The effect of sky diffuse radiation on photovoltaic fields

Photovoltaic fields deployed in multiple collector rows, with two or more modules per collector mounted one on the top of the other, experience uneven incident diffuse radiation due to differences in the modules' sky view factor. The present study emphasizes the difference in the amounts of annual incident energy (direct beam, diffuse, and global) on the top and bottom modules. Static and single axis (South-North and East-West) tracking collectors are analyzed to demonstrate the uneven incident radiation impinging on top and bottom modules. In the three types of analyzed deployments, the top module receives more incident energy than the bottom module; the first collector row receives more incident energy than the second and subsequent rows. These two facts have technical significance because the design of the photovoltaic (PV) system is based on the module's rated power for all modules in the PV field. For example, the bottom module in the second row receives 2.53% less incident global energy than the top module in static fields, 3.33% less in South-North tracking fields, and 1.81% less in East-West tracking fields.