Monofacial and bifacial PV systems – changes in system parameters can affect the bifacial gains

 

  • Scientists from Ghana’s Kwame Nkrumah University of Science and Technology, Bui Power Authority, and the Norwegian University of Life Sciences have assessed the performance of existing and simulated monofacial land-based and floating solar installations in Ghana and compared them with the energy yield of simulated bifacial systems of the same dimensions and design.

The existing installations are a 50 MW ground-mounted PV facility and a 400 kW floating PV array. Both are linked to the 404 MW hydroelectric power plant at the Bui Dam.

“One of the key scientific knowledge gaps missing in the literature review is the lack of comprehensive performance data for land-based and floating PV solar systems (monofacial and bifacial) specifically designed and tested in West Africa’s low latitude regions,” the researchers highlighted. In using different solar integration approaches at the hydropower plant, the group sought to determine the optimal system parameters to enhance performance.

The results of the group’s assessment show the gain of non-optimized bifacial land-based PV and bifacial floating PV (FPV) systems is 2.51% and 4.57% respectively, compared to their monofacial counterparts. The researchers noted that while this was not significant enough to justify installing a new system, additional gains could be achieved by optimizing the characteristics of the system.

For example, changing the ground albedo of a land-based PV system from gravel to a white surface increased the bifacial gain from 5.25% to 14.5%. The team also determined the optimum tilt angle for bifacial land-based PV and FPV systems to be 15% to achieve maximum annual energy generation of 79.5 GWh and 620.9 MWh respectively.

For the study, Bui Power Authority obtained 15-minute step daily measured weather data for 2022, including global horizontal irradiance on a horizontal surface, ambient temperature, and wind speed. The energy generation data available from Bui for the 400 kW operational monofacial FPV system covers the period from September 2022 to February 2023, while data for the energy generated by the 50 MW land-based monofacial system is from the entire year of 2022.

The researchers used the System Advisor Model (SAM) tool and a modified weather file from the National Solar Radiation Database to simulate the performance of a bifacial PV system on water and land. Based on the assessment, the team found that for the best performance and increase in bifacial gain, the parameters for the albedo, tilt angle, and ground cover ratio should be 0.5, 15, and 0.3 respectively.

“With 1% of Africa’s total surface area of water bodies, FPV has the potential to generate 101 GWp of power, a 46.04 TWh annual addition, and water savings of 743 million m3/year,” the academics emphasized. “Installing floating photovoltaic (FPV) panels on hydroelectric power reservoirs could help stabilize hydropower generation during dry seasons, decrease evaporation losses, improve energy efficiency, and support Africa’s rapidly expanding population’s increasing energy demands.”

The full results from the assessment are available in the study “Comparison of ground-based and floating solar photovoltaic systems performance based on monofacial and bifacial modules in Ghana – ScienceDirect,” published in Energy Nexus. The scientists recommended that economic analyses be undertaken because of the difference in costs between monofacial and bifacial PV modules.

Author: Bernadette Geyer

This article was originally published in pv magazine and is republished with permission.

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