Degradation Mechanism Investigation of Extended Damp Heat Aged PV Modules

Abstract

The lifetime and sustained power output of a photovoltaic (PV) module impacts the total number of kilowatt-hours (kWh) produced, which ultimately drives the cost of generated electricity. Because PV module lifetimes are desired to be greater than 20 years, accelerated testing protocols, such as IEC 61215, have been used to assure that a 20 year lifetime is achievable. In particular, the Damp Heat (85°C/85% relative humidity) protocol has been used to accelerate potential degradation mechanisms by increasing the temperature and humidity of the modules under test. This accelerated aging test was applied to PV modules with silicone and ethylene vinyl acetate (EVA) encapsulation materials to compare their performance. These modules were aged in Damp Heat several times longer than the IEC standard of 1000 hours. The modules were periodically analyzed for current voltage (IV) by Sun Simulator to compare the influence of the encapsulant on module power output. At 3000 hours of exposure a significant reduction in power output was noted in the EVA set of modules, while minimal power degradation was observed in the silicone set. The power reduction was driven by reduced Fill Factors (FF) and increased Series Resistance (Rs). These reductions were initially interpreted as corrosion taking place at the electrical interconnects; however, further aging showed a drop in Short Circuit Current(Isc) indicating that other degradation mechanisms could be at work. Analysis by electroluminescence (EL) imaging also indicated that factors other than corrosion at the electrical interconnects may have occurred. This presentation describes the analysis of silicone and EVA encapsulated modules after extended Damp Heat aging to help determine the degradation mechanisms involved in the power output over time.