How is it considered
To calculate shading, an approach called Ray Tracing is used. In accordance with this approach, the tracker surface is discredited by the mesh. For each cell of this mesh, a ray to the sun is built. If there is an obstacle in the path of the ray (for example neighboring trackers), then the cell is considered shaded. If there are no obstacles, it is considered not shaded. Based on the number of shaded and unshaded cells on the tracker, the shading factor for the tracker is calculated. This calculation process is performed for different values of sun height and sun azimuth. The result is a shading table for the tracker. This shading table is then used to calculate the radiation loss due to shading as follows.
For each hour, the position of the sun is determined by sun altitude and azimuth.
The shading factor for the obtained sun altitude and azimuth is found from the shading table by interpolation.
Solar irradiation incident on the PV module is adjusted taking into account the shading factor.
Validation I
Let's first calculate the shading for a layout with trackers located close to each other where row to row = 9 ft.
In PVFARM, based on the Loss diagram, we see that energy losses due to shading for a typical year are 2.962 - 2.259 = 0.703 MWh/m² = 703 kWh/m²
In PVsyst, based on the loss diagram, we see that energy losses due to shading for a typical year are 2986.3 - 2374.8 = 611.5 kWh/m²
We can also compare energy losses due to shading depending on time:
If we compare the table from PVFARM with the table from PVsyst, we can see that shading occurs in the sun height angle ranges: from 0 to 40 degrees.
Validation II
Let us now compare the shading when the trackers are far from each other and weakly obscure each other where row to row = 20 ft.
In PVFARM, energy losses due to shading are 2.962 - 2.680 = 0.282 MWh/m² = 282 kWh/m²
In PVsyst, energy losses due to shading are 2986.3 - 2813.1 = 173.2 kWh/m²
Compare energy losses due to shading depending on time
From the shading tables it can be seen that shading of trackers by each other occurs only at a sun height angle from 0 to 10 degrees. In this range in the shading tables there are only two lines of shading factor values. Therefore, we obtain a large interpolation error for the shading factor when calculating energy losses due to shading.
We can increase the number of values in the shading tables, this will increase the calculation time, but should increase the accuracy of calculating energy losses due to shading.
