a half and the fridge-freezer and house lights ran happily on my new 3kW off-grid inverter until the power came back on.
I feel vindicated... It is worth having off-grid power and someone who knows nothing about lead acid batteries (apart from the fact that they are big, heavy and don't suit the décor in the living room whistle ) can easily monitor battery status if you've got a SmartGauge.   bike:

This calls for some more shopping to celebrate!!!  The new Morningstar TriStar MPPT 60 charge controller has apparently been released, although the bods I previously bought my SunSavers from haven't got any pricing figured out yet... Ivan..?  Are you listening?  ;D


Title: Re: Cobbled together PV in W.Sussex
Post by: StBarnabas on October 23, 2009, 10:18:51 PM
hi Outta
way to go. PV rules! Where am I going to put my stand alone system?


Title: Re: Cobbled together PV in W.Sussex
Post by: Outtasight on October 25, 2009, 08:18:05 AM
Thanks.

Here's a photo of the new Deka battery bank installed.  I left small gaps between them for ventilation but also because when they are charging hard they bulge out a bit.  When discharging they get sucked in a bit - especially the tops of the cells.

What looks like a weird tap on the middle of the bank isn't.  It's just the charge controller temperature sensors which have 8mm insulated lugs so you can fix them to the battery without resorting to gaffer tape.

(http://i36.tinypic.com/2wgt0rt.jpg)

The product sheets were a bit vague about the proper charging regime (conflicting voltage tables for different temperatures).  I mailed the company and a very knowledgeable guy sent me some advice and it turns out their old 2007 technical manual was a bit conservative and it could lead to undercharging.  This fits in with a white paper I read on these batteries in service at a remote PV powered telecoms station.

In other news, I contacted a company via the Energy Saving Trust web site about cavity wall insulation and the boys came round this week to drill lots of holes in my walls and pump 'em full of rock wool.  While sleeving the gas boiler vent, the guy showed me a shocking thing...  Inside the cavity, someone had mounted a second grille over the hole in the inner leaf and this had a fine wire mesh over it.  Of course this was then boxed inside a decorative er... box on the inside so you couldn't see it or get to it.  Fine for the first 10 years but by the time we came to smash out the outer grille that was mortared in, the inner one was totally blocked with grime in the fine mesh.   :fight
Luckily, we have a CO gas alarm in the kitchen and the kitchen door has a draughty cat flap and the larder in the kitchen has two air bricks in it so there was plenty of other ways for air to get in.

Just in the few days since having our walls stuffed, it already seems warmer in the mornings (we turn the GCH down to 14'C at night).  Looking forward to those lower gas and electric bills  :angel:

Desperate was showing us all how to do crazy amounts of zoning on his heating (control freak...) but we just have the one totally inadequate hall stair mounted thermostat  ;)  Changing it from the bi-metal one to a digital one tightened up the hysteresis on the heating control which means you get more consistent temperature and less urge to fiddle with the settings.  It also has two memories which you can toggle by pressing a button on it to flip it between 19'C and 14'C. We've got into a habit of turning it down if we go out or overnight while in bed (where there is plenty of zone heating, I can tell you  ;D).  In the coldest days of the year we leave the GCH on 14'C and use a 1kW electric radiator in the bedroom - that's our zone system.


Title: Re: Cobbled together PV in W.Sussex
Post by: Paulh_Boats on October 25, 2009, 11:16:26 AM
Outta,

Keep up the posting and pics please!  You system is very inspiring and would be ideal for us.

4 batteries would fit in my boat and ballast her for sea sailing. 90% of the year she sits on the front drive, so available for backup power and lighting via my 480W PV (grid-tied).

And when I take her down the Thames you won't believe how peaceful and relaxing an electric outboard engine can be:
http://www.millibee.com/LechladeRaid/Monday
The boat had 8 panels off ebay, about 6W each. Not enough, but every little helps!

cheers
Paul


Title: Re: Cobbled together PV in W.Sussex
Post by: langstroth2 on October 25, 2009, 11:45:52 AM
A bit off topic - but out of interest Paul which slips do you use to launch on the Thames - I've only so far used the public one next to Windsor Sport Centre, which is a nice stretch of Thames thru Eton/Windsor.





Title: Re: Cobbled together PV in W.Sussex
Post by: Paulh_Boats on October 25, 2009, 12:31:44 PM
A bit off topic - but out of interest Paul which slips do you use to launch on the Thames - I've only so far used the public one next to Windsor Sport Centre, which is a nice stretch of Thames thru Eton/Windsor.

Top marks for the best off topic reply!  We (HBBR) launched at the Trout Inn near Lechlade, then 5 days later ended at Beale Park. A friendly chat and a pint with the Landlord gets you a free launch at the Trout Inn, which dates back to 1220.

I used an electric outboard and 85Ah battery first day, charged at Shifford lock but only at 4A so only got a few hours use next day. Had to fire up the smokey 2-stroke and thanks to the Environment Agency's lack of advanced planning there were no convenient charging points along the way. So 4 big batteries might get me all the way when we do the trip next year and double up as a 48V inverter system. There are 20A chargers for motor homes, but that might not be enough for 4 batteries.

-Paul


Title: Re: Cobbled together PV in W.Sussex
Post by: Outtasight on November 02, 2009, 12:21:44 AM
Thanks Paul,

Been busy at work lately so not had much time for updates.  The first of the bad gales swept through here today but the big panels are still on the garage roof (through the magic of ratchet tie-downs whistle). The ones on the wall are quite handy for keeping the driving rain off the woodwork of the patio door.

Earlier this year I found a 3A 24V charger at a car boot sale and they are pretty rare things but like buses, two turned up at once at the last car boot!  There was a 7A one for £2 and then I discovered a brand new, still in the box Yuasa switch mode 6A one for £10.

(http://i35.tinypic.com/efhsnb.jpg)

The switch mode one has now replaced the original 3A one as it has some intelligence (it counts the bulk time and adjusts the absorption time proportionally), has higher efficiency than the transformer based one and doesn't have any AC ripple on the output.  The transformer ones haven't got any capacitors in them so put out full wave rectified ripple chopped by SCRs to limit the absorption voltage... not ideal for gel batteries (even though both claimed to be for sealed batteries).  If I can find some cheap big caps, I might upgrade them but flooded batteries aren't so fussy (and as all the old flooded batts I have kicking around are pretty rotten already, it doesn't matter).

I now use the old 3A one to dump what little excess charge there is on sunny days into the old flooded bank that is still in the living room  ::)  As it will be charged as a secondary bank via the solar mains, it can be some distance away from the main system.  Just as soon as I get some racking for the store room, I'll put the spare bank out there.  It can then be used to support the main bank at night by using the old spare 1kW 24V inverter to run the new 6A Yuasa charger to support the gel bank.  I can slave the small inverter from the SoC alarm output on the SmartGauge.  Obviously it wastes a fair bit of power using inverters and mains chargers like this but it allows me to store more power that would otherwise be lost altogether.  In the summer when there's more spare power available, I can substitute the 3A charger for the 7A one (or even run both in parallel for 10A).

I got the pricing on the new Morningstar TriStar MPPT controllers.  They cost more than the Outback FM60's but have better communications.  One thing I'm trying to confirm from Morningstar support is if they have current limiting.  The tech guy from Deka recommended that I not try to charge the gel batteries faster than their 5hr discharge rate, to stop them from heating up.  That's only 29A charge rate.  The Outbacks have a programmable current limiter so that although the controllers are rated to 60A, they recognised that only large batteries (or AGMs) can actually accept that much current so you can program any current limit between 5A and 60A to suit smaller batteries but using an oversized array for better performance in variable weather.

I've also been beta testing the new version of the Morningstar MSView logging and control software for their software guys.  I'd had trouble with the published version on their web site on my old Windows 98 laptop that I'm using to program the chargers and monitor how well they are charging the new gel batteries.

If they can't make the TriStar limit its current, I may have to either go with an Outback FM60 or possibly just get another SunSaver 15 MPPT.  It has some potential advantage anyway to have three 15A charge controllers as then different segments of the array that are in shade at different times of the day can be tracked individually for maximum power.  It would also get around the current limiting problem as I could stagger the charge set points so that as the battery voltage rises, the chargers would gradually drop out (once the battery voltage has risen above each set point).  That way, absorption current could be limited to the 28A that my two chargers can put out but if a large load was turned on, that would cause the battery voltage to sink towards the lower set point and so the third charger would automatically cut back in to take up the load.



Title: Re: Cobbled together PV in W.Sussex
Post by: Paulh_Boats on November 02, 2009, 10:15:45 AM
Outtasight,

The 24V chargers were a good steal! One idea I had for my boat is a solar charger that easily delivers 20A at 24V or 48V fed by a switched-mode supply (on ebay direct from China). That would give me super-fast charging overnight or a few hours "splash and dash" at a charging point along the river. 

I can't find a 12V charger that gives more than 20A and that's not enough for a 5 day cruise with intermittent charging. Hence the solar charger plus SM power supply idea which I think is more cost effective, with some kind of switch to rewire the 2 or 4 batteries from 12V for the motor to 24V or 48V for charging. Then I get double use from the solar charger when the boat is at home on my drive as a backup supply....just plug the boat directly into the PV.

I wonder how a solar charger and MPPT Soladin would behave together? As long as the solar charger was a linear device I think there would be no interaction.

cheers
Paul


Title: Re: Cobbled together PV in W.Sussex
Post by: rhys on November 02, 2009, 11:48:54 AM
A bit off topic - but out of interest Paul which slips do you use to launch on the Thames - I've only so far used the public one next to Windsor Sport Centre, which is a nice stretch of Thames thru Eton/Windsor.

Top marks for the best off topic reply!  We (HBBR) launched at the Trout Inn near Lechlade, then 5 days later ended at Beale Park. A friendly chat and a pint with the Landlord gets you a free launch at the Trout Inn, which dates back to 1220.

snip
-Paul

And a pint at the Swan at Radcot Bridge I see too!!!


Title: Re: Cobbled together PV in W.Sussex
Post by: Justme on November 02, 2009, 01:33:20 PM

I can't find a 12V charger that gives more than 20A and that's not enough for a 5 day cruise with intermittent charging.




Here you go TRY THIS ONE (http://cgi.ebay.co.uk/Lead-Acid-Battery-Charger-100Amp-12Vdc-230Vac-New_W0QQitemZ120416660010QQcmdZViewItemQQptZUK_Home_Garden_PowerTools_SM?hash=item1c09646a2a#ht_2627wt_939)

They do smaller as well HERE (http://electronics.shop.ebay.co.uk/Batteries-Battery-Chargers-/48446/i.html?_catref=1&_fln=1&_ipg=&_ssn=kipoint&_trksid=p3911.c0.m282)


Title: Re: Cobbled together PV in W.Sussex
Post by: tony. on November 02, 2009, 02:15:19 PM
paul
try rs 361 6248 for a 300va 12 v trasformer, im sure with a bridge rectifier, you've got the basis of a charger.

might suit your needs if your only hooked up for a few hours
regards

tony


Title: Re: Cobbled together PV in W.Sussex
Post by: rob26440 on November 02, 2009, 04:46:55 PM
I use a Sealey Superboost200 to charge my Yuasa battery set.  It can do 24v or 12v and can deliver up to 45 Amps.  (200 Amps for starting a vehicle.)  I bought it new from eBay over 3 years ago for £87 inc delivery.  It has a variety of charging modes.  It charges well and the current drops off to a v. low trickle as the battery voltage rises.  Only issue I have with it is the ammeter is not very accurate, especially at low currents.  I uses a shunt with a 50 Amp ammeter for accuracy. (Unless I have to use the 200 Amp boost!)

Here's a random link to a site selling them but the price seems v. high.  Must be so mewwhere cheaper.  There are other models in the range.
http://www.pvrdirect.co.uk/productinfo.aspx?catref=SUPERBOOST200

Plenty listed on eBay - but the prices seem to have shot up in the 3 years since I bought mine.


Title: Re: Cobbled together PV in W.Sussex
Post by: Paulh_Boats on November 02, 2009, 07:13:30 PM
Thanks everyone - plenty of current all the way up to 100A  ;D

The Sealey is not suitable for a boat, too big for my boat - switched mode is far superior and can be hidden away.

I just have to choose the number of batteries... 2, 3 or 4 and 24V charging makes sense as 24V inverters have lower losses.


cheers
Paul


Title: Re: Cobbled together PV in W.Sussex
Post by: Outtasight on November 03, 2009, 12:52:44 AM
I wonder how a solar charger and MPPT Soladin would behave together? As long as the solar charger was a linear device I think there would be no interaction.

MPPT controllers generally don't like PSUs as they're designed for the weird IV curve of PV.  A 20A PSU will probably not like it when the MPPT controller does it's IV sweep (open circuit to close to short circuit).  At the short circuit end of the sweep you may blow either the PSU as it gets overloaded (or cause a short circuit shut-down in a SMPSU) or the MPPT controller may overload as the PSU will try to present an inflexible voltage at as many Amps as it can muster.  PV is a (sort of) constant current supply whereas a PSU is a constant voltage supply.

A non-MPPT controller should work ok as it will just turn the supply to the battery on and off to keep the battery volts in a safe working area but you'd have to fudge it so that the PSU didn't overload when connected to the battery. Again PV doesn't mind because it will just match the battery voltage and deliver its largely constant current into it.  A PSU will try to pull the battery up to 15V or whatever and the battery will pull as much current as the PSU can muster before it blows up.  Choosing wiring with some resistance to limit the current will sort of work.  I use some specially chosen cable on my 30A lab PSU to limit the current a 12V battery can take to around 30A.  Thinner cables would melt but fatter ones would cause the PSU to overload.  Even so, I have to use the variable voltage control on it to stop it from overloading if the battery is in a low state of charge.  If you do try using a solar controller with a PSU, make sure you use a series controller rather than a shunt controller. A shunt charger regulates the battery voltage by shorting out the PV (PSU) supply...
 sh*tfan:


Title: Re: Cobbled together PV in W.Sussex
Post by: tony. on November 03, 2009, 07:43:20 AM
outasight,

what about using a rf thermostat/setbacktimer, then you could locate it anywhere!!

TONY


Title: Re: Cobbled together PV in W.Sussex
Post by: Paulh_Boats on November 03, 2009, 10:19:44 AM
I wonder how a solar charger and MPPT Soladin would behave together? As long as the solar charger was a linear device I think there would be no interaction.

MPPT controllers generally don't like PSUs as they're designed for the weird IV curve of PV.  A 20A PSU will probably not like it when the MPPT controller does it's IV sweep (open circuit to close to short circuit).  At the short circuit end of the sweep you may blow either the PSU as it gets overloaded (or cause a short circuit shut-down in a SMPSU) or the MPPT controller may overload as the PSU will try to present an inflexible voltage at as many Amps as it can muster.  PV is a (sort of) constant current supply whereas a PSU is a constant voltage supply.

A non-MPPT controller should work ok as it will just turn the supply to the battery on and off to keep the battery volts in a safe working area but you'd have to fudge it so that the PSU didn't overload when connected to the battery. Again PV doesn't mind because it will just match the battery voltage and deliver its largely constant current into it.  A PSU will try to pull the battery up to 15V or whatever and the battery will pull as much current as the PSU can muster before it blows up.  Choosing wiring with some resistance to limit the current will sort of work.  I use some specially chosen cable on my 30A lab PSU to limit the current a 12V battery can take to around 30A.  Thinner cables would melt but fatter ones would cause the PSU to overload.  Even so, I have to use the variable voltage control on it to stop it from overloading if the battery is in a low state of charge.  If you do try using a solar controller with a PSU, make sure you use a series controller rather than a shunt controller. A shunt charger regulates the battery voltage by shorting out the PV (PSU) supply...
 sh*tfan:

All agreed - I would search for a switch-mode PSU with a current limit that would protect the battery with a linear solar regulator (i.e. not a DC-DC converter or MPPT).

cheers
Paul


Title: Re: Cobbled together PV in W.Sussex
Post by: Outtasight on November 04, 2009, 11:32:37 PM
More news on the Morningstar controllers... In fact, the Sunsaver MPPT and the Tristar MPPT can limit their battery current to a user settable value.  The software developers of the MSView programming wizard just didn't bother to include the parameter!  When I asked about the feature, the support guy said he was surprised it had never been spotted before and they'd get the parameter added.  Mind you their "testing team" missed a lot of bugs and issues in the current release, so it doesn't surprise me that much.  ::)


Title: Re: Cobbled together PV in W.Sussex
Post by: Paulh_Boats on November 05, 2009, 11:03:52 AM
More news on the Morningstar controllers... In fact, the Sunsaver MPPT and the Tristar MPPT can limit their battery current to a user settable value.  The software developers of the MSView programming wizard just didn't bother to include the parameter!  When I asked about the feature, the support guy said he was surprised it had never been spotted before and they'd get the parameter added.  Mind you their "testing team" missed a lot of bugs and issues in the current release, so it doesn't surprise me that much.  ::)

Outtasight,

Well done again! That's a great feature - I'm quite impressed by the Tristar design as its rugged and designed to last. They even have a support document showing how to replace the output MOS-FETs in the unlikely case they blow.

At high currents things might get a bit hot if current limited, but careful tweaking of the PSU voltage will keep that under control. Ideally it would be set high enough for the monthly equalisation charge but thats nearly 2V higher than normal. At 20A the heatsink will be a great place to rest a tea mug to keep it warm!  ;D

cheers
Paul


Title: Re: Cobbled together PV in W.Sussex
Post by: rob26440 on November 05, 2009, 12:11:02 PM
Quote
At 20A the heatsink will be a great place to rest a tea mug to keep it warm! 

So that's what heatsinks are for!  How did I miss that after 35yrs in the business.  ::)  You'll be telling me next that delicate components are there to protect the fuses.   ;D


Title: Re: Cobbled together PV in W.Sussex
Post by: Outtasight on November 05, 2009, 05:25:54 PM
At 20A the heatsink will be a great place to rest a tea mug to keep it warm!  ;D

I'd be surprised if it gets that warm.  One of my Sunsavers is often maxed out at the 15A limit and the heatsink barely gets warm, certainly less than 40'C by my fingerometer.  :)

That's one of the things that is supposed to be better about the Tristar MPPT compared to other MPPT controllers on the market - the fact that they have chosen low loss, fast switching drivers.  A PWM controller's losses are dependent on how square the edges of its transitions are between on and off.  If they were perfectly square (zero transition time) the output drivers would consume no power (apart from the "on" resistance volt drop).  That's why they don't need a fan on this design but it's still rated for full 60A output at 40'C ambient.


Title: Re: Cobbled together PV in W.Sussex
Post by: Outtasight on November 08, 2009, 07:12:04 PM
It was a dark and stormy night... (sounds like a book  :) )

Actually, it was and the day wasn't much better.  So, it was indoor tinkering today.  The Yuasa charger is not quite ideal for gel batteries as the Yuasa SLA batteries are a type of AGM battery.  So they set the voltage a little high at 29.0V for absorption.  If I wanted to leave the thing unattended while charging the Deka batteries, I'd have to fix this.

The helpful folk at Yuasa had riveted the case shut but I could see three preset controls on the circuit board and the one closest to the vents was labelled "FV Adj", which I presumed to mean the float voltage.  So it was worth a closer look inside...

(http://i36.tinypic.com/296hd93.jpg)

After drilling out the rivets, I found that the other two presets were for the absorption voltage and a current limiter.  

(http://i35.tinypic.com/2e3abzk.jpg)

The fan cools the heat sinks with the input and output transistors but this isn't what gets hot.  There are some damping resistors on the mains side of the SMPSU that get very hot (measured 130'C) and on the output there's a couple of current sensing resistors (145'C).  The fan doesn't have its intake against the vents so it only sort-of cools the inside.  More like just stirring the hot air rather than any forced ventilation  ::).

Apart from the dodgy cooling arrangements, it looks like an intelligent charger, using a PIC micro-controller as it's brain.

So I connected the charger up to the old flooded battery bank (as it wouldn't mind if I got the voltage a bit wrong) and let it charge up.  When it got to 28.2V, I started tweaking the absorption preset control down and kept an eye on the meter.  Not having any remote temperature compensation and thinnish output wires meant that as the current reduced, the absorption voltage at the battery terminals kept creeping up.  So I adjusted the thing so that it stayed at 28.2V near the end of charge before it went to float.

Actually, at the present room temperature of about 19'C, I should be charging at 28.56V but at least this way I can't overcharge the gel batteries with this thing. The solar chargers are temperature compensated so they will top off the last few percent safely.  This thing is only for bulking up the bank to somewhere near full in mid-winter so it's better to err on the low side.


Title: Re: Cobbled together PV in W.Sussex
Post by: Outtasight on November 21, 2009, 01:50:50 PM
In between bouts of work and rain, I finally managed to lash up the last couple of 80W panels to some wood and they have now replaced half of the 96W amorphous strings with 160W, netting me another 112Wp overall.

(http://i50.tinypic.com/2v14rok.jpg)

This takes me up to 1198Wp installed (although with diode losses and the amorphous panels not being all that good, its real world power is about 1100W).

Incredibly, nothing flew away or got broken in the massive storm last weekend.  The neighbours half built conservatory block wall partially fell down, an old tree fell down in one local road and 2000 homes on the other side of town were without power for 48 hours after another tree took out a power line.  I'm amazed nothing happened to the panels lashed to the garage roof  ::).

The little 15A Morningstar controller continues to soldier on, regardless of it being fed with now more than double its 400W maximum power input.  It regularly spends hours at a time pegged at the 15A limit on sunny days.

Still no sign of anyone getting any stock of the new 60A Tristar MPPT controller though.  At least I hope I can buy one before the VAT goes back up to 17.5% in January.


Title: Re: Cobbled together PV in W.Sussex
Post by: Outtasight on December 09, 2009, 06:41:57 PM
The end of my first year recording power use.  I've posted the graphs in the graphs section.  A grand total of 5.95% of my electricity has been provided by my growing solar system.  Not too bad considering most of the capacity didn't arrive until the late summer.

This week I won a new cheap 40W panel on fleabay to go with the lonely cheapo 40W panel that's been languishing in the garage.  So now I'm up to 1,326Wp in theory but about 1.2kWp with losses.

The new panel isn't bad but not great.  Unlike the Kyocera ones it has no bypass diodes but at £89 including next day delivery, I'm not complaining.  A 40W panel isn't likely to suffer from localised hot spots from shading as it's quite low power and quite a small panel.  Using only two of them in a string it wouldn't even matter as if a couple of cells get shaded, the whole string will probably drop out of the array as the string voltage will drop below that of the rest of the array and the blocking diode will stop any back-flow from the big 160W strings.

I dragged the redundant amorphous array out of the garage and propped it up on the lawn with some building blocks and the new pair of 40W panels are just perched on the bottom of that woodwork.  If I get time, I'll make a couple of rails for them and maybe put them up on the garage roof or mount them flat on the garden wall... In the depths of winter, the sun strikes the wall nearly square-on so they'd be fine like that for now.

In these dark weeks it's been a real struggle to keep the battery charged and the grid charger has had to be pressed into service to save them from over discharge.  The house lights are now permanently back on the grid and only the table lamp and work laptop get to go off grid.  Charging is now mostly confined to about an hour or two around noon with next to nothing before or after that.  Some days it's been like night time all day!


Title: Re: Cobbled together PV in W.Sussex
Post by: Paulh_Boats on December 09, 2009, 10:37:09 PM
Outtasight,

Have you seen any problems balancing the currents through different panels?   I've been racking my brains to think what happens to the PN junctions when they get some extra current forced through them...  the PN junction is already forward biased on, so maybe the extra electrons just flow over the junction without meeting any resistance, which is good.

cheers
Paul


Title: Re: Cobbled together PV in W.Sussex
Post by: Outtasight on December 12, 2009, 01:24:30 AM
Hi Paul,

In any string of cells the total output current will be limited to the weakest cell in the string (or the cell that is weakest by reason of shading which has the same effect as a weak or physically smaller Isc cell).

That's the reason for bypass diodes across each block of 18 cells in most panels.  Some new ones have thin film integrated bypass diodes for each cell now which is "a good thing".

Although PV cells are a PN junction and can be sort of characterised as a diode, they are of course actually current sources and the model diagram is attached.  

The blue current is when the cell is open circuit.  All the photo current effectively flows through the internal diode and makes the maximum voltage drop of the diode appear at the output (the open circuit voltage Voc).  When the cell is short circuited externally, all the green current flows through the short circuit (the short circuit current Isc) and none though the internal diode so zero volts appears across it (and the output).  The maximum power is achieved at the point where enough current flows through the internal diode to make the maximum power voltage across it (Vmp) and at the same time the maximum excess current flows through the external load (Imp).  Imp x Vmp = Pmax.

The current source is what "passes" the bulk current "through" the cell. Their forward "conduction" is determined in the majority by the light falling on them.  When shaded, the current source stops and the cell takes on a shunt resistance Rsh (caused by defects in the silicon) and otherwise would look like a reverse biased diode (not a forward one!).  Without their positive terminal "pushing" current out, the negative doesn't pull current from that side of the junction and it looks like a resistor of about 1kOhm.  The PV diode is also pretty weak and has a reverse voltage breakdown of about -5V so at first the cell will leak current through the Rsh shunt resistance but after the -5V breakdown voltage is breached, the cell will then conduct strongly and self-destruct if the external source is able to deliver lots of Amps.

Unlike a "proper" diode, the PV PN junction is only a thin layer on the surface of the wafer that is susceptible to photons creating electron-hole pairs at the boundary.  The electric field across the PN junction tends to pull the electron away from the hole it was knocked out of by the photon and this electron is picked up by the metal electrode and scoots off round the circuit, coming back to the other side of the wafer, where it meets the spare hole floating about in the P layer that makes up the bulk of the wafer.  This is how the wafer is able to apparently "conduct" a large current without heating up.  In practice, it is only sourcing an electron from one side and collecting one from the other.  The energy to create the "conduction path" and the make the current flow came from the photon.  Turn off the light and the holes stop getting made and the "resistance" of the cell becomes a function of the physical resistance properties of the wafer (Rsh and the small series resistance Rs of the printed on metal contacts) as now there are no holes being made for externally "pushed" electrons to go into and no "released" electrons on the N side that are free to scoot out and round the circuit.  So the junction goes high resistance.

The shaded cell in a 17.5V string can easily have its -5V breakdown voltage overcome by the other cells in series and it will conduct at that voltage and so dissipate lots of power.  A high power string with no bypass diodes can crack the glass the wafer is mounted on through thermal stress.  An 80W 17.5V panel under full load would try to push about 4.57A through the shaded cell and the broken down internal diode will conduct 4.57A at -5V, giving about 22.8W of heating in that wafer!  The bypass diode saves the day as it gives that 4.57A an easy route to get around the shaded cell (as it will conduct at about 0.5V, before the cell's diode can break down).

So bypass diodes on small blocks of cells are "a good thing" because then the rest of the string can continue to source 4.57A but just minus the voltage contribution of the bypassed cells and the voltage drop of the bypass diode itself.  Plus none of the cells blow up.

Modules connected in parallel need blocking diodes because you can see from the model that if you connected another cell (or module) in parallel to the first one and one of them was shaded (or just lower output) then current could flow backwards though the cell (forwards though the internal diode).  With these blocking diodes, if a number of strings are in parallel, they will all contribute some current to the total output so long as they are all pretty close in output voltage.  A higher voltage, high power panel would possibly block others from contributing but a MPPT controller will scan the IV curve and settle on a load voltage that maximises the total power of the entire array.  This is why it's important that a MPPT controller scan for multiple peaks in the power curve and only latch on to the highest overall power peak.  Using multiple controllers allows use of grossly mis-matched sub-arrays.  I've got one controller that works in the 46V range with the Sharp ND170 panels and the other controller is connected to various 35V range strings in parallel.  

The blocking diodes also mean that different parts of the array can output at different times or under different lighting conditions.  Some are angled steeply to catch direct winter sun (if any) from towards the horizon and others are angled shallow to catch diffuse light from an overcast sky.

It seems largely self balancing and I do consider things like putting lower voltage strings closer to the controller (shorter / fatter wire) than higher voltage strings that can be further away or use thinner wire.  It also depends on the power of the string.  An 80W string suffers lower line and blocking diode volt drops at its max power point than a 160W string of the same nominal voltage.

I haven't bothered with expensive Schottky diodes as you can't easily get ones with blocking voltages over 30V, so I just use 600V regular ones.  They lose about 0.8V at full power.


Title: Re: Cobbled together PV in W.Sussex
Post by: StBarnabas on December 12, 2009, 08:52:26 AM
Hi Outa
a very clear explanation. Have an applaud for taking the time to explain in such detail
StB


Title: Re: Cobbled together PV in W.Sussex
Post by: Outtasight on December 12, 2009, 11:31:46 AM
LOL... Thanks.  It's a pity that I didn't go on to then actually fully answer Paul's question about current balancing.  facepalm

When I said the system of parallel module strings was largely "self balancing", I should have explained that if the strings are all of a close voltage range (all are Pmax at 17.5V +- 0.5V for example) then a panel with a higher output Vmp will try to increase the output voltage into the load (assuming it can source enough current to do this).  The lower voltage panels can't keep up (as their Vmp is say 0.5V lower) and their outputs will get dragged up towards the higher overall output voltage.  But at this point, the internal diodes in them start to conduct more of the blue current again (and less of the green) and so their output current collapses as the cells try to get closer to their open circuit voltage (Voc).  But at the same time, the thing swings the other way because the higher voltage panel is now trying to supply the load by itself with no help from the others.  If it can't source all the current by itself or voltage drops across resistance Rs, external wire resistance, blocking diode voltage drops (that increase with current passed) will cause the voltage seen at the point were the other panels are connected in parallel to sag.  If they drop far enough, the low voltage panels will get back into their power band, the blue current decreases and the green current increases and they can start contributing current to the load again.

So in a mis-matched array you do lose a bit of power from panels that have too different voltage ratings but you can compensate by virtue of where you physically put them in the wiring loom as the volt drops from the wiring are quite a significant factor.

What you don't want to do is put a 16.9Vmp 160W panel at the end of 10m of bell wire and a 18.0Vmp 40W panel next to the load at the end of 2m of 35mm2 wire... That would just be silly  ;D


Title: Re: Cobbled together PV in W.Sussex
Post by: davebodger on December 12, 2009, 11:35:35 AM
I haven't bothered with expensive Schottky diodes as you can't easily get ones with blocking voltages over 30V, so I just use 600V regular ones.  They lose about 0.8V at full power.

I found it easy to get Schottky diodes over 30V from Farnell - I recently bought some 60A 40V for under £2 each.
They go up to 60V at reasonable current ratings although the higher voltage ones can be a bit more expensive.

That was a great dissertation on solar cells !
Very informative. Thanks.



Title: Re: Cobbled together PV in W.Sussex
Post by: EccentricAnomaly on December 12, 2009, 02:46:37 PM
Yes, excellent explanation Outtasight.  Thanks, have an applaud.

One word that might be slightly misleading, though:

Quote
...scan the IV curve and settle on a load voltage that maximises the total current contribution of the entire array...

"current" would be better as "power", wouldn't it?


Title: Re: Cobbled together PV in W.Sussex
Post by: Outtasight on December 12, 2009, 04:38:16 PM
Yes, excellent explanation Outtasight.  Thanks, have an applaud.

One word that might be slightly misleading, though:

Quote
...scan the IV curve and settle on a load voltage that maximises the total current contribution of the entire array...

"current" would be better as "power", wouldn't it?

Fair point... fixed now by an edit in the original post :).

On the Schottky diodes, they probably make most sense on a 17.5V array but I'm running at 35V and open circuit that can be up to about 42V for the poly/mono modules I have but as high as 52V for the amorphous ones.  I might look into it though as I'm phasing out the amorphous ones so that would mean I wouldn't need 60V parts.


Title: Re: Cobbled together PV in W.Sussex
Post by: Outtasight on December 25, 2009, 05:10:22 PM
I knew it was a good idea to bodge all my PV on the ground / garden wall / garage roof...  It's within reach of the broom  ;D

Finally got the pair of 40W panels ooop on 'twall at a near vertical angle to catch the 2 hours of feeble solstice sun 8).  Missus noted empty spaces to the right of new "winter panels"... What could that possibly be for?  whistle

(http://i46.tinypic.com/25k4vpj.jpg)

The eagle-eyed will spot that I've given up on alu frames and now have resorted to recycled picket fencing to construct my mounting [ahem] "hardware".

(http://i46.tinypic.com/ej9cp3.jpg)

After some thawing and refreezing though I couldn't shift the ice as it had welded on to the glass but after a bit of sun it would shift.  If I brushed it enough to let some black spots show through, the sun could heat the glass enough to loosen the ice and it would then slide off.  Luckily, with so many independent strings (all mine are 35V pairs) there would be at least some strings working even if others were snow-bound.

It's just a pity I've blown all that solstice battery power on the old incandescent Christmas tree & window display lights in the living room ::).

http://www.youtube.com/watch?v=hRv3ld4Bmoc (http://www.youtube.com/watch?v=hRv3ld4Bmoc)


Title: Re: Cobbled together PV in W.Sussex
Post by: StBarnabas on December 29, 2009, 12:52:55 PM
Hi Outta
great stuff - have been away from a computer for a few days. The StBC PV system has had a few great days 6kWh on the soltise itself and two more days within the past week of 7+kWh.
Sean


Title: Re: Cobbled together PV in W.Sussex
Post by: Outtasight on December 29, 2009, 09:38:15 PM
Hi Sean,

Yeah yesterday was a corker and I even got to run the water heater dump load for 45 minutes... Which almost turned into a faux pas as after the excitement of being able to heat some water in mid-winter, I forgot to put the immersion back over to the mains timer afterwards  :fight

Luckily, the solar power had been just enough to raise the tank from 36C to 40C and so I managed to fill the bath without using any cold water to mix and got away with it. 

Didn't last though and today the sky was as black as the inside of a coal miners underpants.  :(



Title: Re: Cobbled together PV in W.Sussex
Post by: guydewdney on December 29, 2009, 11:25:08 PM
<gloat mode on>

9568 units made so far (about 14 / 16 months)

so much leccy being made - that am switching on 1kw heaters in the kitchen.....


<gm off>


Title: Re: Cobbled together PV in W.Sussex
Post by: Outtasight on December 30, 2009, 11:09:59 PM
Trust the hydro-guy to rain on my parade...



Title: Re: Cobbled together PV in W.Sussex
Post by: Outtasight on February 10, 2010, 09:35:04 PM
After spending most of January brushing snow off the panels only to expose them to a near black sky before trudging indoors to bask in the glow of the battery charger, the Sun has finally started to put in an appearance once again. So the house lights have gone back on to full time off grid operation.

This week has seen some big changes though.  I won a pair of 80W BP380U panels on eBay for £253.  I couldn't put them outside as I've yet to make the mounts for them and it started snowing again today.  So they are propped up in the patio windows on the inside and were connected directly to the battery during a long bulk charge (no risk of over charging the pack today as I'd used quite a lot yesterday).

The other reason why the new panels were bypassing the charge controller is because the little 15A beastie is now bursting at the seams, with over 1kW already crammed into its 400W input  whistle.  It started cutting out in the afternoon sun... massively overloaded, it couldn't throttle back the current and took to sulking instead (I'd had this last February when I'd overloaded the first controller).  Nothing for it then...  New controller time!

Finally, after months of delays and shortages, I've managed to get hold of a new Morningstar Tristar MPPT 60A controller (or at least will have done by Friday, hopefully).  Just in time for weekend tinkering... Wassat dear, something about a romantic weekend?  Sure, pass me that screwdriver will ya?  ;D



Title: Re: Cobbled together PV in W.Sussex
Post by: EccentricAnomaly on February 11, 2010, 09:46:58 AM
The other reason why the new panels were bypassing the charge controller is because the little 15A beastie is now bursting at the seams, with over 1kW already crammed into its 400W input

What this chap (http://community.livejournal.com/green_power_gen/) does (or did, his system's evolved a bit and I've lost track) is point some of his panels east and some west to get a longer day within the capabilities of his charge controller.

Thinking about it a bit - you could point the panels which bypass the charge controller east on the assumption that the battery wouldn't be fully charged early in the day anyway (and if it is then we'll call it an equalization charge).


Title: Re: Cobbled together PV in W.Sussex
Post by: Paulh_Boats on February 11, 2010, 08:35:03 PM
Outasight

Is there any chance you could cobble together a circuit diagram? Would be interesting to learn where the electric string goes!

cheers
Paul


Title: Re: Cobbled together PV in W.Sussex
Post by: Outtasight on February 13, 2010, 12:07:21 PM
What this chap (http://community.livejournal.com/green_power_gen/) does (or did, his system's evolved a bit and I've lost track) is point some of his panels east and some west to get a longer day within the capabilities of his charge controller.

Thinking about it a bit - you could point the panels which bypass the charge controller east on the assumption that the battery wouldn't be fully charged early in the day anyway (and if it is then we'll call it an equalization charge).

I've sort of got that situation now.  If I'd aligned all my panels for peak output, I'd have probably set fire to the little controller  whistle.

Some panels are at very shallow angles to optimise them for summer and others are near vertical to optimise for winter while others are sort of at 45 degrees to balance winter and summer output.  Admittedly, all are pointing due south and this year I might angle some to favour late / early afternoon. Morning is a bit pointless as there's a row of tall trees in the E to SE so I get a lot of problems with shading in the morning.

Here's my new BP panels propped up in the patio window. 

(http://i46.tinypic.com/dnlhdf.jpg)

Really must get round to building a frame as soon as it gets warmer outside.  Having gert big solar panels in yer patio windas does have one side benefit... They absorb more heat than the curtains and act like thermal radiators on a sunny day, making juice and heating the room at the same time...  Bonus!

I'll get round to updating my circuit diagram soon and post it.  It's changed a bit since I last did one for the post about me "Fridgenstein" experiment.


Title: Re: Cobbled together PV in W.Sussex
Post by: Outtasight on February 15, 2010, 11:08:32 PM
It's a bit of a monster circuit diagram... see the attachment (fits nicely on a A3 sheet!).  It's all a "temporary" installation, honest guv'.

The Tristar MPPT-60 and its optional meter front turned up Friday, early AM.

(http://i47.tinypic.com/30kukih.jpg)
Mmmmm Shiny.

Got it all installed on the wall and only demolished one bit of plasterboard corner than will need some plaster patching (ahem...).

(http://i50.tinypic.com/vne8g9.jpg)

I was pootling around in the local HW store looking for rubber grommets to go in the HUGE knockouts (wot don't knock out without a 50lb lump hammer  >:() and saw some neat two slot consumer unit-type-things and next to 'em...  100A dual pole two slot MCBs!  I'd been wondering how to upgrade the existing disconnect switches that I had (puny 20A automotive ones) and had toyed with the idea of 45A cooker switches.  But 45A still isn't enough for a 60A charge controller.  These 100A MCBs are ideal though (assuming they'll actually work at 24V-46V DC).

I'd never got round to putting disconnects on the PV inputs to the charge controllers before but as there were two sets of these things in the shop, I went for it.  So I used one double pole MCB to break the two PV inputs to the two controllers and the other one to break the outputs of the controllers to their fused battery connections.  Of course, normally both breakers will be closed and I'd try not to go opening them when under heavy load (that's how one old 16A switch burned out).  I'd looked at "proper" solar DC disconnects but they are very expensive and I don't actually need switches rated for switching 400V DC.

I uprated all the battery wiring to the controllers (10mm2 all round for the old 15A SunSaver and 20/25mm2 for the new TriStar)...  Pity that the feeder from the junction box outside is only 6mm2. Another project to take care of before it gets too sunny  whistle.

And with a bit of the magic yellow thing in the sky...

(http://i45.tinypic.com/2qs6v6p.jpg)

THAR SHE BLOWS!!!!

Shame about the cheap yellow rubber buttons wot you have to stab quite hard to make work properly.  And the charge status LEDs that don't come anywhere near the window in the front plate so you can't see them properly from anywhere other than straight-on in front of the thing...  Might have to fettle that when the thing's been "run-in".



Title: Re: Cobbled together PV in W.Sussex
Post by: Paulh_Boats on February 15, 2010, 11:42:43 PM
Outtasight,

Thanks for the diagram update - it makes the National Grid look simple  ;)

How do you switch the lights from solar to grid?   Also how do the two controllers react when both feeding the batteries?


I've been toying with the idea of a backup system that steals a bit of power from my Soladin 600 DC feed - a simple PWM controller will ignore the voltage variations due to the MPP tracking and present a steady current load. So in turn the Soladin should find the optimum load point for the remaining current??

The Prostar 30 looks good, but its not cheap whereas a SunSaver might do all I need (also have an ex-equipment SunGuard 4 in the gadget box).

I have a few ideas of running the slow cooker and bread maker from solar to establish off grid independence....similar for emergency lighting.

cheers
Paul


Title: Re: Cobbled together PV in W.Sussex
Post by: Outtasight on February 16, 2010, 01:39:48 AM
Hi Paul,

Where you see a pair of sockets (solar and grid) with a dotted line to a device or circuit, that's just a manual change-over socket.  Nothing more than a 13A plug that can be moved between two 13A sockets.  Avoids having any "dodgy" switches or relays with different phase mains on it which can cause magnetic recoil in transformers if you switch too quickly between sources.  By using a 13A plug/socket it also makes a convenient 3 pole switch that is guaranteed to take more than 1 second to change over so there's no risk of a magnetic recoil surge from the load.

The two controllers co-operate just fine.  They are programmed for the same voltage set points and both have the same remote temperature readings for compensation.  Mostly, they both put out current into the battery but in the final stages of charging, the weaker one (by reason of PV input or output capacity) will sometimes defer to the other one.

So, if the battery and loads are only demanding 5A and both controllers are receiving at least 5A of PV input, one might throttle back to 0A (but not go negative) and the other will sit at 5A.  If neither can deliver the full 5A, then they'll do what they can (e.g. 3+2) as they both want to maintain the same voltage.

If one goes into float before the other then the one that is trying to "float" at a lower voltage will just sit at 0A (again, it won't go negative) until the other one gives up "absorbing" and then they'll both sit at float level.  When I used flooded batteries I used to set just one controller to do equalise charges as that way you didn't get too many equalise charges in a month (it was programmed on a 28 day cycle or after a >70% discharge).  They didn't communicate though so you couldn't tell one to not do an EQ because the other had already done one, so I disabled EQ charges on the other.

It's not an issue with my current gel batteries as they don't need equalisation charges anyway.

A slow cooker might be harder to power than you think.  A typical slow cooker is about 350W and might have to run for 4 hours.  That's a lot of battery juice (if the PV can't keep up).  That's about 64Ah at 24V.

By contrast, I often use a mini toaster oven (450W for 5-10 mins) or a kettle (950W for 3 mins) or a automatic egg steam boiler (350W for 10 mins) or the rice cooker (350W for 20 mins)...  None uses more than 5Ah so even if it's cloudy or early in the morning, I can use them and the PV will put it back quite quickly.

Only on really clear blue sky days can I consider the immersion heater over to solar power (650W for 2-3 hours).  The battery has to be in a high state of charge and I have to keep an eye out for cloudy weather coming so as to make sure that the PV is taking most (if not all) of the strain with the battery just filling in the gaps.

Putting a PWM controller on the same PV input as the MPPT of the Soldin might wig it out.  I had problems with one experiment where I had too much voltage on the input of my SunSaver with amorphous panels in triplets (the open circuit voltage got too close to the 75V limit of the controller).  So I devised a voltage limiter to apply a load across the PV when it was swept by the MPPT sweep.  This clamping of the PV open circuit voltage to about 65V confused the hell out of the MPPT software and it started doing weird things (locking on to non-maximum power points at odd voltages), so I gave up and went back to just pairs of panels.

A simple PWM controller (like the 12/24V ProStar) can't handle the high input voltages of a Soladin PV string.  Only MPPT controllers are designed to work at higher PV voltages (75V to 150V).  I believe the Soladin needs at least a 48-60V nominal array to work.  A 48V ProStar would do though (if using a 48V nominal array) but then you'd need a 48V battery bank and a 48V inverter to do something useful (like run a slow cooker) from it.  Those cheap recycled 3kW UPS inverters you sometimes see on eBay often run from 48V.

Trouble is, the ProStar controllers only use PWM throttling when in their absorption or float phase.  In the bulk phase they connect the PV to the battery directly and so try to push as much current as the PV can deliver into it (maybe with PWM current limiting if you overload the input - the ProStar is rated for up to 25% overload).  If that doesn't wig out the Soladin, I don't know what would  ;).


Title: Re: Cobbled together PV in W.Sussex
Post by: guydewdney on February 16, 2010, 08:11:07 AM
(http://i50.tinypic.com/vne8g9.jpg)

This is in your living room? You arn't married are you!  :o ;D

A good place to find cheap big FOAD switches is fleabay - look under 3 phase switches - no one wants second hand big three phase stuff, I got a pair of 200+ amp switches in boxes for about a fiver - lockable too - so good for the G83 compliance.


Title: Re: Cobbled together PV in W.Sussex
Post by: Outtasight on February 16, 2010, 06:26:06 PM
Quite happily married... but it's probably safest if small children don't come to visit.  Can't have toddlers chewing the battery posts...


Title: Re: Cobbled together PV in W.Sussex
Post by: Paulh_Boats on February 16, 2010, 06:34:59 PM
the ProStar controllers only use PWM throttling when in their absorption or float phase. In the bulk phase they connect the PV to the battery directly

Well that's knock the ProStar idea on the head. Tell me please the TriStar does the job properly  ;D

cheers
Paul

And thanks for the great applaud worthy reply!

EDIT: Just read the TriStar manual and its the dogs doo-dahs. Bulk charging is direct also.


Title: Re: Cobbled together PV in W.Sussex
Post by: StBarnabas on February 16, 2010, 10:23:21 PM
Quite happily married... but it's probably safest if small children don't come to visit.  Can't have toddlers chewing the battery posts...
Guy must have a wife like mine! For me it would be totally inconceivable to have such overt electronics in a living area. Is your Wife an Electrical Engineer?
Sean


Title: Re: Cobbled together PV in W.Sussex
Post by: billi on February 16, 2010, 10:38:59 PM
Quote
Guy must have a wife like mine! For me it would be totally inconceivable to have such overt electronics in a living area. Is your Wife an Electrical Engineer?
Sean

We all know Outtasight is a clever guy , and i expect he has something like that  to calm her down  ;D

Billi


Title: Re: Cobbled together PV in W.Sussex
Post by: StBarnabas on February 16, 2010, 11:01:43 PM
Billi
have an applaud! Made me laugh!


Title: Re: Cobbled together PV in W.Sussex
Post by: Outtasight on February 17, 2010, 12:11:54 AM
ROFL... Nice one.

No, she's just a kind soul that lets me do what I want in my space. The power centre is in the corner of my "cinema" with one wall painted grey as a screen for the video projector and otherwise generally full of AV gear.  The inverter and battery bank are under / behind one of the comfy chairs.  The other half of the living room is separated by a half partition. It used to be two rooms but the previous owner knocked it through apart from the chimney & fireplace that was in the middle of the wall so that had to stay.  That half of the room is "her" side so has the usual dining room / living room accessories and no "weird stuff". 

Besides, she's quite keen on the idea of solar. Her sister and father have both got big grid tied systems on their houses (3kW & 5kW respectively).  Her dads house has the inverter in the dining room on the wall and a massive air source heat pump in the utility room, so it kinda runs in the family...

She probably spotted I was a mad inventor type and was attracted by that  :-*.

That said, when it eventually stops raining / snowing / being dark as night in the day, she'll probably want to be able to see daylight through the patio doors and be able to open them and go outside...  whistle.


Title: Re: Cobbled together PV in W.Sussex
Post by: Outtasight on February 17, 2010, 11:06:25 PM
Some examples of what the built in web server gives you...

(http://i50.tinypic.com/2mzwtjo.jpg)

(http://i47.tinypic.com/2n6gchy.jpg)

Apparently, with an adaptor, the SunSaver MPPT-15 can be connected to the EIA-485 serial bus on the TriStar and then bridged to the Ethernet so that you can remote control and instrument the SunSaver, even though it has no native IP capability.  That way, I'd be able to log data from both controllers and do stuff like intelligent load management.

Even though it was cold outside today, it was at least very sunny and so I could finally make some progress on painting the wood preserver on the frame for the BP panels sitting in the window.  With clear skies above, I managed to run the water heater and the computer room from solar and still had 8A to spare to keep charging the battery.  In about 90 minutes, the water went up by about 9'C.  So, rather conveniently, each 10 minutes of solar power provides a 1'C boost in water temperature.


Title: Re: Cobbled together PV in W.Sussex
Post by: RichardKB on February 17, 2010, 11:31:07 PM
Because you have an MPPT controller you could do with a higher array voltage for your 24V battery setup. I have just checked the datasheet the maximum voltage is 150V this would make it more efficient if you had a higher array voltage, say 3 panels in series or 4.

Rich


Title: Re: Cobbled together PV in W.Sussex
Post by: EccentricAnomaly on February 18, 2010, 10:46:54 AM
Clearly you want the array voltage to be high enough that in low but usable light conditions the Vmp is still enough above the battery voltage that charging can take place.  Also, higher voltages will result in smaller losses in the cabling.  Beyond those considerations, are there any advantages to higher array voltages?


Title: Re: Cobbled together PV in W.Sussex
Post by: RichardKB on February 18, 2010, 12:03:24 PM
Clearly you want the array voltage to be high enough that in low but usable light conditions the Vmp is still enough above the battery voltage that charging can take place.  Also, higher voltages will result in smaller losses in the cabling.  Beyond those considerations, are there any advantages to higher array voltages?

No you are quite right with your statement but with an MPPT controller running with only 32V which is only 4V above the charged battery voltage the controller has very little room to work with.


Title: Re: Cobbled together PV in W.Sussex
Post by: Outtasight on February 19, 2010, 12:33:19 AM
I did try reconfiguring the arrays for 36V nominal a while back but there were two problems... The SunSaver could only go up to 75Voc and I have some amorphous panels that put out 26Voc, so three in series could put out 78V.  I played with a voltage clamp at 69V but the controller didn't like it.  The second problem was that groups of three panels suffered from shading more, especially as the panels are just sort of spread around the garage and garden wall.  What with nearby trees and encroaching shadows from walls and fences and so on, it's easier to keep the more of the array productive if it's broken up into small "cells" that can function independently in patches of light.  If the whole lot was connected in series there'd only be an hour or so in the day when the whole thing was shade-free.

If I get round to mounting the whole lot on the house roof then the shading problem will go away and all the panels will be angled at the same bit of sky so the array will be balanced.  Also, it would be ok to run at high voltage up on the roof - away from the risk of cats chewing the cables and human folk coming into contact with the panels. 

It's worth thinking about though... The 9 main panels on the garden wall could be connected with the 160W 35V panel in series with the others connected in two parallel strings of four to give me 800W at 105Vmp.

I'll stick with my 35Vmp set-up for now.  If you can keep the wiring losses down, the controller actually operates at its highest efficiency at lower voltages.  This is especially true at low powers.  At 100W (common on a heavy cloud day like today), the converter efficiency for a 98Vmp array input is only 90% compared to almost 97% for a 33Vmp input.  So, if you can keep the wiring loss down to 2% or less, running at lower voltages can be advantageous in winter.  Even at the other end of the scale it's better to run at low voltage (33Vmp at 1kW gives 98% efficiency compared to just under 96% at 98Vmp).

Luckily, most of my panels are very close to the controller as they are effectively just on the other side of the wall and the cable run from the outside junction box to the controller input is about 3m.  From the junction box, each pair of panels has its own feed using differing cables from 2.6 to 6mm2, depending on the power of the panels on that leg.  Now that I'm pulling over 20A instead of just 11.5A from that junction box, I'll have to upgrade the feeder to 25mm2 to match the rest of the new wiring I installed for the new controller.

The big Sharp 340W string on the garage roof fares quite well on the SunSaver controller as the pair put out 46.4Vmp. That helps keep the losses down as they are at the end of 13m of 4mm2 wire to the house.



Title: Re: Cobbled together PV in W.Sussex
Post by: EccentricAnomaly on February 19, 2010, 10:07:10 AM
Outtasight, thanks for your detailed and numerate discussion of your experience with your panel setup.  It's really helpful to me, at least, in understanding the practical issues with designing a system.


Title: Re: Cobbled together PV in W.Sussex
Post by: Outtasight on February 28, 2010, 10:28:50 AM
Today's Episode:  Putting the Navvi into Navitron  ;D

I finally got a couple of dry enough days to get the frame together for the new BP380U panels and so out they went, replacing the last of the old 12W modules.

(http://i48.tinypic.com/2dhdxzm.jpg)

This then presented a couple of problems. 

Firstly, the array was now making so much power (I've seen 1,047W logged on the new TriStar controller) that the feeder from the junction box outside has been getting a little warm... Not good.  Both in terms of it (and the chocblocks in the the junction box outside) getting hot and also in the power losses.

Secondly, the change from amorphous to crystalline cells has made the array much more susceptible to partial shading.  Covering one cell with my hand causes the amps to collapse from a string pair.  The overhead wires to the garage cast a moving shadow across the six panels that make up 480Wp of the array and now at least one of the three blocks always had a line shadow across it.

I bought a bigger junction box and used some solid earth blocks to make up positive and negative bus bars.  This connects to the gubbins indoors by 25mm2 jump start cable, eliminating the volt drop and heating problems at even the new controllers 60A maximum.

(http://i49.tinypic.com/4iis03.jpg)

The second problem involved some push fit waste pipe and a lot of digging.  The push fit joints to link the pipes and make the right angles are easy to use and should be water tight with their built in o-rings.  Pretty cheap too.  I was considering using pond hose but it's more expensive and you'd have a hard time feeding the wire through 6m of the stuff.  With the waste pipe I could push the wires through it section by section and then join the sections up when I'd finished.  A bit of oil on the o-ring makes it easy to push them together.

I decided to replace the two other scrawny wires that linked the small strings on the garage roof with a bit of 6mm2 twin and earth cooker wire that I got from a car boot sale last year.  Being only chunky stranded, it was no good for an overhead link as the swaying in the wind would damage the copper but buried underground it's in its element.  I twinned the positive and earth conductors so that (in one direction at least) it is actually 8.5mm2.  That should be enough to allow some modest expansion of the array on the garage roof  ;).

(http://i45.tinypic.com/e0nyc8.jpg)

Here you can see it all fitted together.  I considered putting the CCTV Cat5 cable down it as well but it's not a good idea to run data in the same trunking as high power cables.

(http://i48.tinypic.com/2449kc4.jpg)

In order to keep the peace with 'er indoors, I had to devise a way to do the construction work so as to not make a mess of the lawn. 

The tricky part was cutting out the turf in sections to allow excavation under it.  Laid to one side for later and the soil taken to a hidden part of the garden in buckets to keep it off the rest of the grass.  Here I haven't started digging out yet.  I went about 25cm down in the end.

(http://i45.tinypic.com/33ni6tz.jpg) (http://i47.tinypic.com/2wcln29.jpg)

I was amazed the first time I visited Japan.  I was walking to the hotel after a night out and saw a massive hole in the ground swarming with workers and football stadium flood lights and a huge noise.  I pitied the poor residents their lack of sleep.  But walking back that way the next day, I was stunned... The roadworks were all gone.  Filled in.  Finished... In one night.  British Gas and Thames Water, take note  >:(.

So the missus expected the same service.  Later that night by garden flood light...

(http://i45.tinypic.com/25jea34.jpg)


Title: Re: Cobbled together PV in W.Sussex
Post by: Outtasight on March 01, 2010, 11:08:22 PM
Free hot bath today!

Nearly wall to wall blue sky today and with the added charge capacity of the TriStar, I was able to run round and turn everything on!  The battery had done it's last 20% by about 10am, I turned on the 115V water heater and put all the computers on solar and even the fridge-freezer too.  The 3kW inverter can handle all that lot and a 850W kettle without throwing a wobbly.

The water in the tank is never mains water cold as there's always some dregs of heat left in it from the previous night and so it started at about 29'C at 9.30.  Five hours later the thermostat clicked off at 61'C.  My first full tank of piping hot water without recourse to any mains electricity ;D.

The 650W 115V water heater is just about the right size load for the array as it can service that load and still put up to 8A into the battery to finish off its absorption phase, keep it floating at 1-2A or recover from a short gap in solar power from the odd passing cloud.

By the end of the afternoon, the TriStar read 4.15kWh collected and that didn't include the other controller that I didn't data log today but was also pumpin' out around 320W for quite some time.  Most of that power went directly through the inverter and to the loads as the battery was full and just floated in the afternoon, filling in for the odd cloud or bit of haziness. 

Tomorrow's set to be another bumper harvest day too! 


Title: Re: Cobbled together PV in W.Sussex
Post by: Paulh_Boats on March 01, 2010, 11:24:03 PM
Free hot bath today!

Nearly wall to wall blue sky today and with the added charge capacity of the TriStar, I was able to run round and turn everything on!  The battery had done it's last 20% by about 10am, I turned on the 115V water heater and put all the computers on solar and even the fridge-freezer too.  The 3kW inverter can handle all that lot and a 850W kettle without throwing a wobbly.

The water in the tank is never mains water cold as there's always some dregs of heat left in it from the previous night and so it started at about 29'C at 9.30.  Five hours later the thermostat clicked off at 61'C.  My first full tank of piping hot water without recourse to any mains electricity ;D.

The 650W 115V water heater is just about the right size load for the array as it can service that load and still put up to 8A into the battery to finish off its absorption phase, keep it floating at 1-2A or recover from a short gap in solar power from the odd passing cloud.

By the end of the afternoon, the TriStar read 4.15kWh collected and that didn't include the other controller that I didn't data log today but was also pumpin' out around 320W for quite some time.  Most of that power went directly through the inverter and to the loads as the battery was full and just floated in the afternoon, filling in for the odd cloud or bit of haziness. 

Tomorrow's set to be another bumper harvest day too! 

Great news Outtasight, did you know you can now qualify for FITs if you had grid tie and an Ofgen meter? See:

http://www.navitron.org.uk/forum/index.php/topic,10035.0.html

cheers
Paul


Title: Re: Cobbled together PV in W.Sussex
Post by: Outtasight on March 02, 2010, 11:08:31 PM
Hmmm... had a look though a couple of the referenced threads.  It's a good change for Sean and a few others but the likes of Justme, Billi and me won't get anything out of it, being off-gridders.  I've got the same issues as them in that sometimes I resort to a mains battery charger in the winter to save the bank from rotting and that power is then recycled though the inverter to loads, so a few kWh here and there aren't "renewables" but would go through the total generation meter none the less.  I keep tabs on the grid charger with a separate kWh meter attached to the socket it leeches from and then for my own records, I subtract the charger kWhs from my total generation meter kWhs so I know the net PV generation.

Today was another 4kWh+ day though so I'm still as happy as a person with free hot water  ;D







Title: Re: Cobbled together PV in W.Sussex
Post by: billi on March 02, 2010, 11:24:39 PM
Quote
being off-gridders
 ;D

Never would like to miss what i learnt so far ( i am not a technical advanced person  :norfolk :garden ), but independancy fourced me to that route  ;D

Billi


Title: Re: Cobbled together PV in W.Sussex
Post by: Outtasight on March 04, 2010, 10:04:15 PM
Ahhh... missed a bit... of wiring that is.

Having upgraded the whole path way from the junction box outside to the TriStar and the fuses on the other side of the new 100A battery disconnects with 25mm2 cable, I'd thought I'd cured my unintentional heating elements... But I'd forgotten to upgrade the bit that goes from the fuse to the battery.  I have two fuses, one for each controller but both were still connected with about 50cm of 10mm2, soldered into a single 8mm ring terminal at the battery post.  One is fine as it only has to carry 15A at most but the other is now seeing peaks of 40A and getting a bit warm.

I didn't have any more of the car jump lead, having used it all up already but luckily, I had a bit of 16mm2 that I picked up at a car boot last year. So I made up a new link for the 15A controller with that and used the two existing links combined together for the TriStar fuse, giving it 20mm2

Seems to be running cool now, although following the pattern it'll probably be the turn of the battery to overheat now from over-zealous charging currents  ::). 


Title: Re: Cobbled together PV in W.Sussex
Post by: Outtasight on March 08, 2010, 11:56:52 PM
The last couple of days have just been outstanding for clear blue skies!  In the last 24 hours to noon today, I used 5.3kWh of solar power (mostly on water heating and the fridge)... Just shy of 47% of my total electrical power needs by solar today. Over the whole week to Sunday I averaged 22.6% of requirement.  The combined array made a peak power of 1.36kW today (some way off the design peak of 1.44kW but it seems to drop off as the panels heat up compared to those very frosty days).

The cheap-o no-brand (Chinese) "mono" 80W panels were noticeably poorer than the Sharp and BP poly panels (putting out only 32.0V @ 3.88A in the heat of the noon sun today, compared to 33.0V @ 4.5A - 4.6A for the good brands).  The cheap-o panels Isc was on the money at 5.1A but their Vmp is lower than the other panels so they struggle to put out power in the combined array (dragging the overall Vmp down).  I have to look at upgrading the blocking diode on them to super low Vf Schottky types to claw back some of the voltage loss compared to the other panels.  I'm also guessing the black cells actually get hotter in the sun than the blueish ones and this also makes them put out lower volts under the same conditions...

Even so, I made more than enough power to keep the water heater and the fridge chugging the whole day and keep the battery topped off so it's now not so important that I optimise the array to the nth degree.

Roll on the summer!  8)


Title: Re: Cobbled together PV in W.Sussex
Post by: Outtasight on March 09, 2010, 10:45:05 PM
I was (well still am actually) considering getting the RSC EIA485 adapter for the Sunsaver charge controller.  This would allow connecting it to the TriStar and bridging the Ethernet IP data to it, so that I can data log both controllers from the PC upstairs.  Nobody's got them in stock though and they cost about £60 (a bit of a rip-off for a serial port buffer).

While at a car boot sale (the first of the season locally) I spotted just what I needed for my aged Toshiba laptop for it to do the business downstairs...  A pair of old laptops for £5!!!  Actually, I didn't want the laptops but one had an ancient PCMCIA 10Mbit Ethernet card in it (the Toshiba can't use modern CardBus types).  As it turned out, the two laptops actually worked and could both run XP so no doubt they'll find some use around the house.  It's cheaper to pick up old PCs than buy PIC controllers from Maplins  ::)

Now with the Toshiba able to read the two charge controllers and log them, I could measure total system power.  The Toshiba is a useful laptop as it's an old 33Mhz Win98 machine that can run on just 11-14W of power (11W with the display off) so it runs from the unmetered AC socket on the inverter but doesn't consume too much to do it's work.  In fact, as the generating day comes to a close, I unplug the AC adapter and it runs from its internal battery for a couple of hours.  I managed to find a replacement battery for it on a "laptop batteries R Us" type site and so the machine works as new now.  The laptop cost me £5 but the battery cost £25! 

The logger software can't do the arithmetic to combine the separate figures for charge current but that's easy to fix in Excel as the logger creates simple CSV text files.  I can transfer the days data to the PC upstairs and add a couple of columns to the data (adding the currents together and then multiplying by the battery voltage to give system power).

time (UTC)                                 Battery (V)   Current1 (A)   Current2 (A)   System Current (A)   System Power (W)
2010-03-09T10:30:30.090+00:00   27.29           10.82            3.94             14.76                       402.9
2010-03-09T10:30:45.090+00:00   27.29           12.97            4.61             17.58                       479.8
2010-03-09T10:31:00.080+00:00   27.33           14.13            5.52             19.65                       537.1
2010-03-09T10:31:15.080+00:00   28.33           35.77            11.15            46.92                      1329.3

The Morningstar MSView software can then open the modified CSV file and display graphs of the real and calculated variables:




Title: Re: Cobbled together PV in W.Sussex
Post by: Paulh_Boats on March 10, 2010, 09:12:54 PM
Outasight,

Ooh err misses, you have sexy graphs.  ;D

BTW You can get 29p per kW generated OFF GRID with a non-MCS system. I'll PM the details.

cheers
Paul


Title: Re: Cobbled together PV in W.Sussex
Post by: Outtasight on March 16, 2010, 12:08:39 AM
Thanks for the tip-off...  I'm on the case!

Witness the almost properly installed new (old recycled) Navitron supplied OFGEM Total Generation Meter!  It arrived zeroed and reprogrammed to show 0.1kWh units, making it more useful than the usual setting of showing whole kWh only.

(http://i40.tinypic.com/34isa2q.jpg)

I screwed it down to a chopping board I got at a car boot sale a couple of years ago that I was saving for a bird table but block board isn't very strong against weather so it's now a meter panel. 

The meter has HUGE holes for fat 100A meter tail wires that then block up the hole with their insulation and make the thing safe.  Trouble is, with only 2.5mm2 wire going in, the holes are wide open to small fingers.  Luckily the RCD single size patress box is the right size to cover up the holes and then the wires to the meter can just pass though the box without being exposed at all.  The fused RCD spur unit has a cable grip output for the 4 way socket that divides up to all the other circuits.

These RCD units are much more expensive than plug-in types (almost £28 compared to £7).
Some day when the CD rack moves elsewhere it might even get fixed on to the wall rather than propped up against the patio window...

(http://i42.tinypic.com/9icwm8.jpg)

Let's hope my application for ROCs & REGOs is accepted and I can get on the FIT scheme next month.


Title: Re: Cobbled together PV in W.Sussex
Post by: Paulh_Boats on March 17, 2010, 02:53:16 PM
Outtasight,

Nice job - join the wait-and-see club lol.

I wonder if Ofgem will inspect all these systems, but its the elecy company's responsibility to make FIT payments so the whole thing could become parochial (I love that word  :)).

And will they ever put a seal on the cover?  fpig:

You could use meter tails into a 1G box with choc strip to join to the standard 2.5mm cable. I would say that is essential to meet the 17th (mechanical isolation, out of reach etc).

cheers
Paul


Title: Re: Cobbled together PV in W.Sussex
Post by: Outtasight on March 22, 2010, 11:08:53 PM
Today's thrilling episode is the cheapskate's guide to load automation...

Now that it's getting sunnier, I've started using the water heater again.  The problem is that it uses a lot of power and unless it's a perfectly clear day you get the odd cloud or the weather changes and suddenly its eating up the battery instead of soaking up spare power from the array.  I can run upstairs and turn the thing off and on but that means babysitting a water heater... Not clever.

So... Here's my old Toshiba T4900CT laptop - £5 from a car boot sale.  £25 for new battery. £5 for an ancient Ethernet adaptor that came with two free laptops... I luv car boot sales, me.

This one's a winner as a data logger as it's a P-75 processor that consumes just 11W when snoozing on half speed CPU and the screen and hard disk asleep (coz it's sending the data to a file share upstairs).  Windows 98 runs well on a dozing Pentium with 12Mb RAM... Ahh... those were the days.

The machine is plugged into the SunSaver MPPT charge controller by it's serial interface (only old laptops have proper RS232 ports) and the Ethernet card is plugged into the TriStar MPPT charge controller.  The MSView software just reads off the system parameters and pipes them to a single CSV data file on the file server upstairs.  Up until now it's managed to make some pretty graphs.  Time for some real work.

(http://i40.tinypic.com/vilmw6.jpg)

Velleman make a bunch of kits and this is the K8055 USB I/O card.  You can get one pre-assembled but it's £10 cheaper to get the kit and make it yourself.  So I did.  It also means I could leave out some bits I didn't need and they might come in handy for some other project.

(http://i39.tinypic.com/6r7te1.jpg) (http://i41.tinypic.com/1yllaw.jpg)

The finished article is a useful bit of kit and a bargain at £30.  It has 4 digital inputs (for switches), 2 A/D converters for 0-5V sensors, 2 D/A converters with either analogue 0-5V output or 0-100% PWM signal and 8 digital outputs with LEDs (that could be converted to opto-isolators) and screw terminals for connection to the open collector drivers (the bit I'm interested in right now) for relays and so on.

The whole thing is powered by the USB port itself and works with the pre-programmed PIC controller on board and a supplied DLL for Windows to talk to it.  Velleman provide a bunch of demo code and a test program so you can play with it almost right away.  You can even gang four of these boards together on a USB bus as they have separate address codes that the DLL can talk to.

The plastic box it came in is sturdy and see through and will probably make a half decent case for the finished thing!

(http://i39.tinypic.com/b8nwpw.jpg)

To drive a relay you need an external 12V DC power cube (car boot sale) and a mini 7A mains relay (scavenged from a dead UPS I have).  The relay fits conveniently inside this two way mains socket :D  I love it when a plan comes together!

(http://i39.tinypic.com/2sbwp50.jpg)

I happened to have an old copy of VB6 sitting around in a cupboard and so some fettling of the demo software source code gave me the interface I needed.  I read the Morningstar CSV data file and scan it for new entries (once every few seconds as it is being updated once every 15 seconds by the logger).  The new program builds an output CSV file that has the calculated values for the sum of the charger currents and the total generated power.  These can then be read by MSView on the server to display real time graphs of the total system output (previously I had to doctor the CSV file with Excel to get the graphs I showed earlier).

This program is only really interested in the battery and system state though.  Some rules decide when there might be available surplus power.  It does this by looking for when the battery is getting full at over 27V and with the array power being low (because it has finished absorbing and / or there are no other big loads on - e.g. the kettle).  The program tells the relay to turn on and the water heater starts.  This loads the system by 650W and if there's surplus array power the battery voltage will hold up as it continues to charge or just float.  The array can produce about 1100W on a good day so there should be juice to spare.  If not, the battery volts will fall and then the second parameter watches for this (now ignoring the power output).  If there's not enough solar juice, the battery will fall below float and the relay is turned off until the battery has recovered (back to above the voltage threshold and consuming less than the set power).

I'm still working on it so some things don't do anything yet.  The output check boxes will turn on/off other outputs but the automation works just on output 1.  The inputs are ignored (for now) but could be triggered from any switches (the Smartgauge has a relay output that can be triggered by a low SoC directly).  I've put some safeties on it too - ending the program turns off the outputs first.  A heartbeat senses if the logger has stopped sending data and shuts off the outputs.  Some range validation ensures that you can't put unreasonable thresholds in the variable boxes.

(http://i41.tinypic.com/2n12xi.jpg)

Here's what it did this afternoon as it got progressively more cloudy.  You can see there's enough power to charge the battery quite quickly but not enough to run the water heater so it cycles on and off (very slow PWM).  So I can now leave the thing plugged in all day and the load manager will give priority to charging the battery but whenever there's enough spare power it will progressively dump more and more into the water heater.

You can see where I turned on the 900W kettle for a quick cuppa and this drained the battery a bit.  The water heater shut off (as the volts sagged below the cut-off level) and it stayed off as the volts came up and the power drawn by the battery subsided.  This last bit is important as just looking at the voltage doesn't work because the voltage comes up quickly.  If you watch the power curve as well, you can tell when the battery has stopped absorbing power and it's safe to divert power to the heater.

(http://i42.tinypic.com/f57rio.jpg)

The other outputs aren't used for anything (yet!) but I've got three more of those relays and they'd probably all fit in a typical 4 gang mains adapter  ;D

Morningstar wanted over £130 for their relay driver... 


Title: Re: Cobbled together PV in W.Sussex
Post by: davebodger on March 22, 2010, 11:30:28 PM
Nice.
Did the Velleman kit come from Maplins?
I can see one of them coming in very useful.
I don't like my solar tracker because it gets confused on cloudy days.
  banghead:
I feel a more programmed approach may be in order.  :)


Title: Re: Cobbled together PV in W.Sussex
Post by: Outtasight on March 23, 2010, 01:01:30 AM
Yep.  Maplins do both the kit and ready made versions.

Velleman have a new line of home automation kits (not in Maplins yet) that look very interesting.



Title: Re: Cobbled together PV in W.Sussex
Post by: Paulh_Boats on March 23, 2010, 01:24:58 PM
Outtasight,

Interesting work there, cheers. What would be really useful is turning on AC loads when the sun shines, so that our grid-tied power is used immediately and not exported (the FIT rate is great for generation alone  ;D).
The problem I think is identifying suitable loads and we have solar thermal already.


The washing machine and dishwasher would be ideal candidates but both of them have a Start button, so remote control would require serious hacking. Also wifey sets the machines going on her days off, so the manual solution is good enough.


It might be possible to power-off the fridge early in the morning, say 7am, then power it on when the PV kicks in... around 8am onwards on a sunny day and have a watch-dog timer to force it on by 9am at the latest. Mad Professor stuff perhaps  ;)

The "staring me in the face" solution is of course to charge a battery for lighting/laptops later in the evening - the 20% battery loss, battery costs and battery manufacturing energy (CO2) would have to be much less than the value of the free power otherwise its a waste of time financially and planet wise.


During March we need additional heating so a triac controlled fan heater could provide a varying load to match the PV output. But that assumes the house is well enough insulated to trap that heat for many hours before we return home.

Does anyone have similar "bright" ideas?  ;)

cheers
Paul


Title: Re: Cobbled together PV in W.Sussex
Post by: fred bloggs on March 23, 2010, 03:42:45 PM
Outtasight,

I've been following this post from day one and your have inspired/given me some good ideas. I'm an electronics/electrical engineer and I brought aload of "cheap" PV panels last year to play with, will hopefully be installing them on the garage(man kennel) roof this summer. I've done some VB programming as part of a previous employement (12 years ago) and have already got all the bits and bobs! rescued from various skips at at previous works. Is it possible that you could let me have the VB source code for your "cheapskate" my kind of automation as my VB is very rusty  help: and I need a bit of a push in the right direction!! Im sure that quite a few members would also be interested.

Many Thanks and keep up the excellent posts

Fred


Title: Re: Cobbled together PV in W.Sussex
Post by: billi on March 23, 2010, 11:31:11 PM
Quote
The "staring me in the face" solution is of course to charge a battery for lighting/laptops later in the evening - the 20% battery loss, battery costs and battery manufacturing energy (CO2) would have to be much less than the value of the free power otherwise its a waste of time financially and planet wise.

Paul my prognoses  will be  that "Grid tied " homes will waste electricity /Energy  more easy now , because getting paid for

Or in a rude way , homes  that  export units  to the puplic grid and get paid for these units , are not their units any-more !

Billi


Title: Re: Cobbled together PV in W.Sussex
Post by: Paulh_Boats on March 24, 2010, 12:03:15 AM
Quote
The "staring me in the face" solution is of course to charge a battery for lighting/laptops later in the evening - the 20% battery loss, battery costs and battery manufacturing energy (CO2) would have to be much less than the value of the free power otherwise its a waste of time financially and planet wise.

Paul my prognoses  will be  that "Grid tied " homes will waste electricity /Energy  more easy now , because getting paid for

Or in a rude way , homes  that  export units  to the puplic grid and get paid for these units , are not their units any-more !

Billi

Billi,

That is an interesting viewpoint! Even my small 490Wp system will pay half the electricity bill with FITs income, plus the 15% exported free to use so I understand your feelings.

However I look at it as a green investment with 8.5% return (better than a bank  ;D).... and I still want to reduce consumption as low as possible to save more money and CO2. However I have already signed up to 99% green energy from nPower Juice (offshore wind farm).

-Paul


Title: Re: Cobbled together PV in W.Sussex
Post by: billi on March 24, 2010, 07:49:16 AM
paul
i just have a small and friendly argument on a German PV forum , cause since this year in Germany "exporters" can  use their produced units direct in the house and achieve a bigger profit .
Most exporters seem to use their own produced units sensible . Others start to dump the units into immersion heater ideas  and of course the air source heatpump  idea .
And then there are others that ask me about batteries and store all the units  they produce for their own consumption  and try to calculate their gained profit against the costs of batteries .

Perhaps i am jealous  (not really ) .     But the idea was, i thought a contract between the state and the exporter to receive payments for "Green Energy" to provide that energy towards a "Greener" State

Billi


Title: Re: Cobbled together PV in W.Sussex
Post by: Paulh_Boats on March 24, 2010, 08:13:03 AM
paul
i just have a small and friendly argument on a German PV forum , cause since this year in Germany "exporters" can  use their produced units direct in the house and achieve a bigger profit .
Most exporters seem to use their own produced units sensible . Others start to dump the units into immersion heater ideas  and of course the air source heatpump  idea .
And then there are others that ask me about batteries and store all the units  they produce for their own consumption  and try to calculate their gained profit against the costs of batteries .

Perhaps i am jealous  (not really ) .     But the idea was, i thought a contract between the state and the exporter to receive payments for "Green Energy" to provide that energy towards a "Greener" State

Billi

Good comments Billi!   But I thought the Government wanted us to use PV energy immediately, otherwise it goes out to the grid and comes back in later in the evening from a dirty power station?? 

If our essential electrical tasks are done when the Sun shines... ultimately we need fewer power stations yes? It think that is the logic of the FITs scheme - energy independence.

cheers
Paul


Title: Re: Cobbled together PV in W.Sussex
Post by: Outtasight on March 26, 2010, 02:54:16 AM
Outtasight,

I've been following this post from day one and your have inspired/given me some good ideas. I'm an electronics/electrical engineer and I brought aload of "cheap" PV panels last year to play with, will hopefully be installing them on the garage(man kennel) roof this summer. I've done some VB programming as part of a previous employement (12 years ago) and have already got all the bits and bobs! rescued from various skips at at previous works. Is it possible that you could let me have the VB source code for your "cheapskate" my kind of automation as my VB is very rusty  help: and I need a bit of a push in the right direction!! Im sure that quite a few members would also be interested.

Many Thanks and keep up the excellent posts

Fred

Hi Fred,

Sure, PM me your e-mail and I'll send you the project files.  There's some dodgy stuff in it at the moment like hard coded file paths but you can easily change those to your own or do it properly with a directory combo control or just a text entry field that allows you to enter a file path.  Of course the fact that the program is designed to read a very specifically formatted CSV file means that the thing is riddled with hard-coded stuff so I figured the input and output file paths were the least of my worries.  If I'm going to bodge the hardware, makes sense to keep the faith with code...  whistle

I'm gonna add some extra rules to the thing soon...

There's a condition where the battery has just reached 27.2V using say 150W of charge power but it isn't sunny enough for the array to make more than 200W charge.  This is causing the heater to cycle (it thinks that the battery has stopped absorbing power) and stops the battery from going to absorption mode using all the available <200W charge power.  I'll probably put a check rule in that looks for this rapid cycling (15 seconds duty) and does a "3 strikes and your out" rule to inhibit cycling and just do a "ping test" once a minute to see if the sun has come out yet. If not (indicated by the battery voltage collapsing as soon as the heater goes on) then continue sleeping for another minute.

There's no reason why (given enough "can I be ar~ed" time) I couldn't give the load manager a LUT that lets it predict the maximum power availability given the time of day and the month of the year.  So, if it was January and 2.30pm, it wouldn't even bother trying to seek a water heating opportunity.

Another possibility with the I/O card is to use a small 6V "garden shed light" amorphous panel I have laying about as a pyrometer with a fixed resistive load to feed an "available power" voltage value to the A/D port.  That way the load manager can actually measure how sunny it is and a suitable scaling factor should tell it roughly how much available power there is from the main array (ignoring shading problems).  Given enough observation, the LUT could take care of predicting shading.  The only truly unpredictable thing is the actual solar input power so that has to be measured.  Most other things can be predicted or deduced.

The other aspect of control I need is (ironically) to limit the battery charge current.  The array is oversized now for a 180Ah gel bank and can push up to 50A at full pelt.  The Deka support guy I talked to recommended that you don't go above 30A when in absorption phase by doing something like staggering the chargers so that the big TriStar only charges up to the float voltage and then the little SunSaver handles the absorption phase as it's limited to 15A.  The sales blurb for these batteries says you can charge the battery in 3.5 hours and let the battery draw up to C/3 current (about 60A) but only for float charging at 2.27Vpc.  If you use a 3 stage charger then you should limit the current to C/6 or about 30A in absorption to avoid overheating the cells (gas recombination creates heat).

But the problem with that is that the SunSaver array might be shaded at the time or it might just not be sunny enough to make 15A.

So the plan is to keep both controllers set for full absorption voltage duty but use the load manager to shave off the peaks.  A new variable for the "Heater = OFF" state will test for:

if (Power > 900W AND (charge_state = MPPT OR charge_state = Absorption OR charge_state = Equalize)) then Heater = ON

This will then watch for excessive power generation (that it is assumed is going into the battery) and turn on the 650W load to divert some of it (leaving about 250W for charging at a safe level and other loads.  The charge controllers can report their charge state and so I just added that variable to the others that they log in the CSV file.  The only state where it's ok for the full 1.4kW potential generation to be allowed is when the battery status is "Float" because then it's obviously another load that is drawing more than 900W because a battery in float stage can't draw that much.

Ideally, I'd have an analogue feed from the battery pack shunt so that the load manager actually knew the net battery current to base its decision on but that presents a few problems... One, the I/O board is on the other side of the house.  Two, I'd need to build a differential amp to measure the voltage (0.1mV per Amp at the shunt) and scale it up to the 5V FSD range of the A/D converter. Three, I'd have to isolate that amp from the I/O board as it's measuring a voltage in the middle of the battery bank so can't be allowed to see DC ground or it'll go BANG!

Of course, all this could just be pointing to the fact that I need a bigger battery bank that can handle the peak charge current ::).


Title: Re: Cobbled together PV in W.Sussex
Post by: rob26440 on March 26, 2010, 09:36:16 AM
Quote
Of course, all this could just be pointing to the fact that I need a bigger battery bank that can handle the peak charge current

There are some juicy 12 volt 1600 Amp Hour industrial battery packs going on eBay for £330 each just now.  Bit heavy though, each 2v Cell weighs 100Kg!

If I had enough roof space for panels then I would have bought them!


Title: Re: Cobbled together PV in W.Sussex
Post by: EccentricAnomaly on March 26, 2010, 12:44:49 PM
Ideally, I'd have an analogue feed from the battery pack shunt so that the load manager actually knew the net battery current to base its decision on

Yes, measuring what you're really trying to control seems like a very good idea.

Quote
... but that presents a few problems... One, the I/O board is on the other side of the house.  Two, I'd need to build a differential amp to measure the voltage (0.1mV per Amp at the shunt) and scale it up to the 5V FSD range of the A/D converter. Three, I'd have to isolate that amp from the I/O board as it's measuring a voltage in the middle of the battery bank so can't be allowed to see DC ground or it'll go BANG!

How about putting the scaling amp (if required) and an A/D microprocessor on a little board floating at the battery bank voltage?  Drive it from an isolating DC->DC inverter and opto-isolate the serial digital output to the computer.  This, in a slightly more elaborate form, is what I have in mind for my system.

If you reference one side of the shunt to a point halfway up the range of the A/D so that the other side of the shunt can go either positive or negative relative to it you'll be able to measure both the charge and discharge currents.

What I intend to do is have the main 24 V house bus as the reference voltage of a set of A/Ds floating in this way then sense the voltages at various points in the system relative to this using the various leads as the shunts to determine the currents from various generation sources, to/from the batteries and to various loads.  Also, measuring the ground voltage and various taps in the battery bank using resistive dividers to get general health/state-of-charge information.


Title: Re: Cobbled together PV in W.Sussex
Post by: Outtasight on March 27, 2010, 01:59:46 AM
Rob,

Thanks, I've seen them but two pallets of flooded cells weighing close to 1200kg isn't going to be easy to hide behind the comfy chair (where my 180Ah bank hides now)  ::).  I changed to gel packs to avoid being gassed.  Even the blue SLA 500Ah cells the same guy sells are too big physically to fit there. 

Eccentric,

Thanks for the diagram.  That's sort of what I was thinking of but thinking about it some more today, I'm coming to the view that the most important things to measure would be the available power of the array (quite easy to do) and the power demand on the array (already have this info to hand).  Then it's just simple...

if available power - (power demand + 650W) > 0 then turn the heater on.

This then makes battery charging and other loads a lumped variable that I don't need to care about the detail of.  Time to experiment with some bell wire and that old 6V amorphous panel hanging out the bathroom window...


Title: Re: Cobbled together PV in W.Sussex
Post by: guydewdney on March 27, 2010, 04:19:20 AM
Thats exactly what alan made for me....

http://www.navitron.org.uk/forum/index.php/topic,9072.15.html


Title: Re: Cobbled together PV in W.Sussex
Post by: Outtasight on March 28, 2010, 12:42:06 AM
I remember seeing that thread and the cool resulting gadget.  This incarnation is similar but different.

Similar in lots of ways as it's all based on a PIC that does the communicating (although the rules logic is in a PC attached) and in that the aim is to maximise use of solar power and minimise grid import.  The actual goals are slightly different though as I'm off grid.  A grid tied inverter always puts out whatever current it can as it's designed to export power so its available power is whatever it's putting out at the moment. Its primary load is the grid.  Your gadget looks to take all that available power and use it locally, rather than export it. 

I'm having the opposite problem in that unless a load is presented to the inverter, nothing is generated and the available power of the array is latent power that goes nowhere.  Unless I have some way to measure the actual sunlight, I've got no idea if there will be a torrent of power when I "open the tap", or just a dribble.  I also have to manage the battery so that if there's only a dribble of power available, it has to go into the battery first but after the battery gets full I need a way to use the latent power "overflow".

Even a dribble is fine though.  Keeping with the plumbing theme, I could make use of even a dribble of power as I can store it in the battery (like a toilet cistern) and when it gets full, I can "flush" it for a few seconds burst of high rate flow before having to wait a few minutes to recharge the "tank".

Up until now I've had to do it manually by looking out the window, watching the battery gauges and then running upstairs to "flush the loo".

You could say then that what I'm trying to invent (in true Wallace style) is a Flush-o-matic Dump ValveTM

bike:

Today's tinkering brought some more logic to stop the heater cycling in low light when the battery is near float voltage (but not actually full yet).  It now reads the battery status from the TriStar charge mode and prioritises absorption while scavenging power if there is more than 900W available towards the end of the MPPT bulk charge or absorption phases.  This will limit the peaks (admittedly quite rare though) where the battery might be force fed 50A (somewhat hot for the size of battery).  Now, if the power looks low because the battery is nearly full and the heater turns on as we've guessed there's 650W going spare; two things will happen.  Either the guess was correct and the battery will continue to sit at the absorption set point with the excess  enough to drive the load or we guessed wrong and the volts will drop down from the absorption set point, the TriStar will drop back into MPPT mode and this will then turn the heater off and change the priority back to charging.  Some charge will still be lost from the battery but it should spend more time at or above float level and spend more time in the absorption mode on marginal light days.

The cunning part is using the charge status flags from the TriStar, as the float and absorption voltages aren't fixed but temperature compensated by a sensor on the battery bank.  So I don't need to measure the battery temperature at the load manager as that's already been factored into the status flags for me.  I still use a global low voltage cut-out of 27V because the Float flag remains set even if the battery starts to discharge.  The TriStar has a timer that counts the cumulative time below the float set point and when it's been discharging for a set time it drops back to MPPT charge mode again.  But I don't want to use more than a few seconds here and there of battery power for the heater so when the float flag is set I turn on the heater and watch the battery volts to make sure it stays above 27V so that I know I'm only using solar power for the heater.

As a quick measure of performance, I added a runtime counter that increments every time the heater has been on for one logger interval.  By multiplying the counter by whatever the interval period is (I usually set it to 15s but it could be anything) I can easily work out the total time the heater has been on. But even without working it out, I can see if today is a high-scoring day.


Title: Re: Cobbled together PV in W.Sussex
Post by: guydewdney on March 28, 2010, 09:46:39 AM
to simplify - you have a battery charger with three LEDs on it - bulk, absorb, and float.

You have detected that the float LED is on, and that turns on the heater? when the bulk light comes on, you turn off the heater?


Title: Re: Cobbled together PV in W.Sussex
Post by: billi on March 28, 2010, 05:54:11 PM
sounds complicated to me  ::)  has your new chargecontroller not an  in built secondary control relay  , that can handle these "dump load" ideas ?

Billi



Title: Re: Cobbled together PV in W.Sussex
Post by: Mostie on March 29, 2010, 01:33:17 AM
What about fixing a LUX sensor next to the panels and connecting it to your velleman kit?


Title: Re: Cobbled together PV in W.Sussex
Post by: fred bloggs on March 29, 2010, 09:58:20 AM
Outtasight

Just sent you a PM with contact details, I've just read you're further posts and it has given me a lot of food for thought as I want to run my system "off grid" although we are are grid connected. The panels will be on my garage roof (man kennel) and all the equipment will be inside, its a good excuse to be allowed to play stir:

Many thanks

Fred


Title: Re: Cobbled together PV in W.Sussex
Post by: rob26440 on March 29, 2010, 11:56:28 PM
Quote
I changed to gel packs to avoid being gassed.

Outtasight,

Some 320 Amp 2V YUASA gel cells for sale from the same place item: 220580804843
(15mins from where I live.  Wish I had the roof/garden space for PVs! )


Title: Re: Cobbled together PV in W.Sussex
Post by: billi on March 30, 2010, 12:22:46 AM
rob  
Quote
Wish I had the roof/garden space for PVs!


Nothing is impossible  ;D


But these batteries ?  ::)

Oh i have to modify  
i thought  it was for one battery at 2 volt , but its for 6 .... but still the supplier writes  like the yellow press

Billi



Title: Re: Cobbled together PV in W.Sussex
Post by: rob26440 on March 30, 2010, 09:35:27 AM
Nice one billi!  I can't think of a suitable pun to associate hedgehogs with solar panels.  In fact, I haven't seen any hedgehogs in the garden yet this year - must be still hibernating.


Title: Re: Cobbled together PV in W.Sussex
Post by: petertc on March 30, 2010, 11:02:46 AM
Watch out for the solar spikes  ;D


Title: Re: Cobbled together PV in W.Sussex
Post by: Outtasight on April 04, 2010, 12:28:21 AM
to simplify - you have a battery charger with three LEDs on it - bulk, absorb, and float.

You have detected that the float LED is on, and that turns on the heater? when the bulk light comes on, you turn off the heater?

Sort of... in an over simplified kinda way.  :P

There are two chargers.  Both have LEDs.  I don't read any of them because they don't show the charge mode in a simple way and besides it's easier to read the data from the MODBUS ports.  I then calculate their combined output power and make decisions based on that plus the charge mode, battery voltage and whether the load is currently on or off (having prior knowledge that turning the load on will present a 650W demand means I can try to anticipate what happens if I were to turn it on).

But don't worry, if that appears too simple then fear not, it's still under development...  This week has been busy with work but with the Easter Weekend comes some more software tinkering and a solar input sensor.

sounds complicated to me  ::)  has your new chargecontroller not an  in built secondary control relay  , that can handle these "dump load" ideas ?

Morningstar do sell a relay driver that works with the TriStar and a normal non-MPPT TriStar can drive a DC dump load directly.  But the relay driver is pretty expensive (£133) and you might need a hub as well.  My controller cost £30 plus some monkeying around with VB and left-overs from my parts bin.  The MPPT TriStar can't drive a dump load as it is a series switching battery regulator and besides my dump load is a 3kW 230V AC heater on the other side of the house.

In addition, as well as controlling an AC load remotely (as it is controlled over an IP network, the load could could be anywhere in the world with an internet connection), it also does system data logging.  Being fully programmable, I can fiddle about with just about anything.  Another project in the pipeline is to have the computers upstairs choose their own power supply.  There's enough relay outputs to make a source change-over switch for the computer room UPS that will implement the safety delay required to stop the EMF bounce-back that can happen if you just use a change-over relay on a transformer with unsynchronised AC phases.  One supply needs to turn off, wait for the magnetic field to collapse before re-energising the transformer with the alternate AC supply.

Some 320 Amp 2V YUASA gel cells for sale from the same place item: 220580804843
(15mins from where I live.  Wish I had the roof/garden space for PVs! )

Yeah, I've been watching that seller for a while and these 320Ah packs would be ok if they were NPC ones but they are EN ones that aren't rated for cyclic use.  They'll only last about 250 cycles from new.  Still they are cheap.  I found a UK distributor for the Deka ones I have (now branded as MK Battery).  They're expensive to buy new though (£183+VAT and delivery each).

But back to this week's developments...

Playing about with a lux sensor to improve the estimation of available power.  At first I thought of using a small solar panel to generate a voltage but I happened to have an old light dependent resistor so it was easy to just wire it into the A/D input that has a 5V reference voltage anyway.  I made the LDR just form the lower half of a voltage divider.

LDRs are commonly used in dusk to dawn sensors... with good reason, as I discovered.  They are very sensitive at low light levels - changing from a couple of megohms to about 50 ohms in full sun.  But they aren't particularly linear and so in all but dim light I just got a saturated reading so couldn't tell between 100W solar input and 1kW.  I had to attenuate the light reaching the sensor so that it would work in full sun but at its dusk range.

Cockle shells are a useful thing here.  Impervious to UV (unlike plastic) and whitish in colour with a high opacity (but not completely so), they make good light filters.  I glued the sensor to the inside of a small one and then silicone gooed a bigger shell on top to cut the light even more.  Not shown in the pictures is the final version with outdoor white gloss paint on the top to filter / reflect a bit more light to get the output "just so".  I also filled in the back with waterproof outdoor Polyfilla to seal it up and give it some weight so it wouldn't flap about out on the windowsill where it looks up at the sky.  The shells also serve as a diffuser (being curved) so that the sensor responds smoothly to light hitting it from a variety of angles.

(http://i40.tinypic.com/6zrpyf.jpg)  (http://i43.tinypic.com/1zg4v1f.jpg)

Then I just had to modify the software to read the A/D port, scale the output to make 0 read dark and log the array output against the sensor data for a while to get the thresholds.  Actually, logging the data in Excel and then using the graph trend fit function, I could get a reasonable fit with a cubic term quadratic equation that I might put into the program so that it can estimate the solar input in Watts rather than just numbers but for now this works well enough.

(http://i40.tinypic.com/2nqcvpk.jpg)

The load now cycles much less, although there's quite a big margin of latitude between what the sensor detects and what the array actually produces due to shading of parts of it at early morning or late afternoon.

In other news... I finally got round to making an A frame stand for the old 48W array (rather than just propping it up on a water butt).  I also wheeled out some of the spare 15W panels and lashed them to some wood and threw them up on the roof, boosting installed capacity to almost 1.5kWp (in theory).

(http://i40.tinypic.com/eb3lzs.jpg)


Title: Re: Cobbled together PV in W.Sussex
Post by: Outtasight on May 14, 2010, 06:08:16 PM
I've been away for a few weeks.

We were supposed to be going home to Japan for a month but the ash cloud over the UK put paid to that plan.  So it was a two week break in Germany and then two weeks at home "staycationing".  While out in Germany, I saw literally hundreds of large PV systems installed on houses and businesses and this sort of got me buying stuff again...

Most of the hotels we stayed in had free internet so I ended bidding on some more BP solar panels...

First up was a newish used BP 350J 50W panel for £100.  I thought it was a 12V panel so was bidding on two but only won one of them.  I'd resigned myself to having another "spare" panel looking for a partner but on returning home, I discovered that it's a reconfigurable panel.  That is, it's wired as two 25W 12V panels in the junction box so it could be converted easily to run as 24V.  So up it went on the wall next to the BP 3160S panel.  It's almost the same length so nearly looks like it's supposed to be there.

(http://i39.tinypic.com/2cghf7o.jpg)

Then I found a seller that was doing brand new BP 380J 80W 12V panels for £165 in multiples of 10 but he was prepared to sell me five at the same rate so off we went to Yoorkshire to collect them!  I think they were so cheap because the 380J's aren't on the MCS list so they're no good for FITs installs.  Obviously, now I've got a spare 80W panel looking for a partner but to be honest, I'm running out of places to put these bigger panels...  Maybe I'll sell it to recoup the petrol money it cost to get to Yorkshire or maybe I'll keep it "just in case".

(http://i43.tinypic.com/67jrqc.jpg)

Having another week off work this week, I set to building the mounts for them to go up on the garage to replace the 6x 15W panels.  Half the frame for this job was already to hand in the form of the stainless steel bits from the used BP 380U panels I bought back in February and a couple of good outdoor treated bits of wood I picked up for like £2 at a car boot a couple of months ago (because a good bit of wood always comes in handy later :)).  The wiring was also more of that cheap car boot cooker cable with the old cable added on in parallel to give at least 8.5mm2 in both directions to the junction box at the other end of the shed roof...  Seemed to be doing the job as on a slightly hazy afternoon, the new group of four were pumping out at least 7.5A into the "network".

(http://i42.tinypic.com/35i7mtw.jpg)  (http://i42.tinypic.com/vhynnd.jpg)

I designed this frame to have a lower pitch than the one for the Sharp panels behind it so that in the winter it won't cast a shadow on the Sharp pair.

That lot brings me up just short of 1.8kWp installed now and the 15W plastic panels will become car boot sale fodder...

All that remained was to tweak the load manager settings to take into account that extra available power and so the immersion heater ran for almost five and half hours today - time for a relaxing hot bath, me thinks.


Title: Re: Cobbled together PV in W.Sussex
Post by: StBarnabas on May 14, 2010, 10:30:48 PM
Outta
you put me to shame. Such enthusiasm! superb...


Title: Re: Cobbled together PV in W.Sussex
Post by: Outtasight on May 18, 2010, 07:37:00 PM
Ha hahahaha....  MMWwuuHAHAHAHAHA!!!!  Evil genius type noises from the trap door (remember that claymation series with Willie Rushton doing the voices? - I bought the DVD compilation the other day.)

The problem of having too much charge current reared it's head over the weekend.  The 180Ah bank isn't supposed to like more than 30A of charge.  So, obviously that meant I needed more batteries to soak up the circa 65A I've observed coming out of the solar chargers whistle. The tired wet battery bank I tied in parallel doesn't accept charge very well and doesn't assist much unless the gel bank is depleted quite a bit (it has a lower resistance and higher hold-up voltage than the wet batteries).

I tried reducing the wiring resistance a bit by making up a 25mm2 cable set for it but that didn't change the fact that the 110Ah wet batteries are now only about 35Ah (I measured it on a load test a few weeks back) and that means more than half the plates are inert material that just increases the cell resistance.

I was out in Wales yesterday for a meeting and this meant passing near by Wokingham, where the eBay dealer in used UPS batteries has his "lair".  At £50 each for two year old 105Ah AGM batteries with "one careful owner", it would have been rude not to.  He did also have some Yuasa 150Ah batteries but they were more expensive and too heavy for me to lift on my own.  The Marathon ones are about 35kg and I'm no Schwarzenegger.

Anyhooo...  Here they are

(http://i49.tinypic.com/ifczsi.jpg)

Just got them on a refresh charge now as there's no telling how long they've been sitting in that shed of his  whistle.

I'll have to make up some different ends for the charge wires as the existing ones have those snap-on SAE post terminals and these new batts have 6mm bolts.  Oh, and the bolts he gave me were too long for the blind holes in the terminals ::).  So it's either off to the hardware store tomorrow or out with the Dremel tonight ;D.

The other beauty with these batteries compared to the wet ones or even the big 6V gel cubes is that they can lay on their side and then they are flat enough to be secreted under the sofa.  See...?  There is a plan.

 stir:


Title: Re: Cobbled together PV in W.Sussex
Post by: hawkie on May 18, 2010, 08:19:58 PM
Hi outa

Those batteries look the same as my hawker ones, only difference is the colour I think.

sounds like quite a good deal, they would have been expensive when new.

Hawkie ;D


Title: Re: Cobbled together PV in W.Sussex
Post by: Outtasight on May 20, 2010, 03:01:11 AM
If they work out ok I might get some more.  Got them wired up today and they sat all afternoon on the solar chargers in absorption mode and then I ran a equalise mode to get the whole bank topped off before using any big loads this evening.

The guy had a whole mountain of these 105Ah batteries and some older 100Ah ones (same case size but 3-4 years old model) for £45 each and the steel cabinets to house them (4 shelves of 4 batteries in a data centre rack).  I often have to go out to our office in Reading so it's on the way home.

He had some huge 2V VRLA sealed cells as well but they'd monster the whole living room for a 24V bank and weighed 100kg each!

UPS batts aren't great for solar as they tend to be the type for float duty and in cyclic use they only last about 250 cycles at 50% drain.  But these are cheaper than new leisure wet batteries (that also don't last more than 150-200 cycles) and don't gas ya outta yer house...

The proper solar gel 6V blocks I have were also used ones at £50 each from some dude on eBay but they're rated for 1000 cycles at 50% or even 450 cycles at 100% drain.


Title: Re: Cobbled together PV in W.Sussex
Post by: Outtasight on June 09, 2010, 06:55:43 PM
Guess what?  Those Marathon batts are ok...

So, I decided to get me some more.  Only I didn't have the cash...  Time for a car boot sale ;).

I off loaded nearly all of the cheap Chinese 15W panels (kept two for... err.. sentimental reasons?  wackoold) but managed to shift the rest of 'em and the cheapo 10A charge controllers and some LED bulbs, not to mention a load of those 7Ah SLA batteries the mad Hungarian gave me for free, oh and my "slightly tired" caravan batts...  Made about £250.  Of which, I handed over £200 to a man in a shed in Wokingham for four more of the Marathon batts (incredibly all with the same date code from 2008 on them).

So here they are...
(http://i46.tinypic.com/2lxhx68.jpg) (http://i45.tinypic.com/6ixi5u.jpg)

I figured that as they are only good for about 1/4 the number of cycles as the gel ones, that I should get more of them so that their average level of discharge will be lower than that of the gel bank.  The gel batts are rated at 180Ah and the three pairs of Marathon AGMs are rated at 312Ah.  I've deliberately kept the thin 6mm2 feeder between them and the gel bank so that the gel bank does more of the work.

The car boot sale was quite satisfying too...  Lots of people were interested in my display (a computer fan plugged straight into the panel) and even kids stood a-gog at how you could make electricity from nowhere and enjoyed making the fan go slower and faster just by standing in front of the panel to cast a shadow on it.  All those who bought a cheap solar panel are doomed to become hopelessly addicted to collecting the things now and will all be making 60% of their electricity from solar power in about 2 years time!!!  

Mwahh..ha.Ha.HA.HAA.HAHAHA  stir:


Title: Re: Cobbled together PV in W.Sussex
Post by: Outtasight on June 22, 2010, 10:34:29 PM
Hurrumph....

Automotive blade fuses... PAH!

Don't use 'em.

I had my new batteries connected to the main bank with an in-line blade fuse holder and a 30A fuse.  Not a cheap-o rubbish fuse holder but an RS one.  It was the day after the longest day today and the sun was beating down after I'd more than half drained the batteries watching movies last night.  Pulled 6.4kWh from the system :D.

Today though, the secondary bank was very greedy and spent quite some time sat at about 25-30A charging.  The poor little blade fuses couldn't hack it.  Two of them melted (the plastic holders - not the fuse wire!).

(http://i45.tinypic.com/4ijuds.jpg)

So I replaced the in-line fuse holder with an old 32 Amp MCB that I got at a car boot sale a while ago.  It's better that way any way as it can disconnect the battery if there's a fault and it also serves as an isolation switch.

(http://i47.tinypic.com/14ce912.jpg)

The rest of the afternoon's sun was soaked up without further melting or burning of plastic / rubber / fingers...


Title: Re: Cobbled together PV in W.Sussex
Post by: RichardKB on June 22, 2010, 11:01:39 PM
That looks like contact resistance as only one blade has created the heat.

Rich


Title: Re: Cobbled together PV in W.Sussex
Post by: davebodger on June 22, 2010, 11:41:28 PM
So I replaced the in-line fuse holder with an old 32 Amp MCB that I got at a car boot sale a while ago.  It's better that way any way as it can disconnect the battery if there's a fault and it also serves as an isolation switch.

Errr, Outtasight, aren't MCB's rated for AC switching?
Won't it get upset if asked to work as a battery disconnect when the juice is flowing?
Still, more useful than a car blade fuse anyway.  ;D


Title: Re: Cobbled together PV in W.Sussex
Post by: tony. on June 23, 2010, 07:24:42 AM
there is a derating guide on one of the manufacturers websites, for using dc did have the link saved on a old pc, but old pc not working anymore.

could be hager.

im sure ive posted it here before on other threads

tony



Title: Re: Cobbled together PV in W.Sussex
Post by: KenB on June 23, 2010, 08:25:46 AM
Outtasight,

DC switching is problematic because of the arc that forms when you open the switch. Over a period of time, the intense heat of the arc will melt the contacts - just like an arc-welder.

DC contactors use "magnetic blowouts"  - basically a magnet that drags the arc away from the contact zone - effectively extinguishing it.

I once ran a deep fat fryer on 200V dc in an early demonstration of my Lister gen - whilst the oil heated up perfectly - the poor contacts on the thermostatic swich lasted about 5 minutes.


Ken


Title: Re: Cobbled together PV in W.Sussex
Post by: Outtasight on June 23, 2010, 03:10:08 PM
Couldn't find any info on these specific Mem M6 321QEB Type 1 MCBs but the documentation for the later series of Type B MCBs they made were rated for DC use to 120V.  Those ones use a bi/tri-metal thermal trigger (10s at 5x overload) and powerful spring for time delayed overload trip and a electromagnetic trip for instantaneous (100mS) short circuit breaking.  The electromagnet also serves as an arc "blower" and forces the arc to go through something they called an arc stack that divides the arc into lots of little arcs in series and so it dies more rapidly and diverts it away from the main contacts.

It didn't say whether the MCB is polarised in DC use but I figured if it was then it would be the same sense as when in a consumer unit (so I wired the MCB with the source side on the main bank and charger and the load side on the secondary battery side.  Because there is bi-directional flow of current, it might be wrong for when there is an inverter overload or shorted cell in the main bank but in normal operation the larger current is usually charge going to the secondary bank (up to 30A) and inverter loads are usually in the range of 10-20A.

I don't plan to go opening the contacts when the system is under load / charge.  If I do maintenance on the system, it's usually at night with the inverter off or on cloudy days when there's only a couple of Amps flowing.  I have a shunt in the line so I can tell when it's idle.  The largest current experienced in normal use would be the joining impulse when the two battery banks are connected in parallel.  If one is low and the other is highly charged a massive current will flow for a couple of seconds.

There was a DC usage chart for the newer models and at <48V it was fine to use a single pole MCB to switch the rated current.  For 120V DC they recommended stringing 3 poles in series (so use a 3 phase ganged module and link the phases in series to increase the breaking capacity).

You can pick up old boards with MCBs quite easily at car boot sales for next to nothing (I got two complete sets for £1) as the manufacturers changed the mounting method when the Type B/C MCBs were introduced and so the Type 1/2 ones don't fit and I think the regs now specify that you have to use the newer types anyway.  Besides that, there's a move with the 17th Edition towards heavy use of RCBOs rather than MCBs so lots of MCBs are getting binned right now.

Despite being cheap at car boots, I did notice that they are quite valuable... some web sites have sprung up specialising in selling used old MCBs for those repairing a board with a failed one (customers apparently didn't take well to suggestions that they should spend hundreds of Pounds on a complete new consumer unit because one MCB had failed... can't think why.)


Title: Re: Cobbled together PV in W.Sussex
Post by: tange179 on June 26, 2010, 09:19:16 AM
I have got to say Outtasight, that your posts keep making me smile, your an inspiration to anybody interested in the art of photon control  :angel:

Keep up the good work.

tange179.


Title: Re: Cobbled together PV in W.Sussex
Post by: Justme on June 26, 2010, 10:28:41 AM
The largest current experienced in normal use would be the joining impulse when the two battery banks are connected in parallel.  If one is low and the other is highly charged a massive current will flow for a couple of seconds.


Can I ask why you run the system with twp bat banks rather than one bigger one?


Title: Re: Cobbled together PV in W.Sussex
Post by: Outtasight on July 01, 2010, 11:49:47 PM
Can I ask why you run the system with twp bat banks rather than one bigger one?

Simple evolutionary stupidity and a lack of significant biceps muscles.

All the batteries I have are second hand and coincidentally cost £50 each and weigh 35kg each, irrespective of capacity.

I bought the 180Ah 6V gel packs while actually buying four solar panels from a guy.  I actually went there to pick up two solar panels but he mentioned he had some batteries and some other (non Sharp) but very cheap 80W panels.  At the time, I needed more PV than battery and the batteries were an unknown quantity.  He actually had 16 batteries but I only had enough cash for four batteries and the four solar panels not to mention the lack of space in the car and carrying 190kg of cargo as it was.

After another 8 months of collecting another 480W of very cheap PV, I then had so much PV that the battery was too small and could overload with charge current on a really sunny day.  Plus it didn't have enough reserve to run the fridge and computer room through the night without being substantially drained every night.  I'd never planned to run these things on solar overnight but as the system got bigger the posibility presented iteself.  Your thought process is, "If only I had a few hundred Watts more PV... If only I had a few hundred more Amp Hours of battery..."

Enter the Marathon UPS batteries... Bought from someone near an office I have to go to now and then and cheaper than caravan batteries.  Bought two on a whim to see if they were any good... They are so bought four more so that they'd match the life span of the gel ones in parallel.

The main impediment to larger batteries for me though is their weight.  180Ah 6V and 105Ah 12V weigh in at 35kg each and that's about the limit of what I can lift in and out of the car by myself.

At the moment, the frankenstein bank seems to be doing well.  Both halves share the load and charge quite amicably.  500Ah is about the right size for the array as it can still go from 60% to nearly full in a single sunny day but has enough reserve to run the computer room and fridge freezer for at least 36 hours to 50% DoD over a cloudy day.

More than 500Ah and it will become impossible to keep it at a sensible level of charge from November to February.  I can't use the mains charger any more as that would be cheating, considering I'm trying to claim generating FIT credits for the system.





Title: Re: Cobbled together PV in W.Sussex
Post by: harrier on July 07, 2010, 02:55:09 PM
Hi there
Cobbling together something myself at present
Do youhave any panels for sale at all
And as also in West Sussex would you be up for a coffe and a chat as to how i go forward
Cheers


Title: Re: Cobbled together PV in W.Sussex
Post by: Outtasight on July 19, 2010, 07:00:29 PM
Hi Harrier,

Been away for a while ('puter trouble).  Yeah, if you want to come over and have a gander and see if this "home made solar lark" is for you then be my guest.  PM me your phone and we can go for a pint or summat.

But having read your starter thread, I'd be careful about playing with this stuff.  Although you're not playing with the mains proper, 12V batteries can start fires just as easily and the output of the inverter is going to kill you just as effectively as the "real thing".  A mis-placed spanner or screwdriver can have firework type results...



Title: Re: Cobbled together PV in W.Sussex
Post by: Outtasight on July 19, 2010, 11:59:08 PM
Learned something interesting & important last week...

Cheap nylon ratchet tie-downs are no good for fixing down your solar panels (or anything else for that matter).  After a year exposed to the elements, the UV totally kills the nylon and it takes on the tensile strength of bog paper.

Luckily I replaced the tie down on my Sharp array on the roof that fell apart under the strain of it's own weight just before the unseasonal winter storm we had last week.  Unfortunately, all I had to hand were more nylon ratchet tie downs  ::)

The worrying thing is that big heavy things are tied down to lorries with this stuff.  Steer clear of that artic with the huge plastic tubes strapped down precariously is what I say!     


Title: Re: Cobbled together PV in W.Sussex
Post by: billi on July 20, 2010, 12:14:50 AM
thanks for reminding me .... that is on my to do list , to change/ rip the cable ties  and replace with something everlasting

one day i will be grown up to do things propper from the start  whistle

billi


Title: Re: Cobbled together PV in W.Sussex
Post by: tony. on July 20, 2010, 07:03:56 AM
you get plastic coated metal ty raps, if thats any help.

tony


Title: Re: Cobbled together PV in W.Sussex
Post by: Outtasight on July 26, 2010, 02:19:04 PM
Errgh.... What an unholy mess.

I registered for the transition ROC to FIT migration before the March 31st 2010 cut-off date but then a few weeks later I replaced all those dodgy amorphous panels with nice shiny new BP ones.  The response from OFGEM was long coming and predictable...


"After consulting with senior management they have advised that the
original capacity will eventually receive accreditation and be migrated
to FITs receiving the higher rate of FITs payments as it is commissioned
after 15th July 2009.  The extension would need to have MCS
certification - kit and installer - to be eligible for FITs; if the
installation does not have the appropriate MCS certification the
extension cannot receive FITs payments. We are not able to add the
capacity through the application for accreditation currently with us
given the extension occurred after 1 April 2010. As the installation
commissioned within 12 months, and assuming the necessary MCS
certificates are present, the extension will be added to the original
capacity in the FITs Central Register by the FITs supplier once the
original capacity is migrated and will have the same tariff code and
eligibility date."


Which effectively means that whatever you had installed before April 1st is all you will ever be allowed to register for FITs.  The chances of a MCS supplier certifying an add-on to a DIY system (especially where the certificate is for an existing add-on you did yourself) are probably as close to nothing as you're ever likely to come across.  Then even if by some miracle (or brown paper envelope) you did manage this feat, you'd be limited to extending the system within 12 months of the original commissioning date.  Extensions after that won't be considered as part of the same generator and so you'd need a completely separate system (the new solar panels feeding into a separate charge controller and separate batteries and a separate inverter with a separate total generation meter so you could submit separate readings to earn a lower rate of return on your post MCS cut-off system units)...  Worse is upgrading a middle part of the system (say the inverter) as now you'll have to bin all your working solar panels and buy MCS ones just to upgrade the inverter.  How about the consumables?  Can you even get MCS Certified batteries for an off-grid system?

They didn't directly answer the second part of my question which was, "What happens in 5 years time if I have to replace a failed inverter?  Will the replacement unit count as the pre-MCS installed system or will I have to bin the entire non-MCS system and start again with a new certified system?". The above answer suggests that you'd be stuffed if any post 1st April 2010 change has to be MCS approved.  

How's that for environmentally friendly government?  Land fill sites full of "unapproved" solar kit.

One option is to not bother trying to get the new panels registered for FITs.  This would mean that I'd have to give up on submitting meter readings and use the "deemed output" approach (because I'd have no way to tell which units came from the excluded solar panels and which units came from the included ones).   Under this approach, the FIT provider will guess the output based only on the specification of the generator capacity and type.  Under this model I'd lose the assumed output units of the 180W of removed panels and earn nothing on the 450W of panels I added after April 1st.

In retrospect, it was a good date to choose for the cut-off.  Must have been an April Fool to get involved in this nonsense...  ralph:


Title: Re: Cobbled together PV in W.Sussex
Post by: StBarnabas on July 28, 2010, 05:43:49 PM
Hi Outta
well i have heard little regarding FITs - has anyone actually gotten any news?  You are probably as well off out of it.

Though I did receive 5 copies of this email from GoodEnergy
We are pleased to be writing to you with news that we intend to pay the outstanding credit on your HomeGen account by 13th August.

We understand this payment is much later than we have normally practiced and would like to apologise for any inconvenience this has caused. The delay in resolving any issues has primarily been due to the introduction of the new Feed-in Tariff (FiT) incentive. To accommodate the FiT we have developed a new, bespoke system to manage the accounts of our HomeGen customers. This has taken a considerable amount of our time and resource and has delayed making payments to you but we believe it is essential to prioritise the integrity of our systems so that we can make sure we can offer you an excellent Feed-in Tariff service in the months and years ahead.

While the introduction of the Feed-in Tariff has presented the government and industry with a big challenge, we believe that small-scale renewable energy is revolutionising the UK energy industry. Our customers, as generators and users of energy, are helping drive the shift from brown to green, from big centralised power stations, to thousands of small, distributed renewable generators that are improving the UK’s energy security and making a difference to climate change. By working together, we are making this change happen.

Thank you for your patience and for choosing Good Energy.



Title: Re: Cobbled together PV in W.Sussex
Post by: Outtasight on July 30, 2010, 12:21:07 AM
Well I made some progress this week.

I got a quick reply from OFGEM this time and they said that I could just register for the applicable power output of the pre-April kit.  The post April 1st kit can't count but I can still submit my meter readings.  The FIT supplier will apportion the units based on the ratio of "applicable PV power" to "non-applicable PV power" - basically using 450Wp as a ratio of 1.85kW and not paying me for 24% of the kWh units I declare from my TGM.

He also said that there was a problem with the OFGEM IT system that meant I couldn't update the application myself (as it got locked for edits after April 1st) so he made the changes to it for me.  I had to update the diagram with the new "applicable power" shown and email it back to him.  He then uploaded it to the server for me.

He did say that my application looks good to go now and will be passed on for approval by his manager.  I suppose that means I progress to being on the ROC register and then have to wait to get on the ROC to FIT conversion process.



Title: Re: Cobbled together PV in W.Sussex
Post by: Outtasight on September 17, 2010, 09:17:27 PM
Not much been happening...

Got my ROC2FIT forms from OFGEM filled in - the deadline is Oct 1st.  The ROC application still hasn't been finally accepted but I sent off the paperwork to E-ON to nominate them as my agent for generating credits.

I ditched the old Toshiba laptop as a go-between for the data logger.  Changing my PC upstairs to the Vista machine proved too troublesome for the Win98 machine to reliably connect to the fileshare any more.

So I bought the EIA-485 network adaptor for the Morningstar MPPT-15 controller.  I had a MSC adaptor to connect the controller to the old laptop but the Tristar can only talk to it via a EIA-485 bus.  This is just another type of industrial serial bus.  The instructions said that you had to have 4 core twisted pair but that's for long runs (EIA-485 can go a lot further than RS232 signals).  I only had to connect it to two things on a 30cm bit of string.  It works fine on an old bit of telephone wire.  You have to put 100 Ohm terminating resistors on the ends of the bus (a bit like a SCSI bus) but again I didn't bother doing it properly - I just put one resistor on the end inside the Tristar.  I couldn't find another 100 Ohm resistor to put on the adaptor end of the bus... I know... How cheapskate is that?  But it works fine with just one end terminated.  Only two wires are for the data.  The other two are the bus power that drives all the adaptors on the network.  It needs 8-16V so I couldn't just connect it to the 24V terminals in the Tristar.  Instead I had to use the 12V lab power supply I use for charging phones.  It only consumes about 20mA so it's not a drain I'll worry about.  The MSC adapter gets it's power via the RS232 ribbon cable from the EIA-485 adapter so at least the whole thing works off of one DC supply.

(http://i54.tinypic.com/5yalp2.jpg)

Now the Tristar can bridge MODBUS requests from the IP port and I can gather data from both controllers directly from the MSView software running on the laptop upstairs.  All you have to do is make sure the two charge controllers have different MODBUS addresses.  By default they are all set to 1 so I had to program the MPPT-15 controller via the serial link to the PC to be a different ID number before connecting it to the Tristar.

I think one of the next challenges might be to figure out a way to read the Smartgauge on the network.  It doesn't have a data output (other than a alarm relay) but with some hacking, I could probably connect an interface to the 7 segment LED display driver in it to be able to read the numbers.


Title: Re: Cobbled together PV in W.Sussex
Post by: Outtasight on November 01, 2010, 10:09:21 PM
"I have in my hand, a piece of paper..."

An E-On envelope thudded on the doormat today.  I viewed it ominously...  autumn... gas on... I bet it's another increase in my monthly direct debit.

No!  Whoo-hoo!  It's them accepting my ROC-FIT application and backdating the generating credits back to April 1st!!!   exhappy:   bike:

Pity it's been blacker than the inside of a coal miner's underpants the last few days and I've hardly generated a sausage... Still, at least the summer wasn't wasted...  They owe me a couple-o-hundred squids for the 600kWh I've put on the clock since April 1st...  Enough to recover the cost of the Deka gel batteries in the system. 

My father in law was gloating the other day.  He made about £170 a month from his 6.1kWp array this summer (he's got 28x 218Wp Sanyo HIT panels), and that was net exports after they'd used the ASHP to heat their water and other household usage.  Dunno exactly how the Japanese FIT scheme works but seems like he's minted. 

Roll on next summer  :garden



Title: Re: Cobbled together PV in W.Sussex
Post by: Outtasight on November 30, 2010, 06:58:13 PM
What's that nasty niff?

Oh...  That's the unmistakeble smell of battery gas.  Not good when you're running a bunch of "sealed for life" gel and AGM batteries.  :(

Closer inspection revealed two of the AGM Marathon batteries way out of balance under charge.  I'd been cutting back on usage to get the bank fully charged (as you never know when it will be able to charge again in these gloomy and now snowy days).  The pair in question have some kind of lost capacity problem.  One is getting full or has a higher internal resistance than the other and so the two 12V batteries are out of whack with one sitting at 14.4V and boiling up and gurgling (never a good sound from an AGM pack) and the other is languishing at 13.2V, not even making the float Voltage...  When operating at partial charge, they bumble along without one gassing but the partial charge will soon destroy all the batteries in the bank; not just these misbehaving twins.

Probably the only thing for it is to take them out of service (dropping my bank capacity from 495Ah to 395Ah) and use them as spares for a 12V system where they can run in parallel (and not suffer the series Voltage imbalance stress) or be used just one at a time.  I took them out of service for one afternoon to load test and,  individually, they seem ok.  They just can't "get along" as a series pair.

The only other alternative would be to invent some kind of active pack balancing electronics to bypass some of the current on one or t'other battery when charging; a-la lithium ion packs that have individual cell balancing.  Lead acid batteries (especially sealed ones) would last a lot longer if the makers introduced similar Battery Management Systems (BMS) that makers of more flamable cells are forced to.

Heaven only knows how you manage to keep a 48V AGM pack from self-destructing from inbalance.  Most fork lift packs suvive because the passive balancing they employ is exactly allowing some cells to overcharge and "blow off a little steam", so to speak.

On the upside, I've just started making enquiries about a new 24V 160Ah lithium phosphate battery module from an American outfit that makes large format lithium cells.  Other makers put together packs using small (3-10Ah) cylindrical cells in big blocks with BMS to keep them in check.  International Battery make these new HUGE 160Ah-200Ah cells so the BMS is simpler and the contruction is simpler (and cheaper) as it only has 8 cells connected in series to give a 24V pack.  A lithium pack should offer much more usable power as you can run it in partial charge mode all the time and it won't die like a lead acid pack.  In fact, lithium chemistry prefers not to be kept fully charged for long periods.  Ideal for opportunist solar charging.  Operating in partial charge mode also means not wasting solar power when your battery has gotten full and can't accept any more charge.  If your battery gets full every day, it's too small for the array.  But lead acid chemistry demands that you keep the battery as close to fully charged as possible all the time.

The specs for the pack look promising.  Min working Voltage is 20.0V (the inverter cuts out at 21.0V).  Max working Voltage during charge is 29.0V and the inverter can work up to 30.5V before cutting out.

I'm hoping they'll say that I can use my existing Morningstar charge controllers as they can be programmed to provide Voltage phases (as in bulk, absorption and float phases with different Voltage limits) or even a single Voltage limited output (float only) with a current limit.  Over-current shouldn't be an issue though as the cells are rated for 1C discharge (160A) and C/2 charge (80A).  The inverter load at 3kW tops out at 125A and the most I've ever seen from my solar array was 73A charge.

Check it out here: http://www.internationalbattery.com/news_nov_01_2010.php (http://www.internationalbattery.com/news_nov_01_2010.php)


Title: Re: Cobbled together PV in W.Sussex
Post by: EccentricAnomaly on November 30, 2010, 08:52:10 PM
I, for one, am intrigued by the LiFePO4 idea for off grid.  Came across it the other day while comping my way slowly through this site:

http://www.earth.org.uk/LiFePO4-battery-testing-with-solar-PV-off-grid-system.html (http://www.earth.org.uk/LiFePO4-battery-testing-with-solar-PV-off-grid-system.html)

Though when I've read some more I do plan to write to him as I think he's misunderstood.  He appears to think the BMS will do charge control but my understanding is that it doesn't; it just does low-voltage protection and balancing.  Wookey?  Anybody?


Title: Re: Cobbled together PV in W.Sussex
Post by: Outtasight on December 01, 2010, 05:50:14 PM
The IB BMS does more than just protection and balancing.  It measures state of charge (SoC), state of health (SoH), provides pack temperature control and can talk to external kit via RS232, CAN Bus for automotive / EV applications, and Ethernet for PC data logging and possibly control.

The max working Voltage on the IB pack is quite low at 29.0V.  This equates to only 3.625V per cell.  Lithium cells only really reach peak charge at 4.0-4.1V per cell but they need close supervision at that level and should not be floated at that level.

Most laptop chargers use a low terminal Voltage for charging as it makes the charger simple and safe, but at the expense of never reaching the peak capacity of the cells. 

Hopefully, it will be ok to program the Morningstar controllers to hold the absorption phase Voltage of 29.0V for a short time (maybe just 1 minute) and then revert to a lower "float" Voltage.  The charger has a "float cancel" timer that counts the time that the battery Voltage has been below the float set point (due to excessive load that the charger cannot sustain).  If this time exceeds a limit, the charger re-initiates a boost cycle to the absorption Voltage again.  Thus, even though the Morningstar chargers are intended for lead-acid cells, they could be adapted for lithium cell use.  The charger can also have any temperature compensation slope applied, so that as the battery heats up, the charge Voltage limit can reduce to compensate.  The BMS will operate the built in fan on the pack as required if the cells are getting too warm or even trip a breaker if the pack temperature cannot be controlled by the fan.

The other maker I looked at was LifeBatt (see http://www.lifebatt.co.uk/lifepo4_battery_modules.html (http://www.lifebatt.co.uk/lifepo4_battery_modules.html)) but these are the ones made from dozens of smaller cylindrical cells (but at least are available "off the shelf" in the UK).  The IB one looks more promising as it has Ethernet connectivity and my Morningstar controllers are already connected to my home Ethernet network.

Of course, a lot boils down to cost.  I picked up these lead acid batteries second hand for just £50 each and the gel ones are still going strong after over a year in service (some 450 daily cycles). Only one (or maybe two) of the AGM ones are showing signs of terminitus in their first 6 months of service (180 cycles).  It's hard to compete with good quality, "scrap, industrial waste" batteries.


Title: Re: Cobbled together PV in W.Sussex
Post by: Outtasight on December 18, 2010, 02:30:06 PM
Obviously those guys at International Battery are too busy to talk to me.  They completely ignored my request for more info on their batteries.  Maybe if I posed as a venture capitalist they might pay attention  ::)

Meanwhile, back at the ranch...

Happily, I'm managing to get away with not using any mains battery chargers to keep the batteries healthy but I have to ration the power usage quite strictly (although the missus reckons running 100W of christmas lights every evening for a couple of hours are "non-negotiable base load" ::) ).  This has been made a bit easier now that my program indicates the number of Watt-hours accumulated through the day.  

After the gassing problems earlier, I've taken a less aggressive approach with the charging parameters.  I've now set the big 60A charger to only sit at the absorption limit for 60 minutes unless the battery has been quite deeply discharged.  The other charger has a absorption Voltage limit set 0.1V below the main one so that it will assist the main charger in getting to that point but then will take a back seat (unless there's a load on the inverter) and count its hour down.  With them both set at the same value, they tended to see-saw on and off the limit and this could result in the system as a whole being at the absorption limit for longer than the set time (as each tried to accumulate the time before going to float).  This way, the small charger does its hour straight off and quits to float.  The larger charger is then put firmly in the driving seat and is the main decider of when the batteries are full.  This arrangement can still push the batteries to about 80% quite quickly, but then it doesn't try to push so hard for the last 20% (that was causing the dodgy pack to gas). 

I also got confirmation of my first FIT payment from the electricity company  ;D

The Morningstar MSView software does a fairly decent job of graphing the data from the logger, but I was looking for something that might do a rolling window graph of the last couple of hours (rather than the last couple of days).  There's a good open source bit of software called LiveGraph that does this quite well, and is written in Java.  It can read CSV files, and is very easy to configure with independent scaling factors for variables and colours, grid lines, auto axis scaling and so on.  If you've got Java 6 installed (most who run Firefox browsers will) then all you need to do is unzip the downloaded pack and double click on the Java executable to run it - no installation required.

http://www.live-graph.org/index.html (http://www.live-graph.org/index.html)  

Not much power logged today though... 10cm of snow fell in an hour this morning again.  I cleared the snow from the panels I could reach but then the clouds closed in and it got really dark.  Just tickling the batteries at about 50W, I'm afraid.  Tonight is forecast to be more snow and -8C!!!   freeeze


Title: Re: Cobbled together PV in W.Sussex
Post by: Outtasight on January 03, 2011, 07:16:36 PM
Having taken the suspect pair of Marathon batteries out of service and let them sit for a while, I discovered that there doesn't appear to be anything seriously wrong with them.  I had thought that one was developing a short in one of the cells but watching their Voltages for 3 days open circuit showed steady readings.  The only thing was that one battery consistently read 0.1V lower than the other, but their Voltages tracked each other closely (although not connected together).

So I did what I probably should have done from the start (but was too lazy to);  I tied the mid-points of each string together with an equalising network.  This time I even remembered to put fuses in the links ::).  Normally, the equalising links should carry nearly no current but in a fault they could carry lots of current so the 10A fuses are a good idea.

With the mid-points of the 24V strings tied together, the separate strings have more routes to balance out the upper and lower halves of the strings.  It will have to wait until a sunny day now to see if this means that the #1 battery in string 1 with low Volts will have less tendency to cause the #2 battery to go over-Volts and start gassing.  Alternatively, with the one bad apple in the barrel now linked to the others, it might make the whole barrel go bad ::).



Title: Re: Cobbled together PV in W.Sussex
Post by: wookey on January 04, 2011, 02:10:47 AM
Missed this back in Nov.

Thousandsun don't say what their built-in BMS does, but yes, most suppliers provide a BMS that just does low-voltage and high-voltage monitoring and maybe bypass - i.e. it does not do individual cell balance charging. Anything which can actually disconnect the load or bypass the cell imposes current limits on how the pack can be used. For fully flexible charge control (using off-the-shelf chargers) I reckon the tppacks (aka 'goorum/fechter') charge controller is good gear, although you do get to solder it together yourself (or buy them pre-built from http://www.rechargeablelithiumpower.com/oscommerce2/catalog/index.php.

Mine arrived just before xmas and is currently half-soldered together. After many iterations of design they ended up with various modular components: an LVC/HVC monitor (to live permanently on the battery), a charger CC/CV control module and a multi-channel balancer/charge controller which ensures charging is done whilst being nice to the battery pack. These designs are still evolving and are worth keeping an eye on. You can follow the (epic, 139 page) thread on the design here:
http://endless-sphere.com/forums/viewtopic.php?f=14&t=5416

Lifebatt make very nice battery packs but they are right at the 'luxury' end of the market (and have had some very dubious marketing practices over the years - read all about it on Endless Sphere). You can get the same quality cells/batteries from numerous other sources, for _much_ less money, and given the cost of large LFP batteries that can double the size of pack you can afford.

This area changes on a monthly basis, but manufacturers like Thundersky (recently renamed to Winston battery co) have got themselves a good reputation in the large cell area. They do cells from 40Ah to 2000Ah. So do others: (Sky Energy (to 400Ah), Elite, Foxx Power).

The place to find out more info is electric vehicle forums.


Title: Re: Cobbled together PV in W.Sussex
Post by: Outtasight on January 06, 2011, 11:08:03 PM
Thanks for the interesting links.  What cells are you using and what for? 

The Winston cells are unbelievably massive in capacity (up to 30,000Ah!!!) but no indication of price.  The Lithium Sulphur and Lithium Yttrium cells look like interesting variants, but from what I read, the cost saving of using Sulphur is offset by the high cost of the nano carbon framework that it has to reside in for the electrodes.  Sulphur is a lousy conductor, so a carbon nano "sponge" is required to make the sulphur electrically active.

The BMS looks interesting.  I like the fact that it's not fussy about the charge source; it can be driven from a regular solar charger for lead-acid batteries.

It's a very simple design but looks sound apart from the high power versions dissipating a lot of power as the cells reach full-ish charge and the bypass resistors are switched in.  If you had massive Li-S cells you could even not bother with trying to fully charge them and set the terminal charge Voltage to some way under 4.0Vpc so that when the pack got to be 70-80% charged, you'd just let it float and dump the spare power into a water heater or something more useful than the BMS dump loads.  Lithium cells don't care if they aren't fully charged.  At 80% charge floating you could still use the BMS to do some spot cell balancing, but without every cell switching into bypass, and generating quite so much heat. Or, just do a boost equalising charge to 100% once a month.

It's exciting stuff, and I'll be loathed to buy any new lead-acid batteries if there's something much more durable and flexible just around the corner.  It's such a bind having to limit stored energy use to 50% daily, and more like 10% daily in Winter. Just for the fear of a run of cloudy days trashing your battery because it will self-destruct from simply being partially charged.


Title: Re: Cobbled together PV in W.Sussex
Post by: EccentricAnomaly on January 07, 2011, 10:22:12 AM
I'm wondering if the answer, at least for the moment, isn't a mixture of lithiums and lead-acids.  Lithiums are more expensive than lead-acids, though when you allow for the fact that lead-acid only really has about 10 to 20% of the rated capacity lithium's not quite so eye-wateringly much more.

The other problem with lead-acid (apart from not liking to be discharged) is that you need a long absorption phase.  As Justme often points out this is a PITA if you're charging from a generator.  The same may well be true from PV, I suspect.

So maybe a good scheme would be to have a lithium "front-end" battery which can absorb any available energy and flow it at more efficient rates into the back-end lead-acids.  Similarly for discharge take high currents (e.g., for cooking), from the lithiums if possible then recharge them steadily from the lead-acids in a more-Peukert-friendly manner.

The thing I'd be loath to buy would be an large, inflexible and expensive charge controller which can't easily and efficiently be set up for different systems.


Title: Re: Cobbled together PV in W.Sussex
Post by: Outtasight on January 08, 2011, 11:43:53 PM
Well, I found a US supplier of the LiFePO3 Thunder Sky / Winston cells, and they also do the CALB (a Chinese aviation outfit) ones too.  The prices have really come down a lot!  These guys advertise their prices on a plain old web shop at a flat rate of $1.35 per Ah.  So a 200Ah 3.2V cell is $270.  That means a 4 cell, 12V nominal pack is only $1080 (about £696 at $1.55/£ + shipping from China, duty & VAT).  

http://lithiumstorage.com/ (http://lithiumstorage.com/)

When you consider that's the price for a battery that does 3000 cycles at 80% DoD, and can sit permanently at 20-80% partial charge level with no ill effect, it's a lot cheaper than the 320Ah gel lead acid cells you'd have to buy that are only good for 1000 cycles at 50% DoD.

Last time I asked, MK (Deka) quoted me £285 for 180Ah gel 6V blocks, so £570 for 12V.


Title: Re: Cobbled together PV in W.Sussex
Post by: EccentricAnomaly on January 09, 2011, 11:59:17 AM
Do we know anybody who might be in to importing renewable energy kit suitable for DIYers from China?


Title: Re: Cobbled together PV in W.Sussex
Post by: billi on January 09, 2011, 06:29:15 PM
... one can compare it this way and that way ...


and i still have my reservations  about battery hype in the LiFePO3  direction

Might be  that i am conservative   but still i  hold my hand in lead acid  :snow

Quote
So a 200Ah 3.2V cell is $270.  That means a 4 cell, 12V nominal pack is only $1080
@200 ah   whistle

so about 5500 $ for a 1000 ah 12 volt Battery  ::)

 so still about 2.5 times more than the Rolls with similar  live cycles  ( or close )

(http://www.rollsbattery.com/images/cyclegraph.jpg)

  Will see 

Billi




Title: Re: Cobbled together PV in W.Sussex
Post by: Outtasight on January 12, 2011, 08:02:26 PM
I'd like to see what Rolls say the curve looks like if you discharge their battery between 90% and 20% SoC over a week of partial discharge/charge deficit cycles; leave it bumping along at 20-30% with partial charge/discharge cycles for a week; charge it up over another week with partial charge/discharge cycles to an average 90% SoC and then repeat the three week cycle over and over.  That kind of behaviour usually counts as "wilful abuse" for a lead acid battery, that would invalidate the warranty, but constitutes "normal use" for a lithium one.

The optimised cycle life figure the makers quote assumes a single discharge cycle to 20% (or whatever DoD value) and immediate recharge to 100% in one shot.  Not realistic for a solar installation without a grid charger or diesel generator to hand. 

Solar off grid use never leaves the battery at 100% for any appreciable length of time.  Unless you put the battery on charge and then don't use it in the evenings (wackoold), it's going to spend the majority of every day at something less than 100% SoC.  In December it might not see full charge at all.  I had to leave my bank on charge with no load at all for 13 days in a row to get to full charge over Christmas and the New Year.

UPS batteries meet their manufacturers life expectancy because they sit for 24 hours a day at 100% SoC.  Lead acid batteries make perfect sense in this application. 



Title: Re: Cobbled together PV in W.Sussex
Post by: billi on January 12, 2011, 08:20:56 PM
... ok  accepted  , that the possibility to leave them partial discharged  over longer period is a big advantage  :genuflect


Title: Re: Cobbled together PV in W.Sussex
Post by: Outtasight on January 12, 2011, 08:40:23 PM
LoL... I'm not having a go at you.  :)  Just cheesed off with baby-sitting dodgy batteries.

Speaking of which... Back in dubious second hand battery-land...  We finally had a nice blue-sky day on Sunday and the bank lapped it up... 2.2kWh of DC power absorbed.  The balancing links are helping quite a bit; no suspicious gurgling noises or nasty smells from the end pair of Marathons.  Voltage readings for the whole pack of Marathons still aren't great though.  The lower half reading 14.0V and the top half reading 14.3V at the end of absorption.  I'm still of a mind to try and invent a block balancing circuit, using the same mini dump load technique as for lithium cells.  

I'd need to measure the differential Voltage between the upper and lower half of the bank and then selectively bypass some current through two resistors to nudge the halves to sit at an equal Voltage.  

I've seen a very expensive bank balancing gadget, but that's intended to keep a 24V truck battery pair in balance when you're doing silly things like running a bunch of 12V loads off of one of the batteries.  It uses switch mode tech to redistribute the charge from the high battery to the low one.

http://www.antares.co.uk/prod%20dc%20power%20equaliser.htm (http://www.antares.co.uk/prod%20dc%20power%20equaliser.htm)

My idea is to just dump charge from the high one so that the total bank Voltage is divided 50:50 between the halves to protect one half from under charge and the other from gassing.


Title: Re: Cobbled together PV in W.Sussex
Post by: Outtasight on January 12, 2011, 10:15:18 PM
After trawling around some makers of expensive, high power 12V tap equalisers, I found what looks like I want...  Just a battery balancer for charging control only.  Only £29 (less than 1/10th the price of the big ones but only supports balancing currents of 1A... probably enough for what I need).

http://www.rapidonline.com/netalogue/specs/18-0747.pdf (http://www.rapidonline.com/netalogue/specs/18-0747.pdf)


Title: Re: Cobbled together PV in W.Sussex
Post by: EccentricAnomaly on January 12, 2011, 10:52:56 PM
Here's a somewhat droopy circuit of the sort I have in mind for that application.  Basically a MOSFET to control the dump for each battery controlled, via an opt-isolator (not strictly required for the 'bottom' one), from the output of a microprocessor.

Probably about the same price with more hassle but also more flexibility than the controller you reference if you only have two batteries.  Cheaper if you have, say, four 6 V packs.  Very easy to deal with more than an amp if you want.  Can go on the PWM outputs of the Arduino if that's what's used.  The Arduino could also do a certain amount of logging, reporting, over/under-voltage alarming and the like.

Obviously it'd also need sensing of the battery voltages which could be dealt with using some zeners and resistors on the analog inputs.


Title: Re: Cobbled together PV in W.Sussex
Post by: Outtasight on January 13, 2011, 08:23:13 PM
Nice one.  I might look into arduino a bit more.  Looks useful.  The USB prototyping interface I'm using for my load manager thingy is similar in that it's got a couple of A/D inputs, digital inputs, digital outputs, D/A outputs and PWM outputs, but it's actually a dumb device that relies on being plugged into a PC that runs the software.  Ok for my application upstairs, as it's plugged into a machine that is on all the time anyway, but for this sort of low power programmable thingy, arduino would be great.  

As it happens, your post arrived just after I'd placed an order for two of the Rapid Electronics battery balancers, so that's that line of mad inventorism put on the back burner for a while.  ;D

I'll post more when I get the new widgets.  I ordered two, as I've got my battery bank in two halves (the gel one and the AGM one).  That and they had free postage if you bought two ::)

Quote from the movie, 'Contact' - "First rule of government spending: Why buy one when you can have two at twice the price."   facepalm


Title: Re: Cobbled together PV in W.Sussex
Post by: Outtasight on January 15, 2011, 06:33:17 PM
Bit of a retro post this one... 

Back in October, some guys turned up out of the blue, and chopped down the dead fir trees in the garden of one of the houses that back on to the garage courtyard.  Fascinating watching them take the trees down, a chunk at a time, over two days; most of it went into a giant petrol shredder.  Only the biggest sections of log were taken away whole. 

Helped me a bit in the Winter, as the low Sun used to be blocked from shining on the garage by those trees.

(http://i52.tinypic.com/9ftbfm.jpg)


Title: Re: Cobbled together PV in W.Sussex
Post by: Outtasight on January 28, 2011, 02:11:22 PM
Well blow me down.  The CamdenBoss battery equaliser turned up today (only one mind... the other is still being made by elves somewhere) and it does exactly what it says on the tin.

I didn't even have to cut off the ring terminals, as the holes where the right size to go on the Marathon battery post bolts.  Just a quick phone call to them to ask if there was any specific order that the thing should be wired up in (some old designs could blow up if you wired them up correctly but in the wrong sequence of terminals).  

And away it went...  Being sunny today, the bank has been charging hard (55 Amps at times).  By the time I'd got the wee beastie on the battery, it was still pulling 11A at the absorption point with a variance of about 0.1V for the upper and lower halves.  This is better than it had been, as I have the inter-string balancing connectors between the mid points of the 3 strings of Marathon batteries, but still not ideal.  With the battery equaliser in the circuit, the bank came into almost perfect balance, just 0.02V between the halves.  The little heat sink on the thingy got slightly warm but not hot.

It doesn't matter now that the equaliser is on just one battery string because they have the commoning links between the mid points, so over time the equaliser will tend to equalise the entire parallel pack.  As it's only shunting a maximum of 1A, there'll be negligable Voltage drop across the 6mm2 equalising bus.

Just need the other one to turn up in the post so I can fit it to the other battery bank.

I was looking at LiFeYPO4 batteries again...  found a european distributor for the Chinese ThunderSky large cells.  

http://www.ev-power.eu/index.php?p=p_33&sName=home (http://www.ev-power.eu/index.php?p=p_33&sName=home)

They also do 90Ah 12V lithium monoblocks without a BMS.  Supposedly the internal cells are now so well balanced (through just cell matching quality control) that for lowish power applications you don't need a BMS (provided that you only use one 12V block by itself).  Of course, with my 12V monoblock balancer, I could, in theory, use two such monoblocks in series for 24V without anything bad happening.  They also sell a more sophisticated BMS system to equalise 12V monoblocks, but with over Voltage and under Voltage relay triggers as well, to protect the battery from uncontrolled charge / load.  But I already have solar chargers that can do this and the main load, the inverter, has a LVD trip built into.

I have all the sub-components necessary to start playing with expensive Lithium batteries ::).



Title: Re: Cobbled together PV in W.Sussex
Post by: Outtasight on January 28, 2011, 06:45:49 PM
There was something in the specifications of these little balancers that I didn't appreciate.  It's that they only work at 12.8V and above.  So they only become active when you're charging the battery bank.  Below that charge Voltage (or when just discharging the bank) the balancer doesn't do anything.  I connected a 60W bulb to one half of the bank and it caused that half to drop in Voltage. 

The high power balancers actually will shunt power from one half to the other when discharging as well as charging, so you can run 12V kit from one half of a 24V bank.  But then those balancers cost 10x as much...


Title: Re: Cobbled together PV in W.Sussex
Post by: Outtasight on February 08, 2011, 01:26:41 AM
Still playing with my bike generator  ;D

(http://i38.tinypic.com/29xuckm.jpg)  (http://i37.tinypic.com/2wpmq0m.jpg)

Actually this is it running with a car alternator but it was too hard work as you have to waste a huge amount of power to energise the thing and it has a high cut-in speed (not good when the size of the alternator pulley meant the gearing was only 14:1).

I've been running this thing with a 16 pole DC washing machine motor configured with the stator and rotor connected in series.  It's not even a permanent magnet motor but the series winding plus a tiny bit of residual flux in the core is enough for the thing to self-excite and make about 4A at 12V (actually lots more volts as I've blown up a bunch of 21W brake light bulbs that I was using as current limiters in series with the car battery.

(http://i46.tinypic.com/1g17k5.jpg)  (http://i47.tinypic.com/vxjls6.jpg)

The bike was a £5 car boot find and was ideal as it had a big fly wheel with a smooth edge for the original friction band.  I just replaced the friction band with a ribbed drive belt and lashed up the motor on some wood.

The washing machine motor cost me 50p at another car boot sale and the power comes from the rotor that is series connected to the stator coil.  As it has 16 poles and DC commutator brushes, I don't need to rectify the output.  When using the battery, it needs a diode to stop it from spinning backwards (motoring) and I had to rig a bulb and a press switch to get the thing to self-excite before it could make 12V and so start charging the battery.  Without a battery in the circuit, it can light any light bulb straight off, without the "starter circuit".  The washing machine motor also had a much smaller pulley on it so the gearing increased to about 30:1 so I can pedal at a comfortable pace.

(http://i35.tinypic.com/2ilbtzd.jpg)

The beauty of this arrangement is that all generated current is used to both reinforce the field AND charge the battery / power the load.  The washing machine motor makes use of a tiny residual flux in the core that induces a tiny current in the field coils when you first spin the rotor that flows through the load which flows through the field coil and rotor, making a bigger field current that flows through the load and back through the rotor that makes a very big field current... and so on.

I got to thinking that I wanted to use the bike again and make some proper use of the power.  The problem was that the feedback of series wound generators makes it very efficient, but uncontrollable.  It gets suddenly very hard to pedal and can produce enormous Voltage spikes that would kill lots of expensive things.

So I started playing with using a battery to power the field windings, and that way have a fixed strength field that gives a linear output with speed.  At first I tried a spare 12V battery, but the field winding is only 1.8 Ohms, so I had to use 20W bulbs in series to reduce the current.  This wastes a lot of battery power in the bulbs but it did give me the range of current that I needed.  The house battery is 24V, so I needed quite a lot of field current to get the generator to output that Voltage and make some Amps, without having to pedal too fast.  About 3.5 to 4 Amps is ideal.  If I pedal too fast, the open circuit Voltage can shoot up to about 80V.  I almost blew up a 50V 1000uF capacitor that I'd put on the output to smooth any spikes from the commutator ::)

Then I took a NiCd battery pack from a busted drill and dissected it, stringing out 6 cells on a bit of wood, to give me 7.2V.  That gives me the required 4 Amps without needing any current limiting bulbs or nonsense like that.  The NiCds can charge from a spare solar panel in the day, so the field current is "free".  The cells are a bit manky and old but seem to work, and NiCd cells don't mind being run flat.  I included a 5A breaker as a way to turn the field coil on and off and also for safety.  I got about 8 minutes of pedalling before they died, but I hadn't charged them fully before playing with them so maybe they'll do better after a long slow charge. 

The bike generator is wired into a spur on one of the existing solar panel strings, feeding the Tristar MPPT controller.  This controller is safe up to 150V DC on the input, so it should be ok with the bike. 

I was a bit worried about how the MPPT algorithm would behave with a bike generator, but it actually seems ok.  During the day, the solar panels are making some juice and tend to level out the Voltage, so the MPPT tracks them rather than the much weaker bike source.  I could pedal all I liked, and the DC PV bus just sat at 33V.  Having it use the MPPT control also means that the bike generator can work at the higher Voltage and so line losses are lower but the battery still gets the extra Amps at 24-25V.

I then tried it at night.  To my surprise, it still worked pretty well.  The MPPT sort of settled for 28V to 33V most of the time, although for a while it went up to about 45V.  It didn't hunt too much, and the Tristar has a very fast sweep scan so the motor was only unloaded for a fraction of a second each time.  With the field current set up for a comfortable RPM and load, I wasn't applying so much torque that the motor would over-rev when a scan took place.  It felt like the bike was changing gears on an automatic gearbox :).  Looking at the power trace from the MSView logger, it seemed to make a steady 60W into the house battery.  Result!

Now I just need the NiCd pack to hold out longer and for my legs to hold out too.  ::)


Title: Re: Cobbled together PV in W.Sussex
Post by: StBarnabas on February 10, 2011, 03:29:50 PM
Outta
great work! Have a virtual applaud!


Title: Re: Cobbled together PV in W.Sussex
Post by: Outtasight on February 11, 2011, 12:45:11 AM
Thanks!  

It's working quite well now.  After a few cycles (no pun intended) with slow 8 hour recharges, the NiCd pack is behaving itself better. The cells seem balanced now and none end up being zero Volts at the end of a cycle (pun intended)  ;D

I was doing the weekly shop and noticed this 3m in car power extension.  It has a in-line socket and plug with a switch, LED, and a 10A fuse.  Perfect, I thought... Cut it in half and make it into a battery connector, field coil switch, and battery indicator.

The wire was long enough to just tie the plug to the bike handle bar, and then I can take the battery into the garage, plug it in and turn it on.  No more messing around with chocblocks.

I also bought a 100V 1000uF capacitor to replace the 50V one that almost exploded and improved the smoothing circuit to make an "electronic flywheel".

With the capacitor just connected to the rotor winding, on power dips, the capacitor would actually try to discharge through the rotor winding rather than towards the battery.  With an extra diode before it, the peaks are smoothed and charge is pumped only in the direction of the battery.  I could have just put the capacitor on the left hand side of one diode, but then that would put PV Voltage always across it and risk a serious short circuit hazard if its insulation failed or just might make the MPPT tracking sweep go weird (or something equally unpredictable).


Title: Re: Cobbled together PV in W.Sussex
Post by: Outtasight on March 14, 2011, 02:35:24 PM
Lately, the tupperware solar sensor that is supposed to measure the available solar power has been playing up.  Sometimes reading zero in full sunlight or other wonky values that didn't seem right.  It also was too directionally sensitive - a feature of the old solar panel used that has micro lenses on it that focus the light - but only when it shines square on to the panel.  Also the box itself was possibly causing some shading or variation in light getting through.  On closer inspection, the UV had destroyed the tupperware, making it crack and go brittle.

So the search was on for a small sensor that will be weather proof and less directionally sensitive...

The local Robert Dyas had the perfect bit of bodgineering raw material... a £1.49 solar garden path LED lantern spike thingy.  It had a little amorphous solar panel on the top and all the bits came apart easily to leave the plastic and stainless steel capsule on its own.  I could just rip out the little circuit board with the LED and battery, and connect the wires from the solar panel across a 100 Ohm resistor load in a chocblock (so that the device measures solar power). Then I just had to hot glue up the holes on the base to prevent water getting in.  The hole where the LED came out was just the size to fill with a rubber blanking grommet.

Some of the existing holes for the lantern bit to snap on to were also handy for threading the plastic cable tie through.  I mounted it on a handy hanging basket bracket that was already on the wall when we moved into the house.  This, by sheer coincidence, is at the same angle as the main solar panels.

The amorphous panel has no outer window or lens to restrict the angle of light acceptance and amorphous panels are less sensitive to direction anyway, so it seems to give a good reading through the day.

The output Voltage was a little lower than the old sensor, so I had to recalibrate the measuring software on the load controller to get a proper 100% reading in full sunlight, but it seems to be working well now.  Today's water tank is already up to 33C and the battery hasn't been micro-cycling like it used to when the sensor power readings were off the mark. :)

I might have to tweak the software again in a couple of months as new amorphous panels put out up to 20% more power when new, but quickly settle down to their usual power when exposed to the sun for a few weeks.

I've even got the (still working) white LED, solar controller chip, NiMH coin cell and on/off switch gubbins that I can play with.  Most of that would be worth at least £2-3 if I'd bought it from Maplins.  So the solar panel was actually "free".

Oh, yeah... Like my new multimeter?  It's an antique Micronta (Tandy) analogue (but with FET inputs) 1980's test meter that I picked up at a car boot the other week.  Nowhere as accurate or convenient as a DMM but looks "retro-cool" 8)


Title: Re: Cobbled together PV in W.Sussex
Post by: Outtasight on March 23, 2011, 10:23:44 PM
The new sensor works better than I expected and now the water heater works really well.  Getting good heating yields but not cycling the battery much at all.

I updated the software control a bit to allow a manual parameter for the sensor scale, so that I don't have to recompile the program just because the sensor has been changed for a different one.  I also added a counter for the current and previous day total number of minutes that the heater has run for.

Here you can see the results of a totally blue sky day on the right of the graphs...  Even on the not so good day, the battery Voltage holds up pretty well with the more accurate solar power availability estimate.

Today was the first full solar hot water day of the year.  No gas used and 48C in the tank.



Title: Re: Cobbled together PV in W.Sussex
Post by: Outtasight on April 01, 2011, 02:59:54 PM
After missing out at the police auction in Bristol that was selling loads of recovered stolen PV dirt cheap, and missing out on some other auctions on line, I got lucky this week...

(http://i52.tinypic.com/149oarr.jpg)

Eight 80-85W mono panels (650Wp) for £940... £117.50 each!   bike:

Two are 85W models (a BP and a very old looking GB Sol) and the rest are pretty new Chinese "Klearskies 2000" 80W models.  One had a load of garden fence paint splashed on it but an hour with some water and the Japanese "magic sponge" soon got rid of that.  Quite a feat, considering the glass is textured.
  
Now all I have to do is figure out where to mount them.  facepalm

Strange as it may seem, I'm thinking of selling one of them, as that way I'll have an even number of 80W panels overall.  I'd only gone on to eBay to look for one panel to match up to the odd panel I have on the garage (I bought 5 panels last time).  Although I could use all eight, it would leave me with an odd panel again and it's too much of a temptation to buy "just one more" to make it an even number.  ::)

If I sell one, then I won't have that itch to scratch.

The guy was selling them to pay for his MCS / Part P training and then he'll do his house with a proper grid tied array as his exam install to get certified.  So now I'm sponsoring PV installers to get through college and do things properly by bodging my own system...  There's an irony.

He donated the suspicious 600W Chinese GTI that he'd used with this lot at the back of his garden.  

(http://i55.tinypic.com/eddhu.jpg)

I had a quick look at the innards and was glad that I did.  A capacitor on the output display power supply had swelled up and burst.  

(http://i56.tinypic.com/2vis27q.jpg)

If magic smoke hadn't already issued forth, it soon would have.  As its only the Watt meter on the output and not part of the inverter itself, I bodged on a similar capacitor (but alas too small to make the meter work, but safe enough to make it not work reliably, if that makes sense).  

An initial play with it in the garden yesterday showed that the inverter works, sort of.  I hooked up two 80W panels in series (the inverter works from 28-52V DC) and it made some noise and a plug in AC meter said something like 40W output (it wasn't sunny).  But then it sort of stopped altogether and restarted if I turned the DC off and on again.  Not sure if this thing works properly at all (or ever did...).  But as he gave it to me as a freebie, it can't hurt to play with it a bit.  On the other hand, he did mention that he used to have a 1kW one, but it exploded ::).

It has some appeal though... plugging in maybe just 80W of grid tied power to offset the base load that I can't get off grid.  I could use the old pair of 40W Kyocera panels on the garage and just put the GTI in the garage, plugged into the spur there.  I've some leeches that can't go on solar power (like the clock in the electric cooker, the central heating boiler, and so on).  With a little bit of grid tied power I could null most of that energy import out without losing power to the grid (and I can't get paid for or worse, the import meter may count up even when power is flowing out of the house).

Of course the next thing will be arguing with the FIT bods about having expanded my DIY system.  They may throw their toys out of the pram and kick me off the FIT scheme altogether (fine by me) or they might agree to pro-rate the kWh payments to exclude the additional capacity.  I think they are already calculating it wrong for my existing system; I got my second payment a few weeks ago (only the second statement though as I didn't get approved until December) and it doesn't look quite right.

I'll also now have too much PV for the 60A Tristar controller so I'm going to use some of these panels on a E-W system.  I'll get rid of the mickey mouse 12W & 15W amorphous panels and use the new ones to boost morning and late afternoon production, as off-grid needs a long flat power curve rather than lining all 2400Wp up at the noon sun and over loading the controllers and battery.  I can't even use 2400W as the immersion heater is geared down to just 650W.  But it will mean that I can use that 650W for longer than before and run other things like the fridge longer without hitting the battery at all.

It might even be time to bite the bullet and get a Navitron roof rail kit and talk to the BC bods about allowing me to install this kit on the roof, where it belongs.


Title: Re: Cobbled together PV in W.Sussex
Post by: StBarnabas on April 01, 2011, 03:34:55 PM
Outta
a very good price for PV and I watch this thread with admiration.

Regarding the Navitron rail kit - I had a major job using it fine for small panels but almost impossible with large ones- though maybe it has improved over the past 18 months!

Keep up the excellent work
Sean


Title: Re: Cobbled together PV in W.Sussex
Post by: biff on April 02, 2011, 12:19:21 AM
outta,
      you are a genuine genius but if things go wrong we will lose one of our best bloggers,that grid tie inverter thingymajig looks like old jack changs work and not for nothing it is totally illigal,.years ago i used to have a brotherinlaw,a brilliant electrical draughtsman who accumulated so many accidental blue tatoos on his tongue from pairing live wires with his teeth that it affected his brain and slowed his reactions dramatically,,he began running into the cars in front of him,forgetting what he was doing,,,yes rearending cars, too much lecky in the wrong place can do that to you,
                                                                         biff


Title: Re: Cobbled together PV in W.Sussex
Post by: camillitech on April 02, 2011, 07:45:54 AM
Nice find Outtasight and another great posting  :genuflect

Cheers, Paul


Title: Re: Cobbled together PV in W.Sussex
Post by: Outtasight on April 02, 2011, 10:34:25 AM
Thanks guys...

Sean, the Navitron rail seems simple enough to use (from reading the "how to" guide).  What was it about the kit that made it hard for big modules, other than needing two people to lift the things?  I remember in your thread having a whole saga with the roof bolts and finding spacers and so on for a slate roof but mine is just concrete tiles that interlock (you can just lift them up).  Provided I get the right hangers, it should be fairly straightforward... I hope.

I've deliberately gone for small 80W modules, as it means it's an easy one man lift (that and there's always a surplus of used ones around in that size as people trade up or give up). 

I think my only obvious problem is that some of the panels are different heights (some are 35mm frames, some 50mm, etc.) which means that the inter-module clamps aren't going to work.  But I figured that just meant that I'd need more end clamps so that I could put a group of modules that are the same height together and then start another group that are a different height with another set of end clamps and inter-module clamps.

What I'll probably do is put all the 80W modules on the house roof, as they're at least the same shape and will almost look like they were professionally installed.  The big heavy Sharp 170W modules will probably move to be the patio door "sun shade" and the gaggle of misshapen left-overs can occupy the garage roof.

Biff, yeah... I don't plan using this inverter indoors or leaving it unattended really.  Far too suspicious.  At least in the garage it won't burn the main house down whistle.  I do have a smoke detector, fire extinguisher and first aid kit in my living room, as required by the corporate H&S dudes when I started working at home.  Who knew laptops were so dangerous?  ::)

They've got some fake CE sticker added on to the case as an after thought and no mention of any other standards compliance.  Obviously not G83 certified, but as they are plug-in units to the AC, they had to implement some form of anti-island protection, just so that they didn't immediately kill a load of customers who touched the AC plug pins when the DC side is activated.

It's quite funny, but on the makers web site they have links to YouTube videos on how to test and repair the unit, and they sell kits of spare parts (saves on postage to send the whole unit back for repair).  The MOSFETs seem to almost be "consumables" on this model range  facepalm

Product info
http://www.12vgridtiepowerinverters.com/ProductProfile/PSWGT600-28-52-230 (http://www.12vgridtiepowerinverters.com/ProductProfile/PSWGT600-28-52-230)

"Consumables" page
http://www.12vgridtiepowerinverters.com/Products/parts (http://www.12vgridtiepowerinverters.com/Products/parts)

YouTube "fix it yourself" instruction videos
http://www.youtube.com/watch?v=5h8AesDhhEU&feature=related (http://www.youtube.com/watch?v=5h8AesDhhEU&feature=related)

It doesn't mention on the web shop that prospective owners of their kit need to be electronic engineers, familiar with switch mode power electronics...  Might put folk off.


Title: Re: Cobbled together PV in W.Sussex
Post by: Mostie on April 02, 2011, 05:45:07 PM
Hi, Outta

you may find this usefull http://www.thebackshed.com/forum/forum_posts.asp?TID=3219


Title: Re: Cobbled together PV in W.Sussex
Post by: Outtasight on April 02, 2011, 09:33:46 PM
Wow!  Thanks.

The contents of that thread confirm it then.  These inverters are officially pants.

One of the mods suggested was adding 100,000uF capacitance to the input, replacing some resistors that are under rated for power handling, and replacing the PCB AC fuse that is only rated for 110VAC, despite the unit being sold as for 220VAC (not even the nominal UK 230VAC, which in practice is 240VAC - as measured in my house).

My suspicion that the MOSFETs are "consumables" seems confirmed by users experience of them going pop for no other reason than having switched the AC socket off and on with DC power present.

Although quite a few seem to have gone pop while trying to drive the GTI from a battery bank and not solar panels.  You're not supposed to try and drive the input from a battery, as a GTI is designed to work with a current limited source of DC.  A solar panel or wind turbine is a current limited source but any lead acid battery can muster a current of a few hundred Amps, and this will blow up the DC stage of the GTI before its limiter can kick in (or at best it will put it under a lot of stress).  GTIs are very different beasts to off-grid inverters because a GTI will try to drive as much power as the source can deliver into a near zero impedance AC load (the grid).  It relies on the source power being broadly matched to the inverter power handling rating (plus an overload margin that the current limiter can cope with).  An off-grid inverter will only deliver the AC power demanded by the AC load, so its DC source can have unlimited current capacity (such as a 1000Ah battery bank).   

I've observed one similar effect as mentioned in the thread: The MPPT Voltage wandering off the PV power curve (up towards the Voc of the panels) and the AC output dropping off to nearly nothing (4W).  Removing the DC and reapplying it seems to sometimes reset the MPPT tracking point (but not always).

Seems an all round dodgy bit of kit... only fit for the parts bin.

I might pursue the idea of a small grid tied system but with a proper micro inverter (the Enecsys one I saw at the Eco Build show, that is now in the UK and G83 compliant).  It also works with two 12V panels in series (tracks a Vmp of 27-45V).  It just doesn't blow up trying to.  ::)

http://www.segen.co.uk/Installer/Product/3195/Micro_Inverter_SMI_200 (http://www.segen.co.uk/Installer/Product/3195/Micro_Inverter_SMI_200)


Title: Re: Cobbled together PV in W.Sussex
Post by: ecogeorge on April 02, 2011, 11:13:50 PM

I might pursue the idea of a small grid tied system but with a proper micro inverter (the Enecsys one I saw at the Eco Build show, that is now in the UK and G83 compliant).  It also works with two 12V panels in series (tracks a Vmp of 27-45V).  It just doesn't blow up trying to.  ::)

http://www.segen.co.uk/Installer/Product/3195/Micro_Inverter_SMI_200 (http://www.segen.co.uk/Installer/Product/3195/Micro_Inverter_SMI_200)

Just like the OK4e inverter (100w max 24-50v dc input) I have 5 of these grid tied and registered for FIT.
Anyone got a uk supplier or price on the Enecsys unit?
rgds George.


Title: Re: Cobbled together PV in W.Sussex
Post by: EccentricAnomaly on April 03, 2011, 10:53:59 AM
GTIs are very different beasts to off-grid inverters because a GTI will try to drive as much power as the source can deliver into a near zero impedance AC load (the grid).  It relies on the source power being broadly matched to the inverter power handling rating (plus an overload margin that the current limiter can cope with).  An off-grid inverter will only deliver the AC power demanded by the AC load, so its DC source can have unlimited current capacity (such as a 1000Ah battery bank). 

I think you have a point but I'm not entirely convinced by the way you describe it. There's the common theme of having more panel peak power than the GTI is rated for. As you describe it in those cases on a sunny day the GTI will limit the current to protect itself at which point the panel voltage will rise and still the protection will work. Connect that same GTI to a battery and it'll again protect itself by limiting the current. However, now the voltage will not rise (much) so the protection is even easier.

Basically the GTI protects itself by reducing the output current by reducing the input power: moving away from Vmp in on direction or the other. Above I assumed reducing the input current and thereby allowing the input voltage to rise which wouldn't be a problem with batteries. On the other hand, if the GTI tries to reduce the input voltage by increasing the current the battery is likely to win. Is that what actually happens?

If so, do GTIs have a specification for the maximum current source they can be connected to? The normal limiting specification is maximum Voc but is there also a maximum Isc somewhere in the small print?


Title: Re: Cobbled together PV in W.Sussex
Post by: StBarnabas on April 04, 2011, 11:16:03 AM
Outta
I went for a rear mounting system - very clean but bolts in the back. It is difficult to get into the channal particulary stretching to the other side of a large panel. I was fortunate to have Omar and Stu who are both over six feet. Omar in particular able to reach the bolts as he has very long arms, but they defeated both Stu and myself.

Sean
 


Title: Re: Cobbled together PV in W.Sussex
Post by: Outtasight on April 05, 2011, 06:37:05 PM
Sean,

I should be ok then, as the 80W panels are only 55cm wide, and I'll be mounting them vertically across the horizontal rails.  The big Sharp 170W panels might have to stay on the garage then, as they are pretty wide and heavy.  I've just taken delivery of a load of MC4 connectors... Finally will do things a bit more properly than loads of chocblocks ;D  The new Kearskies panels all have one MC4 connector on them each (he linked them in 24V groups but put the end terminals in chocblocks).  So I figured I'd make up the extensions from the roof to the outdoor junction box using more MC4 connectors and proper solar cable (rather than whatever I had laying about the workshop that day...).

Eccentric,

The issue is with the amount of overload and the response time of the protection circuit.

The DC choppers in the input stage have a limit to how much current they can stand.  But how much current, and for how long is the issue.  They can withstand currents greater than their continuous rating but for short periods.  A MOSFET or IGBT rated for 5A continuous, might survive for 60 seconds at 10A, 5 seconds at 20A, or 0.1 seconds at 40A before the magic smoke appears.

The GTI will be designed (hopefully) so that the system limits the continuous average current to no more than 60% of the component rated current.  If it is derated by design, then it should last much longer.   

The protection takes a time to respond to over current and responds by limiting the on time of the DC choppers.  This limits the average power sent through the transformer and so the average AC power output.  The system is designed to protect the components from excessive continuous power output, beyond the rating of the switches and the transformer windings.  What it cannot do is limit the actual current passed by the DC chopper switches during their "on" periods.  Imagine plugging a 3kW heater into a wall socket with a 3A fuse in the plug.  If we suppose that the mains is DC and not AC, you turn it on, 13A will immediately flow and the fuse will blow in a split second.  Now, say you turn the switch in the wall socket on and off very quickly, so that the switch is on for only 23% of the time and off for 77% of the time.  If you do this fast enough (basically, so that the on time is less than the time it takes for the fuse to blow), the average current will be 3A, measured over some large number of on/off cycles.  But each time it is "on", the fuse is passing 13A and is trying to blow.  It can survive for a while (maybe) because the average current is only 3A but the fuse is suffering 13A "shocks" that will make the fuse wire vibrate and squirm as it heats and cools violently, almost, but not quite blowing.  It's not going to last very long though like that.

By varying the on time of the switches, the average load on the PV, and its Voltage is controlled.  If the on time is increased, the average load current increases and the average PV Voltage drops.  Conversely, if the on time is reduced, average load current is reduced, and the average PV Voltage increases.  The MPPT Voltage monitor on the input tries to maximise the product of the DC current and Voltage to find the PV arrays max power point and track it.  But it must do so looking at the average values (over some short time to give good tracking of variations in light, but much longer than the individual switching cycles of the chopper to get a good average reading).

Where the array is too big, and the output AC power limit is reached, the MPPT will deliberately over-shorten the "on" time of the drivers, reducing average power transmission.  The PV Voltage rises above Vmp as a side effect.  My PWM charge controllers do the same thing when the absorption Voltage on the battery is reached.  The controller no longer tracks the maximum power point of the PV array (as it doesn't need the maximum power) and instead the "on" time of the IGBTs is wound back to feed the battery just enough average current to keep the average battery Voltage where it is desired.  The battery is not being charged with DC.  I put a scope on the battery charge leads and you can see current pulses at a few kHz frequency. The average PV Voltage rises above its Vmp rating, and progressively sits closer and closer to Voc, as the load decreases on it.  If, during bulk charge, there is too much PV current available (more than the programmable battery current limit on the controller), the controller will also drop out of maximum power tracking and over-shorten the switch "on" time to limit the average current to the desired value.

Now, installers (and the GTI designers) recognise that the Wp value of PV is very seldom achieved in the real world.  So they generally install more Wp of PV than the rated (limited) AC power output of the inverter.  The input current rarely exceeds the limit value, and when it does, it generally does so in a slow way (ramping up and down over minutes or hours).  Because the parts have been derated a bit, they can withstand an infrequent but sustained 10-20% overload of current in their on phase (for maybe just a few hours a year) and the rest of the circuit can withstand it too, as the average power is capped to limit the bulk heating of the unit.  You can't go sticking 100% more PV on the thing compared to its rating, otherwise the time it will spend pegged at the limiter and the intrusion into the safety margin of the switches will become longer than intended, and their life will be shortened (like that 3A fuse).  It won't blow immediately, it might take a few months or a few years, but your inverter won't last 25 years.

When I had nearly 400W of PV on my 12V controller that was rated for 200W, it initially limited the current to 15A, but eventually would complain on very sunny days, and shut down altogether, protecting itself from repetitive peak overload currents of 30A in the switches.  A cheaper controller would have soldiered on and blown up.

Now, if you go and stick a big battery on the input of a GTI, the current the switches have to endure during their "on time" will be a couple of hundred times their rated current all the time (only limited by how thick the battery cables are really).  That's where the graph of current vs. life span comes in.  If the components can survive the initial split second overload, and the MPPT protection kicks in to wind down the on time during subsequent cycles before they explode, then they'll live for another day... 

But "...you've got to ask yourself one question: 'Do I feel lucky?'  Well, do ya,... Punk?"

So, my bodging advice would be that if you want to run a GTI from a battery, make sure you use some scrawny long battery cables that can't deliver much more short circuit current than the rated current of the inverter input.  It will work like a ballast resistor and save the MOSFETs blowing up, maybe.


Title: Re: Cobbled together PV in W.Sussex
Post by: EccentricAnomaly on April 05, 2011, 10:00:09 PM
Eccentric,

The issue is with the amount of overload and the response time of the protection circuit.

Ah. Ok.

Good explanation of PWM for this sort of application.


Title: Re: Cobbled together PV in W.Sussex
Post by: Outtasight on April 25, 2011, 12:01:02 AM
Managed to get some of the new panels into service over the last couple of weeks.  Basically, I replaced the 12Wp amorphous panels on the two folding A frames with two of the 80Wp Kearskies panels and the 85Wp BP and GBSol combo.  A bit of woodwork to finally finish off the second A frame... Replacing the old iron gate that was being used as the temporary half of the "A" with some proper wooden legs ;D.

I can't actually use all of the 2.08kWp at the same time, as the Morningstar TriStar MPPT controller is only rated for 60A at 24V, or some 1600Wp (they seem to rate it for the float Voltage of 27V on a 24V system).  I've got 1740Wp installed on that controller (would generate just over 64A), but it points in different directions, so will never make the total power at the same time.

I beefed up the cabling to the new array by doubling up the wiring, to about 2.6mm2 to keep losses down a bit.  I want to resist starting to chop up the 50m reel of 6mm2 proper solar cable I bought the other day.  I almost rang up the supplier to complain about where it was (supposed to be 48 hour courier), but after five days, the neighbour popped round to deliver it on the weekend.  The dozy driver had called while we were out shopping, and dropped it next door, without leaving us a card.


Title: Re: Cobbled together PV in W.Sussex
Post by: desperate on April 25, 2011, 10:13:56 PM
Good work Outta,

I always learn loadsa new stuff from your posts, even though I've no idea what I'm learning, weird wriggly upside down lectrons or whatnot.


Seeya

Desp


Title: Re: Cobbled together PV in W.Sussex
Post by: Outtasight on April 28, 2011, 03:18:42 AM
 ;D

Check out the BDPV graph for today!  (click the link in my sig.)

135kWh generated (used) in April so far.  An "all time record" for me.  I didn't generate this much energy even in July last year (131kWh).  Still three more generating days to go in this month as well... How sunny has April been???  exhappy:

Not much water for the garden though...  I thought two linked water butts were enough.  Good news is there's space for a third one next to the garage.


Title: Re: Cobbled together PV in W.Sussex
Post by: biff on April 28, 2011, 08:47:35 AM
awesome posts outta,
                        great ideas,great stuff.
                                                         biff


Title: Re: Cobbled together PV in W.Sussex
Post by: brackwell on April 28, 2011, 08:48:49 AM
Outtasight,
I am very pleased for you and jealous that i do not have a pv system at the moment. However using

http://re.jrc.ec.europa.eu/pvgis/apps3/pvest.php  

I note that your production is somewhat below prediction and wondered why this might be?

PS I was told by a installer that the increasing data on instillations is beginning to show production greater than predictions!

Ken


Title: Re: Cobbled together PV in W.Sussex
Post by: Outtasight on April 28, 2011, 06:51:31 PM
Thanks everyone!

PVGIS and so on predict grid tied production, where every Watt.hour goes out the door or is used in the home, but either way, it gets metered.  Off grid always shows a much lower apparent production, as the only electricity metered is that used in the home.  Electricity that just gets stored in the battery but not used doesn't show up.  If the battery is full and you're out for the day, your "production" on even a really sunny day can be nil.

That's why I've been developing the automatic immersion heater load controller, so that more energy actually gets used when it's available.  The improvement in this month's figures over last year is probably down to it being sunnier but also by having improved the utilisation of the power.  It isn't accounted for solely by the increase from 1.85kWp to 2.08kWp installed capacity.

It's been consistently sunny enough this month for me to run the fridge freezer on solar almost non-stop since April 1st.  I think there was one or two days when I had to put it back on the grid power at night because there wasn't enough spare battery power to let it run through until dawn.

Another factor is that with a surplus of peak PV installed on an off-grid system, you tend not to see proportional increases in "production" in sunny months.  When there's more than enough solar power available to power your normal loads, the excess gets wasted (1500W available but only 1000W worth of "stuff" turned on means you are wasting 500W of available energy).  But in the dark months, you see more use as the system is grasping at every last photon just to stay alive.  On a bad February day, a 2kWp array might net you 200W of usable power, at most.

Ideally, you'd have a massive battery that never quite got full and you could then use all that energy captured at your leisure.  But lead acid batteries need to be kept nearly full all the time to stop them rotting and when more than 70% full, they don't accept power very well, so you end up wasting it...  Now a big lithium battery or a NiMH one... that would be ideal, as they don't mind being left flat all the time and can absorb loads of energy.


Title: Re: Cobbled together PV in W.Sussex
Post by: billi on April 28, 2011, 08:03:34 PM


 :)

this April is madness...   so much sun  , my relay in the Inverter is switching on an el. heater  , when battery  is full (or reaches fullness ) and that happens before lunch time  most days   ....   while we try to put everything we have in the washing machine   ;D

Some sort of a waste   .... have to think of more ideas , electric driving for a start , but guess will start with an electric moppet first

Billi






Title: Re: Cobbled together PV in W.Sussex
Post by: Outtasight on April 28, 2011, 08:41:58 PM
I presume you meant electric moped (a small battery powered motorised bike) as opposed to an electric moppet (a child-like cyborg)  :P


Title: Re: Cobbled together PV in W.Sussex
Post by: billi on April 28, 2011, 09:46:10 PM
 ::)  sure you are right i meant  something like that

(http://www.gillbach-schuetzen.de/Spass/Moped.jpg)  


Sorry moppet seems to be German Slang   from youngster times .....





Edit : picture disappeared from this message  and i do not know how  :(


Title: Re: Cobbled together PV in W.Sussex
Post by: Outtasight on April 30, 2011, 11:13:37 AM
Nice.  Looks like the external battery pack has cells made from old beer bottles...  Drink and drive?  ;D


Title: Re: Cobbled together PV in W.Sussex
Post by: Outtasight on April 30, 2011, 11:26:46 AM
Dual Power Level Immersion Heater Bodge

The automatic load controller for my immersion heater has been working pretty well.  It turns on and off with the varying power of the Sun.  But it left something to be desired when the battery was starting the absorb cycle.

The battery consumed quite a lot of power, but not all of it.  The immersion heater needed 650W to run, so couldn't.  The result was a period of under utilised solar power in the late mornings, with a trace that looks like this:

(http://i51.tinypic.com/2a9pumu.jpg)

By modifying the step down transformer supply for the heater, I created a dual power heater.  I step down the AC Voltage from the solar inverter with a 4kVA "tool transformer".  It outputs 110V AC from the 230V AC input.  This runs the 3kW heater element at just 650W.

(http://i55.tinypic.com/2aimyio.jpg)

Under software control from the PC load manager, the first relay turns the heater on and off, while a new second relay selects the power level of the heater, depending on the solar power available.

I added a pair of 6A diodes in parallel (for power handling, as the peak current when the heater is on is about 8.4A).  This converts the 110V AC into half-wave rectified DC.  The diodes are rated at 600V so they are pretty bullet proof.  This has the effect of reducing the power consumption of the heater from 650W to just 350W; measured with an AC plug-in power meter at the 230V AC input to the transformer.

The thermostat switch on the heater ordinarily wouldn't like DC power, as it would cause arcing when the contacts open, and this would soon destroy the thermostat.  But as this is half-wave DC, it still has the periods of zero Voltage in each 50Hz cycle, so the thermostat contacts can open and close as normal without arcing.

(http://i53.tinypic.com/o74qio.jpg)

I then had to modify the control software to take advantage of the new dual power heater.

I decided to ditch the purely light level & system power level threshold system, for one that attempts to estimate the array power available for driving the heater loads (at two power levels).

(http://i52.tinypic.com/2my9st1.jpg)

It has a seed value that is the expected array power (the "system size").  It then applies a self tuning modifier to that base value (plus/minus 200W) and then multiplies that by the measured light strength from the new sensor (as a percentage).  This gives me the estimated "array power".  The "system power" is the real measured output power from the Morningstar charge controller log data.  This includes all loads: battery charge load, other loads (e.g. the fridge), as well as the heater load (if it happens to be on).

By comparing the real power output during times when the battery is likely to be fully loading the array with the estimated "array power", the self tuning parameter adjusts the estimate up or down, so that the estimate gets better.  It has some limits set in the routine, so that it does not tune the estimate at very low light levels that would never be enough to drive the heater load.  It also has some fuzziness in the tuning so that if it is within 1% of the real power, it stops hunting.  If the tuning parameter gets bigger than 200W variance, it starts to modify the base assumption about the "system size", saving the change in a config file for next time the program runs.

Most of the estimate tuning happens in the MPPT bulk charge phase, as that is when the battery will absorb all the power the array can muster, and so the "system power" should equal the estimated "array power".  The idea is that the tuning parameter will compensate for the distributed orientation of the panels (some are East-West, some are South, some are at steep angles, some at shallow angles).  The system will also "learn" how dirty the array is (if there has been no rain for a while, and dust has collected on the panels).

The final step is that when the battery enters the absorption phase, the program looks at the estimated array power and subtracts the current "system power", which includes all non-heater loads plus charge demand, and calculates the "available power" for running the heater load.  If the "available power" is greater than the low (350W) heater setting, but less than the high (650W) heater setting, it turns the heater on, and selects "low power" mode (the diode bypass relay is energised, and the normally closed contacts change to be open).  If the "available power" is higher than the high power setting, the diode bypass relay is de-energised, the contacts revert to normally closed position, and the heater receives the full 110 V AC power.

The resulting power utilisation is more even, with the heater able to use low levels of available power and maintain the tank temperature. 350W is enough to very slowly heat the water, or at least compensate for losses through the insulation.  It all helps.  When it's sunny enough, and the other loads are low enough, the heater can run at full power (650W).

(http://i56.tinypic.com/21nfl0k.jpg)

The above trace also shows the water heater interacting with the cyclic load of the fridge freezer.  While the recorded system power varies considerably, note that the battery is given priority in attaining full charge and holding a steady float Voltage for as long as possible.

During the absorption and float stages of battery charge, the heater decision process also includes some "array power" estimate tuning.  If the heater repeatedly has to reduce power to low power, the tuning parameter slowly drifts downwards.  If the heater has to be shut off due to low power, the parameter decreases more quickly.  As a last resort, if the battery Voltage actually drops below the float threshold set in the load controller, then a much more severe adjustment of the parameter occurs.  This behaviour means that on clear sunny days, the heater is given priority and has a tendency to stay on.  On days with very changeable weather, the heater progressively errs on the side of caution, becoming less and less likely to turn on and more likely to turn off or remain in low power mode.  This favours maintaining the battery charge level.

Use of a half-wave rectifier at high power (350W is a significant load) is normally frowned upon, as it presents a very non-linear AC power load (only half the cycle is used).  The plug-in AC meter did show a very bad power factor (PF = 0.5).  This would result in power being wasted in the wiring and generator as reactive power (current out of phase with the Voltage).  But the 3kW inverter is stable into any power factor load (inductive or capacitive), and in the end, the source of the power is a DC battery or solar panel.  With the very large capacitors in the inverter input (for surge delivery), the DC source is not aware of the non-linear AC load, and merely sees a useful reduction in load.  The "bad" AC load does consume more of the available VA capacity of the inverter than a good power factor load would, but provided the total VA load is less than the permissible load, no harm is done.


Title: Re: Cobbled together PV in W.Sussex
Post by: bqjohn on May 05, 2011, 02:15:41 AM
Hi there, would a solid state relay on the immersion heater? driven with an 8-32volt DC pulse to give you more power variation (1%-100%)?
I've never tried done running off an inverter before, only off the mains. I'm looking at matching my load to the sun's output also when I get my extra panels up.


Title: Re: Cobbled together PV in W.Sussex
Post by: Outtasight on July 13, 2011, 10:50:55 AM
Hi... Has it really been soo long since I updated this thread?!!  I did update my proper blog a few times though  :P

Hmmm interesting idea but I think solid state relays don't offer the same level of galvanic isolation that mechanical ones do.  And I thought that solid state relays were just for controlling DC power in cars and the like...  Could be wrong though.

You'd have an issue with trying to make sure you chopped the AC power at the zero crossing points to cut down stress and RF noise but if the switching frequency was low (maybe once a second or the like) then it might be ok.  The problem is that I measure the available power only every 15 seconds but you could use that info to set a switching rate for the intervening 15s period (say 1s on, 1s off for 50% duty cycle or increase it to 2s on, 1 s off...)

Having consulted with OFGEM and the energy company on what impact my adding a load of solar panels to my system would have... Eventually, after about 3 months of e-mails and waiting, they agreed that I was a bit of a weirdo for wanting to make more solar power using some recycled gear and banished me from the land of FIT.

It was an interesting experiment, going through the ROC-RO-FIT process and actually getting some money for my cobbled together solar system, but the constraint on not increasing generating capacity by using more non-MCS recycled panels picked up cheap on eBay was plainly bonkers.  I don't need the money, but I do need the power.  So we parted amicably, and now I'm free to totally encrust my house with even more of the stuff and charge the batteries from whatever sources I like: mains in the darkest days of winter, bicycle generator, Mr. Fusion, or even... [shock horror] a 650W 2 stroke genny I picked up at a car boot for £30 last weekend!

If you're wondering (as I did) why it comes with a pair of wire cutters attached, that was to turn the fuel tap on and off (as the handle has snapped off the tap)...  Apart from that, the thing works ok (or at least it did after I scraped the mud, barley ears and weevils out of the fuel tap inlet - I think "farmer Jones" was trying to run the thing on bio-fuel but had skipped a few steps in the refining process  ::)  Fortunately, the fuel tap also includes a fuel filter so none of the crud made it to the engine internals.

The solar system proved it's worth again last week, as we had an 18 hour power cut... Summat to do with the water board boys out in the street and their giant digger, I'll wager.  Luckily it had been very sunny the day of the power cut and so we still had some solar powered hot water for the evening, but if it had been cloudy the next day or we'd had an extended power cut, I'd thought a backup genny would be useful.  Then lo and behold, this fella turned up at the next car boot - now that's a hint you can't ignore  :)

 


Title: Re: Cobbled together PV in W.Sussex
Post by: Outtasight on July 13, 2011, 05:10:20 PM
Oooh... Look what the post man brought me today!  ;D

This one seems to have an aluminium handle (rather than the pewter one of the original!).  It also has an external fuel filter that screws into the inlet (rather than inside the body of the tap), so that it's at least easier to clean the crud off the external filter.  Scraping it out from the inside was a lot harder when the filter used to be in the removable sump cup at the bottom of the tap.

It went on the genny fuel tank without a hitch and now I have a spare pair of wire cutters in my tool box ;D

The old one must have still been restricting the fuel flow too much as now a couple of pulls on the recoil starter, even from cold, sends the thing roaring into life (well maybe "putting" would be a better description that "roaring").  I'd bought a spare spark plug too, but it doesn't seem to need it now, as it starts and runs just fine.


Title: Re: Cobbled together PV in W.Sussex
Post by: Outtasight on July 13, 2011, 05:46:12 PM
You wait months for a posting, and then three come along all at once :P.

While out in the garden, tinkering with the genny, something went "pop" indoors.

The big Morningstar TS-MPPT60 charge controller sometimes runs quite close to maximum current these days.  On "sunny intervals" days it can especially be subjected to surges, as the sun peeks out from a cloud.  The optical concentration effect of a cloud edge can cause a PV array to surge to as much as 115% of nominal power for a few seconds.

I'd noticed that the link in the 60A fuse on that controller had got warm often when passing high power, and it had bowed a bit and discoloured.  Well at almost precisely 11am this morning, there was a massive surge as the sun came out for 10 seconds; it was all too much for the thermally challenged fuse.

I've not had one blow before, and it's nice to know the glass is strong enough to withstand the arc.  About 5mm of link was vaporised inside the capsule.  I wouldn't warrant the thing working at 48V though, with the much greater potential (excuse the pun) for a sustained arc.  But at 24V, it does the job.

Now I just need to find the space to heap another 320Wp "on the fire", so to speak.  Four of those 80W panels I bought in April are still languishing in my living room :fight


Title: Re: Cobbled together PV in W.Sussex
Post by: EccentricAnomaly on July 13, 2011, 11:28:40 PM
That's a bit startling, not to say disappointing; won't the MPPT60 limit the current without letting the smoke out even just as far as the glass?


Title: Re: Cobbled together PV in W.Sussex
Post by: biff on July 13, 2011, 11:59:52 PM
hi outta,
        your little geni is a beezer,the faulty fuel tap lever was a problem from the moment they came out of the box but once that is sorted you will find that this geni is capable of powering grinders and drills to 1kw without a bother even though it says only 650 watts.
     the throttle govner is cute,very quick to respond to a sudden load.the filter going up into the tank is a better idea than the origional.the geni came origionally with a set of leads to charge 12v batteries.there is a little connection there somewhere.
     getting a proper seal on the tap is tricky,it might take 2 or three efforts with the no14 and it needs to be pulled tight.sometimes the rubber seal supplied does not work. if you are closing it down for a period of time,turn of the tap and let it conk out rather than leave the fuel in the carb,
                    good luck,          biff


Title: Re: Cobbled together PV in W.Sussex
Post by: Outtasight on July 14, 2011, 02:34:30 PM
That's a bit startling, not to say disappointing; won't the MPPT60 limit the current without letting the smoke out even just as far as the glass?

The fuse is an in-line one (not inside the charge controller).

The Tristar does limit the current (to any value you program or a default of 60A).  The recorded surge was 1960W, which was about 74A.  The Tristar was bouncing off the 60A limiter when the fuse went.  The other controller was doing just over 14A (just shy of its 15A limiter) with only a pair of Sharp 170W panels (340Wp). It recorded delivering 376W (110% of PV nominal rating) at the moment the fuse went pop.

The problem is one of the fuse I used being a bit undersized at 60A.  If you run a fuse at its rated current, it will eventually blow (especially if it is subjected to surges which cause thermal shocks to the metal in the link).  I should have used a 70A fuse but they don't make one in this type (60A is the biggest).  I suppose I could reduce the current limit on the controller to 55A, but if the fuse blows once in every two years, then it's not such a big deal.  Nothing else on the circuit gets even remotely warm, as I used 20mm2 cable or fatter throughout and 100A switch gear.

It's pretty rare that the array hits 60A for more than a few seconds, so I'd figured that it wouldn't spend enough time at the limit for it to be an issue.

Fuses get "old" as well...  Putting the new one in, I noticed that it didn't get warm today, with the power of the sun.  Also the Tristar got to the absorption Voltage before the other controller and started blinking sooner.  I put this down to the old fuse slowly degrading with heat, causing its resistance to increase, so it drops more Voltage and heats up more and so on until it finally blows.  The flexing of the link with heat will also cause the resistance of the metal to change over time, as micro fractures in the metal cause it to conduct less well, reducing the fuse effective rating.

In the other controller which limits at 15A, I used a 20A fuse and haven't had a problem.  The 20A fuse also has a link that is apparently gold plated... maybe to prevent surface oxidation from heating.  The 60A one had a plain grey looking link.


Title: Re: Cobbled together PV in W.Sussex
Post by: EccentricAnomaly on July 14, 2011, 06:26:01 PM
Thanks for the clarification, Outta. I guess if a fuse runs warm then it's time to replace it and if the replacement runs warm it's time for a bit of investigation.


Title: Re: Cobbled together PV in W.Sussex
Post by: Outtasight on July 14, 2011, 06:35:35 PM
getting a proper seal on the tap is tricky,it might take 2 or three efforts with the no14 and it needs to be pulled tight.sometimes the rubber seal supplied does not work. if you are closing it down for a period of time,turn of the tap and let it conk out rather than leave the fuel in the carb,

I got lucky and the seal worked.  Good tip on letting the engine conk out from fuel cut-off rather than using the switch.  I'll remember that.

I'd noticed it was pretty quick to respond to changes in load.  I was playing about with a 100W bulb attached to it and the throttle reacts very quickly to the light being turned on and off.  The guy who sold it didn't have the 12V cable set or the plug spanner.  I'm not too fussed about the 12V feed though, as I'll use my spare 24V mains charger anyway.


Title: Re: Cobbled together PV in W.Sussex
Post by: Outtasight on February 09, 2012, 10:19:25 AM
Whoa!  It's been a long time since I posted here.

Quite a lot of changes since July.  Got most of my array up on the roof of the house (where it belongs, rather than on the lawn and patio).

Got some more PV on the cheap from eBay - four cheapie Chinese 100W 72 cell modules.  Interesting because I don't have to use them in pairs like the others.  I put a couple up on the garden wall and have kept one as a mobile one that I use at eco-fairs for demo purposes.  We did an outdoor demo in Horsham town centre to promote an eco-fair at the town hall.  100W of PV can easily run a battery and an inverter to make mains for my friends LED lighting display.

Then things just went along "business as usual" except that I made a lot more power with the PV on the roof.  Much lower shading issues.

December brought the usual "oh no, the batteries are getting old and wonky" blues again and I bought a pair of cheap Chinese 180Ah AGMs that haven't exactly worked out...

All of which brings me to the latest (and certainly most expensive) part of my off grid experiment to date...

I'm converting the battery system to use some new Winston LiFePO4 batteries!

It's a totally new learning curve and I'm approaching the problem with the ususal "pair of pliars will do in the absence of a socket wrench" approach.

BEHOLD!!!  A 400Ah "24V" lithium iron yttrium phosphate battery.  It's only nominally 24V as the 8 cells are about 3.00V when discharged (so 24V) and about 3.35V when fully charged, so 26.8V.  When charging they can go up to 4.00V or 32.0V but I'm advised that it's best to keep them under charged at all times (totally the opposite of lead acid batteries).  The safe top Voltage is about 3.60V or 28.8V - which cunningly matches up nicely to what solar chargers are capable of and inverters can handle.

If you take a middle resting Voltage figure of about 25.0V for calculations then this thing holds about 10kWh of energy, if you push it.  Realistically, you can cycle it to about 80% DoD without harm and it will be good for 5000 cycles of 8kWh. 

Each cell is just under 14kg (including the massive M14 terminal bolts!) and pretty small at just 46 x 6.5 x 28.5 cm in dimensions.

The University of Prague has tested them on the bench in an automated charge / discharge loop for 13,000 10% DoD cycles with no loss of performance, even when charged and discharged at 1.5C rate.


Title: Re: Cobbled together PV in W.Sussex
Post by: stannn on February 09, 2012, 11:13:29 AM
Outtasight
You didn't mention the price. Is 10kWh for the one battery or for 7 of them?
Stan


Title: Re: Cobbled together PV in W.Sussex
Post by: fred bloggs on February 09, 2012, 11:53:01 AM
Nice to see you back Ottasight!!

Thought you given up, although I have looked at your Blog a couple of times.

Interesting stuff with the LiFePO4 batteries! Unfortunately management (Supreme allied command) limits the budget to anything second hand (or free) therefore Lead acid batteries only!!

Very interesting to see someone actually trying this much applaud :genuflect

Please keep all of us updated regularly.

Best Regards

Fred


Title: Re: Cobbled together PV in W.Sussex
Post by: StBarnabas on February 09, 2012, 07:35:30 PM
Outta
welcome back from Japan. I never did thank you for your Christmas card, Very much appreciated thank you. Your new battery technology is something I know nothing about so it will be great to see how you get on. Give my regards to Mrs Outta, Mrs B thought she was great company when you visited.
Sean


Title: Re: Cobbled together PV in W.Sussex
Post by: Outtasight on February 10, 2012, 10:03:39 AM
Hi all.  Sean, it was a pleasure visiting and I'm also glad your friend won the compo for the Hexam hydro project.

@Stan - They are all individual 3.2V nominal cells at 400Ah.  I'm using 8 of them to make a 400Ah 24V pack (more of a hang-over from lead acid and the fact that I'm using a 24V inverter).  At the mid-range pack Voltage of 25V, that makes the whole pack capacity about 10kWh.

Cost... An eye-watering 4096 Euros which translated into £3540 including 20% VAT 2% credit card payment surcharge, 2.5% currency exchange charge (from VISA as it was in Euros to Pounds) and TNT overland shipping (quite quick at 3 days from Prague).  At least when I put the payment in it was the week when all the Euro countries got their credit ratings downgraded and the Euro slumped against Sterling.  Pretty steep but maybe not so far off what a new set of good OPz cells would cost.  

You can't compare Ah like for like with lead acid.  I reckon a 400Ah LiFe pack is equivalent to a 1600Ah lead pack in cost, life cycles and usability.  I'm assuming that you'd have to limit the lead DoD to 20% and the LiFe DoD to 80% to get 5000 cycles.  All the lead batteries I've had haven't made it past 2.5 years in service (850 cycles at best).  I've also got no desire to keep 1600Ah of flooded lead acid behind the sofa in my living room - for starters, the fork lift truck to deliver them won't fit through the patio doors and wearing a gas mask while watching TV might wrankle with the missus.

The final straw was discovering that AGM lead batteries are literally time bombs.  They have a (now becoming recognised) fatal failure mode in that as they get old, they dry out (no big deal other than they die).  Not so...  As they get to being dried out, the gas recombination efficiency increases dramatically and this causes a near death supernova of a positive feedback loop in the float current which heats the cell which causes more current to flow which heats the cell (from recombination heat) and at float while doing nothing in particular... BOOM!

That's why UPS batteries are swapped out way before "end of life".  It's because of the number of them that have melted / caught fire in service.

You can monitor the temperature of the pack and adjust the float voltage down to compensate for the increasing current BUT absolutely nobody has a charger that has a temperature sensor on each and every cell in the pack to spot the one that it going to go boom first...

It's battery russian roulette.  Flooded cells don't do this as when they get old they gas more but the gas escapes from the cell, taking the thermal and chemical energy away with it (to explode in the confined space outside the cell facepalm )


Title: Re: Cobbled together PV in W.Sussex
Post by: Eleanor on February 10, 2012, 11:01:22 AM
Look forward to seeing how you get on with them. It's a good thing they're going behind the sofa - that yellow colour really doesn't go with the carpet  facepalm
What are you planning for your furry friend and do we need to call the RSPCA  :o
Our new bank hasn't arrived yet - you'll laugh, it's FAAM this time. Maybe if we haven't gassed ourselves, blown ourselves up or set ourselves on fire we could compare them in a year or two :crossed


Title: Re: Cobbled together PV in W.Sussex
Post by: Outtasight on February 10, 2012, 01:08:13 PM
Hi Eleanor,

Nice to hear you finally beat the supplier into submission on those pick'n'mix cells your were sold ;D

Just a shame it took a materials scientist and an electron micrograph to get them to 'fess up.

Actually, I was thinking of just putting some glass over the new cells and making them into a coffee table talking piece :P

Let's just hope I don't literally turn them into bricks...  The worlds most expensive Lego set facepalm

The Chinese operator's manual is a bit of a giggle.  Lithium ion cells have had such a bad rep since the manganese cobalt days that Winston include all sorts of additional tests to prove the safety of these yttrium ones.  Including:

Putting them in a fire (to show that while the plastic will burn, they don't explode because of the lithium or the oxide releasing its oxygen - the main cause of manganese cobalt cells going off like bombs),
Soaking a broken one in water (to show that they don't explode because of free lithium coming into contact with water),
Short circuiting to 5000 Amps (to show that although they'll get hot and blow their vents, they  won't explode or catch fire),
Shooting them with a gun (For those in seedier parts of New Mexico who are off grid.  The cell will fizz and pop and vent but not explode or catch fire).

They even made a promo video where you can see the boys at the lab doing all of these things to a bunch of cells for a larf... Including the shooting a cell "gangsta" test.  Quite how a battery technician came to have a gun in the lab is a more interesting question.  whistle


Title: Re: Cobbled together PV in W.Sussex
Post by: Outtasight on February 10, 2012, 01:14:41 PM
Oh, yeah... The dog...

It's my fail-safe backup for stopping the charging cycle... A watchdog timer  tomato:


Title: Re: Cobbled together PV in W.Sussex
Post by: billi on February 10, 2012, 02:48:58 PM
exciting  Outta ......  but surely a big pile   of $$  whistle

Anyhow  can you hook  them direct to a solar  charge-controller ? I read  somewhere   one needs an additional BMS (Battery Management System) ..... 

How does this work ?


Title: Re: Cobbled together PV in W.Sussex
Post by: Outtasight on February 10, 2012, 04:23:26 PM
Yup, it's certainly a hill of beans.  Maybe someone will give me a job as a lithium power systems consultant after I've figured out how not to do it (inventing the Edison way).

Mind you, the house is conspiring against me on this project.  Today the washing machine blew up.  Literally.  It was doing it's spin cycle and a bearing or something let go in the motor and it made a grinding noise and then the whole house RCD popped.  Luckily it had finished pumping out the water and was almost finished.  We managed to get the clothes out but the machine is toast.

I'm reliably informed by one Jack Rickard (of EVTV fame) that I don't need a BMS to run a lithium pack.  If you talk to him and even mention BMSs he gets worked up into a lather.  It's all just a ploy from the battery suppliers to make extra money (and lots of it - a typical BMS can be another £600).  He should know because he's been running several cars powered by these Winston (and other similar prismatic) cells and doesn't use any form of active cell management during charge or discharge.  If you bottom balance the pack and then always undercharge it, you don't get the kind of fires that have burned down the Chevvy Volt.

In most cases it's the BMS that starts the fire.

In my experience it's very easy to arrange for a solar charging system to chronically under charge batteries ;)  But seriously, I do have some ideas on safety controls for this thing.

Stay tuned...


Title: Re: Cobbled together PV in W.Sussex
Post by: stannn on February 10, 2012, 04:35:38 PM
Can't wait! You make me chuckle. I see that if we all get together and order 25000 of these cells, then we can get the price down by a quarter!      fpig:
Stan


Title: Re: Cobbled together PV in W.Sussex
Post by: Eleanor on February 10, 2012, 07:39:23 PM
Presumably the battery survived the wash and spin and it was only the washing machine that failed the destructive testing procedure  sh*tfan:


Title: Re: Cobbled together PV in W.Sussex
Post by: Outtasight on February 11, 2012, 12:10:07 AM
Can't wait! You make me chuckle. I see that if we all get together and order 25000 of these cells, then we can get the price down by a quarter!      fpig:
Stan

You don't need to buy 25,000 cells to get the top discount, just spend more than 25,000 Euros on cells... Still a pretty large group buy.

I bought over 2000 Euros worth, so paid 398 Euros per cell instead of the base price of 461 Euros per cell.  About a 13.6% discount. Then the similar discount bands apply to anything else you buy in the same transaction (the cell straps, terminal bolts, a cell logger were all discounted a bit).

There was actually a much better deal to be had on 200Ah cells that are on sale.  But I wanted at least a 400Ah pack and using pairs of 200Ah cells in parallel would have added another layer of complexity and risk in cell balancing that I just didn't want to get into.

New washing machine ordered...  An LG something or other...  Interesting as it has a A++ energy rating (useful for running on solar power).  It uses a drum mounted direct drive brushless DC pancake motor, making it hopefully last longer than a regular machine with a motor with brushes, pulley and drive belt to go wrong.  The reviews have been good, saying it's very quiet when spinning.  LG warrant the motor for 10 years.  If something else breaks on the machine, the motor will possibly make a quite good generator :D

Meanwhile, the bench PSUs seem to be breeding...


Title: Re: Cobbled together PV in W.Sussex
Post by: Outtasight on February 11, 2012, 07:53:13 PM
Still charging up the cells for the first time...  On no.3 now.  It's talking about 20 hours each, so if I keep at it, I should be ready to build the pack next Saturday.  Maybe allowing for some delays as I don't leave a cell unattended if it's likely to reach the end if I'm not there to watch it finish.

These things have next to no absorption phase. It takes like 19.5 hours to charge from 3.31V up to 3.65V and then in the space of 20 minutes it rockets up to 3.97V.  Then you're into the CV absorption phase where the current tapers down, but unlike a lead acid cell that spends a few hours doing that, a lithium cell quickly hits a brick wall where all the ions have been rammed into the electrode material and that's it, you're done in another 10 minutes.  And that's at a mere 10A charge rate (0.025C).

For more on this week's fun and games, see my blog entries... Now with added YouTubeness.


Title: Re: Cobbled together PV in W.Sussex
Post by: Outtasight on February 13, 2012, 09:53:22 PM
More today on the blog, playing with the alarm output of the CellLog8s that is supposed to provide a control signal for low / high cell and battery pack Voltages.  Sadly, it's only "sort of working".  Another instalment of video in this entry.

If the maker doesn't fix the buggy firmware, I could bodge something external to the alarm port to latch it reliably or use the programmable LVD on the Morningstar SSMPPT-15 charge controller to shut down the inverter.  As a second line of fail-safe, the inverter has a LVD built in, but it's set at 21.0V, a dangerously low cut-off Voltage for the lithium battery pack (just 2.68V per cell).  At this level, the cells are just minutes away from being empty as there's maybe only less than a couple of Ah capacity between 2.50V and 2.00V, below which certain death of the cell awaits.

Lithium cells Voltage falls off a cliff when they get to a critical low state of charge, and, if you're not careful, they fall off the cliff and straight under a bus.


Title: Re: Cobbled together PV in W.Sussex
Post by: biff on February 14, 2012, 09:39:55 AM
Good morning Outta,
                    I wish you luck with your new cells.I hope they do what it says on the tin.The lack of weight is something which is hard to get used to when one is used to FLA batteries.some time ago i bought an s/h   E  bike with  10ah 26volt LiPo battery,the battery weighs just 2kgs. In the beginning i thought the battery was shot so i took the casing apart and discovered one of the wires was loose,meanwhile i had ordered a new battery (350euros a pop),so i ended up with 2 batteries.The old battery is approx 4yrs old and there is no difference that i can see in the performance of each.They charge very quickly and store well.I use the bike when i can,to whizz the 2 mile down to the villiage and 2 mile back.
                                                              Biff


Title: Re: Cobbled together PV in W.Sussex
Post by: Outtasight on February 15, 2012, 02:02:49 PM
Cheers Biff,

I hope so too. 

I saw lots of e-bikes in Japan this time.  Last time about 3 years ago I saw one or two and they were using NiMH batteries.  Now they are all lithium and I saw many people riding around on them in Tokyo.  They're a bit of a liability actually, as loads of people ride them on the pavement and mow you down when walking.  At least when they pedalled you could hear them coming a bit more.  Now they zoom up behind you at 10mph in "electric stealth mode" and ring their bell microseconds before crashing into your back.

I'm still testing out the CellLog8s alarm output.  It's a bit flaky and I'm talking to the manufacturer about a couple of firmware upgrades that would make it work really well as a battery protection system, but it's not quite there yet.

The thing I'm looking forward to testing is the power output of these cells.  They can do up 3C (1200A) continuous and you still get 95% of the 400Ah of energy.  No severe Peukert Ah de-rating for high C loads.  The EV guys are pushing these cells to 6C and they work fine (with some Voltage sag).

Jack Rickard on his EV TV show put a 20Ah A123 cell on the bench and pulled 460A from it with no ill effect or much voltage sag - an astonishing 23C.  He's building a molded pack of 6 of them in parallel to make a 3.2V cell that could deliver over 2,700 Amps continuous.  Enough power (with 57 such cells in series) to launch even a US pickup truck at sports car rates of acceleration with a 490kW motor.

With the typical inverter loads I have of 2A to 120A (<0.3C), I should actually see between 103% and 110% of rated Ah, as the capacity is specified as 100% at 1C discharge rate.


Title: Re: Cobbled together PV in W.Sussex
Post by: Outtasight on February 23, 2012, 12:32:32 AM
Finally got the last of the cells charged up on Saturday and then installed the bank.

All working well so far... No magic smoke and an almost unbelievable ability for the bank to absorb power.  It can sit there soaking up 72A of charge current in sunny spells and keep doing it until it get to be "full", with a very short 10 minute absorption phase.

Then, when fully charged, I measured an estimated 6 milli-Ohms internal resistance - for the whole bank, including all the cell connections.  A Voltage drop of only 0.22V under 35A load.

The M14 terminals are stubby and huge, so I kept my separate terminal block with its more manageable M8 studs and all the connectors from my previous batteries.  I added an extra stud on the negative side for the home made shunt and then connected the battery pack to that point so it's easy to measure net current in/out of the pack and possibly upgrade it to a proper shunt for an Amp-hour counter later.
 
More details and video on the blog.


Title: Re: Cobbled together PV in W.Sussex
Post by: biff on February 23, 2012, 09:20:50 AM
Cool Outta,
             Fantastic step forward in battery evolution.Our dc voltage is 120vdc,so it would take a lotta euros to cover the expense of the replacments. Still i can dream,
                             Biff


Title: Re: Cobbled together PV in W.Sussex
Post by: Outtasight on February 24, 2012, 07:33:10 PM
Depends on how much storage (kWh) you want in the pack.

For 2,300EUR you can get 38x 60Ah cells.  That gives you a 120V nominal pack with 5.84kWh usable storage (80% DoD cycles for >3000 cycles).  If you go easy on them and keep it under 70% DoD, they're rated for >5000 cycles.

Even these small cells can put out 1CA for their rated capacity, so can run a 7.3kW load continuously.  And if the bank gets depleted or sits for days at low SoC, no harm is done.

The real beauty of LiFeYPO4 cells is that you don't need large ones to deliver the power required or to avoid them sitting at low SoC and self-destructing.


Title: Re: Cobbled together PV in W.Sussex
Post by: Outtasight on March 06, 2012, 08:41:09 PM
More updates on the blog...

Actually from a couple of weekends ago, as I wrestled to bodge the CellLog8s into service as a LVD for the inverter.  The OEM partially fixed the firmware on its alarm port, but still not good enough to use my original simple "follower" relay (one that just follows the state of the alarm port and relies of the alarm port logic being right).

So I had to implement some external logic to stabilise it and protect the battery pack that was now fully in service and at the mercy of the inverter and the fridge freezer, switched on 24x7.  Not quite sleepless nights about a bricked lithium pack, but a worry none the less... Running it with nowt for protection from low Voltage instant death than "the LVD of last resort" - the 21V pack LVD built into the inverter.

At least now with my individual cell monitoring based LVD, set to very safe margins, I have what the Army refers to as "defence in depth".


Title: Re: Cobbled together PV in W.Sussex
Post by: wookey on March 06, 2012, 09:43:51 PM
Jack Rickard is a rich idiot who can afford to knacker his very expensive cells. You really want some cell management given the cost of those cells, and your sensible desire to run them for at least 8000 cycles. Yes you can run them without a BMS for some time. I've done this with my own scooter, which has run on a DIY 1kWh 48-cell (3P16S) LiFePo4 pack (headway cells) for about 2 years and 6000km (about 300 cycles). And I was very careful to keep monitoring and topping up cell-sets to all be matching every few days, but eventually a few sets-of-3 got prone to getting over the 3.6V level even on very low charge rates and I even had a couple of short periods over 4V. One set is definately a bit 'tired' in comparison to the others now. Manual balancing is tedious and hard to never screw up.

It took a year for the endless sphere guys to finish their BMS design which is why I was running without it. It may be slightly easier to manage this with a massive pack in your front room, but really I'd take precautions to make it very hard to give any of the cells a hard time individually. At the very least get yourself some celllogs so you get beeped at the moment a cell goes over 3.62V. Check out the endless sphere Mk4 BMS design which does not sit inline and thus have to deal with high currents - it just monitors and controls the charge accordingly. You may have to make some mods to cater for your very large cells in comparison to most ES people who have bike/scooter sized packs. This area is developing fast and things may have changed since I last looked about a year ago.

There is a fine thread on endless sphere where Jack turns up and tell everyone they don't need a BMS. There was a lot of bluster and some useful data, but I was convinced that the other side of the argument had _much _ better data and made a lot more sense. Read that and see what you think.


Title: Re: Cobbled together PV in W.Sussex
Post by: Outtasight on March 07, 2012, 12:45:52 AM
Thanks Wookey,

I'm quite open to all advice on this as it's a whole new learning curve (for everyone).  We've had years to kill lead acid packs and now it's the turn of lithium.

There's probably truth on both sides of the fence between Jack and the ES bods.  Jack is rich and has blown up some cells in spectacular style (especially the A123 20Ah ones) but having watched him for quite a while I wouldn't characterise him as an "idiot".  A bodger, certainly, but no fool.

There are a few things at play here...

One... Guys playing with different types of lithium cells.  They are all a bit different in behaviour.  As Jack has discovered, the A123 LiFePO4 cells have some idiosyncrasies in their behaviour that he's not come across with the larger LiFeYPO4 prismatic types.  Whether that is down to real differences in the chemistry or just a feature of the packaging (the A123 are packaged with a supernano anode that give the extraordinary current delivery capacity) is anybody's guess at the moment.  The experiences are different and maybe not comparable when everyone is using different cells of different construction and capacity.

Two... Orders of magnitude.  10Ah and 20Ah Headway / A123 cells are a whole order of magnitude different in size to the cells I and Jack are playing with.  We're playing with individual cells of 100Ah to 400Ah here.  A charge balance error of 1Ah on a 10Ah cell will probably be a catastrophic 10% over charge or over discharge.  If I'm off on my balance by 1Ah I'll be within 0.25% of perfect.  The absolute worst case Ah I could over charge by is 20 minutes at 60A, 20Ah (5% of capacity per cell).  And I'm only charging to a target of maybe 80% full.

Three... Parallel cells.  Jack's latest failures have almost certainly been in part to not appreciating the implications of point Two, but also an over-confidence in parallel cells behaving themselves.  Any pack using parallel cells is going to be more unreliable.  I've got the dead 12V packs to prove it.  Worse, you can't tell you've got a nearly dead one in parallel with a good one as the good one masks the behaviour of the bad one.  I've also got several dead Sony InfoLithium packs that used 2, 3, or 4 cells in parallel.  The ones that are still firing on all cylinders (pun intended) are the standard capacity packs that use a single series string inside.  So I made a conscious decision to steer away from any more parallel cell set-ups (including the likes of LifeBatt that use big parallel strings of small lithium cells) or the temptation to save a bit of cash and go for an 8S2P pack made from 200Ah cells that were on special discount at GWL.

K.I.S.S rules here for a first foray into new battery territory.  "Keep It Simple Stupid".  One string of 8 cells in series.  No parallel cells.  Trying to keep 48 cells in check is definitely "cat herding" territory ;)

But, yeah... I'm tempted to get another CellLog8s and use a spare 180A relay to crowbar the charge controllers if things get out of hand (a cell based HVD to complement the LVD).  It's only another €27 plus some parts bin kit ;D  Or there's the option to bodge an input on the chargers via the temperature probe to reduce the charge Voltage in a fault condition.

But so far I've not seen more than 50mV delta in the string of cells at the top of charge at 3.50Vpc.  The highest ones got to 3.53V while the lowest one was 3.48V (for the regulated pack Voltage target of 28.00V).  I'd be more concerned if I were charging to 3.60Vpc and the highest was getting to 3.65V, as that's the start of the "hocky stick" zone in the charge curve, where it shoots up to 4.00V for about 6.5Ah of charge input.  I'm aiming to stay well out of the vertical part of the curve.  To get from 3.40V to 3.50V is a LOT more energy input than 3.50V to 3.60V.

At the moment, I'm kinda counting on the fact that the upper charge limit of 3.50Vpc for constant Voltage charging will mean that one cell would have had to gone up to 4.20V (the upper absolute limit on Winston cells) with all the others languishing WAY behind at 3.40V.  This would be the almost worst case which could exist, given that the charger would be happily delivering 28.0V in it's 20 minute long constant Voltage phase and be none the wiser to one cell having gone AWOL.  For this, the cell delta would have to be over 16 times as big as I have seen in the last two weeks charging cycles.  Again, it's an order of magnitude thing.

The 90Ah 12V monoblocks that Winston Battery sell are the same LiFeYPO4 chemistry and have no BMS requirement and no way to even measure the 4 individual cells in the block.  It's a sealed 12V battery.

There is no "cell drift" or "self discharge drift" between cells (at least for these Winston ones).  I measured each cell out of the crate as being within 4mV of each other after 3 months of storage without charge (the cells were "born" on 29/10/2011).  Jack has seen similar figures from cells he's had in storage for a lot longer.  The cells are holding at 6-10mV delta in their normal living zone of 3.270Vpc to 3.375Vpc under load 24x7 from the inverter (even if only the 1.3A idle current).

If anything, it's things like the CellLog8s (and other BMSs) that cause "cell drift".  The CellLog8s by design causes cell drift in 8 cell packs, because the makers tapped cells 1-6 only for power for the CPU.  That means cells 7 and 8 will not be drained, at a delta of a few dozen mAh per day.

Luckily, Junsi published a PCB mod to cure this and I've implemented it so that cells 7 and 8 are also drained at the same rate as 1-6 (I hope).


Title: Re: Cobbled together PV in W.Sussex
Post by: Heinz on March 07, 2012, 10:01:46 AM
Hadn't heard of Jack Rickard so googled him and found EVTV. Man, that bloke can talk for ages without actually saying anything worthwhile. I'm sure there is some useful or interesting info in there but I don't have hours to waste waiting (perhaps in vain) for it  ::)

Outtasight, very interesting thread  :genuflect
Cheers,

H


Title: Re: Cobbled together PV in W.Sussex
Post by: Outtasight on March 07, 2012, 10:58:12 PM
Thanks.  Yeah, Jack often stands and waffles on for ages and I've even had to fast forward through sections where they just sit in the garage drinking bourbon for 20 minutes on camera.  But there are some truly funny moments in the "battery lab".  And I have learnt a lot from watching and reading the blog.

Meanwhile, I've uploaded a video and blog entry on scrounging around the house to make a "5 minute warning" alarm out of the old lead acid battery SmartGauge and a Christmas cracker toy.  ;D


Title: Re: Cobbled together PV in W.Sussex
Post by: Heinz on March 07, 2012, 11:14:19 PM
I wish I could find a way to get paid for 'just sitting in the garage drinking bourbon for 20 minutes on camera' ....  8)

H


Title: Re: Cobbled together PV in W.Sussex
Post by: Outtasight on March 09, 2012, 12:35:19 AM
More catch-up posting on the blog today...

Today's episode is about bottom balancing the pack with a bunch of log data graphs for the discharge curves and then the charge curves.

Nicely shows the radically different behaviour of lithium-ion cells from lead acid ones.

The fact that the terminal Voltage hardly changes at all during charge and discharge (until you get to the saturation / desaturation points) makes it hard to use Voltage as a good indicator of state of charge.  EV people use Ah or kWh counters, which actually do work on lithium cells.  Lead acid cells have massive problems with Ah counters due to the Peukert factor (apparent capacity is inversely related to discharge current) and drift due to self-discharge and a generally lossy charge efficiency.  Lithium cells exhibit 95% charge efficiency, even at charge/discharge rates over 1C.

I'm seeing significant improvements in usable energy usage due to this high charge efficiency alone.

Lead acid cells waste over 20% of all the input energy through charge inefficiency.  This is due to two main effects: heating due to internal resistance and undesirable chemical reactions (gassing and gas recombination in gel and AGM cells).  Lithium cells do not gas in normal use and have VERY low internal resistance, leading to very high charge efficiency - almost as good as capacitors.

Having batteries that are 15-20% more charge efficient is like having a 15-20% bigger PV array or 15-20% longer charging time on a Winters day.  You get more usable energy at night for the same energy input during the day.

So although expensive, lithium cells actually have a bigger payback than just longer cycle life and affinity for partial charge compared to lead acid.


Title: Re: Cobbled together PV in W.Sussex
Post by: biff on March 09, 2012, 09:22:45 AM
Good stuff Outta,
               This kind of information is invaluable to anyone thinking of going down this route.It looks very promising and by all accounts must be the way forward.
      Biff


Title: Re: Cobbled together PV in W.Sussex
Post by: powerbynature on March 09, 2012, 01:42:59 PM
some great information on this thread.  As I've been going down the same route you have managed to give me some ideas although the wife is not happy, on the flip side though my son things it's all great as he gets to help (help as in he's 2 and a half) but they are never to young to learn :)


Title: Re: Cobbled together PV in W.Sussex
Post by: dickster on March 09, 2012, 02:30:56 PM
This is all very exciting, perhaps a good alternative to lead acid, but as a non educated layman, it all seems very complicated. What are the chances of said layman running a set up like yours without the in depth knowledge that you have?


Title: Re: Cobbled together PV in W.Sussex
Post by: Outtasight on March 09, 2012, 04:32:26 PM
All... Thanks for the interest and encouragement.

@dickster:  The charging of lead acid batteries is no less fraught with danger.  In fact more so, especially with AGM ones that can go into thermal run-away quite easily and burst into flames or explode.  In comparison, although the lithium cells require more close monitoring and automation to ensure they don't turn into expensive bricks, they are actually now safer if abused (at least the ones I'm using are).

But it has to be said that this is an experimental power system I have here.  I doubt there are more than a couple of lithium off grid systems in Europe in residential use at the moment.  Products I've heard about are still in pre-production or are just toys (I saw a portable solution that used a 20Ah 12V battery and a briefcase solar panel at EcoBuild last year).  I'm an electronic engineer and seasoned bodger, so it's ok... "Honest, guv' ".

The "lay person" shouldn't be playing with anything more dangerous than AA batteries in their walkman.  Certainly shouldn't be "playing" with a 3kW PV array and a battery bank capable of delivering sustained short circuit currents of 8,000 Amperes...  They definitely shouldn't be hacking the internals of a 230V AC mains inverter that is connected to the kids Playstation!

Having said all that, my wife manages to "operate" the system just fine with nearly no knowledge about how it works.  That's because she doesn't have to "do" anything to it... Just be aware that the house is running on a limited amount of battery power and so be careful not to waste it (leaving lights, TV, laptop on when not needed).  Basic training for all "lay people".

If we don't learn to manage our energy use a bit more intelligently, it won't just be my lights that go out when the energy reserves have been squandered carelessly.


Title: Re: Cobbled together PV in W.Sussex
Post by: StBarnabas on March 10, 2012, 09:50:46 AM
Outta
keep up the excellent work. This thread remains a true gem.
StB


Title: Re: Cobbled together PV in W.Sussex
Post by: biff on March 10, 2012, 11:41:44 AM
Exactly St/B
                This thread really is a true gem with the most modern up to date information available.
                                             Brilliant stuff Outta!!
                                                               Biff


Title: Re: Cobbled together PV in W.Sussex
Post by: wookey on March 10, 2012, 10:31:10 PM
OK 'idiot' is a bit harsh, but he's certainly a man with a huge ego, and ultimately I found other people to be doing a better job of presenting impartial engineering data without excessive bluster. This was the thread:  http://www.endless-sphere.com/forums/viewtopic.php?f=14&t=15247
Read it yourself and see what you think. You clearly understand this stuff so I'll let you get on with it.

You are quite right that the series-only case is a lot simpler and is less likely to have problems. My sets of 3 that have got poorly are almost certainly due to one weak cell in those sets, which after a while ends up hurting all 3. I would love to have some time to take it to bits and check out exactly where I am at, but extension-building has put all my proper electronics-geeking on hold for the last 18 months or so. To put things in perspective my pack is still working fine and shows signs of being able to do so for a long time yet. And if I have to replace 3 or 6 cells, to get it 'good as new' at some point, that's not too big a deal. I can even buy them in the UK now for £14 each.


Title: Re: Cobbled together PV in W.Sussex
Post by: Outtasight on March 10, 2012, 10:54:23 PM
Thanks guys.

Probably now it will go quiet for a while on the thread as the system is in and appears to be working, so it's just a case of letting it run and see what happens.

No news is good news, as they say.

The one area where I'm thinking of change is in how to increase the charge capacity.  The 60A charger is now routinely maxing out and so there's a couple of options... Change the controller for a more powerful one (maybe 100A, but Morningstar don't make such a controller) or split the main array into top and bottom.

The 1,540Wp roof array is just at the maximum 60A battery current limit (in full sunlight and cool weather).  That lot terminates in the upper junction box on the wall with a 35mm2 feeder cable down to the lower junction box that piles the wall, patio and garage PV on top, before going into the house.  The lower arrays are at differing angles and suffer various amounts of shading but add up to another 915Wp (another 35A).

I'm quite surprised the controller hasn't complained at all, with 57% over-current input.  I've seen the posts about a couple of TS-MPPT60 controllers letting go of magic smoke, but that seems to have been an issue with high Voltage handling, rather than over current.  I'm running quite low Voltage but huge current.

If I split the array and use a 60A controller and a smaller 45A controller, I can get the full 95A potential (the MSView log graph was conspicuous by the battery Amps haircut the curve took on, relative to the solar input curve) but it means more wiring, more switchgear, more fusing, higher night time parasitic load and more networking to capture the data from a 3rd controller.

Alternatives do exist... There's the Outback FM80 controller that can do 80A (still not enough for the whole array) or the Midnite Classic controller that can just squeak 94A output.  But then both completely break my logging and AC load management solution, which is built on the Morningstar MSView MODBUS software.  The Midnite Classic does speak MODBUS but the MSView logger doesn't know the Midnite Classic commands or variables...  I'd have to write my own MODBUS client :o

The previous lead acid battery needed over-current protection in the form of an AC dump load.  The new battery can easily charge at speeds of up to 1C (400A) with no supervision and speeds of up to 3C (1,200A) with temperature monitoring and compensation.  In short, it will absorb almost any amount of power that you could conceivably throw at it, up to a 31kWp PV array.


Title: Re: Cobbled together PV in W.Sussex
Post by: Outtasight on March 16, 2012, 03:49:08 PM
Got some graphs up on the blog from the CellLog8s of the pack in operation over a number of days and ranging from quite empty to full.

All the cells seem to be tracking each other quite well and I'm keeping a daily log of the cell differential when making my usual meter readings at midnight.

The CellLog8s has a useful display that tells you the highest and lowest Voltage cell in the pack and the difference in millivolts between them.  You can even program the alarm to sound if the cell differential value exceeds a value, so that you can spot a cell going bad in the pack before it self destructs at the high or low end (under charge or discharge) and causes the rest of the pack to get damaged too.

So far it's reading just a steady 6 to 8mV difference under the usual light load at midnight.  The traces confirm this, showing no serious deviations under high charge rates (up to 76A) or high discharge rates (up to maybe 70A).

More of the house is going off grid now.  I ran a new solar spur up to the airing cupboard and now run the central heating gubbins off grid.  Despite the boiler being in the kitchen and the heating controller being in the kitchen, the whole system was powered from a socket in the airing cupboard upstairs (where the circulating pump is).  So it's easy to unplug it from the grid socket and plug it into the solar one.

Now, with only really a couple of pesky wall-warts for a couple of things in far flung reaches of the house, everything bar the instant water heating shower and the cooker are off grid.  As I write, the wireless energy meter for the utility is reading zero Watts ;D.  In truth, there's some power being still consumed but it's now below measurement levels.

And maybe I don't even  need to bother with the wall warts... It's not just the wireless meter that is reading zero.  The actual utility meter also has a minimum power threshold of recording, below which the LED that usually blinks to indicate the passing of Watt-hours just lights up continuously to indicate that it has stopped recording. These meters have an "anti-creep" mode to prevent spurious billing of energy when the amount is so small that it could just be a tolerance error in the meter itself - say, reading 5W falsely when the consumer unit was actually turned off completely.

So a house can consume maybe 5-10W of energy and pay nothing for it, as the meter will stop.  The meter itself consumes 2W of energy just doing it's thing and we wouldn't want to pay for that.

The weather has been quite kind over the last 3 weeks, but not wall to wall sun.  I've not had to put the house on-grid since installing these new batteries (apart from the maintenance day when recharging after bottom balancing them).  I wonder how long I can run the house without reverting things back to the grid.

E.On don't believe my self-submitted meter readings any more.  I sent some in for the latest bill and they sent a guy out a few days later to re-read them.

Unlike grid tied solar generating stations that still import lots of energy at night (even if they are a net exporter over 24 hours), an off grid station just negates importation and so my import meter is gradually slowing to a stop.


Title: Re: Cobbled together PV in W.Sussex
Post by: Outtasight on March 20, 2012, 06:43:07 PM
Well, according to my calendar, it's been just over a month since I installed my lithium ion battery bank.

It's still working.  I'm still alive.  The sofa is still... not a pile of ash.

Almost on the first month anniversary I did have the battery run out on me in the night, after a run of dull days.  But I propped it up with some help from a hastily bodged together reserve battery (one of my lead acid 12V batteries).  It was just enough to see me through the wee hours of Sunday morning and then luckily Sunday was sunny, so it's back to business as usual now.

I've spotted another bug in the Morningstar Tristar MPPT-60 firmware.  Nothing serious.  The internal logged data on the controller is supposed to record the Pout Max value (the maximum power delivered to the battery in a day) but the logged figures are off by a factor of 10 (maybe they just forgot the decimal point!).  It logs my peak ouput power as 15,000W... I wish  ;D

While I was at it, I pestered them on when they are going to release a 100A version of the controller.  The lady replied, "I'll forward it to the tech department and we'll get back to you."  Yah... Right.

I pointed out that Outback and Midnite solar both have 80-100A controllers out in the market, but I'd prefer to stick with Morningstar (if only so I don't have to reprogram my load controller).

The Tristar will handle 3.2kW of PV, but only with a 48V battery.  I have 24V everything now, so I'm not going to change to suit them.  Besides, the only reason most people go to 48V is because you couldn't easily get a lead acid battery to do more than 3kW load at 24V.  You have to keep the current down to get the rated capacity.  C/10 is about as good as you can get.  That meant a 1000Ah battery could do 100A at 24V for a 2.4kW load.

Going to 48V meant you could have a 1000Ah bank and still only do 100A but get 4.8kW load on it.

Going to lithium means you can have a 26V, 400Ah bank and do 1C continuous load for 400A at 26v = a stonking 10.4kW load... Enough for an instant water heating shower with change to run a toaster.

So the makers of solar chargers are going to have to up their game, because much more power is available at lower Voltages than before.

Hell, if I was to start again, I might even consider using a 24V nominal PV array (like I do now to keep the wiring cost down) but use a 1000Ah 13V (4 cell) lithium bank.  The fewer and bigger the cells, the easier it is to manage them.  You'd just need a MPPT charge controller that can handle 250A at 13V...  tumble:


Title: Re: Cobbled together PV in W.Sussex
Post by: Outtasight on March 23, 2012, 09:28:20 AM
The guys at Morningstar sent me a reply.  One of the techies said that the reason the Tristars only go up to 60A is because of the relationship between the switching devices they use and the size of the heat sinks required.  The heat generated increasing with the square of the current.  So increasing the current with the same type of switching device from 60A to 100A requires a lot more cooling.

The Tristar MPPT60 already has a quite impressive bit of finnage on the outside and on my system that is pegged at the 60A limit for a couple of hours a day now, it gets pretty warm.  Still cool enough to touch but definitely very warm.

Midnite and Outback both use fans to cool their controllers and so can increase the current the controller handles but Morningstar are sticking to their design principle of only using passive cooling.  I kinda agree.  When I went to the Earthship near Brighton (why does a house with some passive heating, rainwater harvesting and PV have to have such a hippy name?  It's counter-productive to getting the technology adopted by "Dave from Croydon"), I saw an Outback controller hard at work with the fan going and full of dust.

He didn't rule out them building a more powerful controller, but they have nothing in the pipeline.

A pity as there are a lot of advances in MOSFET and especially IGBT devices that are getting ever lower "on" resistance and faster slew rates that reduce the big heating effects when switching in PWM situations.  These are all being driven by improvements needed in EV motor controllers, where you have a 190V battery and a 200kW motor and a PWM speed controller that needs to deliver over 1,000A at 190V.

So it should be getting easier to do 100A at 24V with the same size heat sink.   Granted the EV controllers have fans and even water cooling, but they are handling 100 times as much power.

No word yet from their software guys yet on the spurious power reading in the logs.  They asked me for a copy of the log file from the controllers memory and went off to check out what might be wrong.

Meanwhile, on the blog... I've been experimenting with eeking up the final charge Voltage a bit on the lithium battery bank.


Title: Re: Cobbled together PV in W.Sussex
Post by: marktime on June 11, 2012, 07:01:13 PM
You're on the telly :)


Title: Re: Cobbled together PV in W.Sussex
Post by: Outtasight on July 24, 2012, 12:16:03 AM
Ha ha... Yeah as well as doing the Britain in a Day film, BBC South Today did a 2 minute feature on my solar system as a trailer for the film on the morning news.  I haven't seen it because our digital telly is from the London region and it only went out on BBC South.  But some random woman at a lavender farm we were visiting a couple of weeks ago remembered me... She was giving me funny look and I was wondering if I'd had a wardrobe malfunction when she suddenly blurted out "You're that solar guy from the news, aren't you?". 

That aside, things are going well at the ranch.  156 cycles and counting with no problems.  After tinkering with the charge settings over a few weeks, I settled back on the original settings, with a short 30 minute absorption charge at 3.50Vpc (28.0V for the pack).

Did about 12.5kWh today with 4.1kWh in the water tank via the immersion heater.


Title: Re: Cobbled together PV in W.Sussex
Post by: StBarnabas on July 24, 2012, 06:42:46 PM
Great stuff Outta. Sadly you did not break into the Northumberland Region TV region! Great things are going well and your batteries are surviving the strain!
Sean


Title: Re: Cobbled together PV in W.Sussex
Post by: biff on July 24, 2012, 07:29:03 PM
Good stuff Outta,
              Hopefully we will get a look at you in the near future.It sometimes takes a week or 10 days for juicy news items to drift across the pond to Donegal.We will be keeping an eye out for you,especially your lightweight yellow battery bank.
                                                                      Biff


Title: Re: Cobbled together PV in W.Sussex
Post by: Outtasight on August 11, 2016, 09:07:57 AM
Well that escalated slowly - to paraphrase the inter-social-web.

I turn my back on this forum for 4 years and suddenly this section is full of people with their 48kWp to 500kWp off grid systems.

I came back after remembering there's somewhere you can use REALLY great emoji (way better than from my smartphone on Twitter).

 ;D  whistle wacko :norfolk fpig: sh*tfan: facepalm

We need all of these for UK energy policy debate right now.


Title: Re: Cobbled together PV in W.Sussex
Post by: biff on August 11, 2016, 09:24:20 AM
Good to see you back again Outta,
                   I trust that everything is well with you. Loads of questions for you but don,t worry if you don,t want to say.
   I am curious as to how your yellow east European super batteries did. Did they live up to your expectations,? :genuflect
  The battery world has made many great leaps forward and the flow battery might be the one to put your money on.
                                                                 Biff


Title: Re: Cobbled together PV in W.Sussex
Post by: stannn on August 11, 2016, 10:28:41 AM
Yes, welcome back Outtasight. We've missed your insight ;D and humour.
Stan


Title: Re: Cobbled together PV in W.Sussex
Post by: billi on August 11, 2016, 12:36:11 PM
fabulous  to hear from you again , Outa  ;)


Title: Re: Cobbled together PV in W.Sussex
Post by: Outtasight on August 14, 2016, 09:45:26 AM
Good to see all the "usual suspects" still here.

The lithium battery has worked out rather well and in fact I got a second 400Ah pack to run in parallel with the first.

In true bodger style the new cells sit on a fetching oak coffee table that was going 'cheap' at Homebase.

(http://i67.tinypic.com/4uaond.jpg)

This takes me up to about 20kWh of storage and the rest of the system around it looks like this:

(http://i64.tinypic.com/2s1m843.jpg)

There's some new switchgear and after 8 years the installation has become a bit less 'temporary' with the addition of a metal consumer unit to replace the 4-way adaptors and a meter screwed to a breadboard (not an experimental circuit board but actually a board for bread).

But the changes were mostly driven by a power upgrade and shift in usage.  In Feb 2016, our gas boiler broke and I decided to scrap my gas supply and go electric only in the house.  If we're going to ween off of fossil fuels, it has to start at home.  And so it did.

But this dramatically increased the amount of electricity I need and the 3kW inverter wasn't butch enough any more.  It also had the disadvantage of not allowing me to switch the multiple off grid loads to be grid connected in the numerous 'greenouts' I've endured.  Greenouts are like blackouts but caused by intermittent or inadequate renewables.  So I tried out a new and quite cheap 6kW UPS inverter.

(http://i64.tinypic.com/2a7g01v.jpg)

It's a low frequency type (unlike the Cotek SK3000 which was a high frequency type).  This makes it less efficient and has massive transformers in it, a bit like the Victron Multiplus or Quattro which I've used in a project but this inverter was just £700.  The Victrons run to about £3500.

This is essentially a big UPS.  It connects to the grid and has switchgear inside to select either grid power to the output or inverter battery power.  It can optionally charge the battery too, as the inverter is bi-directional.  It can't export energy to the grid (the Victrons can) and the charger isn't great, so I ended up buying three heavy duty switch mode power supplies to form a modular 2kW programmable battery charger.

(http://i67.tinypic.com/2gxnyoy.jpg) chargers

More bodgetastic stuff to come, but I must go off to our usual car boot sale today to see what junk I can pick up for next to nothing.


Title: Re: Cobbled together PV in W.Sussex
Post by: biff on August 14, 2016, 10:04:10 AM
I know Fairway,
            I am sure you could see the longing in mine eyes.
  I did not have the nerve to invest in those yellow beauties when Outta did and he went
  and got the same again. It take confidence. I still have my 2 ton of lead acid so i cannot complain
  but some time ago, i bought a lecky car and stuck 8 x 100ah sealed lead acid batts in it. The tyres
  went almost flat and it squat on it,s suspension. I remembered Outta,s yellow treasures and thought
  that they would just be the job.But the money, ! They don,t come cheap.
                                                  Biff
                               


Title: Re: Cobbled together PV in W.Sussex
Post by: MR GUS on August 14, 2016, 11:01:22 AM
Good to see you still living dangerously Outtasight! (by that I mean what under modern parlance much favoured by gvt "services" wanting to spin something) ..we are all clearly potential subversives if they wish to have a go at us right.

Yellow perils ticking over nicely evidently.  exhappy:


Title: Re: Cobbled together PV in W.Sussex
Post by: Outtasight on August 14, 2016, 03:03:01 PM
Some 1637 daily cycles on the original battery pack and still grinning.

I've still only got the very basic battery monitoring system (BMS). There was no need for a battery management system. The difference being all that meddling with the cells to actively balance them that a battery management system tries to do (usually with fire engine calling results).

With these cells, you bottom balance them once in their lifetime and that's it. They don't go out of balance.

I still have the CellLog8 watching each individual cell on the original pack. But it just serves to trip the inverter when the low battery threshold is reached, as over discharge will damage them immediately and permanently. 

The second battery pack has a prototype 'per cell' monitor on it but actually I just use the left-over Smartgauge monitor I used on the lead acid pack to monitor the pack voltage and control the chargers.

(http://i68.tinypic.com/nvbqr6.jpg)

The SoC gauge on the Smartgauge doesn't work with lithium packs but it can switch to read just voltage on the display and it has two threshold alarms that I could use to drive a contactor in the consumer unit. The contactor controls the AC supply to the battery chargers. When the battery gets low-ish, it enables the chargers. They are also connected to a timer switch that turns them on during Economy 7 hours only. So on bad solar days, the Smartgauge decides when to allow the battery chargers to run from Economy 7 electric.

(http://i65.tinypic.com/2udxah4.jpg)

The other high voltage alarm on the Smartgauge turns the chargers off when the pack voltage rises to a certain level. This isn't "full battery" level, but rather a level where enough energy has been put in to get by on and then the solar can do its stuff again.

The inverter will switch to UPS bypass if AC is connected to its input. The timer and a contactor do this. But if I want to force the system to stay on battery all night, I can switch the AC off either by cancelling the timer 'on' program on the timer or just kill the supply with the master breaker (but I have to remember to turn it on again later, whereas the timer will do this automatically).

The battery only charges when the inverter is in bypass. The chargers don't like a lot of load ripple and trip out if the inverter is running and a large load is put on it.

The UPS is a cheap design and doesn't sync the incoming mains to the inverter phase, so at random, when the switchgear in the UPS switches, it can cause a massive phase mismatch surge. To stop false tripping of the master breaker, I had to buy a special Type D 20A one that has a high surge margin.  The 32A ring main supply breaker at the house consumer unit had to be upgraded to a Type C (normal ones are Type B).

The right-hand half of the consumer unit is just the distribution for the the inverter output, which still goes to parallel off grid wiring around the house.

(http://i64.tinypic.com/okcop.jpg)

The rest of the gubbins on the board are a grid kWh meter and the inverter output kWh meter and a Owl monitor, then a battery disconnect for the solar chargers.


Title: Re: Cobbled together PV in W.Sussex
Post by: Outtasight on August 14, 2016, 03:56:09 PM
The outside hasn't changed too much.

(http://i64.tinypic.com/2exsuh0.jpg)

There's still the random assortment of panels around the house and on the garage, now totalling 3.585kWp (in theory).  A slight upgrade, as I bought a 305Wp panel for £185 from a solar installer who had surplus. That forms the shade on the wall over the kitchen window.

(http://i65.tinypic.com/23u75ur.jpg)

Another more significant 'upgrade' was moving the pair of 200Wp panels to be on the garage roof.  This reclaimed the patio for plants and also means that those panels don't suffer the shading from the garage in winter. The sun gets so low in the sky from November to the end of January that the lower half of those panels on the patio were always shaded.

(http://i67.tinypic.com/2mw9tlt.jpg)

While one pair of portable 40Wp panels are still on an A frame and move about as the seasons change.  These and a another pair of 40Wp panels mostly try to do something in the late afternoon western light.

(http://i63.tinypic.com/mlmel2.jpg)


Title: Re: Cobbled together PV in W.Sussex
Post by: biff on August 14, 2016, 04:43:19 PM
Outta. That is excellent news on the cell front,
                                  Just needing the one controller and the single discharge to the bottom. I compliment you on sharing this with us.
   A lot of folks are like myself,reluctant to dig the hand into the pocket and fork out but fair play to you, you have gone and put the money down on the cells and
   succeeded in making it work. :genuflect
                                   Biff


Title: Re: Cobbled together PV in W.Sussex
Post by: Mostie on August 14, 2016, 05:51:01 PM
Brilliant.... bodgeneering a plenty  :genuflect


Title: Re: Cobbled together PV in W.Sussex
Post by: todthedog on August 15, 2016, 06:56:31 AM
Outta fabulous.  It makes me happy just to see your work. ;D


Title: Re: Cobbled together PV in W.Sussex
Post by: Outtasight on August 15, 2016, 09:08:44 AM
Thanks all.

I recently bought a PS4 and if energy were a game, I'd hope to have bagged the "Top Bodger" trophy by now. ralph:

As it is, I'd be content with the crew bonus power-up in 'World of Tanks'. If you're playing in British tanks, they get a 5% boost to skills if you buy them 'tea and pudding'.

More to come.


Title: Re: Cobbled together PV in W.Sussex
Post by: biff on August 15, 2016, 09:16:11 AM
This we have to see Outta, :crossed
                          Biff


Title: Re: Cobbled together PV in W.Sussex
Post by: fred bloggs on August 15, 2016, 10:27:56 AM
I'm also glad to see you back, thought you had emigrated to foreign shores.

Look forward to further updates.

Best Regards

Fred


Title: Re: Cobbled together PV in W.Sussex
Post by: Scruff on August 15, 2016, 11:37:55 AM
 :genuflect

(http://vladsokolovsky.com/forums/public/style_emoticons/aaa/popcorn1-smiley.gif)


Title: Re: Cobbled together PV in W.Sussex
Post by: Tiff on August 15, 2016, 02:52:53 PM
Great stuff, pleased you are back and sharing your adventures with us!


Title: Re: Cobbled together PV in W.Sussex
Post by: Outtasight on August 16, 2016, 10:02:04 PM
Ever seen those cheap Chinese generators that you often see at car boot sales?

(http://i67.tinypic.com/nfjyf5.jpg)

You know, those "6500W" 3-phase generators with an name resembling a cross between processed cheese and an 80's German techno band? The ones that some people buy without realising what "3-phase" means? (other than it has a volt meter that goes up to 450V AC and sockets that don't fit 13A UK plugs?)

Well, I bought this one brand new for £150 and he even delivered it to my house from the car boot sale. He drove off, thinking, "Tank god I got rida dat ting, so I did!" - (yes he was Irish).

But I had a cunning plan...

Remember these?

(http://i67.tinypic.com/2gxnyoy.jpg)

I've been playing with backup generators for a while. Starting with this one:

(http://i63.tinypic.com/de9qi9.jpg)

The generic Chinese 650W single phase, 2-stroke smoker. £35 from a car boot with free grass in the fuel filter.

It kinda worked with one of the chargers but that wasn't enough, although the fumigation of the neighbourhood was.

So I sold that at a car boot (for £50, minus the grass in the fuel filter) and got one of these:

(http://i67.tinypic.com/262mnbp.jpg)

It was a bit better. Even more noisy but being a 4-stroke engine, easier to start and largely smoke-free. Still only good for running one charger. So I sold that and bought the soft cheese techno generator.

With three extension cables and some adapter plugs, each phase can run a charger at 15A (400W) for a total charge rate of 1.2kW. The thing will run the chargers at up to 20A each (540W / 1.6kW) but it's prone to cutting out after about 30 minutes. At 1.2kW it seems happy to run continuously.

The latest in 2016 spreadable dairy synth electricity looks like this:

(http://i66.tinypic.com/19l05e.jpg)
(http://i63.tinypic.com/ht5nnp.jpg)
(http://i63.tinypic.com/24mfjhz.jpg)

Quite a lot of 16.6kHz ripple from the (digital?) AVR.

But with a EMI filter on each extension lead, you get rid of the ripple and are just left with a 50Hz triangle wave.  Close enough to a sine wave to not start a fire, I guess.

(http://i64.tinypic.com/23uyxl.jpg)
(http://i63.tinypic.com/10yia1y.jpg)

Beats the gnarly SIP generator waveform...

(http://i67.tinypic.com/2r43q0z.jpg)

The harmonics on that couldn't be filtered and almost cooked an energy monitor that I was using. I sold it to an Irishman and as he drove off I thought, in my best Japanese, "Kamisama! Nuguushimashita... Aaa, yokatta, yokatta!" (God! I got rid of it. Thank goodness!)

So now I can actually charge my house battery at night, in a power cut. It still requires ear defenders and, at 1.2kW, it will still take 16 hours to fully recharge the battery. But should the occasion arise, the neighbours will be in no doubt that I have electricity and they don't.

 bike:


Title: Re: Cobbled together PV in W.Sussex
Post by: biff on August 16, 2016, 10:14:28 PM
I am soooo Shocked Outta,
                        The poor Irishman was only trying to help you. I have no doubt that he knew who you were and was only trying to help you with your electrical problems.
   He is probably now on his bended knees in church, praying to god that you got the phases in the right order , you know,? the last one goes in first and the first one comes out last.
   He more than likely wrote it all down for you. Don,t worry about your £150,00 , It is surely in the hands of some charitable thrust by now, :cross
                                             Biff
   But that is a cracking good idea with the phases.


Title: Re: Cobbled together PV in W.Sussex
Post by: billi on August 17, 2016, 01:06:44 AM
i rather invest in more PV    than  relying on generators too much  , i lost a few gensets   .... worked them too hard (my mistake probably )

It works fine with me since years with a honda clone   petrol now  and  just do not stress her   ;)  too much







Title: Re: Cobbled together PV in W.Sussex
Post by: Tombo on August 17, 2016, 07:29:46 AM
Hi Outta, Good to have an update on your electric string wizardry. 
Can you clarify for me please, your 6500W  cheesy techno genset only produces a 1200W continuous output, spread across all three phases?
Thanks and good wizard-ing.


Title: Re: Cobbled together PV in W.Sussex
Post by: Outtasight on August 17, 2016, 08:47:54 AM
Yep, the 1.2kW was evenly spread across all three phases.

For a laugh I tried plugging a 1kW heater into one phase with the others unloaded and the volts on the unloaded phase shot up and the volt meter on the thing read 450V.  The stator phases are excited by the same rotor coil and the AVR has to balance providing more excitation for the heavily loaded phase against over-excitation of the unloaded phases, producing excess voltage on them with no load to pull it down.

It does seem to have some protection though. When I tried cranking up the charger power to 25A (675W) each, the generator would labour and then one of the phases would cut out leaving the other two generating.  So it has some per phase sensing of load or over-voltage and will kill an output.  It does try to restart the phase after a few seconds but the inrush current on the charger and the large step load of the charger finishing its self test and turning on the output causes the phase to crash again.

If I keep the per phase loading of chargers to 15A, the generator is happy enough to have the chargers all turn on at roughly the same time and restart any one of them when running.

I agree Billi, it'll be interesting to see if the engine on this thing lasts long enough on load to need an oil change.  There's no way I'd use it to try and go off grid. Using off peak grid power to reduce my grid bill is a much better option. Cheaper, more reliable, cleaner for the environment (as 54.9% of it is nuclear power and most of the rest is renewables).

As you can see from the photos, I'm maxed out for PV unless I rip it all off and rebuild with modern 330Wp panels and all new or expanded solar chargers.

The system I have is now not about going off grid any more, but sheltering me from grid outages as our crumbing power generation fleet disintegrates and we have black-outs from the dithering and ineptitude of those in control of it.


Title: Re: Cobbled together PV in W.Sussex
Post by: Tombo on August 18, 2016, 05:26:16 AM
Thanks  Outta for the detailed reply. 
Perhaps the 6500W refers to peak output, like cheap stereos where PMPO output is quoted rather than RMS.  In the case of your genset, I imagine this was calculated by the energy expended when running flat out with petrol tank on fire stir:



Title: Re: Cobbled together PV in W.Sussex
Post by: Outtasight on October 09, 2016, 11:06:04 PM
Hmmm... Upgrades! (Nero - The Matrix Reloaded)

For a very long time, my system has been over-subscribed.  That is, it has had more PV on its chargers than they could output.

This often meant that the main Tristar MPPT-60 was maxed out at 60 Amps and the upper limit of charge power of it and the two little 15A chargers was 90A, or 2250W (at 25V) to 2430W (at 27V).  The current limit is the same regardless of battery voltage, so the maximum power delivered increases as the battery voltage increases.

But last week I picked up a used Tristar MPPT-60 and here she is!

(http://i66.tinypic.com/2e1yq8w.jpg)

(http://i65.tinypic.com/2uiart4.jpg)

With these four chargers, each fed by a different section of the array, I now have a total of 150 Amps of charge capacity which more than equals the amount of PV I have (3580Wp).  At 25V this gives 3750W and at 27V, 4050W.

The new charger on the left takes the feed from the 1640Wp of panels from the roof, while the old Tristar takes part of the wall, patio and garage array (minus the bits that are wired into the small SunSaver chargers already).

We haven't got the high noon sun of the summer now but today the array, on its first day of testing with the new charger, managed to squeak 3486W for 15 seconds into the battery, just shy of 130 Amps.

(http://i67.tinypic.com/2ep57qw.jpg)

(http://i66.tinypic.com/t87r60.jpg)

I modified the load manager software to read the extra logged channel from the new charger, so the stats and graphs are fine.  Both the Tristars are Ethernet enabled, so I could connect to them over the LAN.

I upgraded the firmware on both chargers as I'd not noticed that there were new versions.  Morningstar seem to have finally fixed the issue of the firmware not doing an EQ cycle on the first day (when they're programmed to do one every day).

The eagle eyed (and with long memories) among you may notice that there are some new buttons on the load controller program.  This was to have the water heater come on at a pre-set time and timer, now that my gas boiler is no longer with us.  It still takes 5 hours to heat the water, because it can only go at 650W, but at least we always have hot water in the evenings without me needing to remember to set the boost.  I can also dial in up to 5 hours in 30 minute steps manually on the timer too.



Title: Re: Cobbled together PV in W.Sussex
Post by: eabadger on October 10, 2016, 07:25:35 AM
hello looking good, was that the mppt off ebay?
have gone back a few pages in this post and cant see any more info about the "load manager" is this yours?
i am in process of upgrading my syste,. i have two new tsmppt60 a hub1 and rd1 to add to my existing mppt60 so interested in aggregating data.
i had a couple of mppt fail, not sure why did wonder if it was static discharge after electrical storm, both replaced under warranty, i like the one we have so decided against cheep mppt and went for it.
not sure about doing the battery route, due to cost.
how is your three phase generator going? even on expensive sets sometimes they only monitor one phase for the avr, if you identify the phase they use, use this as your main loading phase, the chinese amaze me with power rating stickers, what is engine horse power? this will be the deciding thing.

steve


Title: Re: Cobbled together PV in W.Sussex
Post by: biff on October 10, 2016, 08:12:20 AM
I have run Chinese genis for years,
                                 Generally speaking they are fine and most of my experiences have been good. I found that the windings are susceptible to damp and dust,
      The yanmar clones go for ever but the geni can and do blow the diodes or shake a wire loose behind the dash.
      Yes, many are way over rated, I have one that says 10kw in big bold letterrs and it has the small Yanmar clone. It is also pull start ;D with no lecky starter.
      It is easy enough started with a power drill. I bought it over 12 years ago and I am stuck with it because I am the only one who can start it. Nobody else wants to
      fool around with a power drill with no power.
       I try and steer clear of Mppt,s, There are not many that can handle 140volts ;D
                                                     Biff


Title: Re: Cobbled together PV in W.Sussex
Post by: eabadger on October 10, 2016, 08:16:55 AM
morning biff, morningstar can do 150v and they now have a new 600v dc mppt. but given price of panels now, maybe mppt days are numbered? however i like the remote monitoring as my solar shed is about 150mtr from house.

steve


Title: Re: Cobbled together PV in W.Sussex
Post by: Outtasight on October 10, 2016, 08:49:41 AM
Nope, a mate of mine locally is packing in his off grid experiment. He's got trees growing in front of the array on public land and the shading on his house got to the point where it didn't work.

He had his first one blow up too. This one is the replacement which has worked fine for a few years.  Mine was one of the very early ones in the UK and has been fine apart from some software bugs (mostly cosmetic, apart from the minor EQ scheduling issue).

It was rumoured (somewhere - don't ask me to find the link) there might have been a firmware issue with doing a soft reset via MODBUS. My mate's one went pop while powering on. I've always made sure to reset my controller only when there was no/low load (or do upgrades at night) and then follow the instructions in the guide (open the array disconnect first and then the battery disconnect.  Restart is the reverse process).

The generator is a toy, sitting in the garage. Not used it except for testing whether it would work at all with my chargers. Backup from the grid is much cheaper and, mercifully, automatic. As the inverter is a UPS, it can source select just by applying AC to the input and the off-peak timers and battery monitoring gear sorts that out for me daily. Using the generator is a last resort (for a dark and stormy night).

The load manager program is mostly mine, based on a VB6 driver & demo app for a Velleman USB I/O board from Maplins.

http://www.maplin.co.uk/p/velleman-usb-interface-board-prebuilt-kit-l92bl (http://www.maplin.co.uk/p/velleman-usb-interface-board-prebuilt-kit-l92bl)

The data acquisition is done by MSView (provided by Morningstar) and outputs to a .csv file that my program then reads and does a bunch of stuff and writes another consolidated .csv file that MSView then opens to draw the graphs in real time.

The graph engine in MSView hasn't been updated in yonks and only has a 16 bit DLL that does the data point management so after a few days it grinds to a halt and crashes. These days I only use the graphs for diagnostics after upgrades. If you don't use the graph module and just use MSView as the data logger, it runs happily for months without restarting.

I sometimes think about trying to get into writing a standalone app on an Arduino, directly reading the MODBUS registers and so on but this works and the laptop server is always on anyway, so I could never be arsed.

VB6 is very long in the tooth and I have to run it in a virtual WinXP machine these days as it won't run on Win7.  Maybe when it finally becomes impossible to maintain the code I'll make an effort. Until then, the motto remains, "Don't touch it. It works."  :crossed


Title: Re: Cobbled together PV in W.Sussex
Post by: Nickel2 on October 10, 2016, 10:49:50 AM
...given price of panels now, maybe mppt days are numbered? ...
Hmm, not so sure about that. Panels are designed to be worked to produce their optimum output. To me. not using an mppt is like driving a car with the handbrake left on because you get free petrol. Surely energy efficiency is what we should all be promoting, rather than wasting a commodity because it is cheap.


Title: Re: Cobbled together PV in W.Sussex
Post by: eabadger on October 10, 2016, 11:57:10 AM
the two i lost were both after storms, but who knows, i have now wirelessly decoupled the incoming telecom from the lan as this seemed most likely point of entry, but i also considered the issues discussed on web, morningstar were better than the dealers at accepting fault, dealer tried to make out it was over voltage but morningstar said unit was protected against over current and voltage so could not be the issue!!
i already use the morningstar software was just looking at seeing combined but now think that is what the hub1 does but not by tcp/ip

steve


Title: Re: Cobbled together PV in W.Sussex
Post by: biff on October 10, 2016, 11:59:48 AM
I would not know a lot about Mppt controllers,
                                             However, i have a decent memory for installation failures and noticed that Mppt controllers had been present in almost 90% of the hassled ones.
     My base voltage is 120volts not 48volts and that does make a difference. ;D.
   So I do not use tristars or Xantrex or big names at all. Instead, i use 2kw Chinese w/t controllers that take 600watt in solar as well. So if they take 2kw from the wind and 600watt from the sun,
   they should be cushy with 2.2kw from 2 strings of solar pv. 1100watt each,
   In their normal use these wind turbine controllers divert the power to two big resistors but in our installation The resistors are bypassed and our 2 x 2kw x 138vdc immersion heaters make use of
   anything above this 138vdc. So instead of using the W/T controllers 3 phase entry i use the solar entry and the amps and the volts come up on the dash giving me an excellent indication of how
   each pair of arrays is performing. It is really simple and easy to understand. The 120volts system allows me to group different panels together and if their voltage amounts to something between
   130vdc or 150vdc,then I can chain then in series as long as the amp ratings are withing .3 of each other which generally speaking has been the case with me.
   I think what happens with the Mppt controllers is that the original installation was set up and calculated to work within a certain safe parameter, giving a certain safe tolerance but then something
   in the installation would be changed and the Mppt controller which would have organised its own way of coping with the Original installation would cope with the added power for a certain length
   of time until the power coming in over loaded the system and then the Mppts get confused and bad things would happen.
   This is the impression that I formed over the years. I may be wrong but my assumed that if these members who were a lot more clued up on Electricity toys than I was, were having all this hassle
   then there was not much hope that I was going to get away Scott Free, because back then I was always fiddling  and poking at things.
   At present there are 3 x 2kw controllers in the system including the one that handles the 2kw charger input if needed, If ever one of these controllers gave up,the others would have no problem
   coping,The whole installation is module based, I can remove any controller and the system will still perform, We might have one tank remaining cold for a short while until the controllers is replaced.
  Maybe if I took the time to try and understand the Mppts a bit better I might be a fan but they seem to be that bit too complicated for me.
                                                                   Biff


Title: Re: Cobbled together PV in W.Sussex
Post by: Outtasight on October 10, 2016, 07:01:39 PM
Basically, whatever works for you, works.

The TS-MPPT-60 is pretty robust though. I connected about 2.8kW of PV to the controller that is only designed to output 1.6kW. It just limits the output current, sitting pegged at 60A for hours in summer.

All grid tied solar inverters use MPPT inputs so it's no longer a "dark art". Many inverters sport two independent MPP trackers, for those who have split east-west arrays.

The new Tristar TS-MPPT60-600 is a result of advances in power electronics (solar and electric cars) with the ability to accept a 100-525VDC input from a solar array. The normal working voltage of all residential grid tied solar inverters with 14x 60 cell modules in a single series string is about 420Vmp at just 9 Amps (making cabling very easy but requiring a lot of respect for wiring terminals).

Soon nobody will do an install with an array at 35VDC and use 25mm2 cable runs and big parallel junction boxes, like what I dun  facepalm

I say "soon" because there is the matter of cost. The new 600V Tristar is over double the price of the 150V model at £1400 and still only charges at 60A into a 48V or 60V battery.

My PV array is such a Frankenstein work of random sized panels that it will pretty much only work at 35VDC, even though I should now reconfigure it for 105VDC operation to cut the distribution losses. The little 15A chargers are only good to 70V input. I'd have to bin the entire array and start again to use a single 420V string.

The other trend is towards very high voltage batteries, again borrowed from electric cars that use 400V batteries.  Now we're full circle and the 420V PV array is a good match for charging a 400V battery without lots of expensive DC-DC conversion power electronics. It remains to be seen how many fires we see from the long series-parallel strings of tiny (3-4Ah) battery cells used. Historically, a bad idea in battery bank design.

Tesla have almost cracked it, with only a handful of incendiary batteries but Samsung are struggling at the moment to keep ONE cell under control in their Note 7 phone with a 15 watt USB charger. stir:


Title: Re: Cobbled together PV in W.Sussex
Post by: Tiff on October 10, 2016, 07:57:51 PM
Great stuff, pleased to see this thread still going.

I wonder how many on here have started out with a small experimental system that has grown incrementally?

Sometimes I wish I could go back in time knowing what I know now and start again.


Title: Re: Cobbled together PV in W.Sussex
Post by: Outtasight on October 10, 2016, 10:14:02 PM
I've always said that collecting solar panels was akin to collecting garden gnomes.

You get one, then another, then a few. Then you're featured on BBC South Today as the guy in the  "And finally..." story.


Title: Re: Cobbled together PV in W.Sussex
Post by: biff on October 11, 2016, 11:07:40 AM
Orrible bad news from Samsung this morning,
                                 Everyone has been asked to switch off their phones,even the replacement ones, sh*tfan:   arrrghhhh. No I don,t have one but I know who does. ;D
  On the subject of solar panels. I bought some of the earliest PV panels almost 10 years ago,2 x 80watt x 12volt jobbies. I removed them from the roof of our house last week with the i
  intention of cobbling them together(great word that Outta,)with other used but newer pv panels. I have enough to reach the magic figures 137vdc+ but one thing I noticed was that these
 older pv panels were quite amaturish  and not in the same class as the newer pv panels. So vast improvements were made. The old panels had a smaller area,, 30mm right around and the frames,
 junction boxs and the cables were rather poor quality. I cannot deny that they worked first class while we used them on our old original 12volt house system. They did indeed do a great job but
 the newer panels are without doubt much better all round.
  Folks might wonder what on earth I am doing working PV with W/T controllers but it is not as daft as it first seems. The W/T controllers have a built in "Divert to dump" which is 138/9vdc and
 would be the same as 14volt in the corresponding 12volt installation, That is a bit low but what happens is,that it takes the best voltage for heating water,any lower would prevent the bank
 from getting a fair charge and any higher would needlessly spend excess energy pushing uphill for no real gain. I can boost the bank by dropping one of the dump load immersions for a few hours
 each month or running the charger @ at 147vdc x8amps, bearing in mind that our bank very seldom drops below 123/4 under load.
 Then there is the problem of trying to remember, how we put these works of art together. For a while I was stumped to remember some of my own moves, In fact it took me a few days to figure out correctly
 how I strung the whole lot together. I had Mrs Biff in mind and wanted her to be able to start the charger and bring it onstream. It is now a very simple matter but i had to strip out a lot of  unused
 wiring,take the 230 generator another 100ft away from the house and the charger another 20ft beyond that. The RE ac cables are colored white and the 230 generator cables are colored orange
 The 120volt charger is permanently connected and delivered direct to the Bank meaning that it does away with the need to switch over. We just start the Charger and carry on as before, The
 charger automatically ups the charge in dc the more power we take from the bank. So anyone listening to the engine of the charger would note that it sounded more relaxed the more load put
 on the bank which would be the complete opposite to the AC generator.
   There was a time back in 2010 when i could not even walk out the front door into the sunshine. i was quite ill in fact. The system ran itself but the batteries were without care all summer, by the
  time I was able to walk down and have a look inside the cells,they were all bone dry on top freeeze. I filled the 60 cells to the top with rain water and went back to bed. Yes i break a few rules .
  I could maybe have one of those self watering jobbies installed into the bank but unlike the smaller banks, it does not need water near as often and a monthly check is suffice. The summer sun does
  speed up the evaporating process but that is to be expected. I now use proper cell water.
  So If I were to give anyone advice on this type of installation, i would simply say. "Map everything and color code it all"  "Document and date all changes"." Beware of the month of March,especially
  if you have been futtering and improving over the previous winter". March has caught the best of us out.
                                                                               Biff
   


Title: Re: Cobbled together PV in W.Sussex
Post by: Outtasight on October 12, 2016, 05:48:44 PM
Good advice man, and I hope you're fine now.

I've got the same motivation to automation as you - the missus! She doesn't like touching anything to do with the solar stuff. When I had the two battery banks separated, I did train her to press an "enable" button on the inverter and flip a AC change-over switch to select it.

But now I've got the two 400Ah banks in parallel in one bank - another experiment in li-ion battery behaviour. What happens when you parallel two battery strings, one with 1000 cycles on it and the other, brand new. So far, the answer is - no problem. It didn't work out well for my old lead acid bank of random strings of batteries paralleled.

But today's post is a warning to would-be purchasers of new kit. If you're buying anything American, buy it NOW!

The Pound fell to a 168 year low today against the Greenback so I ordered a LCD display front panel for my new Morningstar charger. When UK stocks run out, they'll be buying it in from the US at the new exchange rates.


Title: Re: Cobbled together PV in W.Sussex
Post by: Tinbum on October 12, 2016, 11:37:20 PM
the two i lost were both after storms, but who knows, i have now wirelessly decoupled the incoming telecom from the lan as this seemed most likely point of entry, but i also considered the issues discussed on web, morningstar were better than the dealers at accepting fault, dealer tried to make out it was over voltage but morningstar said unit was protected against over current and voltage so could not be the issue!!
i already use the morningstar software was just looking at seeing combined but now think that is what the hub1 does but not by tcp/ip

steve

I had a problem with a Morningstar MPPT and they were excellent about it. Within a week I had received a replacement direct from America. They were very interested in the actual sequence of events of how it failed and of the physical fault within the unit. I didn't have to return the old unit and in the end I repaired it (less than £5 in parts) and I am still using it 2 years later.

With these controllers I think its a case of turning of the PV before the battery- which goes against the sequence for most inverters.


Title: Re: Cobbled together PV in W.Sussex
Post by: Outtasight on October 13, 2016, 08:39:46 AM
Yes, that's the sequence recommended in the user guide. Disconnect the PV first (and I'd only do that when the power input is low or off at night).

I guess one feature that they could add is a "shut down" command from the LCD screen menu or a special way of pressing the reset button. If it commanded the charger to stop charging (so there was no current flowing) then you could quiesce the system and open the contactors without interrupting any big current flow.

There is a way to do it remotely by setting the "charging disconnect" coil in the MODBUS control register from MSView. I use the "EQ triggered" coil quite a lot when testing, especially on the little SunSaver MPPT chargers as they have no buttons or anything on them but I can remote control them through the IP to EIA-485 bridge on the Tristar.

But it is a failing in the design that the controller could be damaged if running at power and the battery fuse or breaker to the charger trips unexpectedly (and I have had 60A fuses blow on me from age related thermal cycling stress). But so far I've not had a controller go pop.

I had to rebuild my Cotek 3kW inverter once as the entire bank of DC push-pull driver MOSFETs exploded (quite literally). The cause of that was an AC side IGBT going internally short circuit and generating a massive overload.

(http://i67.tinypic.com/2ikb04j.jpg)

A quite complicated design as it has a brain board that does the control and then two 1.5kW power modules in parallel. A DC-DC converter steps 24V up to a couple hundred volts and then a H bridge (just like in grid tied solar inverters) makes the 230V AC.

The parts were about £30 but it took 2 days of de-soldering and re-soldering to get all the parts replaced. That's why the supplier said they were "uneconomic to repair" out of warranty. In warranty, they'd just bin the whole unit or replace a board/module and pass the cost to the manufacturer.


Title: Re: Cobbled together PV in W.Sussex
Post by: biff on October 13, 2016, 09:26:30 AM
I would love to be able to fix such things,
                               I have a few controllers that need fixing but there will come the day that i will have the confidence to tackle them, meanwhile they wait patiently.
  Some weeks ago I got a visit from a friend who complained that his inverter was not strong enough to power his large cow byre lights,  a row of large twin florescence lights,60watt a time,
  The whole show is off grid and powerd by a Y/S 600watt W/T and 2 x 80watt pv panels,I gave him a very good 700watt sine wave inverter and that evening i got the call .He siad that it would
  light one light and then conk out when he tried to light the rest. So he tried different suggestions but the results stayed the same. I asked him to change the dc leads coming from the Bank,24v.
  And then he mentioned that he had a fuse on the line,a small thin wire fuse.. ;D I have heard nothing since.
                                                                                             Biff


Title: Re: Cobbled together PV in W.Sussex
Post by: Tinbum on October 13, 2016, 10:01:31 AM
Yes, that's the sequence recommended in the user guide. Disconnect the PV first (and I'd only do that when the power input is low or off at night).


That's been added to the  manual since I bought mine!!


Title: Re: Cobbled together PV in W.Sussex
Post by: Outtasight on October 20, 2016, 01:41:07 PM
Energy efficiency matters when you're off grid (or trying to be).

I'd got an 8 port Ethernet hub a few years ago at a car boot sale to run the lounge network.

With an increase in gadgets and now two Morningstar charge controllers using Ethernet, I ran out of ports on the hub and it was getting a bit unreliable, sometimes losing connections.

So I bought a second hand 10/100 switch to replace it. This has 16 ports instead of 8 and should perform better as it is a switch rather than a hub. Pretty cheap at just £17 and no need for a gigabit speed switch.

(http://i67.tinypic.com/2vi10r9.jpg)

But technology has advanced in power use as well. This 16 port switch uses much less power than the old hub (5.4W against 14.4W), saving 9 watts. That's 0.216kWh per day, 1.512kWh per week, 78.6kWh per year. Important, as the network switch is on 24x365.



Title: Re: Cobbled together PV in W.Sussex
Post by: fourfootfarm on February 09, 2017, 08:33:30 PM
Just read though this whole thread and its thought inspiring pioneering stuff.

Thanks for the contribution Outta


Title: Re: Cobbled together PV in W.Sussex
Post by: Scruff on February 22, 2019, 09:21:42 PM
(https://thumbs.gfycat.com/SarcasticWelloffFinch-max-1mb.gif)

Clicky (https://www.youtube.com/user/OuttasightPV/videos)

 :genuflect


Title: Re: Cobbled together PV in W.Sussex
Post by: billi on February 22, 2019, 09:37:38 PM
 true , Scruff , some  fab people here and have been , hope they   will revisit 


Title: Re: Cobbled together PV in W.Sussex
Post by: stannn on February 22, 2019, 09:42:47 PM
I second that billi. We loved his battery adventures.
Stan


Title: Re: Cobbled together PV in W.Sussex
Post by: biff on February 23, 2019, 03:28:56 PM
I Totally Agree Billi,
                Outta is sadly missed. He posted loads of interesting stuff.
  Hopefully some day he will rejoin us and give us his latest updates. :genuflect
                             Biff
  NB, I watched His 2012 video  A day off Grid and Outta looked exactly like I imagined him to look like.  :crossed   Thanks Scruff,


Title: Re: Cobbled together PV in W.Sussex
Post by: roys on February 24, 2019, 01:10:55 PM
What 2012 video biff, sounds like the sort of thing I would like to watch, also agree his sparky experiments were very interesting.


Title: Re: Cobbled together PV in W.Sussex
Post by: biff on February 24, 2019, 02:41:14 PM
Hi Roys,
          Click on Scruffs "Clicky" in the previous page and it opens out into a whole pile of Utub videos that Outta had done.
   The last one in Line is one of Outta himself + his neighbor putting up a few panels on the back of his house.
  Outta has always had his own way of doing things but this control department was a real learning curve for me.
                   ,Good luck   Enjoy, :crossed
                                     Biff


Title: Re: Cobbled together PV in W.Sussex
Post by: roys on February 24, 2019, 04:57:13 PM
Cheers biff, now the rugby has finished guess what I am watching 😀


Title: Re: Cobbled together PV in W.Sussex
Post by: biff on February 24, 2019, 05:09:36 PM
Outta is worth watching.
         He has all kinds of good moves. These were the early days of pv and Li-po4. I think Outta bought the Wintons eastern Europe. There is loads of info on balancing the cells and I remember the different options he employed.
It was great reading here on Navitron and we all benefited from it. You never know he might just grace us with his presence and update us all. I hope he does
        Biff