In this paper, a comprehensive method for evaluating energy losses of a grid-connected building integrated photovoltaic (GC-BIPV) system due to partial shading is described. The method consists to make a comparison between theoretical and measured (monitoring data) curves of the maximum output energy produced by a GC-BIPV system installed at Jaen University (Spain). The results showed that loss of energy is 1.79 kWh/day, which corresponds to a shading factor of 14.4%. (C) 2012 Elsevier Ltd. All rights reserved.