Abstract Reliability is an important parameter for the user of photovoltaic (PV) power systems. A methodology for the analytical treatment of the reliability of PV systems is proposed in this paper. The method depends upon the logic of the fault-tree technique. The reliabilities of the different components of a PV system are used to predict the reliability of the overall system. Today's most commonly known systems are considered and a reliability formula is developed for each system. The methodology presented is appropriate for a wide range of applications and system types.