Temperature Effect

The efficiency with which a PV cell converts incident light into electrical power varies with the temperature of the cell. The Temperature Effect describes how the output of the PV plant is affected by this change of efficiency with temperature.

To evaluate the annual Module Temperature Effect \(\Delta_{\text{temp}}\) we compare the output of the plant array operating at the reference condition cell temperature of \(\Tcref\) (25 °C under STC) with the output of the plant array operating under the same irradiance conditions but at the modelled cell temperatures \(T_{\text{c}} \left( j, t \right)\). In both cases, the module performance is modelled at the reference irradiance \(\Gref\) (1000 W/m² under STC) then scaled by the ratio of the actual irradiance to the reference irradiance to equalize the total irradiation converted by the module whilst simulating module operation (and hence efficiency) at reference irradiance to isolate the temperature effect.

The nominal plant array electrical power at time \(t\) under STC conditions is:

$$P_\text{array,npmc,STC} \left( t \right) = \sum^{N_\text{submodules}}_{j = 1}{\frac{\Geff \left( j, t \right)}{\Gref} P_\text{submod,npmc,STC}}$$

The array electrical power at time \(t\) considering the modelled cell temperatures is:

$$P_\text{array,npmc,Tc,Gref} \left( t \right) = \sum^{N_\text{submodules}}_{j = 1}{\frac{\Geff \left( j, t \right)}{\Gref} P_\text{submod,npmc} \left( \Gref, T_\text{c} \left( t \right) \right)}$$

\(P_\text{submod,npmc}\) is calculated in each case using the \(\Delta_\text{npmc}\) value specific to the appropriate module type for each value of \(j\) (if there is more than one type of module in the plant array).

The Temperature Effect at time \(t\) is:

$$\Delta_\text{temp} \left( t \right) = \left( \frac{P_\text{array,npmc,Tc,Gref} \left( t \right)} {P_\text{array,npmc,STC} \left( t \right)} - 1 \right) 100 \% $$

As before, the powers can be averaged over longer periods to derive monthly or annual values for the Temperature Effect, taking care to de-season annual results.