The PV performance modeling application, PVsyst, implements a cell temperature model based on the Faiman module temperature model.  The form of the model is:

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

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 $eta_{m}&space;=0.1$.

Values for $U_0$ and $U_1$ can be calculated which correspond to the reference parameters for the Sandia Cell Temperature Model. The PVsyst model can be approximated as

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

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

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

$T_{c}&space;\approx&space;T_{a}+E_{POA}&space;[\frac{\alpha&space;\left&space;(&space;1-eta_{m}&space;\right&space;)}{U_{0}}&space;-&space;\frac{\alpha&space;\left&space;(&space;1-eta_{m}&space;\right&space;)&space;U_{1}}{U_{0}^{2}}\times&space;WS]$

Similarly the Sandia Cell Temperature Model can be approximated as

$T_{c}&space;=T_{a}+\frac{E_{POA}}{E_0}\Delta&space;T&space;+&space;E_{POA}&space;\times&space;e^{a+b\times&space;WS}$

$T_{c}&space;\approx&space;T_{a}+&space;E_{POA}&space;\left(\frac{\Delta&space;T}{E_0}&space;+&space;e^{a}&space;\left(&space;1&space;+&space;b&space;\times&space;WS&space;\right)&space;\right)$

$T_{c}&space;\approx&space;T_{a}+&space;E_{POA}&space;\left(\frac{\Delta&space;T}{E_0}&space;+&space;e^{a}&space;+e^{a}b&space;\times&space;WS\right&space;)$

Equating terms gives the following equations that relate the PVsyst cell temperature model parameters $\alpha,&space;eta_{m},&space;U_{0},&space;\rm&space;\&space;and&space;\&space;\it&space;U_{1}}$  to the Sandia Cell Temperature Model parameters $a,&space;b,&space;\rm&space;\&space;and&space;\&space;\it&space;\Delta&space;T$ :

$\frac{\alpha&space;\left(1&space;-&space;eta_{m}&space;\right&space;)}{U_{0}}&space;=&space;\frac{\Delta&space;T}{E_{0}}&space;+&space;e^{a}&space;\Rightarrow&space;U_{0}&space;=&space;\frac{\alpha&space;\left(1&space;-&space;eta_{m}&space;\right&space;)}{\frac{\Delta&space;T}{E_{0}}&space;+&space;e^{a}}$

$-\frac{\alpha&space;\left(1&space;-&space;eta_{m}&space;\right&space;)}{U_{0}}&space;\frac{U_{1}}{U_{0}}=&space;e^{a}b$

$-\frac{\alpha&space;\left(1&space;-&space;eta_{m}&space;\right&space;)}{U_{0}}&space;\frac{U_{1}}{U_{0}}=&space;e^{a}b&space;\Rightarrow&space;U_{1}&space;=&space;-\frac{e^ab&space;\alpha&space;\left(&space;1&space;-&space;eta_{m}&space;\right)}{\frac{\Delta&space;T}{E_{0}}+e^{a}}$