ptrzn avatar image
ptrzn asked

Off grid sizing advice please

Hello all,

I'm working on an off-grid setup and getting a bit stuck on sizing the PV array and finding the appropriate MPPT. I have roof space for 18 panels, facing South @ 60deg angle, single surface (shading is not an issue) and want to maximize production in the winter, maybe even oversizing the array somewhat to compensate for the lack of sun, if this makes sense.

- MultiPlus-II 48/5000/70-50-GX

- 3x Pylontech US 3000C 72Ah 48V

- SmartSolar MPPT 250/100 Tr VE.Can

- 16x 360W-24V Mono - trying to find the optimal capacity

- backup diesel generator

1. How would it be optimal to wire the panels? The calculator suggests this MPPT in 3 series/6 parallel configuration, but the min. PV voltage @ max temp seems out of the ideal range (84.4V).

2. Would I benefit from using higher capacity solar panels, e.g. 450Wp, in terms of having more reserves during winter? If so, would I need to daisy chain an additional MPPT?


Any advice, suggestions, pointers appreciated.

Thanks in advance, cheers,


MPPT Controllersoffgrid
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1 Answer
seb71 avatar image
seb71 answered ·

In my area, 60-cell PV panels/modules have the best price per Watt.

You could go with two 150/60 Smart Solar chargers, using 3 parallel strings of 3 modules (9 modules) on each. Some redundancy.

Since it's off grid, if you can add one more battery.

I would get a normal Multiplus (or Quattro) and a Cerbo GX (without display). Not a Multiplus-GX.

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ptrzn avatar image ptrzn commented ·

Thank you for your suggestions, I'll definitely take the 2 MPPT route as redundancy would be important indeed. Also the separate Cerbo.

In terms of the PV panels, what panel capacity would you go with?

Thanks again.

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seb71 avatar image seb71 ptrzn commented ·

I got 60 cell 280Watt polycrystalline panels. Cheapest I could find at that time (price per Watt).

The better panels make sense if you want more power for a certain available space. I suppose this is very important on a boat or RV. But less so on a house (usually).

Also there might be some savings for mounting system, wiring, connection boxes if you have fewer, but higher power modules.

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ptrzn avatar image ptrzn seb71 commented ·

Thanks for that, it didn't occur to me to rank by price/W - this helped a lot in narrowing down what's out there on the market. Much appreciated.

What I'm still wondering, though, is this value in red color - could this be a problem? As summers are more and more hot here in Central Europe, I'd like to make sure that the system has enough buffer for low voltages at extreme temperatures.


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seb71 avatar image seb71 ptrzn commented ·

The PV array voltage must always be under the solar charger maximum (at all weather conditions and temperatures) to not damage the solar charger and at least a few Volts (such as 5V) above the battery voltage, to be able to charge it. So I can't explain why 81.8V is shown in red.

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ptrzn avatar image ptrzn seb71 commented ·

Cool then, thanks.

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