Analytical transfer equations for the spectral modelling of III–V multi-junction concentrator solar cells

The varying shape of the direct normal irradiance (DNI) spectrum is mainly determined by air mass (AM), aerosol optical depth (AOD) and precipitable water (PW). Unlike some previous studies that aimed at modelling the spectral impact on photovoltaics (PV), a recently published method takes these parameters into account when modelling spectral effects on concentrating PV. A short review of this method is provided initially in this paper. Then, this work presents the results of an empirical validation for a typical lattice-matched 3J GaInP/GaInAs/Ge solar cell during four specific days selected from a wider 3-month experimental campaign. During this period, spectral DNI measurements were recorded at 5-minute intervals and combined with the spectral response of the CPV solar cell considered to calculate measured values of the spectral factor (SF). Results show how predicted values of SF are in close agreement with measured ones as root mean square error (RMSE) values do not exceed 2% for all the days analysed. Further, negligible values of mean bias error (MBE) are obtained. The best results are obtained in days with moderate values of AOD and PW -RMSE around 0.5%- while modelled values of SF get worse -RMSE slightly less than 2%- in days with extreme values of such parameters. Last, the method investigated here yielded a value of RMSE of 0.8%, which is far below 2.3% obtained by applying the other methods for the whole 3-month period under study.