In this contribution a simulation procedure is described which was developed as a working tool to calculate the energy output of building-integrated photovoltaic (PV) arrays experiencing shading or reflection effects. A three-quadrant solar cell model incorporating the reverse bias characteristics and breakdown voltage is verified by current-voltage (I-V) measurements performed on commercially manufactured mc-Si solar cells under controlled laboratory conditions. For the simulations, a point matrix giving the irradiation distribution over the PV array is calculated for each hour using a raytracing technique. With a raytracing technique, shading of both beam and diffuse irradiation as well as primary and secondary reflections can be modelled. The results of two case studies simulated using this technique are presented and analysed. In conclusion, general guidelines based on the simulation results are drawn up. These guidelines aim to assist architects and engineers in planning an optimized layout strategy of building-integrated PV arrays to reduce energy losses caused by shading.