On the use of reference modules in characterizing the performance of bifacial modules for rooftop canopy applications

The growth of bifacial systems in different photovoltaic (PV) applications is driving new requirements in measuring the effective irradiance for bifacial PV. Non-uniformity of rear irradiance may have a significant impact on the proper characterization of the system. It also has implications on modeling rear irradiance and consequently on performance prediction. In this work, we present a simple way of constructing an irradiance sensor from a commercial bifacial module and the application to performance and rear-side irradiance variability of a small rooftop bifacial PV system is analyzed. In addition, assessment of some commonly used models based on the view-factor approach is performed using as reference the front and rear irradiance simultaneous measurements from the bifacial reference module. The use of bifacial reference modules implies some benefits over arranging calibrated cells for determining rear irradiance, due to their higher field-of-view and representativeness of the response of the system to be monitored. This work also illustrates the high variability of rear irradiance in small systems and the impact of the edge effect. The results here can contribute to a better knowledge of the use of these reference modules as effective irradiance sensors for very bifacial PV configurations.