Impact of the constitutive behaviour of the encapsulant on thermo-mechanical damage in (c-Si) solar PV modules under thermal cycling

Abstract

The damage mechanism of encapsulant in solar cells with both lead-free and tin-lead solder as interconnecting material is examined by numerical investigation using finite element analysis (FEA). The magnitude of the damage was evaluated to determine the impact of different constitutive models of the encapsulant. Three different constitutive models of the EVA encapsulant namely: linear elastic material model (LEMM), temperature-dependant linear elastic material model (TDEMM) and linear viscoelastic material model (LVMM) were presented for the study. A test region average (TRA) thermal cycle generated from the in-situ climatic condition was used as the thermal load and boundary conditions for the study.Results from the numerical study show that the constitutive behaviour of the encapsulant has a significant impact on equivalent von-Mises stress and maximum principal strains in the encapsulant. The results of Equivalent von-Mises stress show a very high value of 4.857×107 Pa in the EVA material using LEMM whereas the lowest equivalent stress value of 525.83 Pa was registered in the EVA material when LVMM was used. Furthermore, life of the soldered joint from accumulated creep energy density (ACED) using LVMM of the EVA material yielded 23.4 years for the PbSn soldered interconnection. A result which correlates with reported field studies. This research proposes the LVMM as the most appropriate material constitutive model for modelling EVA encapsulant. The systematic technique employed in this study would be useful to the thermo-mechanical reliability research community and PV design and manufacturing engineers in the determination of accurate constitutive material model for robust thermo-mechanical analysis of solar PV modules.