Radiometry in photovoltaics: calibration of reference solar cells and evaluation of reference values

The key quantity in the calibration of solar cells and photovoltaic modules is the short-circuit current of the device generated by a reference solar radiation with 1 kW m(-2) total irradiance and with reference solar spectra l irradiance distribution. Thus, (i) double spectral mismatch between test and standard device and between test and reference solar spectrum; and (ii) the calibration transfer from low to high irradiance level (non-linearity effects) may affect the calibration value. An overview of primary and secon dary calibration procedures is given, focusing on the primary calibration m ethods applied by the four qualified laboratories establishing the World Ph otovoltaic Scale (WPVS) traceable to the International System of Units (SI) . The differential spectral responsivity method of the Physikalisch-Technis che Bundesanstalt (PTB) is described in more detail. Finally, different app roaches are illustrated for the evaluation of a reference value, including the WPVS, based on the results for twenty transfer/travelling standards of the international comparison among eleven participants that was carried out to establish the WPVS.