Advice Needed Solar Panel Shading

[Tim Mackinlay]

What is the best panel (in the 80 to 100 watt size) to use where the
panel might get shaded? It's for use on a sailboat.

Tim

 

[Danno]

What is the best panel (in the 80 to 100 watt size) to use where the
panel might get shaded? It's for use on a sailboat.

Tim

I currently use a "normal" silicon panel (blue colour) and a smaller PV film
(brown colour), tested both by partially shading with a thick towel. The silicon
panel's output dropped significantly, almost completely IIRC, while the film
performed admirably, almost no change in output. Both are made by ICP.
I recently spoke with my PV dealer, he suggested Unisolar amphrous panels for
partially shaded use. He told me they had actually tested them after firing
bullet(s) through them, and they still put out 80% of rated output.

 

[Windsun]

Despite any hype you may have read about "shade tolerant" panels, there is
no such thing.

Shade = less light - as much as 96% less.

Less light = less power produced. Regardless of the panel.

 

[R.E.P.C.O.]

never ever try and get a warranty claim on a Unisolar panel as Unisolar
never have warranty claims and you are left high and dry with Unisolar hosed
panels.
Unisolar have even changed to metal that rusts and of course it will not be
their problem
The other issue with Unisolar they fail to publish their proper temperature
ratings on their website as in cold to cool conditions Unisolar is useless
garbage.
There is no panel that is any good for partially shaded use
Have you considered why there are no other mainline panel manufacturers that
make garbage like Unisolar

 

[Windsun]

Baloney.

We have sold over 1000 Unisolar panels in the past 10 years and have never
had a problem.

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never ever try and get a warranty claim on a Unisolar panel as Unisolar
never have warranty claims and you are left high and dry with Unisolar hosed
panels.
Unisolar have even changed to metal that rusts and of course it will not be
their problem
The other issue with Unisolar they fail to publish their proper temperature
ratings on their website as in cold to cool conditions Unisolar is useless
garbage.
There is no panel that is any good for partially shaded use
Have you considered why there are no other mainline panel manufacturers that
make garbage like Unisolar

I currently use a "normal" silicon panel (blue colour) and a smaller

PV

film
(brown colour), tested both by partially shading with a thick towel. The silicon
panel's output dropped significantly, almost completely IIRC, while the film
performed admirably, almost no change in output. Both are made by ICP.
I recently spoke with my PV dealer, he suggested Unisolar amphrous

panels

 

[Danno]

Tested how?

???
In my first post I said I tested it by shading each panel with a thick towel,
and posted the reaction. Granted, it was hardly scientific, but then, I would
say that my description was accurate enough for anyone (other than someone
looking for an argument) to realize it wasn't a controlled experiment with any
degree of legitimate science.

What output were you measuring?

I checked the meter on my charge controller, it measures amperage being
passed to the battery pack. I'd cover about 10% of the silicon panel, and output
would plummet. Shade 1/2 of the PV film (albeit smaller) panel, and the relative
change was less. While shading the silicon seemed to result in about 80%
reduction in output from the panel, shading the film panel seemed to change
output only by about 30% of its capacity.

You can't shade a panel
without affecting its power output. The best you can hope for is that if
you block, say, 50% of the incoming light the panel's production will
not drop by more than 50%.

If you are shading a panel and seeing almost no change in output, I
suspect you are measuring open-circuit voltage. That might give you some
idea how the individual cells inside the panel are interconnected, but
it won't tell you much else. Try repeating your experiment and measuring
short-circuit current. Better yet, repeat it and measure both voltage
and current while the panel is loaded.

Thanks, I'll pass. I'm satisifed with the result I gained from my little
impromptu experiment. I do kinda wonder if someone accurately measures output
in shaded situations though. While most PV panels are going to be mounted
optimally, I think there are more circumstances to exploit the sun under less-
than-ideal situations. Maybe an index of shaded output would help the industry?

As long as bypass diodes are correctly installed, crystalline silicon
panels should function just fine under partial shading. And I've seen
several crystalline panels with bullet holes that were still functioning
at 50-75% capacity. It was the ones that were kicked in with combat
boots that didn't want to work anymore....

So if they had been kicked in with hemp sandals they may still have worked?

 

[Windsun]

What you are overlooking here is the fact that some panels have internal
bypass diodes around each cell. That I am sure is the one that dropped 30%.

When you shaded the other one you essentially turned off that cell, and with
no bypass diode in the panel, the output from ALL the cells was reduced, as
it all has to go through that turned-off cell.

It is a function of panel design, not of what the panel is made from.

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[Danno]

What you are overlooking here is the fact that some panels have internal
bypass diodes around each cell. That I am sure is the one that dropped 30%.

When you shaded the other one you essentially turned off that cell, and with
no bypass diode in the panel, the output from ALL the cells was reduced, as
it all has to go through that turned-off cell.

It is a function of panel design, not of what the panel is made from.

Yes, I agree. I had only ecently learned about internal bypass diodes, I
believe my panel on order has them (Sharp 123 <grin>). It would seem ICP's
silicon panels do not possess them though.
Thanks for the post.