Solar roof rack shading?

Cbessler

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Jul 29, 2021
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Hey everyone. Had a few questions I couldn't really find the answer to online so thought I'd ask here. I have a 2014 fwc fleet with 350w of solar installed on top. I ran the outer edge of my solar panels in the installed thule tracks then added a t channel track virtually down the middle and they are all installed via bolts and nuts etc. Been great and have had no issues with the install.

Looking to carry a surfboard or different things on the roof now and had some ideas. I want to scoot some of my solar panels down to make room for yakima or thule feet and cross bars. I have enough space in ome gap but need to make another one.

Do you think running a rack bar across the panel would cause enough shade to make the panel not work? I would plan to take the board off the roof when parked. My solar is set up in series right now due to the small roof sized wiring coming into my mppt charge controller. They are renogy flexible panels.

Thanks!
 
Here is a pic of my setup to help
 

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Partial shading of even one cell on a 36-cell solar panel will reduce its power output by as much as 50% (assuming series connection of cells). Some panels do better than others.

 
If your panels are 18-21 volt then I would stick to Serial wiring and watch your shading.

If your panels put out more than 21 volts, consider wiring them in Parallel as this will help when one panel is shaded.

My panels work around 28 volts so in Parallel I get more current (amps). If you got panels that work at 18 volts that is to close to what the plus 3 volts the charge controller needs. So you run them in Series to gain the advantage of increasing the voltage so the charge controller has plenty to work with.
 
This is why I carry a separate 100 W Renogy folding panel with a long wire that I can put out in the sun when my rooftop panel is shaded. I too travel with boats on top. When I am driving, no problem, but once I stop I don't always want to unload the boats.
 
I can't say for your panels, but I have a Renogy solar suitcase and have just waving my hand over the panel in direct sun can quite significantly reduce power. I was surprised by this as well. But, in real world use, even a branch slightly shading the panel reduces its efficiency considerably more than you would expect.

Except for driving, of course, I often wonder how folks with rooftop solar panels enjoy parking in direct sun! (Perhaps this is why folks require so many more panels than I do?)
 
Some solar collector panels are "shade tolerant". I believe this consists of a diode in each cell that lets current from the other cells pass through, even if that cell is shaded.
 
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