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Forum Index : Solar : PV panel oriantation vs horizon shading

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zaphod

Regular Member

Joined: 03/06/2018
Location: United Kingdom
Posts: 93
Posted: 08:56am 10 Jan 2019
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Like 99% of installations I see around here my panels are mounted on the roof in portrait (longest side vertical). Now in the UK winter is upon us and the sun is low in the sky, fortunately my roof is quite steep (52deg) so I still get a reasonable output however being a bungalow with a low roof some items on the horizon now shade the panels when they do not in summer. The horizon shading starts at the bottom of the panels and creeps up as the sun sinks in late afternoon.

The panels are 10 rows and 6 columns with shading diodes connected across each pair of columns however the shading occurs across all columns at once hence the diodes do nothing and the string output current is reduced to that of the shaded cells alone.

I now realize that if the panels were orientated in landscape (longest side horizontal) the shading diodes would work as intended as the horizon shading would blank out entire rows at once forcing the shading diodes to conduct across unproductive rows maintaining the strings output current to that of the unshaded cells.

Am I missing something here or are most installations not good with horizontal horizon shading ? Edited by zaphod 2019-01-11
Cheers Roger
1Kwp DIY PV + Woodburner + Rainwater scavanger :)
 
Revlac

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Joined: 31/12/2016
Location: Australia
Posts: 1022
Posted: 11:57am 12 Jan 2019
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Just out of curiosity I thought I would try shading 6 cells in a row then shade 10 cells in a row using a broom handle to simulate the wire shadow you have.

The results were no difference either way, shading 10 or 6, as for the orientation, We have panel's mounted longest side horizontal and longest side vertical.

I think the longest side vertical orientation is mostly for the rail mounting and easy wiring string configuration.

Perhaps I should have added some photo'sEdited by Revlac 2019-01-13
Cheers Aaron
Off The Grid
 
zaphod

Regular Member

Joined: 03/06/2018
Location: United Kingdom
Posts: 93
Posted: 10:18am 13 Jan 2019
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Thank you so much Aaron, I have no sun at the moment or at least not enough to show a shadow so I tried simulating it instead, here is the output of a single panel with first no shading, then one row of 6 then one row of 10 cells the shading factor being *0.25). When the shading diodes are active (10 cells shaded) the output has the classic twin peak mpp's (140 & 70W) that some controllers )including I suspect mine) get confused by (they latch onto the wrong peak).
I apologize for the poor image quality this is a bit of problem when printing plots from LTspice.
Edited by zaphod 2019-01-14
Cheers Roger
1Kwp DIY PV + Woodburner + Rainwater scavanger :)
 
Revlac

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Joined: 31/12/2016
Location: Australia
Posts: 1022
Posted: 11:20am 14 Jan 2019
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Ok I see how that works, Looks like long strings (grid tie systems) would have more issues than these short low voltage strings, with shading.
The test I did the other day was just on one panel of a 2 panel string running on PWM (3 string's on that CC).

So I had another go today late afternoon, this setup is pole mounted (250W panels) MPPT Charger and has 3 horizontal strings, the idea at the time to make it this way was because the big trees across the road would shade the bottom row late afternoon and progressively shade further up.
Still can't tell if the Diodes are doing anything.


The current reading on the bottom set of panels was down somewhat compared to the middle row when partly shaded, as expected, But before and after this the MPPT remained at 100 volt total string voltage, once the top row stated to get shaded the voltage drops to around 75v, getting dark

I would expect that the charger stayed on the high voltage string for the max power point, However I think this would be different If I was using all the power available.

Had plenty of power anyway and a bit of shading late afternoon has not been an issue as it is dark in about half an hour.
In this case short string's low voltage was the better option, I think, and I'm happy with the way its working.
Hope I haven't mist the point.
Cheers Aaron
Off The Grid
 
zaphod

Regular Member

Joined: 03/06/2018
Location: United Kingdom
Posts: 93
Posted: 01:57pm 14 Jan 2019
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Woww impressive picture, in this horrible police state someone would nab me for sure for having a pole mount like that, we are only allowed flat to the roof or ground mount on the ground :(

Anyway I noticed the letters PWM & CC in your reply, could this be doing battery charging ? It might be possible according to your load and controller indeed you would not see any difference.

Here is a pic of my minimalist array mounted in the prescribed manner :)




And thank you again for your help :)
Cheers Roger
1Kwp DIY PV + Woodburner + Rainwater scavanger :)
 
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