Irradiance Effect

The efficiency with which a PV cell converts incident light into electrical power varies with the intensity of the incident light. The Irradiance Effect describes how the output of the PV plant is affected by this change of efficiency with irradiance, with the baseline being the power generated by the modules under reference irradiance \(\Gref\).

To simulate the operation of the modules operating under an irradiance of \(\Gref\) but with the same total available resource (i.e. irradiation) as is available when operating under \(\Geff\), we model the operation of the modules under irradiance \(\Gref\) but for a period factored by \(\Geff / {\Gref}\). This allows us to evaluate the change in module efficiency resulting from the different irradiances.

The plant array power with each submodule at MPP under effective irradiance and temperature is:

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

As before, \(P_\text{submod,npmc}\) is calculated using the \(\Delta_\text{npmc}\) value specific to the appropriate module type for each value of \(j\).

We compare this with \(P_\text{array,npmc,Tc,Gref} \left( t \right)\) calculated previously to give the Irradiance Effect at time \(t\):

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

Average power over time to prepare long-term averages; do not forget to de-season when calculating annually-representative results.