DIY solar install guide

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Re: DIY solar install guide

Postby Neddy » Sat Aug 01, 2015 1:13 pm

This shadow cut the panels output by 50%
Image

This shadow was sufficient to reduce the panel output to zero.
Image

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Re: DIY solar install guide

Postby mattn » Sat Aug 01, 2015 2:10 pm

Given many motor homes have lots of shadow making things on the roof, and limited space for panels, it might be reasonable to presume that at any given time of day and orientation to the sun, shadow will fall on a part of the area covered by panels. In that case, would it be better to have a number of smaller panels = less chance of losing the entire potential output of the array by one small shadow, than one or two large panels?
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Re: DIY solar install guide

Postby Nut17 » Sat Aug 01, 2015 4:05 pm

One of the main reasons I went with 135w semi flexible panels, was to minimise the effect of shading. You can see in the photo below that two panels adjacent to the slide out awning roll are being effected by shade in the late afternoon. The other reason was down to weight. To fit the same capacity in conventional glass panels would have been close to 120kg. The semi flexibles added up to just under 22kg.
Image
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Re: DIY solar install guide

Postby muzzanic » Sat Aug 01, 2015 5:24 pm

On both of our vans I have fitted a controller per panel as well so that 1 shaded will not drag the other 1 down, Much easier of course if you only have the 2 panels like us, But when I fit a 3rd panel it will have it's own controller.

Note; It can also be said that with a big panel that you stand to loose more if some shade gets to it, So you win some you loose some.

This does however show that having a lot of solar is a good idea so that you can get the bulk of your charging done while the sun is still at it highest, Rather than having to rely on every scrap of sun you can.

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Re: DIY solar install guide

Postby NeilV » Sat Aug 01, 2015 5:52 pm

So if I have both panels on one controller, but they each have their own link to the controller... Surely only the affected panel would drop output, as they aren't dependent on each other that way?
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Re: DIY solar install guide

Postby Neddy » Sat Aug 01, 2015 6:47 pm

If you have two panels linked to the one controller, the panels must be connected in Series or in Parallel.
Either way, a drop in the output of one panel reduces the output of the other.
Series wiring gives the greater losses.
The only way the output of one panel cannot affect the output of the other is if they have separate controllers.

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Re: DIY solar install guide

Postby Neddy » Sat Aug 01, 2015 7:48 pm

Nut17 wrote:One of the main reasons I went with semi flexible panels was to minimise the effect of shading. You can see in the photo below that two panels adjacent to the slide out awning roll are being affected by shade in the late afternoon.
Unfortunately Chris, in this instance the thin flexible panels have maximised shading losses!
Framed rigid panels of the exact same size would raise the panels just a few centimetres and the shadow cast by the awning at that time would have been totally avoided.
While the shadow affects only a small area of those two solar panels, because it takes out two entire rows of cells the effect of this shading is severe.
Those two panels have probably had their output halved. If the affected panels were each wired in Series with two unaffected panels, the sum total of each string would be zero.
Effectively, you have then lost 4 of your 8 panels.

The weight saving with flexible panels is a powerful argument for their use in your situation, Chris,
but they do nothing to minimise the effect of shading - quite the opposite, in fact.

Neville.

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Re: DIY solar install guide

Postby Teardrop » Sat Aug 01, 2015 9:58 pm

I remember a few years ago reading about the use of bypass diodes within some solar panels to effectively route power around shaded cells and minimise losses. In other words, some solar panels may be much better than others to cope with shading. I think I will do some shading experiments on ours in due course to see what the actual effect is. Our recently installed solar panels have been installed far to close to our satellite dome (my fault, I assumed the installer being a reputable company would have known the obvious), but shading losses do not seem anywhere near as bad as what I thought may occur.

Dene


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