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.