NOCT (Duffie and Beckman)

Method

The cell temperature rise above the ambient air is the rise at nominal operating conditions, 800 W/m² at 20 °C ambient, scaled in proportion to the irradiance. The light the module turns into electricity does not heat it, so the rise is reduced by the module efficiency over the transmittance-absorptance product of the cover and cells. The wind cools the module through the heat-transfer coefficient 5.7 + 3.8 v W/(m²·K) of Duffie and Beckman, with v in m/s, relative to its value of 9.5 W/(m²·K) at the 1 m/s wind of nominal conditions, with the weather file's wind speed times 0.51, the factor for arrays mounted less than 6.7 m above the ground. The irradiance is the effective irradiance on the front side, after the glass-reflection step and after the spectral modifier when that acts on the effective irradiance. The nominal operating cell temperature is 45 °C, and 49 °C on rooftop racking, where the modules sit close to the roof. The module efficiency is the module model's reference efficiency: the efficiency at standard test conditions, or the representative module's when the module model uses one. The temperature follows the weather of each timestep with no lag.

Settings

Setting	Value
Nominal operating cell temperature $T_{NOCT}$	45 °C; 49 °C on rooftop racking
Transmittance-absorptance product $\tau\alpha$	0.9
Wind factor	0.51
Lowest wind speed $v'$	0.001 m/s

The math

$$T = T_{amb} + \frac{G}{800}\,(T_{NOCT} - 20)\left(1 - \frac{\eta}{\tau\alpha}\right)\frac{9.5}{5.7 + 3.8\,v'},\qquad v' = \max(0.001,\ 0.51\,v) \tag{1}$$

where

Symbol	Meaning	Unit
$T$	the cell temperature	°C
$T_{amb}$	the ambient temperature	°C
$G$	the effective irradiance on the front side	W/m²
$T_{NOCT}$	the nominal operating cell temperature	°C
$\eta$	the module's reference efficiency	—
$\tau\alpha$	the transmittance-absorptance product	—
$v'$	the wind speed at the modules	m/s
$v$	the wind speed	m/s

References

1. Duffie & Beckman, Solar Engineering of Thermal Processes, 4th ed., Wiley 2013
2. Gilman, DiOrio, Freeman, Janzou, Dobos & Ryberg 2018, SAM Photovoltaic Model Technical Reference Update, NREL/TP-6A20-67399
3. NREL SAM Simulation Core (SSC) source code, release 2026.7.3, github.com/NatLabRockies/ssc: shared/lib_cec6par.cpp, cec6par_module_t and noct_celltemp_t; ssc/cmod_pvwattsv8.cpp, the module parameters of each module type

API

thermal.model = noct, thermal.transient = false

Symbols follow the symbol registry.