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bobby-gallahue asked

Mismatched Solar Panels - Can this setup be salvaged

Wanted to try to fit solar panels around my Maxxair fan so opted to go with mismatched Solar panels. Did a good amount of research and thought i had concluded on a good plan to wire them all in Parallel. The panels are similar in Voltage but not in Amps. However realized i might have a problem when I was watching a video yesterday that stated there is a minimum voltage for MPPT Solar Charge controllers. I dug in a bit and it seems that Victron solar charge controllers need battery voltage (12v) + 5v to start charging. The lowest voltage for my panels is 17.95. However it seems that the panels likely won't reach that voltage until mid morning if at all, leading to a solid amount of effeciency loss

Panel stats

Panel Wattage 175 watt 100 watt 50 watt 50 watt
Optimum Operating Voltage (Vmp) 17.95V 20.3V 18V 18V
Optimum Operating Current (Imp) 9.75A 4.93A 3.01A 3.01A

Wired in parellell, 99% effeciency could be achieved. But I don't see any other configuration (series or series parelell) where I could even get about 70% efficiency.

I've purchased a Victron MPPT charge controller. Is there another option that might work or a panel configuration i'm missing

Solar Panelcharge controller compatibility
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1 Answer
JohnC avatar image
JohnC answered ·

Hi @Bobby Gallahue

That 5V margin applies to the Voc of the panels, rather than Vmp, and that's usually a few V higher. The mppt will then attempt to track Vmp, and it must be just 1V higher than Vbat. Once you have direct sun on them this should be achievable, but you might miss the (limited) production your panels might glean at dawn and dusk. Usually shade from cloud won't affect this very much. So it's worth a try.

The alternative would be to string the 2x 50W units in series, and the 100W and 175W in another series string. This will turn the 175W panel effectively into a 100W, so you'll lose 75W of the total.

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bobby-gallahue avatar image bobby-gallahue commented ·
@JohnC Hey john, appreciate the reply. That is very good to know. The Voc in the array is 21.6 so that seems like a decent buffer on the 12v battery bank.
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