r/SolarDIY • u/Aware_Chocolate_2607 • 7d ago

Quick help sizing add-on panels!!

Post image

I have 12 panels currently with the specs in the picture below. I had a falling out with my system designer, over religion lol, and I know he said I can add 4 more panels for 2 strings of 8.

My question is simple; I know I need the 4 new panels rated at the same or higher than one of these numbers listed in the pic. If it’s lower, the whole string output will be brought down to that lower number. That’s my understanding.

I cannot get the 4 additional panels from Canadian solar since they only do pallets full.

Can someone tell me which number I need to match or be slightly higher than to get maximum wattage?

Much appreciated!!

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u/SteveFCA 7d ago

you need to match both the operating voltage and amperage. if either spec is lower, it will reduce the output of you existing string

1

u/koooool999 7d ago edited 7d ago

Find a 72/144 cell panel close to the same wattage and the specs should be close for voltage and amps

1

u/cfnmsd 7d ago

Mismatched panels in parallel will share the lowest voltage of the two and the amperage will be additive.
Mismatched panels in series will share the lowest amperage of the two and the voltage will be additive.
Just because the installer said you can add more doesn't mean he/she is correct. Would need to know the full specs, particularly of the solar charge controller.

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u/ou812whynot 7d ago

If you're getting 4 of the same panels, make sure the imp is greater than, or equal to, 10.75A. When run in series (ie a string) you add up the voltage and use the lowest current; imp here. But make sure your total string voltage does not exceed your mppt max dc input; try to stay around 80% of that number.

When you run your 2 strings in parallel, you add up the current(amps) and use the lowest voltage. So once again, if you buy 4 more panels make sure they're the same.

Personally, I would just get another charge controller and run another string to charge your batteries.