Effect of Temperature and Humidity on the Degradation Rate of Multicrystalline Silicon Photovoltaic Module

In a PV module, the relative humidity (rh) of a front encapsulant is different from that of a backside encapsulant (rh(back)). In this study, the effective humidity (rh(eff)) in a PV module was investigated to study the effects of moisture variation on the degradation rate (R-D). rh(eff) represents uniform humidity in a PV module when it is exposed to certain damp heat conditions. Five types of accelerated tests were conducted to derive the relation between rh(eff) and rh(back). rh(eff) showed a linear relationship with rh(back) at constant temperature. Two types of models, namely, Eyring and Peck models, were used for predicting the R-D of PV modules, and their results were compared. The R-D of PV modules was thermally activated at 0.49 eV. Furthermore, the temperature and rh(eff) history of PV modules over one year were determined at two locations: Miami (FL, USA) and Phoenix (AZ, USA). The accumulated R-D values based on the temperature and rh(eff) of the modules were calculated by summing the hourly degradation amounts over the time history.