Thermomechanics of PV Modules Including the Viscoelasticity of EVA

We quantify the thermomechanical stresses in a crystalline photovoltaic module during thermal cycling between -40°C and 85°C with the help of a Finite-Element-Analysis of a 60 cell module. The quality of the simulation model is verified by a comparison to displacement experiments where the thermomechanical deformation of solar cells in a PV laminate is measured [1]. We find that the key feature in the simulation model is the viscoelastic material model for the EVA-encapsulant in order to obtain a good agreement with the experiments. The simulated stresses in the solar cells at -40°C are compressive and reach values of up to 75 MPa. In contrast, the back sheet is at -40°C under tensile stress of 45 MPa while the 4 mm thick glass experiences very low stresses. The EVA deforms with principal strains of up to 23% which proofs the EVA’s mechanical function as a compliant buffer layer. The change in the distance between two solar cells depends on their position in the module: close to the center the gap change is 120 μm (150°C to -40°C) while at the module edges the change in the cell distance is 170μm.