FEASIBILITY STUDY OF THE CORRELATION BETWEEN DAMP HEAT TEST AND ACCELERATED WEATHERING TEST METHODS FOR BACKSHEETS

摘要

As the main critical parts in a photovoltaic (PV) module are polymeric materials, the aging behavior of backsheets is crucial for the whole photovoltaic module. In many standard backsheets polyethylene terephthalate (PET) is used as core layer. This is the reason for the high influence of the aging behavior of PET on the whole backsheet and therefore also on the whole PV module. Currently the standard test method for lifetime evaluation of backsheets of PV modules is a damp heat (DH) test at 85°C and 85% relative humidity (RH) for up to 2000 hours (h). The test duration of 2000 h equals approximately 3 months, which is a long time for material development. Further acceleration can be achieved by an increase of temperature, humidity and pressure - a so called pressure cooker test. To analyse differences in thermal and mechanical properties the aging behaviour was investigated by differential scanning calorimetry (DSC) and tensile tests. Thermal and mechanical properties showed a good correlation between pressure cooker at 120°C and damp heat test, with the constraint of presumable differences in the failure mechanism.