The PV performance modeling application, PVsyst, implements the following cell temperature model:
$$T_{c}= T_{a}+E_{POA}\frac{\alpha \left (1-eta_{m} \right)}{U_{0}+U_{1}\times WS}$$
where
- $$T_{c}$$ is cell temperature (°C)
- $$T_{a}$$ is ambient air temperature (°C)
- $$\alpha$$ is the absorption coefficient of the module (PVsyst default value is 0.9)
- $$E_{POA}$$ is the irradiance incident on the plane of the module or array ($$W/m^{2}$$)
- $$eta_{m}$$ is the efficiency of the PV module (PVsyst default is 0.1)
- $$U_{0}$$ is the constant heat transfer component ($$W/m^2{K}$$)
- $$U_{1}$$is the convective heat transfer component ($$W/m^{3}sK$$)
- $$WS$$ is wind speed (m/s)
PVsyst says little about what values to use for $$U_{0}$$ and $$U_{1}$$. Note that the current default values assume no dependance on wind speed ($$U_{1}$$)
- For free-standing arrays the current default is : $$U_0$$ = 29 $$W/m^{2}K$$; $$U_1$$ = $$0$$ $$W/m^{3}sK$$
- For fully insulated arrays (close roof mount) the current default is: $$U_0$$ = 15 $$W/m^{2}K$$; $$U_1$$ = $$0$$ $$W/m^{3}sK$$
PVsyst users can also enter a NOCT (Nominal Operating Collector Temperature) in place of $$U$$ values. The program then automatically calculates $$U$$ values based on $$\alpha=0.9$$ and $$eta_{m}$$.