FEM simulation of deformations and stresses in strings of shingled solar cells under mechanical and thermal loading

Among several new module concepts and cell architectures, shingled solar cell interconnection is a promising technology to realize increased power output (higher power densities) by increased active cell area and low electrical losses. In shingled modules the pre-cut crystalline cells are placed like roof tiles on top of each other, resulting in a string in which there are no empty spaces between the cells. The series interconnection of the different pre-cut cells is achieved by electrically conductive adhesive (ECA). In general, thermo-mechanical stresses in PV modules origin 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). In this context, demands for a better understanding of interconnection failure modes arise to ensure the success of this new module concept. The current study applies structural mechanic 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. The simulations use a multi-scale modeling approach, i.e. a full-scale shingled module is used to receive realistic environmental inputs and provide boundary conditions for a submodel for a detailed stress analysis of the shingle joint and the adjacent silicon cells. Viscoelastic modeling is used with the objective of capturing the rate and temperature dependency of polymeric materials, i.e. the encapsulant and the ECA interconnect, to allow for more accurate modeling of the material response. The objective is to reduce overall stress on the shingled strings and ECA joints and perform a sensitivity study on potentially adaptable design and material parameters (e.g. joint thickness, joint width and cell overlap).