Comparison of Reliability Tests by Characterization of Degradation in Photovoltaic Modules

The recent large scale deployment of multi crystalline silicon photovoltaic (PV) modules in the field has risen the need for indepth studies of degradation in a fast and efficient manner. In this context, different standard test procedures as specified under IEC 61215 viz. thermal cycling (TC), humidity freeze (HF) and damp heat (DH) have been developed for crystalline silicon PV modules [1]. These tests undergo different degradation mechanisms on application of various environmental stress factors in an accelerated frame and help in assessing the reliability of the modules in a short period of time [2,3]. These different tests when exploited in PV modules, checks for the module reliability on different aspects such as high temperature effect, thermal ramping, and humidity ingression effect etc. These aspects essentially affect the module performance individually or in combination to one another. In order to understand the modules behavior under these stress factors, a comparative study of these standard reliability tests can be helpful. Earlier, illuminated current voltage (I-V) analysis has been used for extraction of global electrical parameters in relation to the degradation observed after these tests [4]. However, I-V analysis alone cannot be used for defect analysis as it cannot map the cause of the degradation. It is essential to obtain spatially resolved information of the PV modules to understand the channel of degradation. Hereof, Electroluminescence (EL) and Dark lock-in-thermography (DLIT) in addition to non-spatial IV investigation can be used for detection and analysis of defects in PV modules.