Mechanical problems of novel back contact solar modules

In this paper, the mechanical integrity of interconnect structures of different types of photovoltaic modules is analyzed by FEM-simulations. The goal is to develop a theoretical framework for the systematic understanding of mechanical behavior of photovoltaic modules. The results of this investigation figure out, where are critical locations in the photovoltaic module assembly that limit the module lifetime. Another goal is to show, how changes in the assembly technology (e.g. geometries, processes, materials) will have an effect on the overall reliability of the photovoltaic module. FEM-Simulations were carried out, in order to analyze the mechanical stresses, which were built up during the operation of the photovoltaic modules. Thermo cycling test between -40°C and +80°C were simulated. These tests are used in the qualification procedure for photovoltaic modules according to TEC/EN 61215. The results of the study show that stresses during the assembly and the operation occur in different locations in dependence of the assembly design. Tn the traditional modules the silicon underneath the busbar and the copper ribbon crimp between two adjunct cells are the locations where most of the damage is likely to accumulate. In contrast to this the solder joints in the outermost row of the back contact cells are the critical locations in the novel back contact design. The paper will explain the differences of thermo-mechanical behavior between the designs.