Higher output on cloudy days?

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Mariner777
Mariner777 Solar Expert Posts: 29 ✭
in Solar Beginners Corner #1
Oddly I noticed a new peak output occured yesterday and it was during a cloudy day. The array put out about 10 extra amp hours and was showing higher current readings then normal on cloudless hot sunny days. I have two hypotheses as to why this could be.

1 My array is on a sailboat so shading is a big issue - perhaps there was more light scattering from the clouds that ameliorated the shading problems that normally plague my array.

2 The clouds made for a cooler day and the panels did not get as hot as they usually do in full blown summer sun where they are likely well over 100 degrees most days. It was maybe 15 degrees cooler so perhaps that lead to the increased output.

Odd and counterintuitive that my highest amperage recorded occurred on a cloudy day anyone else experience such things? Any ideas why?
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  • Cariboocoot
    Cariboocoot Banned Posts: 17,615 ✭✭✭
    #2
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    Re: Higher output on cloudy days?

    Actually it's not that mysterious. You've noticed all the elements that cause it.
    The cloud cover causes a diffused light that gives a more even lighting throughout the whole day, instead of the rising/falling intensity of the sun's arc. Cooler temps always help output too. Add in some "lensing" from the moisture in those clouds and yes you can end up with more Watt hours on a cloudy day - if it's the right kind of cloudy day. The black thunderheads won't do it. ;)
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  • BB.
    BB. Super Moderators, Administrators Posts: 33,443 admin
    #3
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    Re: Higher output on cloudy days?

    Also, the output of a solar charge controller depends on the state of charge of the battery and current loads... If the battery is full and no loads, the charge controller will "stop charging" in the middle of the day (go to float with very little charging current)--This too will reduce your logged output from the charge controller.

    If your battery has been discharged deeper than usual--You may see more AH of charging.

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
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  • mike95490
    mike95490 Solar Expert Posts: 9,583 ✭✭✭✭✭
    #4
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    Re: Higher output on cloudy days?

    I saw this happen often on my grid tie, hazy light clouds, no big peak at noon, but a stable output all day long.
    Powerfab top of pole PV mount | Listeroid 6/1 w/st5 gen head | XW6048 inverter/chgr | Iota 48V/15A charger | Morningstar 60A MPPT | 48V, 800A NiFe Battery (in series)| 15, Evergreen 205w "12V" PV array on pole | Midnight ePanel | Grundfos 10 SO5-9 with 3 wire Franklin Electric motor (1/2hp 240V 1ph ) on a timer for 3 hr noontime run - Runs off PV ||
    || Midnight Classic 200 | 10, Evergreen 200w in a 160VOC array ||
    || VEC1093 12V Charger | Maha C401 aa/aaa Charger | SureSine | Sunsaver MPPT 15A

    solar: http://tinyurl.com/LMR-Solar
    gen: http://tinyurl.com/LMR-Lister ,

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