Solar Panel Wattage Mismatch

Looking to upgrade my solar a bit....and running into a little bit of a problem (but maybe not). This question could be asked before, but couldn't find the thread.

Current panel is a Renogy 160 watt poly, it appears they no longer produce these (have e-mail/call into customer service). I thought it would be easiest just to add the same additional panel to get up to 320 watts, but that also feels like a little bit of overkill.

Did a little bit more search on "mixing" panels in parallel:

https://solarpanelsvenue.com/mixing-solar-panels/

My thought was to just throw on 100 watt panel (and upgrade charge controller from Victron 75/15 to 100/30).

Seems like the limiting factor is the lowest voltage of the panel in parallel. Looked at some specs and the "optimum operating voltages" of the 160 watt and 100 watt actually aren't all that different (18.6 and 17.9).





optimum operarting









Voltage

Current

Power

160 W Poly

18.6

8.6

159.96

100 W Mono

17.9

5.72

102.388









260 combo

17.9

14.32

256.328


There actually doesn't appear to much power loss at all....anyone have any experience with mismatched panels like this?

Best,

Ruck

I started with a 100 watt panel and added a 150 watt panel later. Works great. I do believe both of my panels were 17 volt but its been a while since I installed them.

Thanks Craig, looks like in my above post the tables didn't post, but this is what was provided by the mfg:

160 watt panel; 18.6 optimum operating voltage, 8.6 optimum operating current
100 watt panel; 17.9 optimum operating voltage, 5.72 optimum operating current

the math for the proposed system was 17.9 (lowest optimum operating voltage of the two panels) x (8.6+5.72) = ~256 watts

seems like minimal power loss due to the similarities in the "optimum operating" voltages.....

If you have an MPPT controller, put the panels in series rather than parallel. The controller won't care, and no loss.

With miss-matched panels with different currents you definitely don't want to put them in series. With the two panels in series, the output current will be limited to that of the lowest output panel, or 5.7A. In series, you will get a maximum of 5.7A * (18.6 + 17.9)V = 208W. In parallel, you would be limited to the lower voltage (17.9) but still get the sum of the currents, so the maximum power is (5.7+8.6)A*17.9V = 256W. In short, in parallel you will get close to the maximum for the two panels.

In general there is not a huge amount to be gained by putting the panels in series as opposed to parallel with the exception of if your wiring is significantly undersized or you spend a lot of time at low illumination levels. Look at your solar panel output early in the morning, I think you will find the voltage rapidly rises (to Voc), it is the current that increases as the illumination increases. Thus the amount of power lost before you get above the MPPT turn on threshold is minimal.

Series also creates issues if you ever want to add a portable panel in parallel with your roof top panels.