A simulation model of the irradiation and energy yield of large bifacial photovoltaic plants

Abstract

Open questions remain regarding the use of bifacial photovoltaic (PV) modules, such as how to link the energy-yield modelling of large bifacial PV plants with further on-site measurements campaigns, the effect of the non-uniformity of the rear irradiance, as well as the convenience of varying the geometry of the plants to enhance the bifacial contribution. A simplified two-dimensional view factor model for bifacial PV plants is presented in this paper, as well as a specific definition of performance ratio (PR) for this type of installations. This model has been implemented in SISIFO --an open simulation tool --for static structures and horizontal single-axis trackers. Yearly energy yield has been simulated for two representative static and tracker PV plants located in Madrid with an albedo of 0.3 and a bifacial power coefficient of 0.7, resulting in yield increases driven by rear irradiation of 8% and 7%, respectively. In general, the influence of varying structure height is lower than that of row-to-row spacing. The model also reveals a non-homogeneous rear irradiance. This question of non-uniformity of rear irradiance is analyzed in light of experimental 10-month observations in a 6.6 kWp PV system. The average of the rear irradiance observed at the center and at the two borders of the PV array is an adequate predictor for DC power estimations. A pioneering chapter of bifacial PV modules industrialization that took place between 1984 and 1989 in Spain, and probably the first application of view factor to model bifacial PV modules, are also presented.