Scientists have devised a pre-processing algorithm for various PV simulation tools to calculate the expected performance of solar farms installed on hilly slopes. Validation against experimental setups demonstrates an error margin of less than 3%.

Researchers from Bangladesh’s East West University have developed a novel approach to analyze bifacial PV systems on inclined terrains. The technique introduces a precursor formulation that can be integrated into existing PV simulation models lacking hillside farm capabilities. “A full reformulation for bifacial systems would require substantial effort, so we proposed an initial calculation step compatible with any conventional PV model,” corresponding author Mohammad Ryyan Khan told pv magazine.

 

“The method involves recalculating the solar trajectory and irradiance (direct and diffuse) from the perspective of a sloped surface and feeding these values into a standard PV model. The updated inputs ensure the output reflects a PV array on a slope,” the researchers explained. “This allows designing and analyzing PV farms for any slope and orientation without modifying other parts of existing models.”

 

The technique comprises three stages: modeling solar paths on specific hills, correcting irradiance values, and integrating with existing models. In the first stage, the global coordinate system is rotated according to the slope’s orientation and angle, generating a modified solar path from the tilted surface’s viewpoint.

 

In the second stage, diffuse horizontal irradiance (DHI) is adjusted based on the slope’s sky view factor, while direct normal irradiance (DNI) remains unchanged. The revised DHI accounts for the limited sky exposure of hilly surfaces. Finally, the corrected incidence and solar angles are input into PV models, which treat them as flat-ground data.

 

The team validated their model through multiple methods: self-validation showed errors within 2% in most cases, and benchmarking against PVsyst (which supports sloped terrain) yielded comparable results. They also built a small-scale experiment with a monofacial panel array on a 20° east-facing slope, mounted flat at 51.5 cm height and 28.5 cm width.

Conducted on the East West University rooftop (23.8°N, 90.4°E) over 10 days in February–March 2022, the experiment measured output every 2 minutes from 6:30 am to 6:00 pm, integrating data to calculate daily energy production. Using measured global horizontal irradiance (GHI) as input, the model simulated the same setup, showing a daily error below 3% compared to experimental results.

 

In a final demonstration, the team applied their precursor formulation to PV-MAPS software, testing 20° slopes facing north, south, east, and west. Panels (monofacial or bifacial) were mounted parallel to the slope. Bifacial simulations assumed a bifaciality factor of 1 and albedo of 0.2, with all panels at 16.8% efficiency and 1-meter height.

 

As expected, bifacial systems outperformed monofacial ones, with annual energy yields ranging from 211.33–290.45 kWh/m²/year for bifacial arrays versus 187.18–259.72 kWh/m²/year for monofacial systems.

 

“Our model streamlines numerical analysis of bifacial arrays on slopes,” the team concluded. “It enables performance prediction and design for mono/bifacial farms, tracking systems, and agrivoltaics on inclined surfaces.”