Module Temperature Derating

Calculate detailed voltage and power derating across temperature extremes for NEC 690.7 compliance.

Module Voc (V) Open-circuit voltage at STC

Module Vmp (V) Max power voltage at STC

Module Isc (A) Short-circuit current at STC

Module Pmax (W) Maximum power at STC

Temperature Coefficients (from datasheet)

Voc Coefficient (%/C)

Isc Coefficient (%/C)

Pmax Coefficient (%/C)

Modules in Series

Lowest Expected Temp (C) For max Voc calculation

Highest Expected Temp (C) For min Vmp calculation

Inverter/Charge Controller Limits

Max Input Voltage (V)

MPPT Range Min (V)

Temperature Derating Results

String Voltage Range

Cold Temperature (Max Voltage)

Module Voc @ Cold -

String Voc @ Cold -

Voltage Increase -

Hot Temperature (Min Voltage)

Module Vmp @ Hot -

String Vmp @ Hot -

Voltage Decrease -

Power Derating @ Hot

Cell Temperature -

Module Pmax @ Hot -

Power Loss -

String Power @ Hot -

Inverter Compatibility

Max Voc vs Limit -

Min Vmp vs MPPT -

Temperature Coefficient Formulas


                        Voc(T) = Voc(STC) x [1 + Coeff x (T - 25)]

                        Vmp(T) = Vmp(STC) x [1 + Coeff x (T - 25)]

                        Pmax(T) = Pmax(STC) x [1 + Coeff x (T - 25)]


                        Cell Temp = Ambient + 25C (typical estimate)

NEC 690.7 Requirements

Max system voltage must account for lowest expected ambient temperature
Use temperature correction factors from NEC Table 690.7(A) or manufacturer data
String Voc at coldest temp must not exceed inverter max input voltage
String Vmp at hottest temp must stay within MPPT operating window

Typical Temperature Coefficients

Panel Type	Voc (%/C)	Pmax (%/C)
HJT/IBC	-0.23 to -0.26	-0.26 to -0.30
Mono PERC	-0.27 to -0.30	-0.34 to -0.38
Standard Mono	-0.30 to -0.33	-0.37 to -0.42
Polycrystalline	-0.33 to -0.36	-0.40 to -0.45