This paper presents a method for assessing the reliability of large-scale grid-connected photovoltaic systems. Fault tree and probability analysis are used to compute the reliability equation and the developed model is applied on military-standard data and on data taken from scientific literature. The method provides a tool useful to single out the different impacts that the large number of components belonging to the photovoltaic field and the SOS (Balance of System) chain have on system overall reliability, hence granting the possibility to design and implement more effective monitoring/diagnostic strategies and maintenance plans. (C) 2011 Elsevier Ltd. All rights reserved.