Inhomogeneous rear reflector induced hot-spot risk and power loss in building-integrated bifacial c-Si photovoltaic modules

A building-integrated bifacial photovoltaic (BF-PV) module is a strong candidate for realizing zero-energy buildings because it can achieve high power output by collecting light from both the front and rear sides of the building. However, harvesting non-uniformly distributed rear incident light is a very challenge issue in BF-PV. In this study, we empirically investigated the effect of an inhomogeneous rear surface on the power and reliability of a BF-PV. The mini-module test showed that a non-uniform rear reflection triggers a current mismatch among cells, resulting in the overheating of cells above the low reflectance surface. In particular, a large difference in the reflectance inside the rear reflector installed close to the module increases a hot-spot risk. This risk can be reduced by minimizing the variation of the reflectance, as well as elongating the distance between the cell and the reflector. A theoretical calculation based on empirical results indicated that an inhomogeneous rear reflector results in power loss or a reliability issue in BF-PV modules. Hence, the rear surface of a BF-PV module should be carefully designed or considered in order to maximize its performance and reliability.