Outdoor degradation of CdTe modules at open circuit and at maximum power point

A combination of outdoor exposure and laboratory measurements were utilized to characterize the differences in degradation of commercial CdTe modules in two operating modes. The degradation mechanism was observed on an array of 8 CdTe modules operated outdoors in open-circuit conditions. In contrast, a similar array of 8 grid connected PV panels operated at the maximum power point did not show any degradation over the same period of time. Of the degraded panels, Voc and FF degraded 6% and 7% respectively. Electro-luminescence imaging showed large dark areas in the degraded modules. Spectral response measurements showed enhanced response at blue wavelengths but significantly reduced response at red and near infrared wavelengths. Results suggest that degradation studies at representative field conditions are equally important as the standard accelerated ageing methods and should be taken into consideration.