Progress in photovoltaic module calibration: results of a worldwide intercomparison between four reference laboratories

Abstract

Measurement results from a world-wide intercomparison of PV module calibration are presented. Four PV reference laboratories in USA, Japan and Europe with different traceability chains, measurement equipment and procedures, as well as different uncertainty estimation concepts, participated. Seven PV modules of different technologies were measured (standard and high efficiency crystalline silicon, cadmium telluride, single- and double-junction amorphous and micromorph silicon). The measurement results from all laboratories and for all devices agreed well. Maximum power for the crystalline silicon samples was within ±1.3%, for all thin-film modules roughly within ±3%, which is very good compared to past intercomparisons. The agreement between the results was evaluated using a weighted mean as reference value which considers result-specific uncertainty, instead of the widely used unweighted arithmetic mean. A further statistical analysis of all deviations between results and corresponding reference mean showed that the uncertainties estimated by the participating laboratories are realistic, with a slight tendency towards being too conservative. The observed deviations of results from the reference mean concerned mainly short-circuit current and fill factor. Module stability was monitored through repeated measurements at Fraunhofer ISE before and after measurements at each of the other participating laboratories. Based on these measurements, stability problems that occurred for some thin film modules and influenced the results could be analyzed and explained in detail.