The PV performance modeling application, PVsyst, implements the following cell temperature model:

$T_{c}=T_{a}+E_{POA}\frac{\alpha&space;\left&space;(&space;1-eta_{m}&space;\right&space;)}{U_{0}+U_{1}\times &space;WS}$

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 ($U_{1}=0$)

• 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 $\alpha&space;=0.9$ and $eta_{m}&space;=0.1$.