2x2 Solar Panel Array Shadow Limitations

[CA_Traveler]

How does a 2x2 series/parallel panel array perform with partial shadows and bypass diodes with a MPPT controller? For example using 30V panels with 3 bypass diodes each and one panel has shade causing two bypass diodes to conduct.

One set of panels is producing 60V and the other set 40V but they are connected in parallel. My guess is that the 2 40V panels are going to basically be seen as an open circuit and will not contribute any amps.

[2oldman]

After giving it some thought, I presume the mismatched voltage solar panels in parallel *should* act like a strong battery in parallel with a weak one. The strong one will spend its time trying to charge the weak.

Maybe not a perfect comparison, but that seems to be what the article says.

[JiminDenver]

I'll through the charts. I have a mismatched parallel test too.

[2oldman]

CA Traveler wrote:
But what is produced when the panels are parallel connected to one controller?

I can't answer directly, but I did find Solar panels of differing power. Scroll down a bit to find this section.

Good article.

It's been my understanding that parallel panels should be closely matched by voltage, series by amps.

[JiminDenver]

By going 2x2 and having each set on it's own controller, you will be limiting the affect of shading on the whole array. 2x2 on one controller means the low set will limit the unshaded set just as all four in series would.

[CA_Traveler]

Yes I was just ignoring the bypass diode loss. The actual voltage drop needs to include the bypass diode drop. Perhaps 0.5V and a total voltage loss 10.5V per bypass diode.

[CA_Traveler]

2oldman wrote:
Shading is a complicated subject. I think about all you can do is shade them yourself and test. Not sure why you have disparate voltages.

Yes it's complicated.

I have 3 panels in series and have posted threads showing the effect of bypass diodes and I'm not in a position to test a series/parallel setup.

I'll try to clarify the voltages - Two panels in series and not connected to the other 2 panels will produce 60V. The other 2 panels have a shadow that is causing 2 of the bypass diodes to conduct which means that the voltage for those panels would be reduced by 2/6*60 = 20V or the panels by themselves produce 40V.

Both of these sets of panels will produce the expected power when each is connected to it's own MPPT controller. But what is produced when the panels are parallel connected to one controller?

[time2roll]

I believe your assumption is correct. In parallel the shaded panel will basically drop out. In series you lose voltage of the shaded section only. I also believe you lose a bit more than 10v per section because you are pushing through the diode.

Typically I recommend all series or all parallel. The series/parallel would seem to be inferior during shade issues. Unfortunately you are probably up against the controller Voc limit.

[JiminDenver]

My test with shaded panels in series pretty much matched the results of the mismatched panels test. The weakest panel rules.

I was hoping to mount the system here soon but falling down some stairs is going to keep me off ladders for a bit. I plan on some winter sun/ cold temperature testing in the mean time, I'll toss some more shade test in there too.

[2oldman]

Shading is a complicated subject. I think about all you can do is shade them yourself and test. Not sure why you have disparate voltages.