This paper explores different approaches to thermal performance estimation for ventilated photovoltaic (PV) facades. In particular, an extension of the familiar heat loss and radiation gain factors (U and g values respectively) has been employed to take account of the energy transfer to the facade ventilation air. In total, four terms describing ventilation gains and transmission losses in terms of irradiance and temperature components are defined which characterise the performance of the facade in total. Steady state analysis has been applied in order to express these four parameters in terms of the detailed heat transfer process within the facade. This approach has been applied to the ventilated PV facade of the public library at Mataro, Spain. Monthly U and g values have been derived and the associated thermal energy gains calculated for various climates. An alternative, simpler approach views the ventilated facade as a single solar air collector. The applicability of the standard expression for solar collector efficiency has been investigated through examination of the Mataro data. Summer and winter energy yield calculations carried out on this basis have been compared to the four parameter approach. (C) 2003 Elsevier Ltd. All rights reserved.