Accelerated Service Life Testing of Photovoltaic Modules

Temperature, temperature cycling, water and UV radiation are considered as main degradation factors for PV modules by causing hydrolysis and photodegradation of polymeric components and corrosion of glass and of metallic components like grids and interconnectors. The temperature is very important for the degradation of the PV modules, because it determines at least the reaction rate for the degradation processes caused by the other degradation factors (e.g.hydrolysis by humidity and photodegradation by UV light). Modelling of the service life of modules applied in different climatic regions requires knowledge about the transient temperature load. A model, which allows calculating the module temperature as function of the ambient temperature, the global irradiation and the wind speed, facilitates the use of any time series of climatic data for a climatic region of interest. This data could be provided by weather services, test reference years or via the Internet. The microclimatic stress level of UV radiation and moisture on the PV modules is modelled as function of the module temperature and the important climatic parameters. Simple time transformation functions were used for the design of appropriate accelerated service life tests. The evaluated testing times differ up to an order of magnitude for different climatic locations, depending on the kinetics of the dominant degradation processes.