Two-Dimensional Representation of the Bidirectional Reflectance Distribution Function of Photovoltaic Modules

The optical reflectance properties of PV modules can be described using the bidirectional reflectance distribution function (BRDF). In this paper, a simplified two-dimensional approach to represent the BRDF is proposed. The shape of the solar reflectance image on the PV module is described by comparing a mathematical model and two measurement approaches. For standard PV modules using anti-reflective solar glass, the shape of the solar reflection image is regular and typically elliptical and depends on the angle of solar incidence α. The elliptical shape is described using a diagram for each horizontal and vertical axis based on the constant luminance zone. The dimensions of the axes are approximated using an empirical mathematical function. The result can be used to include glare information in the data sheet of a PV module and to correctly implement the phenomenon of beam spread in tools for glare hazard analysis.