Determining Direct Irradiation on Surfaces in a Complex Urban Environment for BIPV Installation

Abstract

The number of installations of PV modules in residential areas has been increasing rapidly over the last years. Often PV modules are installed on rooftops of buildings in a complex urban environment, in which nearby buildings may cast shade on the modules for some period of time. In this contribution we present a method to calculate the direct solar irradiation on building surfaces taking into account the shading. This irradiation is required to work out the energy yield of PV modules mounted on these surfaces. The calculation is realized by taking the ratio between the direct annual solar irradiation a surface receives taking shading into account, and the potential direct annual solar irradiation without shading. We denote this ratio as the shading factor. For this method we make use of freely available software with which position and height information of surrounding buildings can be constructed, and with which the shade of these buildings on the building under investigation can be calculated. By applying this method over the entire year, the shading factor can be obtained for all building surfaces. The method has been applied to the building of the Faculty of Electrical Engineering, Mathematics and Computer Science of Delft University of Technology. We demonstrate that the shading cast by buildings and other obstacles is calculated accurately. Comparisons with measurements show that the method predicts the shading factor very well, allowing an accurate estimation of PV system electricity yield.