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bret-marro asked

MPPT calculator

Hi all. I'm looking at an MPPT solar charge controller for my 4kw system. After entering all the numbers on the online calculator tool it is recommending the 250/70 unit. The max current output (PV max. current @ MPP max. temp) is 68 amps, which is a PV Power Ratio of 100%. Given it's very close to the maximum of the MPPT controller, can anyone see an issue if I went up the next size to 250/100? I'm just curious if there is a drawback to going larger as far as efficiency is concerned and why the calculator suggest this particular one. Thanks,

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JohnC answered ·

Hi @Bret Marro

The way I read this is that you're worried about exceeding the "/70" output rating. This isn't a problem, as if you do it will just clip to 70A and any power available above that will stay in the panels.

Bear in mind that solar production comes on in a 'bellcurve', lower in the morn and afternoon, peaking somewhere in the middle. So if you clipped it would be for a short time anyway. You may never actually see it hit 70A, if your batteries are well up in V by then. Maybe when you have a load/export on, batt V is down, and you have a 'cloud-edge' solar event, it might. But it wouldn't matter anyway, it won't hurt anything and usually be fleeting anyway.

You could use a /100 if you want, these things are designed to be efficient over the whole range, as they spend most of their day producing at lower output than rated.

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bret-marro avatar image bret-marro commented ·
Thank you so much. You covered it perfectly.
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