Vtoc and Vtmp units in nameplate ratings

konstantin.neo
konstantin.neo Registered Users Posts: 19 ✭
in Solar Beginners Corner #1
While using the outback string sizer I have noticed that Vtoc and Vtmp units given by pv manufacturers can be Volts/°C or %/ºC
The Vtoc and Vtmp values that the String Sizer uses have units of Volts/°C.
How can I convert %/ºC to Volts/ºC ?
Thanks.
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  • BB.
    BB. Super Moderators, Administrators Posts: 33,642 admin
    #2
    Re: Vtoc and Vtmp units in nameplate ratings

    Take:
    • Voc * %/oC * (1/100) = Vtoc/oC
    • Vmp * %/oC * (1/100) = Vtmp/oC

    and you should be OK (as I understand).

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
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  • konstantin.neo
    konstantin.neo Registered Users Posts: 19 ✭
    #3
    Re: Vtoc and Vtmp units in nameplate ratings

    Voc=37.64
    Vmp=30.5
    Voltage temp coefficient -0.35 %/°C

    Vtoc= 37.64 V / 100 * 0.35 = 0.13174
    Vtmp=30.5 V /100 * 0.35 = 0.10675

    I did like this, I guess that is correct.
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  • BB.
    BB. Super Moderators, Administrators Posts: 33,642 admin
    #4
    Re: Vtoc and Vtmp units in nameplate ratings

    Just to clarify--I would write the equation this way:
    • Vtoc = 37.64 * -0.35 / 100 = -0.13174 V/°C
    • Vtmp = 30.5 * -0.35 / 100 = -0.10675 V/°C

    So you don't have the confusion of order of operation:
    • Vtoc= (37.64 V / 100) * -0.35 = 0.13174 correct
    • Vtoc= 37.64 V / (100 * -0.35) = 0.13174 incorrect

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
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