Shadows and Panel performance

lazza

HI

Yesterday we had to travel a long way to do an installation-- the place chosen to put the panels by the client happen to be partly shaded by a tree in the afternoon.. great! However, due to fear of theft and the fact that we hadnt been able to visit the site previously, we did the installation in the prepared area- there was sadly no other viable option.

• As the installation is of 6, 24V panels in parallel, I understand that the shadow will only affect the output from the affected panel, allowing more or less correct functioning of the other 5.
• If they were in series, for example in an MPPT set-up.. the whole series would be reduced to the current output of the worst affected panel.

Am I correct in these 2 assumptions?

ggunn

Re: Shadows and Panel performance

lazza wrote: »

HI

Yesterday we had to travel a long way to do an installation-- the place chosen to put the panels by the client happen to be partly shaded by a tree in the afternoon.. great! However, due to fear of theft and the fact that we hadnt been able to visit the site previously, we did the installation in the prepared area- there was sadly no other viable option.

• As the installation is of 6, 24V panels in parallel, I understand that the shadow will only affect the output from the affected panel, allowing more or less correct functioning of the other 5.
• If they were in series, for example in an MPPT set-up.. the whole series would be reduced to the current output of the worst affected panel.

Am I correct in these 2 assumptions?

Yes.

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CATraveler

Re: Shadows and Panel performance

My underestanding is that with a series connection the bypass diodes will bypass the panel or portion of a panel that is shaded.

Let's try an example, 2 150W 30V 5A 6x10 panels with 3 bypass diodes.

In parallel with full shade on one panel you'll get full power from one panel. In serial with full shade on one panel you'll get full power from one panel minus the bypass diode drop. Let's assume the diode drop is 0.5V so you'll have 5A*(30-1.5)=142.5W. So I agree that parallel is better in this case.

But RV's are often subject to partial shade from a variety of sources. Let's consider partial shading on say 1/3 on the panel covered by a bypass diode. In this case parallel will give you full power from one panel. Serial will give you 150W+5A*(20-0.5)=247.5W from both panels.

Serial panels with bypass diodes and partial shading have advantages.

It's also been posted on these boards that some mount their panels in landscape mode so that accumulated snow on the bottom of the panel allows the upper portion to continue to operate.