The PV performance modeling application, PVsyst, implements the following cell temperature model:
$$T_{c}= T_{a}+E_{POA}\frac{\alpha \left (1-\eta_{m} \right)}{U_{c}+U_{v}\times WS}$$
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)
- $$U_{c}$$ is the constant heat transfer component ($$W/m^2{K}$$)
- $$U_{v}$$ 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 $$U_{c}$$ and $$U_{v}$$. Note that the current default values assume no dependence on wind speed ($$U_{v}$$)
- For free-standing arrays the current default is : $$U_c$$ = 29 $$W/m^{2}K$$; $$U_v$$ = $$0$$ $$W/m^{3}sK$$
- For fully insulated arrays (close roof mount) the current default is: $$U_c$$ = 15 $$W/m^{2}K$$; $$U_v$$ = $$0$$ $$W/m^{3}sK$$
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 $$\eta_{m}$$.