Solar panel performance in cloudy conditions

Submitted: Saturday, Jul 19, 2008 at 01:54

ThreadID: 59896 Views:8836 Replies:6 FollowUps:2

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ben_gv3

Hiya Solar gurus,

Does anyone know the performance degredation of solar panels (mono/polychrystalline) when under cloud?

I know that output is zero if 1/3 of the panel is under shade but what about cloud cover? I know the density of the cloud cover is variable but does anyone have a rough guide?

I also know that performance degrades the higher the temp.

TIA

Ben

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Reply By: Member - joc45 (WA) - Saturday, Jul 19, 2008 at 09:48

Saturday, Jul 19, 2008 at 09:48

Hi Ben,
cloud's a bit like 'how long's a piece of string'. Regardless of whether you're using mono, poly or amorphous panels, you'll get quite a drop in output with cloud cover, just how much depends on the density of the cloud cover.
I've been in the Kimberley in 32deg, quite overcast weather and seen the panel output drop to 1/4. Not good when trying to run a fridge in those temps.
Cheers,
Gerry

AnswerID: 315991

Reply By: bruce - Saturday, Jul 19, 2008 at 10:38

Saturday, Jul 19, 2008 at 10:38

A lot of people rave on as to how good these panels are...we have a 85w Suntech brand that when it has full sun on it , it is brilliant ...but.. get any shade and I mean any shade on it and it is next to useless.....cloud cover is about the same....when camping it is just about a full time job keeping shade off it...even if the dog lays down in front of it...no power....cheers ?

AnswerID: 315998

Follow Up By: Mainey (wa) - Saturday, Jul 19, 2008 at 14:54

Saturday, Jul 19, 2008 at 14:54

Bruce
Yes, Suntech panels are lower priced (said nicely) than most other Solar panels, and their overall performance is simply relevant to their low prise.

They will put out their rated Amps in good conditions, but in not so good to 'average' conditions you get the "next to useless" performance as you have described.

The more expensive and also technologically advanced Solar panels will work in very cloudy and partially shaded conditions quiet well by comparison, it's a case of you get what you pay for.

Mainey . . .

FollowupID: 582323

Reply By: Topcat (WA) - Saturday, Jul 19, 2008 at 11:31

Saturday, Jul 19, 2008 at 11:31

Uni-solar solar panels are somewhat more shade tolerant than multi-crystalline solar panels (such as Sharp, BP, Suntech, and Sunpower) because each cell cuts out only when totally shaded.

AnswerID: 316007

Reply By: Best Off Road - Saturday, Jul 19, 2008 at 11:58

Saturday, Jul 19, 2008 at 11:58

I have had a Uni Solar (amorphous) panel for 3 years. Whilst an amorphous panel will outperform a mono or poly when overcast, the output is so reduced as to be next to useless. They even claim to prduce power in Moonlight, but I would suggest it wouldn't be enough to charge a moblie phone.

The term "Solar" is a misnomer. They are in fact "light energy" panels and only perform well in bright light. In fact heat is an enemy of the poly/mono; they lose about 20% of their efficiency when the panel gets over 25C. Amorphous panels continue to produce 100% efficiency in any old heat.

However, amorphous panels are a lot bigger for a given output.

For real expert advice google up Collyn Rivers.

Hope this helps.

Jim.

AnswerID: 316013

Reply By: Mainey (wa) - Saturday, Jul 19, 2008 at 16:04

Saturday, Jul 19, 2008 at 16:04

Ben, there's no single correct answer for your question, because various Solar panel brands, using different technology, will give different performance characteristics.

I assure you the more technically advanced Solar panels will work far more efficiently than the less technically advanced Solar panels, even from the same manufacturers.
Sharp make various *types* of Solar panels in the same Wattage range, the more sophisticated panels will out perform the less technically advanced panels.

My Sharp (polycrystalline) panel will actually increase the Amperage output when in *white* cloudy conditions, the Amps can be seen to increase on the LCD screen of the Solar controller when the white clouds pass overhead.
My Solarex (BP multycrystalline) panel and even the less expensive Sharp panels will not give this same performance increase!

Mainey . . .

AnswerID: 316032

Reply By: Paul Grabonski. Vic - Sunday, Jul 20, 2008 at 18:26

Sunday, Jul 20, 2008 at 18:26

among the major solar panel manufacturers like Kyocera, Mitsubishi, BP, Suntech, Sharp, Honda, Siemens there will not be 1% difference in output. If an 80w panel is rated at 80w they will all give you the identical output in the same conditions. There is no difference. Any solar panel regardless of type reduces output in cloud and all brands reduce the same. you will not find data on the net to prove otherwise.

AnswerID: 316191

Follow Up By: Mainey (wa) - Monday, Jul 21, 2008 at 16:59

Monday, Jul 21, 2008 at 16:59

Paul,
Yes, your correct IF we are talking about "maximum rated output"
However, some Solar panels will, in low light, have reduced output or even stop working, when others will continue to work fully or to some degree.
I can, and have proven that with my two Solar panels, giving different performance with the same cloud system overhead.

Sharp 123 watt Solar panel specs. :-> Link <-:

(for a much clearer vision, just click to enlarge my "picture" below, you can clearly see the Sharp is very different in appearance to the BP panel beside it.
Because of the surface coating on my Sharp panel it gives more efficient low light performance, notice how it looks very similar to a Unisolar panel in appearance)

My Sharp Solar panel is superior to the BP panel in low light conditions, as it starts producing Amps before the BP starts and continues after the BP panel has stopped.
However NOT every model in the Sharp solar panel range will return this same performance, if it looks like a "multi-crystal silicon solar cell" panel it will work similar to a "multi-crystal silicon solar cell" panel.

Mainey . . .

FollowupID: 582626