# Combining panels with different voltages

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I have four 100W Siemens panels on the roof of my RV. I would like to add two more panels, but can't find panels with an exact voltage match. Will it cause a problem if I add panels with an output voltage that is higher or lower?

• Solar Expert Posts: 10,300 ✭✭✭✭
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Re: Combining panels with different voltages

it shouldn't be all that critical. some here say within 10%, but i'll say the same to +5% more.
on rereading i'll clarify 0% to +5%.
• Solar Expert Posts: 5,436 ✭✭✭✭
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Re: Combining panels with different voltages

The only problem (assuming +-10% difference) will be, assuming the array is wired in parallel, will be the total array Vmp will take on the Vmp of the lowest volatage panel. You could always run two controllers, one for each sets of panels. There is no detriment to running 2 charge controllers in parallel, but I personally wouldn't worry about it unless it is ~5-10%

Tony
• Solar Expert Posts: 413 ✭✭
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Re: Combining panels with different voltages
campboss wrote: »
I have four 100W Siemens panels on the roof of my RV. I would like to add two more panels, but can't find panels with an exact voltage match. Will it cause a problem if I add panels with an output voltage that is higher or lower?

Depending on how the four existing panels are wired, the voltages and currents of the panels, and the maximum Voc of your charge controller, one solution =might= be to re-wire as two old panels and one new panel in series. But that requires that the difference in Impp between the panels be smaller.

My suggestion would be to look for panels with the same current and go the route I just described, or perhaps look for panels where the voltage is close to 1/3rd of the existing strings and use three instead of two.