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Old 31-07-2014, 11:45   #1
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Solar Partial Shading, is this a Problem?

Hello all,

I was looking at my panels today and noticed the wiring was shading some parts of the panels. It's only a few wires here and there (see photo below) but I was wondering if this would cause any noticeable drop in power output?

If so how much would I be looking at and would it be worth me tidying up the wiring (I didn't install this myself)?

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Old 31-07-2014, 11:51   #2
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Re: Solar partial shading, is this a problem?

Definitely tidy up the wiring and let us know what happens.
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Old 31-07-2014, 12:07   #3
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Re: Solar partial shading, is this a problem?

It's pretty easy, percentage of panel shaded will just about equal percentage of full power output loss for the current conditions.


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Old 31-07-2014, 12:14   #4
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Re: Solar partial shading, is this a problem?

If that is in the series dirrection, it could easily be 20%. Because it affects pannel voltage, the loss is not area-proportional. Just pitiful workmanship.

Shading in the parralel dirrection is propotional to area.

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Old 31-07-2014, 12:45   #5
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If it's a single panel with 36 cells all the cells are in series. A single wire going down a half a dozen cells can easily cut your output in half
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Old 31-07-2014, 13:40   #6
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Re: Solar Partial Shading, is this a Problem?

In a Sail Magazine test last fall, Nigel Calder showed that shading 2.5% of a solar panel could reduce output by over 60%
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Old 31-07-2014, 14:01   #7
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Re: Solar Partial Shading, is this a Problem?

Woha. Numbers all over the place.
I'm going to tidy it up and report back.



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Old 31-07-2014, 14:35   #8
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I have 2 100w panels on deck. With sunshade up in full sun I'm lucky to get 4 amps out of them. Un shaded it gets close to 11 amps. I move the panels to differant location when anchored with shade up. In the Keys.
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Old 31-07-2014, 14:42   #9
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Re: Solar Partial Shading, is this a Problem?

Quote:
Originally Posted by simonpickard View Post
Woha. Numbers all over the place.
I'm going to tidy it up and report back.
Measuring is best.



None of the numbers are wrong. It depends on the panel layout, solar intensity, battery state-of-charge, and the shape of the shade. But the clear conclusion is that loss is not proportional to shaded area. When I see guard rails over a panel I snicker. Even rigging wires matter, and sail and boom shadows are fatal. Often I swing the boom way off to the side, secured by the preventer, when at anchor.
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Old 31-07-2014, 14:56   #10
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Re: Solar Partial Shading, is this a Problem?

The other day I found out the effect of bird poop on my panel.

Straighten up those damn wires!!!!!!!!
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Old 31-07-2014, 17:47   #11
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Re: Solar Partial Shading, is this a Problem?

Well that's one of the reasons why I want to cover my pilot house, this way any inefficiencies are overcome by sheer area and angles. It's definately cheaper to buy cells than to buy panels and you can even buy manufacturer seconds which have a chip in it here or there, but the cells still work even if not optimally. You are going to chip a few yourself anyway. That's one reason why panels are so expensive, because the chips break easily, so there is loss in shipping and assembly too,
And they (the producer) usually tries to put them in a rigid frame.

If you don't mind doing it yourself you can make a much larger capture area for much much less money


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Old 02-08-2014, 05:22   #12
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Re: Solar Partial Shading, is this a Problem?

Just reporting back to this thread..

I tidied the wires up, nothing is shading the panels now.

Wow.. What a difference. I don't have an amp meter yet but whereas before I was noticing a slow drop in volts during the day I'm now seeing the reverse. I.e. the solar is keeping on top of everything and topping the bank up.

Crazy, I guess it was losing quite a few watts due to just those few cables putting shade onto a few cells.

Thanks again for the advice!

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