winter vs. summer derating table

guy_c
guy_c Registered Users Posts: 7
Hello,

Can someone point me to a resource giving, per earth coordinates, the insulation comparison between winter (sunny day) and summer (sunny day), in a power/area units.

The reason is that I try to figure out the quality of cells I bough before assembling them into panels and, right now (winter in Israel) I find a power which half the announced one (1.7W actual vs. 3.5 announced)

Thank you in advance for your time

Guy

Comments

  • mike95490
    mike95490 Solar Expert Posts: 9,583 ✭✭✭✭✭
    Re: winter vs. summer derating table

    I don't know if PV watts caculator covers your area, but winter days are shorter, and more air in the path, so power is expected to be reduced.
    http://www.pvwatts.org/
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  • BB.
    BB. Super Moderators, Administrators Posts: 33,402 admin
    Re: winter vs. summer derating table

    I don't have anything handy... But you can use a "known good" solar cell and connect it to an Amp Meter.

    When shorted, the current of a cell is proportional to the amount of sunlight on the cell.

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • icarus
    icarus Solar Expert Posts: 5,436 ✭✭✭✭
    Re: winter vs. summer derating table

    Insolation is one issue, but local weather/climate/cell temperature can have huge effect on output, that may not be reflected in a seasonal Pv watts calculation.

    Local haze, morning fog, cool breeze off of water etc can all have a significant effect. The reality is that most of the Calculators get you pretty close, but every installation is going to be different.

    Tony
  • stephendv
    stephendv Solar Expert Posts: 1,571 ✭✭
    Re: winter vs. summer derating table

    PV-Gis is an online calculator that includes Israel.
  • tallgirl
    tallgirl Solar Expert Posts: 413 ✭✭
    Re: winter vs. summer derating table
    mike90045 wrote: »
    I don't know if PV watts caculator covers your area, but winter days are shorter, and more air in the path, so power is expected to be reduced.
    http://www.pvwatts.org/

    Total daily power is reduced, but peak power can be well above STC. I've seen 108% of STC with the cold spell we had here recently. The flip side is miserably hot summer days, and I don't know if PV Watts compensates for hot panels.
  • guy_c
    guy_c Registered Users Posts: 7
    Re: winter vs. summer derating table

    First I want to thank you all for taking the trouble to answer.

    Special thanks to Stephen; Indeed this resource is what I was looking for. If their calculator is accurate there would be a 1:1.87 ratio from Jan to August

    Special thanks to Bill: This a nice pragmatic solution

    Guy