Will this off grid system work?

kwill808

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Oct 4, 2021
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I'm totally new to solar and trying to learn as much as I can about it. My hope is to come up with a system that will be able to power a 2800 sq ft off grid home in Tennessee. The home is in early stages of being built and we are new to the state so I'm very fuzzy on what my power usage is going to be. I know that determining usage is a critical step when planning a system so as things develop I will try to flesh that out. That being said I have also been researching prices on the various components I think I will need for my system and was looking for guidance and advice on what I have come up with thus far just as a sanity check.

Inverter: 2 x LV6548
Panels: 24 x Used Sunpower 435W
Batteries: 6 x EG4 48V 100AH

Cost of these components total $12450 which I know doesn't include everything I would need but I believe covers the big ticket items I would need. That price point seems more than reasonable for the application it would be serving.

Please let me know if this arrangement will not work either in specification or in estimated application of powering such a home. Also, any comments on my take on price point would be appreciated as well. Thanks in advance.
 

mopat

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I think those panels have Voc=85.6 and the LV6548 max PV voltage is 250.

How are you planning to configure these 24 panels; seems like three in series may exceed LV limit?
 

kwill808

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Taking your question into consideration, I took some time to brush up on my understanding and try and plan something out. If I put 3 panels in series that would result in 256.8 Voc, 5.97A and 1305W. I think if I put 3 of of those series in parallel that would result in 256.8 Voc, 17.91A, and 3915W. The LV6548 controller could handle 250V max Voc, 18A max PV input and 4000W max PV array power putting all stats either very close or slightly over their break point. As you stated the problem area would be exceeding the max Voc by 6.8V. Please tell me if any of what I stated is wrong as I'm still learning.

If my understanding is correct, 6.8V seems like a small margin. Would the fact that the used panels are 2 years old possibly drop the panel Voc? I believe I have read that colder temperatures can spike voltage on panels which would obviously be a concern with this configuration being so close to the limit of the controller. Is there anything I could do to regulate voltage prior to input into the controller to account for the margin or any spike behavior?

Thanks for the reply.
 

MisterSandals

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If my understanding is correct, 6.8V seems like a small margin. Would the fact that the used panels are 2 years old possibly drop the panel Voc? I believe I have read that colder temperatures can spike voltage on panels which would obviously be a concern with this configuration being so close to the limit of the controller. Is there anything I could do to regulate voltage prior to input into the controller to account for the margin or any spike behavior?
Max input voltage has proven to be THE specification to not violate. And while 6.8V seems like a little to you, there are quite a few internal components that depend on that limit. And, as it gets colder than 25 deg C, the voltage increases further.

2S is clearly your limit.
12P would require significant paralleling and fusing for the 12 2S strings.

It’s an unfortunate mismatch.
 

kwill808

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Thanks for your response MisterSandals. Would something like this workout?

2 x SUNPOWER® E-Series Commercial | E20-435-COM and 1 x SUNPOWER® E-Series Commercial | E20-327-COM in series in 3P

My understanding is the series would be 236.1 Voc, 5.97A and 1197W. 3 in parallel would be 236.1 Voc, 17.92A and 3591W. Can I put the 327W panel in series with the 435W panel? If so, is my understanding correct on the stats of this array? Would this work with the LV6548? Is the 250V Voc per PV input for the LV6548?

Even if this would work out, I am not sure where I'll be able to find the 327W panels for sale but at the very least hopefully this will be a useful exercise to help me a create a better understanding of how to put together the various components of a solar system.
 

RV10flyer

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Unless you have a gas water heater, gas furnace, gas stove and gas dryer...you’ll need more than that. My 2800 sqft all electric with 16 & 20 seer heat pumps consumes an average of 60 kWh per day. I have a 20000 pv array to install soon. Two solark 12k, 107 kWh battery bank, 10 kw Honeywell propane generator.
 

kwill808

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Wow! 1800kWh per month? In looking up average usage per month by state, Louisiana came in at number 1 with 1273kWh. It's hard to believe that with an efficient home you'd be putting number 1 to shame. That being said, I'm not saying you're wrong because I don't have numbers myself. The specs of that system are definitely way out of my budget and if that is what is required to power my off grid house I will be forced to seek grid power.
 

wattmatters

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My understanding is the series would be 236.1 Voc
How cold is the coldest they will get? A temps fall, the Voc of panels goes up. There is also a temp coefficient rating of -0.35% / °C. The Voc is at STC of 25°C, which means at 0°C (32°F) Voc is increased by 9%. If it get's below freezing then you'll need to account for the potential for an even higher Voc.

236V + 9% = 257V at 0°C.

Unless you can be certain about the minimum temperature never getting that cold, I would hesitate to use such panels with that controller.

Either:
- Lower wattage rated panels with lower Voc would be better suited so you can get more of them in each series string, or
- an inverter/controller with a higher Voc rating
 

Wellbuilt

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Wow you guys use a lot of power there , I have a off grid cabin @ 2800 sf plus garage and use 3200 to 5000 wats a day
I use a out back 3600 watt 48volt inverter charger with4500 watts of solar . I have 10k in my system but I need second charge controller to hook up 3600 more watts of solar .
I have led lites frig freezer tv ,radios well pump 4 ceiling fans i have every thing I need but a washer and dryer
I have gas appliances .
I use 2 to 300watts running and less over nite .
It cold up here so I don’t need ac at all .
It’s really to cool to run the ceiling fans I use them mostly in the winter .
 

RV10flyer

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Lol. We are 100kwh a day in summer
Jan-Feb runs 70-80 kWh per day due to heat pumps, more lighting needed and not drying the clothes on the line. This is why my panels are going to be at 53 deg and I’m at 38 deg Lat. When you have a family, heating water with electric is expensive. I am going to engineer and install my own heat pump water heater and dryer, so that will help.
 
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bushi12

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Sep 19, 2021
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Thanks for your response MisterSandals. Would something like this workout?

2 x SUNPOWER® E-Series Commercial | E20-435-COM and 1 x SUNPOWER® E-Series Commercial | E20-327-COM in series in 3P

My understanding is the series would be 236.1 Voc, 5.97A and 1197W. 3 in parallel would be 236.1 Voc, 17.92A and 3591W. Can I put the 327W panel in series with the 435W panel? If so, is my understanding correct on the stats of this array? Would this work with the LV6548? Is the 250V Voc per PV input for the LV6548?

Even if this would work out, I am not sure where I'll be able to find the 327W panels for sale but at the very least hopefully this will be a useful exercise to help me a create a better understanding of how to put together the various components of a solar system.
Screenshot_20211009-205847_Yahoo Mail.jpg
I had the same question and emailed them. This what the response I got in reference to each input.
 

raurre

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I Have purchase the same equipment that you have. I wonder if there is a practical way to maintain a small load on the panels so they are never under a open circuit circumstance?
 

mopat

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I Have purchase the same equipment that you have. I wonder if there is a practical way to maintain a small load on the panels so they are never under a open circuit circumstance?
Could I suggest to you that you start another thread with your question?
 
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