Photovoltaic module power rating per IEC 61853–1: A study under natural sunlight

Power rating of photovoltaic modules at seven irradiance and four temperature matrix levels of IEC 61853-1 standard is one of the most important requirements to accurately predict energy production of photovoltaic modules at different climatic conditions. Actual outdoor measurements do not necessarily yield exact values as outlined by the power rating matrix so translation of these values is necessary. The primary objective of this work is to validate, based on outdoor measurements, the translation procedures as delineated in IEC 60891 standard and the bilinear interpolation method developed by NREL. These translation procedures were applied for four different module technologies: Mono-Si, a-Si, CdTe, and CIGS. To obtain data at various irradiance levels, different mesh screens with varying light transmittance were used with known transmittance values. To obtain data at various temperatures, the test module was pre-cooled in an air-conditioned wooden cabinet or an environmental chamber and then a series of current-voltage measurements were carried out under sunlight while the module warmed up naturally. To obtain data at temperatures higher than 45°C, the test module's backsheet was covered with a thermal insulator. The device linearity of all the four modules was determined using IEC 60904-10 procedure. An extensive validation analysis of the four translation procedures indicates that all the four procedures are remarkably accurate within an average error of 3% and RMSE of 4.5%.