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Tobias Franklin avatar image
Tobias Franklin asked

MPPT Performance

I have a;

6 panel 420w array at 85v that feeds into a 150/45 victron mppt and a

4 panel 330w array at 70v that feeds into a 100/20 victron mppt.

The array size difference its about 63% so in my head I would expect that to be the difference in watt output between the two (both have the same orientation outside).

But the actual watt difference is quite large, the larger array actually outputs about 120% as much power as the smaller array.

My question is, are the smaller capacity mppt's less efficient at managing the array even though the numbers are within tolerances? Am I likely to get closer to my expected outputs if I used say a 150/35 on the smaller array? Or is the difference purely down to the panel efficiency?


1683188366162.png


you can see the huge difference above

MPPT ControllersSolar Panel
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1 Answer
nickdb avatar image
nickdb answered ·


MPPT efficiency doesn't vary with size.

You have 20A x battery voltage available on the smaller one, so at 48V that is 960W.

For 45A you can produce 2160W at 48V.

So there is pretty much a 125% difference in generation ability.

Your voltages are quite low and you need battery +6V to start the MPPT, so in poor light conditions your MPPT's are unlikely to start, the smaller one will be worse as it has the lowest voltage array.

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Tobias Franklin avatar image Tobias Franklin commented ·
thanks for your answer - I understand that is peak generation but if both mppts are under conditions where neither is pushing close to 20A would you not expect the difference to reflect the panel sizing instead eg closer to 60%?


I would then totally understand that the gap would widen as the 20A output peaks out and the larger mppt pushes up towards its 45A maximum.

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