EL inspection of thin-film PV modules in between field operation

Homogeneity and stability of thin-film photovoltaic modules are of key importance for their long life-time and successful competition with other photovoltaic technologies. We have exposed and tracked three commercially available thin-film modules in outdoor conditions during the first months of operation. Before the start and periodically in-between the outdoor operation in maximum power point condition electroluminescence (EL) inspection and standard test condition (STC) performance data were measured. While the initial efficiency of thin-film silicon (both amorphous as well as micromorph tandem) PV modules decreased (-12% and -7%, respectively), the CIGS PV module´s STC conversion efficiency improved (+13%) during the period of the first 144 kWh/m² of solar irradiation. Much larger changes of EL intensity compared to the initial STC efficiency decrease have been observed in both thin-film silicon and CIGS PV modules indicating much higher sensitivity of EL to the temporal changes during operation.