Reliability of crystalline silicon photovoltaic laminates: Test development and finite element analysis

The use of finite element analysis (FEA) and lab testing is gaining acceptance within the photovoltaic (PV) industry and is being increasingly used to “design-in” reliability into a product by investigating damage based on anticipated field conditions and environmental stressors. This paper presents a case study on the use of FEA to predict crystalline silicon (c-Si) cell fracture within a laminate subjected to bending loads (analogous to stepping loads during installation and loads experienced under rack-mounting and seasonal wind and snow conditions). Challenges related to development of a material model (that could be incorporated into the FE models) for c-Si cells are discussed. The use of electroluminescence (EL) as a diagnostic technique to detect fracture of c-Si cells within laminates is discussed. Finally, the use of in-situ Voc measurements during three-point bend testing in detecting failure events (in un-aged laminates and those aged under accelerated testing conditions) is also described. This could potentially be a new test method to investigate the effects of accelerated testing on the mechanical integrity of different parts of the electrical assembly such as the cells, weld and solder joints.