Acceleration Factor Determination for Potential-Induced Degradation in Crystalline Silicon PV Modules

Potential-induced degradation in conventional p-type silicon-based photovoltaic solar cell modules is described as a failure mechanism involving positive ion migration, understood to be primarily Na⁺, drifting from the glass to the cells in negative-voltage arrays. Acceleration factors for this mechanism are determined for silicon photovoltaic modules by comparing the module power during degradation outdoors to that in accelerated testing at three temperatures and 85% relative humidity. A lognormal analysis is applied to the accelerated lifetime test data considering failure at 80% of the initial module power. Activation energy of 0.73 eV for the rate of failure is determined for the chamber testing at the constant relative humidity, and the probability of module failure at an arbitrary temperature is predicted. Estimation of module power in-situ in the environmental chamber is achieved using dark I-V measurements transformed by superposition. By this means, the power of the degrading module can be semi-continuously determined so that statistical data for multiple modules undergoing potential-induced degradation can be easily and accurately obtained.