Correlating long-term performance and aging behaviour of building integrated PV modules

Abstract

Because building-integrated photovoltaic (BIPV) modules are fully integrated into a building envelope, the back of the module can be exposed to little or no ventilation, resulting in increased operating temperatures. As the temperature increases, the performance of the modules decreases, and the durability of the module and its polymeric components (e.g., encapsulant and backsheet) may be impacted. Over the years, three different PV test stands were monitored in Canobbio (southern Switzerland) in different configurations: open-rack, BIPV partially-ventilated and BIPV insulated (non-ventilated) to investigate the effect of the operating temperatures on the long-term energy performance of the different BIPV module types. In this study, the PV modules installed in these test stands were thoroughly examined by: (i) evaluating the long-term performance of the modules, and (ii) establishing a correlation between the electrical performance and changes in the properties of the polymers used in the laminate. In general, we observe that: (i) for some bill of materials (BOM), the higher thermal stress of BIPV configurations can accelerate the degradation, particularly of the encapsulant, leading to current losses attributed to the polymer (discolouration); (ii) in some cases, the higher thermomechanical stress can lead to a higher rate of damaged cells and cell interconnects, resulting in fill factor losses; (iii) on the other hand, a careful selection of the BOM and system design (with adequate rear ventilation) may mitigate the issues related to higher thermal and thermomechanical stresses.