Development and thermo-mechanical reliability assessment of fiber reinforced polymers in lightweight PV modules towards vehicle-integrated photovoltaics

Abstract

Weight reduction by omitting the use of bulky glass in c-Si photovoltaic (PV) modules is an important consideration of module development for vehicle-integrated photovoltaics (VIPV). Various approaches to achieve lightweight modules are proposed, yet there are many concerns regarding the reliability of such modules compared to standard glass-glass or glass-backsheet configurations. In this work, we investigate the thermomechanical behavior of LW modules with a multiwire design specifically aiming to VIPV applications. The developed modules consist of a commercially available carbon-fiber reinforced polypropylene backsheet and are compared to glass-fiber reinforced polypropylene backsheet modules. To enhance the thermo-mechanical reliability, polymer encapsulant and interconnection foil are substituted by glass-fiber reinforced composite encapsulant with the carbon-fiber reinforced polypropylene backsheet, thereby leading to similar to 2.9% fill factor (FF) decrease with a limited degradation after 200 thermal cycles. A failure mechanism analysis using electroluminescence and X-ray-based micro-tomography is carried out after thermal cycling tests, clearly demonstrating that thermal stresses introduce deformation of wire interconnects. A modified high-temperature thermal cycling test (-40 to 110 degrees C, 3.5 h) is implemented to observe the fast degradation of interconnects in compliance with VIPV conditions. The resulting fatigue stresses account for wire breakage in-between cells in the glass-fiber reinforced polypropylene module, while this effect is less pronounced in the carbon-fiber reinforced polypropylene backsheet module, indicating better thermo-mechanical reliability of the carbon-fiber reinforced polypropylene backsheet module. Herein, the current results could provide guidelines for lightweight PV module design (with a weight of 4.8 kg/m(2)) in the thermo-mechanical aspect. This research sheds light on the potential of lightweight modules specifically for VIPV applications.