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Energy/Electricity Storage and Use/Grid Connection => Off-Grid, Batteries & Inverters => Topic started by: nominous on August 13, 2015, 10:44:45 AM



Title: Off gird battery voltage
Post by: nominous on August 13, 2015, 10:44:45 AM
I'm curious what voltages people who are off gird run their battery packs at?

24V, 48V, higher ?

What are you running at and what is the determining factor for that ?
Inverter input ? Safety ? Charging controllers, etc ?


Title: Re: Off gird battery voltage
Post by: biff on August 13, 2015, 11:33:05 AM
Good question,Nominous,
                      The simple answer is,that everyone has their own ideas and they pick a voltage that suits them. Most folks start off at 12v on small scale installations, just to get to see how it works and then they realise that higher voltage travels better and the cables don,t have to be near as thick.
  Then they try and match inverters,,You do get 36v  and 90v inverters but not many. The most popular are 12v, 24v and 48v, all in, 48v seems to be the most popular with off-gridders
  With 48v you can buy a large 48v forklift pack to suit and there is a hell of a lot of power in that.
 But lets say you want a system that can dump big dc volatge into immersions, without using complicated boxs of tricks, say you go up to 120v like Roger and AG, The cables are even thinner again and the fuses are down to 20amps. However the voltage is at a dangerous dc level,,but knowing what you know and you are going to be extremely carefull even with lower 48 voltage,you forge ahead and go the 120v route. Then you would need 60 forklift cells in series, !
  So really, there are advantages and disadvantages but 12v is not really advisable for serious off grid work. All your finance could be taken up in jump lead thickness copper leads and really heavy connectors and the jump from 12v dc to 230vac is hard work for any electrical circuit.
   I would say, most off-gridders run 48v and even I have worked a 48v system in our shed for years. However going up to 120volt and the 60 forklift cells means that you grab the energy quicker and can run your system with very little discharge rate. We go for weeks without dropping below 125volts and our power demand is only a tickle on the bank.
  The other big advantage is that you can buy pv panels and configure them almost any old way to hit the 140v bracket in the strings without the nuisance of having to use a mppt controller so the system is a lot more reliable. Now these are my own conclusions and I know that other opinions differ but that is the beauty of the forum, somewhere in between lies the truth.
                                              Biff


Title: Re: Off gird battery voltage
Post by: jonesy on August 13, 2015, 12:22:43 PM
I suspect you'll get a lot of answers on this thread.
I ran 24V/800Ah upto 1kva, then 96V/50Ah upto 3kva.  I also had 200V/7ah DC just to run CFL lights as this saved a huge amount of battery power over night. The ADSL router likewise was straight off the 24VDC.  The lighting battery was only 7Ah, but could run the house for a few weeks without charging, as the currents are around 10mA/lamp.  It came about after about a week of no sun in December, and the inverter quiescent + lights, router took too much, it all adds up.  I came within a few hours of needing a genny, then the sun came out.
My choice was based partly what I had to hand + spares.  I also had 48V/2kva gear, but as I had no spare that only lasted a week after the fan failed and it went pop very noisily.
My 1kva inverter wasted ie quiescent about 25W. The 3kVA about 100W. I ran the 1kva most of the time as our base load was trivial and was often less than the quiescent.  I switched over to the 3kva for the washing machine, big tools etc. No inverters ran over night as that was simply a waste of 25W x 8 hours - batteries are expensive so I used to molly coddle them.
I'd never go lower than 24V.  It is always the battery amps that scare me.  A 2.4kW load needs 100A @ 24V.  That's a thick, expensive cable to keep the volts drop down.  Equally, you need a good battery to delivery it. Get to 96V and it's only 25A, and a 4mm cable is plenty adequate, or 2 x 2.5mm, which is often lying around the house.
I havent looked for a couple of years, but 48V inverters were tricky to source. The newest sunny island is 48V up to 6kva, with an impressive quiescent of 30W (IIRC) Equally charge controllers above 48V are hard to find.  I used to use 2 x tristar stacked to get 96V. I did try direct panel connection like Biff, but as the batteries approached full charge, the panel open circuit voltage pushed me too high and the inverter tripped out on high volts.
I'd say there is no real extra safety issues with higher battery voltages.  You need to cover all joints either with a nice box, or individual covers at any voltage. Whilst there are regulations for touch voltage (50V), these tend to be based around adults.  Pets/animals and toddlers are inquisitive and can be injured on much lower voltages/currents.
Where some people fail on off-grid is incorrect (or non existent) neutral earthing and protection on the AC side. A 4kVA sunny island SI4.4M-11 (for example, but its likely all inverters are like this) won't clear a 10A type B MCB (6A max), but plenty install 32A MCBs for the ring main etc, so straight away a live to earth fault on say a washing machine case won't clear the breaker in the required 0.4s.
Protection and safety are tricky at any voltage.
As Biff says, each to their own.


Title: Re: Off gird battery voltage
Post by: billi on August 13, 2015, 12:38:21 PM
48 volt would be my choice  today ,   but my 24 volt setup  is performing fine  , since years


Title: Re: Off gird battery voltage
Post by: Billy on August 13, 2015, 07:16:22 PM
Ditto.  I would go 48V but like billi says my 24V is fine and dandy after nine years.   ;D


Title: Re: Off gird battery voltage
Post by: marcus on August 13, 2015, 07:58:36 PM
if you get a UPS/inverter at a good price then that defines your operating voltage.

otherwise, as a rule of thumb i'd say:

small system running most things at battery voltage with occasional/small inverter: 12v as there's lot's of stuff that'll run direct off the battery.

medium system with inverter, where you tend to keep loads to match available power coming in, and only run one 'big' load at a time then 24v is better than 12v and you can still get lots of stuff to run direct off the battery for optimum efficiency, and you won't need specialist d.c. breakers/switches.

full house system - if you want to run your house like you're on grid so OH/kids can plug anything in anytime - then 48v or more is probably best. Although there's nothing actually stopping you making such a system work at a lower voltage - it's just the currents & cables start getting heavy.

I'm running 24v and not planning to change - I live by myself and tend to be a bit minimalist when it comes to energy consumption.


Title: Re: Off gird battery voltage
Post by: Justme on August 13, 2015, 08:46:38 PM
Whilst I agree with the higher is better advice you can do it lower.

We started off with a small 12v system. Due to budget we could never change enough of it in one go to be able to change the voltage. So we now have a whole house 3kVa system run on 12v.

If the inverter/charger went now I would switch to 48v.

It would mean a reduction in battery capacity as we have 30 x 2v cells. So would need to take 6 cells out & rewire the rest to 48v.

Keep the cable short between inverter & battery.

Ours are still 120mm2 CSA. Recommended is 95mm2.


Title: Re: Off gird battery voltage
Post by: nowty on August 13, 2015, 11:13:14 PM
I am running 24v, slightly less efficient than a 48v system but I am on and off grid so I donít need a huge amount of power or capacity from the off grid part.

24v means I only need half the number of batteries, but gives sufficient capacity for my needs.


Title: Re: Off gird battery voltage
Post by: billi on August 14, 2015, 03:37:48 AM
Quote
full house system - if you want to run your house like you're on grid so OH/kids can plug anything in anytime - then 48v or more is probably best. Although there's nothing actually stopping you making such a system work at a lower voltage - it's just the currents & cables start getting heavy.

hmm ....  i need/have  2 outback mppt  chargecontrollers for my 4000 watt pv  and 24 volt setup  .... in a 48 volt  system i only would need 1     , this is a big difference 


Title: Re: Off gird battery voltage
Post by: camillitech on August 14, 2015, 06:44:32 AM
I would say, 'off grid' caravan, garden shed or boat then 12 or 24v. On the other if you want to run a house and family and you want any kind of 'normal' life then get the highest voltage you're comfortable with. Me I'd go 60, 72 or even 120V if manufacturers started to make inverter/chargers of those voltages. if your comfortable with using a UPS then I see nothing wrong with going 400v if you're happy working with lethal voltages. For now I'll stick with 48v, one advantage of which seems to be that it's easier to pick up a cheap 48v inverter than a 24v one, seen a few large Victron's and Studer's go on eBlag for much less than the price of a 24v one. Indeed just bought a BNIB Outback GVFX 3048 for less than £700 delivered, almost £1000 below new price  :o

Cheers, Paul 


Title: Re: Off gird battery voltage
Post by: nominous on August 14, 2015, 10:34:28 AM
Thanks for the replies. It makes for very interesting reading.
What made me ask was because I've been reading the specs on older solar inverter units.
They tend to have very high minimum input voltages. But they can produce rock steady sine waves, grid isolated and lots of power.
Designed for long term use.

Going back to what someone said about wiring (in my car audio days I was running AWG4, a mate was running 0 if not 00 !!) that would make a lot of sense, but with the down side of more observance of protection and safety.
With more car battery packs likely to come on the market, these are held at higher voltage strings. Getting used to working on high DC voltage is going to become more common.


Myself, there is no chance I'll go off grid where I currently am. We don't have the space or the lifestyle to support it. In the future maybe, who knows...


Title: Re: Off gird battery voltage
Post by: billi on August 14, 2015, 11:23:31 AM

What made me ask was because I've been reading the specs on older solar inverter units.
They tend to have very high minimum input voltages. But they can produce rock steady sine waves, grid isolated and lots of power.
Designed for long term use.

can you  provide a link or a name of those inverters ? are you talking about battery-inverters ?


Title: Re: Off gird battery voltage
Post by: heatherhopper on August 14, 2015, 12:06:48 PM
24v system for coming up five years. Choice was dictated by budget (2x24v Inverters and 680ah bank were cheaper than 48v at the time) and original Turbine choice which was also a budget choice and intended as a stop gap. Given a larger budget 48v would have been the preference and when an upgrade is necessary (expect this to be when the batteries and/or inverters need replacing) this would still be the intention although it depends entirely on what is available at the time. All the reputable manufacturers have 48v inverters to choose from currently and there are plenty of s/h options but 24v is less well covered.
24v has been entirely adequate as things have turned out and there is a small bonus with the 180a charging capacity of the two inverters. A bigger bank would always be useful - at least 1000ah to reduce diesel use but this is very low anyway. All AC coupled makes a big difference of course. We now operate pretty much as a "normal" household although still weather dependent. This means all the white goods including tumble dryer and electric cooking as conditions dictate (these have been acquired retrospectively to take advantage of the excess power when available - which is 50%+ of the time).


Title: Re: Off gird battery voltage
Post by: biff on August 14, 2015, 01:07:36 PM
I don,t want to sound like I am blowing my trumpet here,
                                                   And I know that a lot of happy 48v off-gridders would scorn the 120v installations but you do get a real leg up with the higher 120v systems.
 There are the UPSs to match them and the heavy iron core low frequency inverters available as also.
 
(http://s15.postimg.org/8t2y6qs0n/DSCF0122.jpg) (http://postimg.org/image/8t2y6qs0n/). I regard this baby as the best thing going in inverters. This is built to not break down. It is designed to sort out its own problems and if something like lightening decides to knock it out, it will switch over to another brain and keep working. It will tell you exactly where the problem lies and when lightening did strike some years back and blew it,s brain, it was able to restart again with the Chinese inverter providing the boost. They are normally good cold starters, once it got up and running I could remove the boost and then it set about telling me what happened and what module I needed to leave it 100% again. The Brain Module cost £100.00 to replace s/h and took less than 2 minutes to do so while all the time the machine kept working. I kept it running so that it could tell me exactly what was going on.
  I grouse against the present day inverter builders simply because they are aware that the technology to design and built good machines already exists but they will not do so because they make more money out of all your misfortunes and every so many years you have to update, they add on all these totally unnecessary bells and whistles that set the model apart from the last one. They are money spinnners while your systems are lying crocked. To design a system based on modules would cut out the installers and the Buy 3 get one free lark ,join our club.
  It is a bit like bringing religion into politcs, it will impede advances in the long term.
   Off=gridders should only need to take a few minutes and replace a faulty module, then they can shop about at their leasure and find the replacement instead of getting clobbered for a ransom. Sure these inverters are guaranteed but you are paying dear for it and it don,t last forever. These companied would be better to take a leaf out of APC,s Symmetra rm and build better to last longer.
                                                                   Biff


Title: Re: Off gird battery voltage
Post by: nominous on August 14, 2015, 02:00:16 PM
can you  provide a link or a name of those inverters ? are you talking about battery-inverters ?

no. I'm talking about solar inverters. Or wind. The SMA stuff actually, but I suppose anything.
Unless I'm missing the key to the puzzle, they would be just as happy converting 300Vdc into 230Vac as they would from a solar panel.
But they wont do anything to manage your battery bank. You'll be doing that with something else.

The new old stock stuff which is not G83 and sells for buttons on ebay. Still worthy for off grid.
Cheap enough to have a spare or two lying around.


Title: Re: Off gird battery voltage
Post by: jonesy on August 14, 2015, 02:24:51 PM
no. I'm talking about solar inverters. Or wind. The SMA stuff actually, but I suppose anything.
Unless I'm missing the key to the puzzle, they would be just as happy converting 300Vdc into 230Vac as they would from a solar panel.
If I understand you correctly, then you are missing the key.
A solar inverter/grid tie inverter GTI will not work with a battery.  Well, it will, but you will kill the battery.  The GTI will take the power out of the battery to the limit of the GTI. So if you have a 1kva GTI, it will take 1kva out of the battery until the battery is completely flat. It's technically possible to manage the (newer) GTI, like the sunny island does, using frequency control, but that would be a interesting personal project.
The 2nd problem is that the GTI won't island, unless you know how to over-ride the built in anti islanding.  Some of the non-G83 may island, but IIRC the non-G83 was because there were not 2 means of anti-islanding, so you had to install a 2nd one to meet G83.
I do agree with you that theoretically they would make a nice inverter.


Title: Re: Off gird battery voltage
Post by: biff on August 14, 2015, 03:33:59 PM
Then of course,
                 If you are just talking about solar powered inverters, you can work without a controller and just a voltage relay to dump the excess,letting the battery itself provide the resistance. This would entail a bit of trial and error but a 330watt array dumping straight into a 850ah x 24v forklift pack during the height of summer would need a slight little top up every 14 days if you had no divert to dump and no load. You could hard wire any inverter you like to the pack with a sensible inline fuse. I used to think that putting the fuse next to the battery pole (which was originally advised) was a good idea but then common sense dictated that it be as far away as possible from the bubbling gas.
  A rated 330watt array can provide a steady 450 watt+ at noon, just think of the extra profit that the energy supply guys were making before the advent of immerSun.
 The whole renewable energy idea boils down to a question of balance. Balancing what you need, with what you can get by with,and what you can afford to supply.
  As time goes on, betters idea will surface as they already have and we would be sensible to adopt them and make the best of them.
                                                                     Biff
                                                   


Title: Re: Off gird battery voltage
Post by: nominous on August 14, 2015, 04:43:46 PM
A solar inverter/grid tie inverter GTI will not work with a battery.  Well, it will, but you will kill the battery.  The GTI will take the power out of the battery to the limit of the GTI.
Assuming you are islanded, then will it only take out of the battery to satisfy the demand of the devices connected to the island ?
Because it cannot supply more than is demanded upon it. But in a grid tie situation the grid is "demanding" whatever the inverter can manage to output.
Else where does the excess power go ?
Same operation as a non-grid tie inverter.

Quote
The 2nd problem is that the GTI won't island, unless you know how to over-ride the built in anti islanding.
I may suck here again from poor terminology, but reading the manual for the older transformer sunnyboys, you can set them up to operate without syncing to a grid.
Apparently.

Quote
I do agree with you that theoretically they would make a nice inverter.
OK, so I'm not totally off the right track :)


Title: Re: Off gird battery voltage
Post by: biff on August 14, 2015, 04:52:59 PM
               "Same operation as a non grid tied inverter" ;D
             Errrrrr Not quite,
                        If only it were that simple,
                                Could be big bang, lots of black smoke,,great variations of explainations and big hole in pocket.
                                                                           Biff


Title: Re: Off gird battery voltage
Post by: skyewright on August 14, 2015, 06:00:06 PM
Assuming you are islanded, then will it only take out of the battery to satisfy the demand of the devices connected to the island ?
What's missing with a GTI is (among other things) something to handle putting charge into the battery. That's why things like the SMA Sunny Island & Victron MultiPlus/Quattro are described as Inverter/Chargers, i.e. they are dual role.



Title: Re: Off gird battery voltage
Post by: Tiff on August 14, 2015, 06:51:41 PM
Assuming you are islanded, then will it only take out of the battery to satisfy the demand of the devices connected to the island ?
What's missing with a GTI is (among other things) something to handle putting charge into the battery. That's why things like the SMA Sunny Island & Victron MultiPlus/Quattro are described as Inverter/Chargers, i.e. they are dual role.



You can always charge from seperate charger or solar charge controller.


Title: Re: Off gird battery voltage
Post by: skyewright on August 14, 2015, 07:00:20 PM
You can always charge from seperate charger or solar charge controller.
Indeed, and using a separate charger/controller brings us back to the (currently) more 'normal' 12V/24V/48V battery choices, which nominous felt a GTI might get away from because if its high DC voltage spec (unless I'm misunderstanding).


Title: Re: Off gird battery voltage
Post by: woodi on August 17, 2015, 11:01:40 PM
We are 24v here, with 1000ah, and a couple of Victron Multi 3000 inverters in parallel. We've an Aurora 3600 GTI ac coupled to the output of the multis. It needs 50v to wake it up, but works great with the Multis. 4kw solar and 3kw wind runs our place with a 'normal' set of appliances, and we've just moved over to a series of storage and immersion dumps to reduce our woodfuel consumption. We'd probably go with 48v if doing it again, but the setup we have just crept up on us. I sold a couple of Sunnyboy GTI's to pay for some of this kit as I was worried about the whole AC coupling idea, but it has turned out well with the Aurora to manage the wind generation.


Title: Re: Off gird battery voltage
Post by: jonesy on August 18, 2015, 09:38:58 AM
A bit more info, nominous
http://www.anotherpower.com/board/index.php/topic,1044.msg10320.html#msg10320 (http://www.anotherpower.com/board/index.php/topic,1044.msg10320.html#msg10320)
TBH you need to read the entire thread to understand the post I've linked to. What the guy has done is take a 6kW bidirectional charger/inverter and add a (large) choke.  The choke allows his GTIs to connect to the inverter without blowing it up, and then the inverter will charge the batteries.  However, if the batteries don't take enough load, or load isnt taken on the AC side, the GTIs trip out on over voltage.
The rest of the link describes a second mod he did to replace the enormous transformers they came with, which gave a high quiescent power of around 150W.  After making a large toroid replacement he got the quiescent down to around 30W, which rivals the big brand devices for a fraction of the cost, if you have the time and patience. If you aren't worried about the quiescent, then the same trick of adding a choke might even work on any transformer based inverter/charger.
GTIs are just 'all or nothing' inverters.


Title: Re: Off gird battery voltage
Post by: biff on August 18, 2015, 09:58:46 AM
                          "GTI are all or nothing inverter"
       That is a pretty good description of a GTI Jonsey,  :crossed
                                                  Biff


Title: Re: Off gird battery voltage
Post by: camillitech on August 18, 2015, 09:16:13 PM
The choke allows his GTIs to connect to the inverter without blowing it up, and then the inverter will charge the batteries. 

I tried reading the whole thread Jonesy but it was way over my head. Unless I'm missing something, I have been doing this for years without a choke and charging my batteries. Trace 4548e, SMA Windy Boy 1200, Powerspout hydro turbine. You can do it with any Bi directional inverter with a transformer so long as you do not exceed the charging capacity of the inverter. Of course you need some form of 'diversion load control' but in my book that's essential with any kind of turbine and preferable to 'throttling' solar anyway.

https://lifeattheendoftheroad.wordpress.com/2012/05/15/commissioning-the-powerspout/

My new system is a mixture of both AC and DC coupled sources, the AC side of things being handled by 'cheap as chips' GTI's. One of the advantages being that you can upgrade to a higher battery voltage without affecting anything coupled via the AC side. Of course it's got disadvantages too, but Woodi, Heather Hopper and I have got grid tied wind turbines 'for buttons' and successfully integrated them into 'off grid' systems.

Cheers, Paul



Title: Re: Off gird battery voltage
Post by: biff on August 18, 2015, 10:45:30 PM
So lets say,
            You had 3.8kw of pv going into your bank,and you happen to have some spare PV left over, enough Panels to produce 210volts @ 970watt.
 and you have a grid tied inverter as well. It is a 2.5kw jobbie with a voltage range of 195v to 500volts.
  The specs say that the Inverter is Bi-directional,
  So I just wire the inverter into the house, wire the PV into the inverter and sit back and enjoy life,?
  The extra power that is not going to be consumed goes back to the bank and goes out again into the dc immersion dumps,? or I can add another controller2kw to the bank to take care of the excess.
  Could that possibly work,?
                               Biff


Title: Re: Off gird battery voltage
Post by: billi on August 19, 2015, 12:11:24 AM
can you  provide a link or a name of those inverters ? are you talking about battery-inverters ?

no. I'm talking about solar inverters. Or wind. The SMA stuff actually, but I suppose anything.
Unless I'm missing the key to the puzzle, they would be just as happy converting 300Vdc into 230Vac as they would from a solar panel.
But they wont do anything to manage your battery bank. You'll be doing that with something else.

The new old stock stuff which is not G83 and sells for buttons on ebay. Still worthy for off grid.
Cheap enough to have a spare or two lying around.

a link would help ,    a quality  5000  watt MPPT charge  controler is under £500     a  decent offgrid inverter including a  pv chargecontroller is only similar money  ....





Title: Re: Off gird battery voltage
Post by: camillitech on August 19, 2015, 06:16:25 AM
So lets say,
            You had 3.8kw of pv going into your bank,and you happen to have some spare PV left over, enough Panels to produce 210volts @ 970watt.
 and you have a grid tied inverter as well. It is a 2.5kw jobbie with a voltage range of 195v to 500volts.
  The specs say that the Inverter is Bi-directional,
  So I just wire the inverter into the house, wire the PV into the inverter and sit back and enjoy life,?
  The extra power that is not going to be consumed goes back to the bank and goes out again into the dc immersion dumps,? or I can add another controller2kw to the bank to take care of the excess.
  Could that possibly work,?
                               Biff
Aye Biff,

and this is exactly when AC coupling starts becoming useful, when you've run out of roof space and  want to put panels a long way from your battery bank.

You will need a total diversion capacity of around 5kW and an 'off grid' inverter with enough charging capacity to cover the 970 Watt of PV, so at least 20 Amps @ 48V or 40 @ 24V. You can have as many controllers as you like, I have 4 and you can either set them all at the same voltage or at slightly different voltages to bring immersions on sequentially. I've done both and it works well.

Cheers, Paul


Title: Re: Off gird battery voltage
Post by: billi on August 19, 2015, 08:31:48 AM
.... one can run  quite long distances  between PV  and battery with an Mppt chargecontroler  ..... a 500 meter roll  6mm2 solarcable is about £200

-as an example- that would cover about 6000 watt of PV  50 meters away from the battery and charge controllers  @ 120 volt (PV)


Title: Re: Off gird battery voltage
Post by: biff on August 19, 2015, 10:10:37 AM
This is interesting,
                I know it has been pitched into the forum before but I shied away from it because of my very high dc voltage,( for exactly the wrong reason.)
   Our system sits @ 139volts most days that have a bit of sunlight and it is easily understood at present. Just 4 strings of 120volts and a wind turbine that can deliver a nice 1kw easily in moderate wind.
 At the moment the solar and the wind turbine compliment each other. The wind turbine takes it easy while the sun shines and the breeze is under force 4 but once the sky gets overcast and the pv drops off the W/T is back on the job again,holding the voltage up until the sun comes out again, This means that most of the PV goes into out tanks.
  Yesterday was a cracker of a day, The rads and our new stove was quite warm to touch and for a while around 6ish is was a bit uncomfortable but well within the systems safety limits, the second C/H pump did not start up.
  I would love to give the grid tie a try and learn how to manage it but we just do not have the power use to justify any further additional pv, bearing in mind that I have plans for building a duel pmg wind turbine over the winter months, This should deliver at least 2kw because of the bigger blades. (I,m hoping)
 Just this week, I stripped out our old 12v x 800ah standby system. The batts can be put to a better use and the pv will go on to be part of a larger array. Our generator only fires up for checking over and maybe do a couple of washing machine washes every 4 months, so diesel lasts a long time, since the digger was sold.
  There is no getting away from it, Grid-tied ac coupling is the way to go if you have the use for it and more have than one dwelling to power. Here at Chez-Biff ,there is just She and I and the hounds,Even Der Shed is now plumbed into our grid and its own 48v system made redundant.
What we have got is tailor made for us, but you never know. I always look to improve and update.
                                                         Biff


Title: Re: Off gird battery voltage
Post by: camillitech on August 19, 2015, 12:46:31 PM
.... one can run  quite long distances  between PV  and battery with an Mppt chargecontroler  ..... a 500 meter roll  6mm2 solarcable is about £200

-as an example- that would cover about 6000 watt of PV  50 meters away from the battery and charge controllers  @ 120 volt (PV)

This is very true but if you already have an outbuilding several hundred meters away that's  connected to your AC bus then you do not need any cable, just a GTI. For example, I power up a broadband mast that is 1260M away from my battery bank and it gets full sun all year. The mast uses about 85W, now if I could be bothered to carry a 250W panel up there with a micro inverter on the back then it would feed the transmitter when power was available from the panel. The beauty is that the excess would then contribute to my house loads any any excess would end up in the battery bank. The only limit being the size of the AC cable that supplies the mast and the size of your 'off grid' inverters charger. Sure, one day I may well do the very thing, the point is that it's 'horses for courses' if your panels and battery bank are nearby then it doesn't make a lot of sense. It probably does not make much sense if you've got a ground mount 100m away. However, if your 'ground mount' happens to be a shed that already has power then it's well worth considering.

(https://lifeattheendoftheroad.files.wordpress.com/2014/10/020_thumb.jpg?w=716&h=479)

Half of this array is AC coupled and half 'straight to battery', the cable for 'straight to battery' cost far more than the GTI did. Of course I could have used an MPPT controller but it still would have cost more as the shed already had power. I've simply 'maxed out' the AC coupling capacity of my 'off grid' inverter now so everything else has to be DC. However, there's nowt wrong with that, it's far simpler. And anyway, I do like playing around with this stuff  8)

Cheers, Paul


Title: Re: Off gird battery voltage
Post by: biff on August 19, 2015, 01:29:16 PM
I like the idea of a grid-tied inverter in the Shed and the 210v array down in that area.
                                                   However, can you switch them on and off,if i felt that the system was needlessly generating power and just simmering the batteries.? As you know, i have 2 ton of forklift batts and I know that all this water heating, hastens the need to top up the batts more regularly.
  It would be extra handy if I could just go out and switch off the grid tied inverter and let the 210 volts go off into cyberspace. Or find a way to cover the panels.
 The grid tie inverter that I have in mind is a 2.5kw one with a massive heat sink and is really heavy to lift,never mind carry. The only thing that stops me from going near it is the amount of small connections for all the bells and whistles.It looks like there is a load of faffing about with a laptop and routers..a very weak point in my way of life. Up until now, I could always get things to fit properly with my lump hammer and chisel  ;D or is it was really complicated ,I could reach for the saw.
  Joking apart, it is indeed a very clever way forward.
                                      Biff


Title: Re: Off gird battery voltage
Post by: skyewright on August 19, 2015, 04:47:51 PM
.... one can run  quite long distances  between PV  and battery with an Mppt chargecontroler  ..... a 500 meter roll  6mm2 solarcable is about £200

-as an example- that would cover about 6000 watt of PV  50 meters away from the battery and charge controllers  @ 120 volt (PV)
So how would that be wired up? 6000W is about 24 panels? The 500m roll & 50m distance means you've up to 10 lengths of cable? How does the juice route from the panels to the MPPT?


Title: Re: Off gird battery voltage
Post by: billi on August 19, 2015, 05:37:41 PM
3- 4 panels in series      and then run those several strings   to a busbar  next to the Mppt controller

there are Mppt controllers upto 600 Voc on the  market


Title: Re: Off gird battery voltage
Post by: skyewright on August 19, 2015, 06:53:08 PM
3- 4 panels in series      and then run those several strings   to a busbar  next to the Mppt controller
there are Mppt controllers upto 600 Voc on the  market
Thank you.
If I go for some off-grid PV my max run would be ~ 25m. At battery voltages (even 48V) that seemed to suffer a lot of losses, but higher voltages to an MPPT doesn't sound so bad...


Title: Re: Off gird battery voltage
Post by: billi on August 19, 2015, 07:27:03 PM
My panels are ca  25 m away from my 24 v batt ....I  paired 2 panes  to 66 volt mpp   , but fortunately  I had thick cables left from  a wind turbine   .....   
 General I think ac- coupling  is for sure an option , but one should not forget the fact that one would need then an inverter/charger unit  and those can be  pricy .....


Title: Re: Off gird battery voltage
Post by: jonesy on August 20, 2015, 02:06:49 PM
The choke allows his GTIs to connect to the inverter without blowing it up, and then the inverter will charge the batteries. 
I tried reading the whole thread Jonesy but it was way over my head. Unless I'm missing something, I have been doing this for years without a choke and charging my batteries.
You're not missing anything.  Some inverters will take a GTI and some won't. The powerjack one wouldn't, but with a bit of tinkering, the guy realised a simple choke made all the difference. In one post he says he didn't destroy the inverter, but the MCB tripped.  That would give me the confidence to try with my UPS. 
Do remember folks that the prospective short circuit current from any inverter is very low, so use type B MCB (most common in UK) and start with say 3A when 'testing' a GTI connection.


Title: Re: Off gird battery voltage
Post by: camillitech on August 20, 2015, 09:05:28 PM
 That would give me the confidence to try with my UPS. 

Now I'm sure we'd all be interested in how that goes Jonesy, apart from the awful efficiencies of most UPS's, that's been the one thing that's put me off using them. The high idle current of some models and the poor chargers I could live with, the inability to 'AC couple' I couldn't. If there's one thing cheaper than secondhand GTI's it's barely used and high quality UPS systems.

Keep us posted and good luck, Paul


Title: Re: Off gird battery voltage
Post by: nominous on September 16, 2015, 03:36:30 PM
Indeed, and using a separate charger/controller brings us back to the (currently) more 'normal' 12V/24V/48V battery choices, which nominous felt a GTI might get away from because if its high DC voltage spec (unless I'm misunderstanding).

No, I may have been being more basic ie: thick.

I was thinking bigger bank of batteries, smaller cables, lower losses, with the panels tired to the batteries from the DC side.
The GTI tied to the batteries as an inverter. I suppose how it used to work before AC coupling.

What I don't understand (100%) is how the GTI just draws all the power it wants to.
With that thought now placed in my mind, I assume that if there is a grid connection but it were some how restricted, the transformer would just heat up, lots.
ie: the GTI operates effectively as a short, and the grid allows the transformer to dump the power that would other wise build up as heat.
The power converted has to go somewhere, either to an electric load, else heat. Which would explain the max power conversion if it were connected to batteries.


Anyway, the talk about idle loads from inverters suggests DC loads would be better where ever possible.
Sooo..... what loads do you need to run which cannot be transferred to DC equivalents?


Title: Re: Off gird battery voltage
Post by: rogeriko on September 16, 2015, 09:49:39 PM
Skyewright said

If I go for some off-grid PV my max run would be ~ 25m. At battery voltages (even 48V) that seemed to suffer a lot of losses, but higher voltages to an MPPT doesn't sound so bad...


When you are direct charging batteries from solar panels forget about the cable losses because the panels will just produce higher voltage to cover the loss. For example a 28 volt panel producing 5 amps into a 24 volt battery will produce 24x5= 120w if there is a 2v loss in the cable the panel will produce 2 extra volts to overcome the losses ie 26x5=130w. If you measure the volts at the panel end it is 26 and at the battery end its 24, but you still get your 5 amps. Its very important to match the panels to the batteries, for 48v system you needat least 60v panels add a couple of volts for cable losses and you need 65v. There are lots of 33v panels out there just put 2 in series and parallel as many pairs as you want.


Title: Re: Off gird battery voltage
Post by: skyewright on September 17, 2015, 10:06:15 AM
When you are direct charging batteries from solar panels forget about the cable losses because the panels will just produce higher voltage to cover the loss. For example a 28 volt panel producing 5 amps into a 24 volt battery will produce 24x5= 120w if there is a 2v loss in the cable the panel will produce 2 extra volts to overcome the losses ie 26x5=130w. If you measure the volts at the panel end it is 26 and at the battery end its 24, but you still get your 5 amps. Its very important to match the panels to the batteries, for 48v system you needat least 60v panels add a couple of volts for cable losses and you need 65v. There are lots of 33v panels out there just put 2 in series and parallel as many pairs as you want.
The idea of saving the cost & complexity of a controller or 2 is very attractive. Pity the very well priced panels I've been looking at (& which I think would need to be in series pairs for an MX60/80 or Victron Blue Solar 150/70 or 150/85 anyway) are only 30Vmpp...

On a quick search the only 33V I found were some Norwegian Crystal at much higher cost. Anything else I should be putting into the search engine?


Title: Re: Off gird battery voltage
Post by: rogeriko on September 17, 2015, 10:10:10 PM
30v panels are perfect. The VOC will be much higher. You only need full power when the batteries are below 60v, when they reach 60v they are fully charged and you need less amps anyway. In actual fact 28v panels would be fine too because after 56v the amps will taper off and trickle charge the batteries. PV panels are constant current devices even if you short them out you only get the amps they are designed for.  MPPT controllers are expensive and completely unnecessary (exept for 12v systems because 12v panels dont exist) MPPT controller or 4 more panels, easy choice..


Title: Re: Off gird battery voltage
Post by: billi on September 18, 2015, 04:42:18 AM
aaaaahm,  a say 60 amp  standard chargecontroler like a morningstar tristar   is about 200 pounds cheaper than a  mppt controller of that size like an wellestablished  outback fm 60 /or midnite classic , so after cable reduction costs  , we talk about  approx/estimated depending on distance   100 pounds  difference , and surely a granted  improvement of performance ...especially  on not so sunny days

and  ad another 100 pounds to that standart pwm controller if u want a display fitted...


if we are talking about high ampere controllers here , the price difference  between standard pwm controllers and more efficient  mppt controllers , then the mppt one wins   ....

and the selection of available panels then is huge ...

billi



Title: Re: Off gird battery voltage
Post by: skyewright on September 18, 2015, 09:50:46 AM
aaaaahm,  a say 60 amp  standard chargecontroler like a morningstar tristar   is about 200 pounds cheaper than a  mppt controller of that size like an wellestablished  outback fm 60 /or midnite classic , so after cable reduction costs  , we talk about  approx/estimated depending on distance   100 pounds  difference
Unless I'm missing something, rogeriko  is suggesting no controller at all, so the difference in cost is based on the whole cost of the controller, so around £5-600 per 4-5kWp of panels & no difference in cabling since the panels would need to be in series pairs[1] paralleled at a combiner anyway to be within the spec of the controller?

I could of course be wrong...


[1] sets of 3 in series would also get within 150V, but here at least that wouldn't work well with likely mounting arrangements.


Title: Re: Off gird battery voltage
Post by: billi on September 18, 2015, 10:35:22 AM
yep , i know , but  i cannot recommend  an offgrid system without a charge controller ....   batteries need proper care

i accept  the fact that one can  attach  some  non regulated power sources to a battery bank to a limited extend   , but certainly not,  as a general rule,  to work with out any charge control

there are so many aspects to consider  and  i am  pretty sure , there is a reason why my battery is  already  12 years old ..., and she wouldnot  be a live today , without a charge-controller

the midnite classic lite 200  as an example , can manage 5 panels in series or about 160 volt mpp and 4000 watt of panels  for  430 pounds ... 

there are surely  ways to reduce costs , and we all love that hunting for the best value for dollars , but  we have to  consider that  over a long period , its not just a pizza we eat in 10 min and shlte out after an hour

billi




Title: Re: Off gird battery voltage
Post by: camillitech on September 18, 2015, 10:51:53 AM
but  we have to  consider that  over a long period , its not just a pizza we eat in 10 min and shlte out after an hour

billi




 :hysteria  :hysteria What about using the Inverter to switch on AC loads as charge control ? Not as sophisticated but could be an option ?


Title: Re: Off gird battery voltage
Post by: biff on September 18, 2015, 11:59:39 AM
I have run experiments (still at it)
                        On solar PV charging straight into forklift packs without controllers. I have also tried it with sealed lead acid batts, (NOT ADVISABLE,!!) with the sealed plated removed but the rubber tops still on. So a 100ah x 48pack taking a charge from a 165watt x 72v panel will pop the rubber tops off the cells in quick succession after a period of about 10 minutes. So obviously the voltage is a bit too high, however,i can reroute through the controller and keep a steady 56v going non stop,
   I can boost the forklifts the same way, letting them climb steady but they can resist the charge better,still if left unattended they will gently simmer and the battery fluid will evapourate in summer in less than 3 weeks if no load is applied, The array is only two 165watt panels vmp36 with Y connectors for the 24 volt forklift pack and plugged in series for the 48v pack.
  I know that If I ran the systems with a more suitable panel voltage, say 30volts,the battery fluid would not evapourate as quickly. So I have come to the conclusion that for peace of mind, the controller such as a xantrex c40 would be well worth the extra 100euros.
                                                           Biff


Title: Re: Off gird battery voltage
Post by: rogeriko on September 18, 2015, 09:23:03 PM
Of course you should use a pwm controller, plenty of 48v 60A controllers around for 40 pounds thats 1/10th the price of a mppt. My original comments were that you dont need really heavy duty cable. As long as the cable is rated for the current a few volts lost along the way will be taken up by the panels.


Title: Re: Off gird battery voltage
Post by: billi on September 19, 2015, 11:52:13 AM
hi roger

time flies   ..... i get a 60 a  mppt controller capable 150 volt input  for close nothing  today


 just as a present with an 4000 watt  pure sinewave off grid inverter .....