Panels test different than summer time

KhellSkKhellSk Registered Users Posts: 82 ✭✭
edited December 2018 in Advanced Solar Electric Technical Forum #1
Hello everyone,

I have these panels that last summer with full sun on, tested 20v and 3.3 amps

Did the same thing couple days ago (winter) with clear sky facing sun as well

Tested 20v 1.25amps
@Photowhit ( panels alone, no load ,no battery, no charger)

Whats going on ?
_____________________________________________
[2x Flooded  6v 210ah][12v 30a 400wMax CC]
[5x 48w 15.9Vmp + 1x 100w 17Vmp]


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  • PhotowhitPhotowhit Solar Expert Posts: 5,496 ✭✭✭✭✭
    #2
    Are you testing them 'short circuit' not connected to anything? Or are these measurements off a charge controller?
    Home system 4000 watt (Evergreen) array standing, with 2 Midnite Classic Lites,  Midnite E-panel, Prosine 1800 and Exeltech 1100, 660 ah 24v ForkLift battery. Off grid for @16 of last 17 years. Assorted other systems, and to many panels in the closet to not do more...lol
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  • EstragonEstragon Registered Users Posts: 4,482 ✭✭✭✭✭
    #3
    Winter sun is much weaker than summer in most places that get snow.
    Off-grid.  
    Main daytime system ~4kw panels into 2xMNClassic150 370ah 48v bank 2xOutback 3548 inverter 120v + 240v autotransformer
    Night system ~1kw panels into 1xMNClassic150 700ah 12v bank morningstar 300w inverter
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  • BB.BB. Super Moderators, Administrators Posts: 31,329 admin
    #4
    It is amazing, but by our eyes, a 50% reduction in light is barely perceptible.

    Low winter sun angle, any haze/smoke/clouds, and you will get reduced current (Isc is more or less proportional to the amount of sun on the panel).

    If all of your identical panels are reading the same Isc current (short circuit current), then all is fine. If you have one panel that is reading 50% or less of the Isc of others measured in the same place, same angle, and same time--Then that panel (or its connections) are questionable.

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
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  • KhellSkKhellSk Registered Users Posts: 82 ✭✭
    #5
    BB. said:
    If all of your identical panels are reading the same Isc current (short circuit current), then all is fine. If you have one panel that is reading 50% or less of the Isc of others measured in the same place, same angle, and same time--Then that panel (or its connections) are questionable.

    -Bill
    All are approx the same. Its impressive that it isnt perceptible like you said. I really wonder what people do during winter... my charge controller cannot take more than 400w. To compensate for the lack of luminosity i would need to double my array but a charge controller is limited.


    How would one find a good balance  between C rate and amd wattage winter compensation
    _____________________________________________
    [2x Flooded  6v 210ah][12v 30a 400wMax CC]
    [5x 48w 15.9Vmp + 1x 100w 17Vmp]


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  • BB.BB. Super Moderators, Administrators Posts: 31,329 admin
    #6
    PWM controllers do not have the ability to regulate the "extra current" from a solar array. You are stuck following their array configuration requirements.

    MPPT type controllers are more flexible--And you can over panel to a degree just fine. There are secondary issues (any electronic device running at max current gets warmer than one running at 80% of rated current--Extra heat is always a difficulty... Can cause shorter life for electronics, especially if there is poor cooling / warm closet space). Oversize array in hot summer climate in a hot garage/battery shed--Your choice...

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
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  • KhellSkKhellSk Registered Users Posts: 82 ✭✭
    #7
    Thank you
    _____________________________________________
    [2x Flooded  6v 210ah][12v 30a 400wMax CC]
    [5x 48w 15.9Vmp + 1x 100w 17Vmp]


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  • softdownsoftdown Solar Expert Posts: 3,495 ✭✭✭✭
    #8
    Have you adjusted your panel tilt for the changing orientation of the sun? In my area, accurate orientation varies from ~ 22 degrees in June to ~52 degrees in December. 
    First Bank:16 180 watt Grape Solar with  FM80 controller and 3648 Inverter....Fullriver 8D AGM solar batteries. Second Bank/MacGyver Special: 10 165(?) watt BP Solar with Renogy MPPT 40A controller/ and Xantrex C-35 PWM controller/ and Morningstar PWM controller...Cotek 24V PSW inverter....forklift and diesel locomotive batteries
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