In this study, a theoretical ventilated photovoltaic (PV) facade, which functions as a pre-heating device in winter and a natural ventilation system in summer and reduces PV module temperatures, was analysed. The interrelationship between an optimum proportion of transparent window (and an opaque PV module) to the total facade area, and the variables relevant to the energy performance was assessed. The design parameters under consideration have been categorised according to climate, building characteristics, facade configurations and PV system elements. One outcome of this investigation is a new index, effectiveness of a PV Facade (PVEF), that has been developed to evaluate the overall energy performance of a PV facade with regard to the proportion of useful daylight that may displace the use of electric lighting, and the electricity generated by the PV modules to the heating and cooling energy consumption within a building. In conclusion, the electricity generation and the factors, affecting the ventilation performance of a ventilated PV facade, have been presented.