Solar Panels

One for the Solar Wizzkids, If mounting a Panel under a set of roof bars will the shadow of the bars stop the panel from working.

Thanks in advance,

Ross.
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Reply By: 4X4Treker - Sunday, May 30, 2010 at 22:46

Sunday, May 30, 2010 at 22:46
In short yes, any shadow on the solar panel will effect the performance, solar panels by design require full sunlight to operate at peak performance.
AnswerID: 418857

Follow Up By: ChipPunk - Monday, May 31, 2010 at 02:58

Monday, May 31, 2010 at 02:58
4x4T - do you mean shading one section can kill the WHOLE panel?

I didn't think they would stop working - just operate with lower output (because of the shade).

Some newer cells use "slithers" where "loss of output" is proportional to "loss of sun" - ie, the amount in shadow.

I think in older/conventional panels, a shaded cell will "choke" other cells' output.
IE - if an entire "section" is shaded might the whole panel stop working.
(A panel is several "cells" in series, but it may have a few of these series "strings" in parallel . One "break" will stop a "string of cell's", but not the others (assuming no inter-string discharging...) But is shading one full cell equivalent to a break - or is it still conducting - just not contributing? Something tells me it is a break...)
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Follow Up By: Maîneÿ . . .- Monday, May 31, 2010 at 04:38

Monday, May 31, 2010 at 04:38
Ross,
I would not even consider using them under the conditions you nominate because their output will never ever be reliable, as it will vary all the time, pretty much as ChipPunk has said, and as he says it's also dependant on the panel design, hell he makes it sound complex though, as it will be :-))

Maîneÿ . . .
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Reply By: Grungle229 - Monday, May 31, 2010 at 07:27

Monday, May 31, 2010 at 07:27
Hi Ross,

The panel would be very ineffective if partially shaded. I did a test on mine using a Fluke multimeter in series with the load to see how much shading affects these panels. At full sun production if I moved my hand over a single cell slowly, current production would drop from 4.8 Amps to 2 Amps when 1 cell was a third shaded to under 1 Amp when 1 cell was three quarters shaded.

Try it to make your only conclusion however.

Cheers
David
AnswerID: 418868

Reply By: jdwynn (Adelaide) - Monday, May 31, 2010 at 07:50

Monday, May 31, 2010 at 07:50
Ross, we were experimenting with shade effects last Christmas. Was generating about 8-10amps with our 2/80w Sharp panels. Shaded 75-100mm strip across panels – I believe placing shade across width stops the ‘flow’ of electricity. Mainey might be able to be explain why – read about it once, can’t remember now why this happens. Flow dropped to about 0.9amps. We have polycrystalline panels and I believe other panels types not so affected by shade. Cheers
AnswerID: 418875

Reply By: Alloy c/t - Monday, May 31, 2010 at 08:19

Monday, May 31, 2010 at 08:19
Depends on panel brand /make , Unisolar panels still work when part shaded although at reduced output.
AnswerID: 418879

Follow Up By: hl - Monday, May 31, 2010 at 10:10

Monday, May 31, 2010 at 10:10
It doesn't depend so much on brand/make, rather "type".
Poly or monocrystal panels will drop output significantly if even just a part of one cell is shaded, with amorphous panels partial shading has little effect.
However, the downside is that amorphous panels are about twice as big for the same output.
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Follow Up By: Maîneÿ . . .- Monday, May 31, 2010 at 11:10

Monday, May 31, 2010 at 11:10
Some solar panel brands have significantly different technology or can it be called 'types' with-in their range, some smaller companies just have the one 'type' of panel design, you have to compare various panels directly against each other, not just single out brands or types.

Yes, the amorphous panels will give less problems with shading, not nil problems but less, but on the other hand they are much less efficient initially, (7 Amp per sq mtr) of same physical size anyway.
But that has been done to death elsewhere on here anyway.

I've seen 1.1 Amp delivered from my system in totally overcast conditions when raining and the sun is not even visual, I would suggest not many panels can make that claim.
Some panels will even work *inside a tent* most won't, so it’s not the brand but the technology used in the panel that give the superior performance.

Maîneÿ . . .
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Follow Up By: Maîneÿ . . .- Monday, May 31, 2010 at 11:23

Monday, May 31, 2010 at 11:23
something happened in the copy/paste and some information was 'lost'

Yes, the amorphous panels will give less problems with shading, not nil problems but less.
On the other hand they are much less efficient initially, max of 3.9 Amp per sq mtr so for the portion of the day it's in the sun and they have not replaced as much as a Mono or Multicrystalline panel @ >7 Amps.

Maîneÿ . . .
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FollowupID: 689065

Reply By: ChipPunk - Monday, May 31, 2010 at 10:47

Monday, May 31, 2010 at 10:47
My co-residents reckon shading usually does "choke" the whole output.
The shading is like squeezing a water hose - it cuts the lot.
It is not like eg: "10% in shade therefore (only) 10% less output".

But some panels are assembled differently - ie, paralleled strings (rare?) or "slither" construction.

Mono- or poly-crystaline won't matter.

When driving, it's trivial (use your alternator output instead... efficiency!!).
And when camped, I'd remove the shading racks or have the panels on removable else hinged racks for at least some improved alignment. (20° is about 10% less output.) Else add mirrors....


Triviality follows:
Sorry for any earlier complication. One minute of checking would have saved 10 of writing, and 100 of confusion. (I blame it on the night's earlier "expert" claiming certain solar power outputs. He was a bit stumped when I pointed out the max of about 1kW per square meter of solar energy at the earth's (equatorial) surface - their collector then needed 1,000 sq kms instead of 10... LOL!)
AnswerID: 418894

Reply By: Member - mazcan - Monday, May 31, 2010 at 11:08

Monday, May 31, 2010 at 11:08
hi ross
the bottom line or the crukz of the matter is
yes
they are called solar panels because thats where they work to their best ability in the sun- it's elementary and simple !!!
if they were efficient in the shade i guest they 'd have called them shade panels
to put the solar panels under roof bars would be detrimental to it's output rate at all times because at no time no mater what the situation was regarding the sunlight could it be expected to produce full capacity partly shaded by roof bars
in other words your not giving it a fair go mate !would be like connecting 12volt lights to a 6volt battery???
imho it really defeats the purpose in other word to me why bother
imho its either roof bars
or
solar panels
not both
do a test yourself with a solar panel set it up in full sun and connect a multi meter to the output side then
shade it with the equivalent of bars or anything for that matter your leg /arm or body and you will quickly see how the output voltage drops off
this subject has been delt with before some time ago i recall the same question was asked
but i dont have the thread number
cheers
hope this of help
AnswerID: 418896

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