Improved Calculation of the Power Gain of Vertical PV Modules due to Ground Reflection Using the Ground View Factor

The calculation of the irradiance of vertically mounted building-integrated PV modules is less accurate than for PV modules that are mounted with tilt angles of less than
$50^\circ$
. The irradiance reflected from the ground is more relevant for vertically mounted PV modules, since the influence of ground reflection also increases with increasing module tilt angle. We compare five models that calculate the diffuse horizontal irradiance from the given global horizontal irradiance and then transpose the diffuse horizontal irradiance to the irradiance on the vertical plane facing south. We present a ground view factor with which we calculate the insolation reflected from the ground onto a PV module and compare these results with the established method for calculating ground reflection. Using our approach and measured global and diffuse horizontal irradiation, we calculate the global vertical irradiance for a 12-month period. We compare the results with the measured global vertical irradiance. By using the ground view factor, we reduce the deviation between the measurement and the calculation of the cumulative insolation at the façade by up to 9.4% compared with the irradiance calculated using established methods for ground reflectance after this 12-month period.