COMPARISON OF DEGRADATION MECHANISM OF PV MODULES BETWEEN UNDER LONG TERM FIELD EXPOSURE AT A HOT-HUMID ENVIRONMENT AND UNDER DH TESTS

摘要

Degradation of the photovoltaic (PV) modules exposed for 18 years at a hot and humid environment (at Miyakojima Island) and that of PV modules subjected to the extended DH tests (1000 h～4000 h) were studied. The similarities and differences in degradation mechanisms between both modules were examined. We found both modules showed similar degradation to each other, such as views of dark regions in electroluminescence (EL) images and primary cause of power losses (a series resistance increase). Furthermore, it was observed that power losses of both modules were caused by an increase in contact resistance of Ag/Si interface of finger electrodes. Observations of cross sectional contact interface by an electron microscope suggested that a lead-glass layer at the interface probably plays an important role during contact degradation in acidic environment. On the other hand, however, detected amounts of residual acetic acid in the Miyakojima modules were roughly only 1/10 of those in the DH degraded modules And a clear correlation between the amount of residual acetic acid and the power loss of the module, which was shown in extended DH modules, was not shown in outdoor exposed modules including Miyakojima modules.