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Author Topic: Off gird battery voltage  (Read 7483 times)
biff
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« Reply #30 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
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camillitech
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« Reply #31 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.



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  Cool

Cheers, Paul
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http://lifeattheendoftheroad.wordpress.com/

'Off grid' since 1985,  Proven 2.5kW, Proven 6kW direct heating, SI6.OH, 800ah Rolls, 4.75kW PV ,4xTS45, Lister HR2 12kW, , Powerspout pelton, Stream Engine turgo, 60 x Navitron toobs and a 1500lt store. Outback VFX3048 and 950ah forklifts for backup,
biff
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« Reply #32 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  Grin or is it was really complicated ,I could reach for the saw.
  Joking apart, it is indeed a very clever way forward.
                                      Biff
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skyewright
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« Reply #33 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?
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David
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billi
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« Reply #34 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
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« Reply #35 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...
« Last Edit: August 19, 2015, 06:56:13 PM by skyewright » Logged

Regards
David
3.91kWp PV  (17 x Moser Baer 230 and Aurora PVI-3.6-OUTD-S-UK), slope 40, WSW, Lat 57 9' (Isle of Skye)
billi
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« Reply #36 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 .....
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« Reply #37 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.
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camillitech
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« Reply #38 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
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'Off grid' since 1985,  Proven 2.5kW, Proven 6kW direct heating, SI6.OH, 800ah Rolls, 4.75kW PV ,4xTS45, Lister HR2 12kW, , Powerspout pelton, Stream Engine turgo, 60 x Navitron toobs and a 1500lt store. Outback VFX3048 and 950ah forklifts for backup,
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« Reply #39 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?
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rogeriko
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« Reply #40 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.
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skyewright
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« Reply #41 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?
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David
3.91kWp PV  (17 x Moser Baer 230 and Aurora PVI-3.6-OUTD-S-UK), slope 40, WSW, Lat 57 9' (Isle of Skye)
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« Reply #42 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..
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billi
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« Reply #43 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

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skyewright
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« Reply #44 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.
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David
3.91kWp PV  (17 x Moser Baer 230 and Aurora PVI-3.6-OUTD-S-UK), slope 40, WSW, Lat 57 9' (Isle of Skye)
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