Characterization of the Spectral Matching Ratio and the Z-Parameter From Atmospheric Variables for CPV Spectral Evaluation

The spectral matching ratio (SMR) and the Z-parameter are indexes used to assess the direct solar spectrum and its coupling to the multijunction solar cells employed in high-concentrator photovoltaic systems. An experimental campaign based on component cell sensors equivalent to a lattice-matched GaInP/GaInAs/Ge solar cell was carried out in Jaén, South of Spain, in order to measure the spectral data required to obtain these indexes. The main atmospheric parameters influencing the solar spectrum were simultaneously registered. An analysis of the data was carried out to characterize the spectral indexes by simple expressions as a function of air mass, aerosol optical depth, and precipitable water. As a result, the indexes are approximated with root mean square errors between 5.18% and 6.49%. The expressions for the SMR between the top and middle subcells and between the middle and bottom subcells were compared to other expressions proposed in the literature. The SMR between the top and bottom subcells and the Z-parameter were characterized from atmospheric variables for the first time. This study is an alternative method for the spectral evaluation of high-concentrator photovoltaic systems without using any relatively expensive measuring equipment, given that a meteorological database is available for a particular location worldwide.