n-dee avatar image
n-dee asked

overpowered mppt - bad or not

I got an 250/100 on our modules on the north-side of the roof.
The modules only make 1500w peak, and i assume that they'll do only 3500 in Summer

Does it make sense to switch to 250/70 or doesn't it matter?

MPPT Controllers
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1 Answer
Jons Collasius avatar image
Jons Collasius answered ·

Use the MPPT Calculator from Victron. Then you have certainty.

Too many watts (W) don't matter a lot.

Too many amps (A) don't matter a lot.

Too many volts (V) will kill your MPPT immediately.

Your modules will not deliver 3500 Wp in summer if they are specified as 1500 Wp.

You will have the highest output in spring, when it is still nice and cold and the sun is beating down.

In the summer it is too warm and the solar cells deliver less in the heat.

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n-dee avatar image n-dee commented ·

Oh I've got 10800wp :-) but 40 degree north - 6pcs x 6 in parallel at 300wp
MPPT Calculator will tell you that this is not allowed. But max Voltage was 210v.

Highest output therefor will be in summer. (40deg north)

Got them REALLY cheap thats why...

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Kevin Windrem avatar image Kevin Windrem n-dee commented ·
Make sure you calculate max voltage from the open circuit voltage corrected for lowest temperature (voltage goes up as temperature goes down).

Victron MPPT controllers have a max input voltage and max input current specs. The input voltage spec is most critical but also make sure you don't exceed the maximum input current even on a goo day.

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n-dee avatar image n-dee Kevin Windrem commented ·
Yeah - did that, all good.

Just the question if it makes sense to switch to a smaller one

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Alexandra avatar image Alexandra ♦ n-dee commented ·
3500w ÷ 48V = 72A

Will you loose much? No

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