partial shade panels

jdfnnl · August 2020

My planned system involves a couple 100W Renogy panels mounted under a roof rack that causes roughly and eighth of the PV area to be covered full time. I was thinking of connecting them in series to minimize the wiring clutter, but then remembered parallel is usually better for partially shaded panels due to differing voltages, though these panels will each be shaded equally. I wonder if I should stick with an MPPT and series wiring or if parallel would really be superior, in which case a simple 20A PWM would suffice?

mike95490 · August 2020

Shading reduces panel voltage as 0.5v segments are shadowed (actually the amps are cut off, and then the voltage crashes) and sections of the panel activate the bypass diodes to keep from total shutdown.

Not knowing how your panels bypass diodes are laid out and the cell arrangement vs the Shadows, I don't know if any configuration will be viable. You might have to place 2 panels in series to maintain charging voltage, and then you are wasting power with voltage mismatch. Try it and see what happens is all I can suggest.

BB. · August 2020

I would suggest the PWM controller and connecting the panels in parallel (assuming "12 volt" panels and a 12 volt battery bank).

I always worry that the bypass diodes can get hot and overheat/fail in bypass operation (Power=Voltage Drop * Diode Bypass Current). And solar bypass diodes have very poor heat dissipation (glass panels, plastic J-Boxes, etc.).

It is just my concern/choice. System design wise, connecting several 12 volt panels in series with an MPPT charge controller is "fine" too. I am not sure you would see any harvest advantage between MPPT and PWM setups.

-Bill

NANOcontrol · August 2020

With a 12V parallel system the bypass diodes would never work. Bypassing half the panels voltage would result in panel voltage less than battery. In series it could go into bypass. There is one panel company that has bypass diodes for every cell. That has to make them expensive.

RCinFLA · August 2020

Be careful of Renogy 100w panels. If they are mono cells, Renogy skimps on cells with only 32 or 33 cells. Those panels are okay if you only plan to use with PWM controller for 12v battery but do not have enough overhead voltage for most MPPT controllers, unless you stack multiple panels in series.

mountainman · August 2020

With 4 100 watt renogy panels in parallel on pwm controller
Production was better with pwm than mppt.
Especially In Partial shade.
I tried mppt with all in series.
2 in series and 2 in parallel
even tried all in parallel.

partial shade panels

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