Siemens solar CIS photovoltaic module and system performance at the National Renewable Energy Laboratory

This paper evaluates the individual module and array performance of Siemens Solar Industries´ copper indium diselenide (CIS) polycrystalline thin-film technology. This is accomplished by studying module and array performance over time. Preliminary temperature coefficients for maximum power, maximum-power voltage, maximum-power current, open-circuit voltage, short-circuit current, and fill factor are determined at both the module and array level. These coefficients are used to correct module/array performance to 25°C to evaluate stability. We show that CIS exhibits a strong inverse correlation between array power and back-of-module temperature. This is due mainly to the narrow bandgap of the CIS material, which results in a strong inverse correlation between voltage and temperature. We also show that the temperature-corrected module and array performance has been relatively stable over the evaluation interval (≈2 years)