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buddyseattle asked

Which MPPT should I buy for my two 175 Flexible Panels

This is my first post here and am looking for beginner help on an MPPT selection.

I used the Victron MPPT Calculator and selected a quantity of 2, 175W Flexible solar panels in Parallel. Which is what I have in route to me now.

It suggested the SmortSolar MPPT 100/20. Which I have on order. I wanted to confirm this is the right unit and makes sense to have a unit with max input of 20A at 12V?

Using what I know I would think 350W is closer to 30A on a 12V system. It does say in the notes that if more power is connected the controller will limit the input.

I am concerned that this controller will not give me the full potential power to charge my house batteries of 400AH Lithiums. I don't want to buy more than to meet this need, and only want one controller to keep it simple.

I know the voltage of the panel is greater than 12V, so is that what makes this the right unit?

Any other suggestions are welcome!

Thanks in advance!


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MPPT Controllers
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2 Answers
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kevgermany answered ·

Firstly, the numbers in the 100/20 mean max input voltage/max output current. As panels produce higher voltages than the battery voltage, there's no specific input current rating, input current will always be less than output current.

Batteries will be charged at about 14.2V, (most people work on 12V although incorrect). 350W@ 14.2V is roughly 25A. So max output will be clipped by the mppt. What other parameters did you put in the spreadsheet?

There's a case for oversized panels if they're installed in low light conditions, such as northern Canada as the panels won't get enough light to produce full power. But based on what you said so far the controller would appear to be undersized.

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buddyseattle answered ·

Thank you. Is it realistic that the panels on a typical day in the 70's that the panels would hit this max wattage output or would I just be sizing up for a more theoretical potential rather than reality? I am based in the NW, so we do have long summer days.

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kevgermany avatar image kevgermany ♦♦ commented ·
Good question. I see more than the rated panel output on good days, but I'm in the South of Germany, panels on a campervan. You may find something online for your area. But otherwise it's guesswork. I was in Scotland recently, thought there was something wrong as solar output was so low (50% at best), tested when I got back and got 110%.
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