Novel Accelerated UV Testing of Field-Aged Modules: Correlating EL and UV Fluorescence Images with Current Drop

Encapsulant discoloration, a commonly occurring and serious field degradation mode, can be replicated by exposing modules to UV light. Increasing the UV light intensity and the testing temperatures reduces the required testing time. Calculating activation energy using Arrhenius equation for the encapsulant discoloration requires short-circuit current data (or yellowness index data) at multiple temperatures over significant time period. A method of simultaneously obtaining four temperatures in four photovoltaic modules in a single walk-in accelerated UV weathering chamber which drastically reduces the required time and resources is presented. Field-aged modules with visible encapsulant browning were selected for the accelerated testing to determine the wear-out failure mechanisms rather than the early life and midlife failure mechanisms conventionally determined using fresh modules. These modules have been subjected to a very long UV exposure of 450 kWh operating at high temperatures. This work demonstrates that a fast, repeatable, and non-contact UV fluorescence setup can be used in the accelerated testing programs and in powerplants as a standardized technique for an early encapsulant browning detection.