A team of researchers from France and Italy has developed a tool for optimizing tilt angles in bifacial PV power plants across Europe.
They have made the tool available for free on a web-based platform, saying that it could be highly valuable for local authorities, developers, and decision-makers in assessing the feasibility of installing bifacial solar systems in their regions.
“Our approach considers both self-shading from multiple rows and the potential distant obstructions caused by the surrounding terrain,” said corresponding author Professor Apolline Ferry to pv magazine. “A second novelty is the analysis of the impact of the topography. Bifacial PV systems can particularly benefit from mountainous environments, due to enhanced ground-reflected radiation from complex terrain and high ground albedo during snow-covered periods. Therefore, understanding how mountainous terrain impacts PV systems is crucial for maximizing energy production.”
The novel model assumes south-facing bifacial PV plants. It divides Europe into 2,382 points and, for each point, it uses a typical meteorological year file with an hourly temporal resolution. Those files include, among other parameters, direct normal irradiance (DNI) and diffuse horizontal irradiance (DHI). Those are used for the Perez All-Weather Model (AWM), which calculates how the irradiance spreads across the sky dome.
“A cumulative sky radiance is built for each location and an iterative search for the best tilt angle is performed to maximize the annual energy yield (on both front and back surfaces considering direct, diffuse and reflected energy) of south-facing modules, with both ground albedo and PV row spacing taken as parameters,” explained the team.
Its analysis showed that latitude is the primary influencing factor for optimal tilt angles, with average values of 36° for Finland, 29° for France, 27° for Italy, and 26° for Greece, when the ground coverage ratio (GCR) is set to 0.5 and the albedo is 0.2. Results have also shown that GCR is also a significant parameter: across Europe, optimal tilt angles are 25° to 65° when the GCR is set to 0.05, but 15° to 42° for a GCR value of 0.5.
To better understand mountainous terrain, the team used a 5 km by 5 km resolution and analyzed the French Alps. “As demonstrated by a more refined analysis of the French Alps, the correlation between tilt angle and sky view index (SVI) is significant. Specifically, higher SVI values lead to a reduction in the optimal tilt angle, facilitating improved collection of solar radiation from the unobstructed sky,” they found.
“While we expected terrain to have an impact on optimal tilt angles, we were surprised by the magnitude of the difference in optimal tilt angles between mountainous and lowland areas at the same latitude, as well as by the high variability in mountainous environments,” Ferry concluded.
Their findings were presented in “Optimal tilt angles for bifacial photovoltaic plants across Europe based on cumulative sky and Typical Meteorological Year data,” published in Solar Energy. The research team comprised academics from France's University Savoie Mont-Blanc and Italy's University of Genoa.
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