Design stage of 6kwh Off grid home -Inverter input?

[Kapowzers]

Hello all,

I am in the process of building an home that by necessity will be fully off grid with no chance of grid tie in the future. Our daily winter usage will be 6kwh, array size will be 6KW to help with the poor winter potential at location. (Vernon, BC).
I am trying to choose what inverter to run and have the following in mind, 48v Diy Lifepo4 battery system, generator support. Schneider XW+ 6848 or stacked SW4048s seem like a good option but mainly looking for some experienced insight as there seems to be endless options and configurations out there. Thanks! I have enjoyed the wealth of knowledge this forum has to offer.

 

[Shinebox]

Both Schneider and SMA Sunny islands are good solid options. A lot of people are also using SolArk. If it were me, I would go with SMA SI with midnite charge controllers.

 

[Kapowzers]

I think I may end up with the Outback Radian GS8048a, great generator support, a low frequency transformer style will suit our offgrid needs better, plus having a few spare parts for it will be nice too.

 

[Bvillebob]

If you haven't, you might want to check out the Youtube videos by Curtis Stone "The Urban Farmer", he's building an off grid house in your area. His system is enormous, but it might give you some real world numbers for winter output and such since it's been operating all winter. Getting power in the winter is the challenge, with the low sun angle and short days, at least you don't have the permanent clouds that the coast has.

 

[Kapowzers]

Bvillebob, thanks for that referral, we are indeed very close to each other and will have to watch more of his stuff. Wow that's a huge system he put in, 20kw array, 2000AH storage & big generator. We will have more modest needs and I am prepared to run the (small) generator to help get through days of darkness. I'm hoping 5 of the EG4/Gyll batteries will be enough, if not I can always buy more.

 

[neuropa3]

I need Help in understanding something. I am in the process of building a off grid system I have purchased 24 250watt panel. I have 2 48 volt 100 ahh Lifepo4 server batteries from signature solar. A GroWatt 5000 es. Now what I don't understand is the PV input max on the MPPT on the growatt is 22 amps. So I guess the question is the max is 22 amp per panel or string or whole system cause that makes no sense to me. Thanks

 

[MichaelK]

22A would be the COMBINED amperages of all the strings added together. Normally, you have several solar strings, which in your case can go as high as ~270VDC. Each parallel string of panels comes into a combiner box controlled by a breaker, then the combined strings, totaling no more then 22A is fed into the inverter.

 

[neuropa3]

22A would be the COMBINED amperages of all the strings added together. Normally, you have several solar strings, which in your case can go as high as ~270VDC. Each parallel string of panels comes into a combiner box controlled by a breaker, then the combined strings, totaling no more then 22A is fed into the inverter.

so here is the specs on the panel 250 W, IMP 8.3A and 37.2 VOC. I actually have 27 of them but at this time I planned on a 24 panel array. I am trying to figure out how to do the strings I first though a 4S6P but that is way to much. So then I though of a 8S3P that may be too much. Any Ideas would be greatly appreciated.

 

[neuropa3]

so here is the specs on the panel 250 W, IMP 8.3A and 37.2 VOC. I actually have 27 of them but at this time I planned on a 24 panel array. I am trying to figure out how to do the strings I first though a 4S6P but that is way to much. So then I though of a 8S3P that may be too much. Any Ideas would be greatly appreciated.

Update I got my 5000es and it says 18 amp not 22 amp so did signature solar sell me an older model?

 

[MichaelK]

so here is the specs on the panel 250 W, IMP 8.3A and 37.2 VOC. I actually have 27 of them but at this time I planned on a 24 panel array. I am trying to figure out how to do the strings I first though a 4S6P but that is way to much. So then I though of a 8S3P that may be too much. Any Ideas would be greatly appreciated.

What are your winter lows like? Your drop-dead voltage limit is 450V (please reconfirm that number), which can not be exceeded. The problem is that your Voc reading of 37.2V is at room temperature (25C), and it is very well documented how voltage goes up as the temperature goes down. At freezing, your "can not exceed" Voc is going to be ~400V, and at a frigid -40, ~360V. Use Midnight's string calculator to determine the exact value for your particular panel.

So, just to make the math easy, let's take the 360V value. If you wired nine panels in series, you would get a Voc of ~ 335V, which is ~25V less than the 360V limit. I believe the conversion factor for -40C is 1.25X, so the array putting out 335Voc at room temp will put out ~419Voc at -40C.

If you wired eight panels in series, you would get a Voc of ~ 298V, which is ~62V less than the 360V limit. I believe the conversion factor for -40C is 1.25X, so the array putting out 298Voc at room temp will put out ~373Voc at -40C.

So, I think a string of eight is going to be safe for your machine. The question for you though is do you think that 298V is safe for you? To me, that's quite a scary voltage, and I would be extremely cautious wiring something like that together.

The second issue though is your amperage. With each string putting out 8.3A, three in parallel would be ~25A. That exceeds your controller limit by a significant margin. One option that could work for you is to face each string in a different direction, say SE for string 1, S for string 2, and SW for string 3. So, in the morning, while string 1 is at full output, string three is angled 90degrees away from the sun, and it's output will be very low.

BTW, with three strings, it's a code requirement to have each string either fused or breakered. Personally, I prefer breakers, so I would recommend getting a combiner box, with 12A breakers. I myself use Midnight's 6 breaker model

 

[neuropa3]

Thank you this system is going at 6200 feet above sea level in Wyoming avg winter temp is about -1.5 C. What I don’t understand is the growatt 5000es is rated at 6000 watt array so why is rated amps only 18 does not make sense there is no way to get 6000 watts and only 18 amps.

 

[MichaelK]

Thank you this system is going at 6200 feet above sea level in Wyoming avg winter temp is about -1.5 C. What I don’t understand is the growatt 5000es is rated at 6000 watt array so why is rated amps only 18 does not make sense there is no way to get 6000 watts and only 18 amps.

Sure, just do the math. 6000W/18A = 333V. Imagine two stings of panels putting out 9A each at 333V. 18A X 333.3V =6000W. A 72-cell panel in the 350W range would be a good candidate for that. Nine in series would be around 333V. Since your unit can handle voltages as high as 450Voc, it's possible, though as I mentioned above, not necessarily the best idea.

Now, about being in Wyoming, you'd better use the 1.25X conversion factor for winter lows. Better, use Midnight's string tool to get an accurate prediction. Do NOT use your average winter low. Use the 20-50 year recorded low.

MidNite Solar - Classic Sizing Tool.

MidNite Solar is the industry leader and manufacture of quality Renewable Energy System electrical components and E-Panels.

www.midnitesolar.com

If you want to stick to the 6S4P configuration you mentioned above, four 8A strings would overload your controller with too many amps. But, using the same strategy I mentioned above, you could orient 1 string SE, 2 strings S, and 1 string SW. BTW, I love touting my rotating array frame design. I show it to people every chance I get. If you build four of these frames, each can hold as many as six panels. By rotating your arrays East and West, you'll guarranty you'll never surpass 18A.

 

[neuropa3]

Thanks for all your help. Growatt has a string calc as well only problem with it is does not list the SPF 5000 ES(US). Prob will just buy a second one. Once again thanks for your help.

 

[LazyDragon]

Bvillebob, thanks for that referral, we are indeed very close to each other and will have to watch more of his stuff. Wow that's a huge system he put in, 20kw array, 2000AH storage & big generator. We will have more modest needs and I am prepared to run the (small) generator to help get through days of darkness. I'm hoping 5 of the EG4/Gyll batteries will be enough, if not I can always buy more.

Do you already have a generator picked out? For a small, quite inverter generator, check out the westinghouse iGen4500DF. It runs nice and quiet on propane. Most importantly, it has electric start WITH an electric choke. True push-button remote start. You can start the gen without going outside. It has a remote control, but the range on it is limited. I used a Switchbot Bot to manually push the start button. https://www.switch-bot.com/products/switchbot-bot
The gen also lends itself to some light-weight heat recovery. The engine exhaust is separate from the heat venting, so I piped the engine heat into my battery compartment to give them a bit of heat during the cold weather.
My place is also roughly 6kwh/day. This past winter, I typically ran the gen for 50 minutes about 3 times per day. I would run the gen during times of other higher usage, such as the dishwasher/shower/etc. Its more efficient to use the gen power directly than store it.
The gen says 4500w, but that's on gas. It's 3300 on propane, and I ran it at 2000w which was the max for my battery charger.

 

[12VoltInstalls]

One option that could work for you is to face each string in a different direction, say SE for string 1, S for string 2, and SW for string 3. So, in the morning, while string 1 is at full output, string three is angled 90degrees away from the sun, and it's output will be very low.

I love that approach after I tried it and it was better than expected.

In cold sunny snowy reflective winter, though, you can get pretty high volts and amps beyond what the calculations would tell you. I’m not sure I’d depend on the directional panels to keep things playing well (my two 400W strings achieved 94.x volts and well over 11A in January. Not a problem for my setup, but taking the principle- if you get ridiculous output like I have you could have unwanted results)

I might feed the growatt a safe configuration and put the rest of the panels through an Epever mppt that can handle the amps but with a 150- or 250V open circuit limit. Redundancies never hurt anyway imho.