Light-soaking and power measurements of thin film modules

Stabilized electrical performance data are necessary to compare different types of modules in the emerging thin-film-PV market and as basic information for energy yield calculations. The problems with accurate power measurements of thin film modules are well known. The module test-standard IEC 61646 ed. 2 tries to take this into account by demanding light-soaking and repeated STC-measurements which leads to time analysed procedures. The stabilisation behaviour over time of short circuit current, open-circuit voltage, efficiency and filling-factor is compared under the influence of different illumination conditions for various types of CdTe, CI(G)S and a-Si modules. Therefore, I-V-curves are measured with high frequency during outdoor exposition and indoor exposition to 1000 W/m(sup 2) irradiation from a class B solar simulator in a climatic cabinet under temperature-controlled conditions. The different modules are held in MPP conditions between the measurements. The results are compared with STC measurements according to IEC 61646 procedures. To describe the development of the performance of the different types of thin film modules, suitable mathematical approaches are taken to describe the different developments during the process of light soaking. It turns out that the different module types behave very differently and some types need very long times until a stabilised state is reached..