Photovoltaic (PV) modules receive both direct light from the sun and scattered light from the sky, ground and nearby objects. The calculation of incident irradiance becomes complex when nearby objects cast shadows or reflect sunlight onto the PV modules. In this paper a flexible irradiance model is presented that takes all these effects into account by combining a so-called sky map, obtained from the Perez model, with a sensitivity map, generated using a ray tracing software. This irradiation model is validated for a PV facade that combines PV modules with mirror reflectors and is shown to be a flexible tool to accurately predict the irradiance distribution. (C) 2017 Elsevier Ltd. All rights reserved.