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Tests conducted by Canadian researchers at the NREL test site in Colorado have shown that high-density polyethylene-based ground reflectors can significantly increase the performance of bifacial photovoltaic plants. They highlighted that the profitability of this technology depends strictly on the location and warned that combining it with inverter trimming should be avoided.
Researchers at the University of Ottawa (Canada) have studied the effects of using an artificial reflector in the ground in large-scale bifacial photovoltaic plants and have found that it can increase the energy generation of a facility by up to 4.5%.
According to Mandy Lewis, lead author of the research, “it is essential that these reflectors are placed directly below the solar panels, not between rows, to maximize this benefit.” “These results are especially significant in Canada, where snow cover persists for three to four months a year in large cities such as Ottawa and Toronto, and 65% of the countrys surface is covered in snow more than half of the year.” .
The research team conducted their analysis on a 75 kW bifacial system based on horizontal single-axis tracking (HSAT) and located at a National Renewable Energy Laboratory (NREL) test facility. of the US Department of Energy in Golden, Colorado. “We studied a single row of PERC+ modules with a bifaciality factor of 70%,” he explained, noting that the tests were conducted over 4 months. “Module-level power and weather data were measured at 1-minute intervals and averaged to the right to obtain 15-minute power values.”
The scientists used a high-albedo, UV-resistant, artificial high-density polyethylene (HDPE) reflective material supplied by the German company Solmax Geosynthetics. Its sun-weighted reflectivity reached approximately 70%. They evaluated five different reflector configurations: with 100% ground coverage; with 50% and 25% ground coverage, both centered on the torque tube; and with a soil cover of 50% and 25%, both centered in the center of the open ground between rows.
The performance of the reflector-dependent parts of the PV system was compared to that of the reflectorless module rows. The modeling presented a root mean square error (RMSE) of 5.4% per hour and showed an increase in total annual irradiance of 8.6% and an annual energy yield of up to 4.5% when a reflective material of the 70% to a single axis tracking system. The optimal reflector placement turned out to be centered directly under the torque tube for all reflector sizes.
A more detailed economic analysis also revealed that reflector technology can achieve profitable installation costs of between $2.50 and $4.60 per m2. “In systems with a higher initial LCOE it is possible to achieve higher material costs. For example, in Seattle (Washington), with 60% reflective material, the installation costs achieved are between $3.40 and $6.00 per m2,” the researchers emphasize.
Furthermore, they highlighted that the profitability of reflectors depends strictly on the location, and that solar radiation levels play a key role. They also recommended avoiding deployment of floodlights in projects with inverter clipping, which occurs when the DC power from a PV system is greater than the inverters maximum input size. “Inverter trimming significantly affects systems that incorporate artificial reflectors, reducing annual energy gain and shifting the ideal location of smaller reflectors in some locations,” they warned.
Their experiments are described in the paper “ Artificial Ground Reflector Size and Position Effects on Energy Yield and Economics of Single Axis Tracked Bifacial Photovoltaics ” bifacial with single-axis tracking), published in Progress in Photovoltaics . “These results are especially valuable for Canada and other typically cloudy countries, since power increases of 6.0% were observed in cloudy Seattle, compared to 2.6% in arid Tucson,” the researchers emphasize.
Another research group at the University of Ottawa has recently developed a new technique to measure the energy performance of bifacial photovoltaic systems. The new scaled back irradiance (SRI) method supposedly improves IEC measurements by taking into account the effects of the spectral albedo of different ground covers in its calculation of the back irradiance of the bifacial system. |
