Influence and characteristic of shading on photovoltaic performance of bifacial modules and method for estimating bifacial gain

Bifacial PV modules have unique advantages in low-carbon building applications such as BIPV systems but often suffer from the shading problem resulting from higher surrounding objects or building facades. Point-blank quantitative studies of PV performance of bifacial modules operating in actual environments as affected by shading on PV cells are lacking due to the difficulties of analysis caused by the existing multiple variable factors. By constructing an experimental comparison system on a flat roof of a building, we experimentally tested and analyzed the comparative variation characteristics of PV performance of bifacial and mono-facial modules under different shading area fractions. The results show that from the viewpoint of photoelectric efficiency, the PV performance of both bifacial and mono-facial PV modules clearly varied with the shading fraction of PV cell in some linear rules, though it is difficult to find regularity from the perspective of output power which was also affected by dynamic solar radiation intensity. An abnormal phenomenon emerged that the photoelectric efficiencies of the bifacial modules with small shading fraction were higher compared to the case without shading. Based on the findings of the experimental results, a regression approximation method based on shading test results (RAST Method) is further proposed to analyze and calculate the bifacial gain of bifacial modules. In the case of the existing roof installation, the mean bifacial gains of the two bifacial modules with different inclination angles were 8.86% and 11.30%, respectively.