MPPT Performance

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question

Tobias Franklin asked May 4, '23

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?

you can see the huge difference above

MPPT Controllers Solar Panel

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Answer 1 · 2023-05-04T08:20:48Z

nickdb answered · May 04, 2023 at 08:20 AM

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 commented · May 04, 2023 at 08:26 AM

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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nickdb ♦♦ Tobias Franklin commented · May 04, 2023 at 08:39 AM

Different types of panels will produce different power levels, it will also be affected by orientation, shading etc.

You could have losses in wiring/connections.

I would check each panel/string individually to make sure they are uniform.

I would look at the mppt stats - PV voltages etc.

Without knowing the orientation and local environment it is guesswork.

MPPT's also don't load balance, so depending on loads, one may produce the majority of power.

In ideal conditions, good wiring and the same orientation with no shading, you would expect the difference to be aligned to the panel specs.

But ideal conditions rarely exist.

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Tobias Franklin nickdb ♦♦ commented · May 04, 2023 at 09:05 AM

I decided to sneak out and switch the panel feeds over in the combiner box and route the smaller array into the larger mppt.

Seems like the larger mppt is quicker to ramp up and adjust to passing clouds etc but it wasn't getting measurably higher wattage out of the array.

So I guess that answers that then.

I'm not wildly impressed by these Eurener 330W panels (although they do look great) I'm pretty sure they are also all working fine as I can top out the max 20A output of the mppt in direct sunlight at midday which on paper I can only do with all 4 panels working to spec.

The others are Trina 420W panels and they are real bang for the buck in terms of performance!

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