FEM Simulation of Influence of Different Polymeric Encapsulation Materials and Backsheets on Deformations in Strings of Shingled Solar Cells under Mechanical and Thermal Loading

Among several new cell architectures and module concepts, shingled solar cells interconnection is a promising technology to realize increased power output (higher power densities) by increased active cell area and low electrical losses. The direct interconnection by a slight overlapping of solar cells, using electrically conductive adhesives (ECA) as joint material, requires a sound understanding of the loads the ECA joint faces during module lifetime. In general, thermo-mechanical stresses in photovoltaic (PV) modules arise from external forces deflecting the module (e.g. wind or snow covering the module) and variations of temperature, hence stresses induced by differing coefficients of thermal expansion (CTE) of the different materials in the module laminate. The current study applies structural mechanics simulations based on the Finite Element Method (FEM) to investigate the impact of external mechanical and thermal loads on strings of shingled solar cells within a PV module according to well established standards IEC 61215:2-2016 (mechanical loading) and IEC 61215:2005 (thermal loading). The objective is to perform a sensitivity study on the influence of using different polymeric encapsulants and backsheet with the purpose of reducing stresses in the ECA joint and the adjacent silicon cells. Therefore, two newly developed encapsulants for photovoltaic applications, namely thermoplastic polyolefin (TPO) and polyolefin elastomer (POE) are compared to the most widely used ethylene vinyl acetate (EVA). Furthermore, co-extruded polypropylene (PP) as well as laminated polyphenylenether (PPE), polyethylene terephthalate (PET) and polyvinylidene fluoride (PVDF/PET/EVA) backsheets are compared to a standard glass-backsheet module. The numerical analyses enables to directly analyze the internal stresses in the PV module and specifically the local stress distribution for the shingled interconnection. Viscoelastic material modeling is used with the objective of capturing the rate and temperature dependency of polymeric materials to allow for more accurate modeling of the material response.