Determination of PV module power output degradation after long term operation

This work has been undertaken to examine the warranties offered by the PV module manufacturers for degradation after long term field operation under Thailand weather conditions. Samples from the four lots of PV modules comprising on mono crystalline, poly crystalline and amorphous silicon, with different duration of field operation ranging from 9 to 14 years were tested for I-V curve characteristics under field conditions and measured values were corrected to Standard Test Conditions (STC) values by using correction procedure inscribed in IEC 60891 standard. The corrected values of output power and other parameters were compared with nameplate data for calculation of degradation during the period of operation. The actual degradation in output power for two lots of mono and one lot of poly crystalline silicon was found remarkably high (3.9, 3.0 & 2%/year) when compared with the warrantees (0.8-1%/year generally). However, interestingly the lot comprising on thin film amorphous-Si modules showed higher values of output power than nameplate. There were no visible defects in the modules except yellowing and discoloring. The enhanced degradation rates can be attributed to the quality of modules along with the effects of harsh field weather conditions.