A Canadian research team has applied the new guidelines to ground coverage ratios in 31 locations in Mexico, the United States and Canada. It found that the new formulas show that the factors affecting the loss of energy yield between rows are highly dependent on latitude.
In a study published in “Optimal ground coverage ratio for tracked, fixed-tilt and vertical solar photovoltaic systems for latitudes up to 75° N” Solar energyScientists said the new guidelines can be applied to projects based on both monofacial and bifacial modules located at latitudes between 17°N and 75°N.
They specifically chose 31 locations in Mexico, the United States, and Canada.
“Where possible, locations represent multiple diffuse fractions within a given latitude range, and the diffuse fraction is defined as the annual mean between diffuse horizontal irradiance (DHI) and global horizontal irradiance (GHI),” they elaborated. “The analysis we present is for North American locations, but covers a wide range of operating conditions, including diffuse fractions between 0.23 and 0.55, mean GHI-weighted ambient temperatures of -4 C to 31 C, mean GHI-weighted albedos of 0, 10 to 0.65 and city heights 1 to 1,600 meters.”
The Canadian team used PV performance prediction software Duet, an open cloud-based solar project planning tool developed in-house by the University of Ottawa, to create 3D models that include installation structures and multiple rows.
“The optical calculations are then performed taking into account direct beam radiation, anisotropic diffuse sky radiation, and ground-reflected radiation by segmenting the modules, the ground, and the diffuse sky dome into patches,” the researchers explained. “The shading algorithm is implemented using a deterministic ray-intersection method that captures the effect of objects in a 3D view.”
The academics said the Duet software is capable of converting radiation power profiles into time-phased cells I–V curves through a temperature- and irradiance-dependent single-diode model and note that they calculate the effect of ground coverage ratios between 0 and 1 on both single- and bifacial fixed-tilt and horizontal single-axis tracking (HSAT) systems.
The research team found that the GCR can vary smoothly between 0.15 and 0.68 for fixed-tilt systems and less significantly between 0.17 and 0.32 for HSAT systems, and said that in both cases the values depend strongly on latitude. “Similarly, the optimal tilt for fixed-tilt arrays varies greatly from 7° above lat-tilt to 60° below lat-tilt, depending on latitude and GCR,” it pointed out, adding that vertical systems are less sensitive to latitude.
The researchers also found that bifacial PV systems require up to 0.03 smaller GCRs than monofacial GCRs. “Since latitude was the dominant factor influencing the energy yield loss between rows, our results should provide an estimate of the performance of similar PV arrays worldwide,” they concluded.