This paper presents a probabilistic model applied to a hybrid solar-wind power system (HSWPS), which is equipped with either a one-axis or a two-axis solar tracking system. Within the framework of a case study, the potential of the developed probabilistic approach is presented, and the effect of the solar tracking systems on the annual energy gain is discussed. Specifically, the impact of a tracking system on the probability density function (PDF) of the power produced by a photovoltaic system (PVS) is evaluated through the first four moments (mean, variance, skewness and kurtosis) of a PDF. Finally, to estimate the impact of a tracking system on HSWPS energy performance, a reliability analysis is performed using the energy index of reliability (EIR), which is directly related to energy expected not supplied (EENS), given different annual load scenarios. (C) 2010 Elsevier Ltd. All rights reserved.