Experimental Investigation of the Shading and Mismatch Effects on the Performance of Bifacial Photovoltaic Modules

Bifacial photovoltaic (PV) modules are drawing increasing attention because of their potential in gaining extra energy from the rear-side irradiance. However, the rear-side irradiance can cause the performance of bifacial PV modules to be different from the performance of monofacial PV modules under shading and mismatch conditions. For bifacial modules, two factors can lead to the irradiance mismatch: the front-side partial shading and the rear-side irradiance inhomogeneity. This experimental work aimed to study the impact of these two factors on the performance of bifacial PV modules. The effect of front-side partial shading was investigated by comparing the electrical and thermal behavior of bifacial and monofacial PV modules under different shading conditions. The influence of rear-side irradiance inhomogeneity was investigated by analyzing the operating voltages of the solar cells in a bifacial PV module under certain typical installation conditions. To further explain the origin of the mismatch effect, a diode model circuit was applied in the analysis. The results indicate that even when the bypass diode of the bifacial PV module was activated, the shaded bifacial cells still received extra irradiance and produced higher heat. Thus, in most cases, the mismatch caused by the front-side partial shading may result in a greater reliability risk for the bifacial PV modules compared with the monofacial PV modules. For the mismatch effect of bifacial PV modules caused by the rear-side irradiance inhomogeneity, the significant reliability issues (such as reverse bias of solar cells and hotspot problems) would rarely happen, mainly because of the limited inhomogeneity of the equivalent irradiance and logarithmical increasing relationship between the voltage deviation and irradiance deviation of each solar cell.