FEM simulation of deformations in strings of shingled solar cells subjected to mechanical reliability testing

Among several emerging interconnection technologies, shingled solar cell interconnection is the technology to realize highest power densities in solar modules. Its main feature is the replacement of ribbon stringing with direct interconnection by a slight overlapping of the solar cells using electrically conductive adhesives (ECA) as joint material. To succeed in a highly competitive market, this type of interconnection still has to prove its reliability, which requires a sound understanding of the loads this ECA joint faces during module lifetime. This study applies structural mechanic simulations based on the Finite Element Method (FEM) to investigate the impact of external loads according to IEC 61215 on a string of shingled solar cells within a solar module laminate. Linear elasticity is compared to the more realistic viscoelastic modelling of the encapsulant (EVA) and the ECA with the objective of reducing computational effort, which is caused by viscoelasticity. We found that linear elasticity can be applied in comparative studies to investigate the potential of different geometric designs to reduce mechanical stress in the joint. When it comes to the calculation of absolute values for stress and strain the strong viscoelastic properties of EVA and ECA cannot be neglected.