Mechanical problems of novel back contact solar modules

The mechanical integrity of interconnect structures of different types of photovoltaic modules is analyzed by FEM-simulations. The goal is to develop a systematic understanding of the potential thermo-mechanical damage by a detailed theoretical analysis of the mechanical behavior of important structural elements in photovoltaic modules. The results of this investigation allow to identify critical locations in the photovoltaic module assembly that limit the module lifetime.FEM-simulations were carried out in order to analyze the mechanical stresses which were built up during the operation of the photovoltaic modules. Two types of photovoltaic modules were considered – traditional modules which consist of H-patterned solar cells connected by a tabber–stringer process and novel modules which consist on back contact cells interconnected by a flexible PCB back sheet. Thermo cycling tests between −40 °C and +80 °C were object of these theoretical investigations. Practically these tests are used in the qualification procedure for photovoltaic modules according to IEC/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. In 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.