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PVWatts System derates and Inverter model

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  • PVWatts System derates and Inverter model

    Dear Solar Panel talkers,
    For the last couple of days I was trying to understand the "math" behind PVWatts v1 using their PVWatts Version 1 Technical Reference.pdf.

    For some reason the System Derates and Inverter Model are parts where some uncertainties arise.
    I tried using their PVPerformance modeling steps but didn't get the answers.
    I would be very grateful if some of the experts around here could give me some hand.


    10) System Derates:
    P'dc - derated DC power
    Pdc - DC power
    ξsys - overall system derate
    ηinv - inverter efficiency at maximum power (suggested to be 0.90 < ηinv < 0.96 in this topic)

    Code:
    P'dc = Pdc * ξsys/ηinv
    question 1:
    Does PVWatts team by default offer value of 0.77 for ξsys?



    11)Inverter Model

    Pinv,dc0 - inverter DC rating
    Pac0 - inverter AC nameplate rating
    ηop - inverter conversion efficiency at operating conditions

    Code:
    Pinv,dc0 = Pac0/ηinv
    f = P'dc/Pinv,dc0
    
    if (f >= 0.1) and (f <= 1):
        ηop = 0.774 + 0.663 * f - 0.952 * (f^2) + 0.426 * (f^3)
        Pac = Pdc' * ηop * ηinv/0.91
    
    else if (f > 0) and (f < 0.1):
        ηop = -0.015 + 8.46 * f
        Pac = Pdc' * ηop * ηinv/0.91
    
    else if (f > 1):
        Pac = Pac0
    question 2:
    So does Pac0 = Pdc0 (Pdc0 by default is 4000 Watts (4kW) ??)


    I aslo contacted the PVWatts team, and got response that they do not support the v1 anymore.
    Thank you for the help.
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