We have made a 20cm x 20cm tandem photovoltaic (PV) window and developed a numerical model to investigate the energy performance of a building that would be equipped with such PV windows. The inside of the double-glazed window incorporates a tilted dichroic filter which is transparent for visible solar light and reflecting for near infra-red light. As a result, the transmitted visible photons are partially absorbed by a transparent organic solar cell while the reflected NIR photons are sent to silicon solar cells located in the frame of the window. To investigate the potential benefit of the technology, the net energy balance (NEB) simulation includes the choice of the location, the use of the building (residential or office), the percent coverage of the façade by the PV windows, etc. Several case studies are presented to emphasize the key points which influence the net global benefit of the window.