In this study, a thermodynamic model of a solar assisted heat pump system with energy storage was developed. The model consists of thermodynamic correlations concerning the fundamental equipment in the system such as solar collector, energy storage tank, compressor, condenser and evaporator. Some model parameters of the system were calculated by using experimental results obtained from a pilot plant. Simulation studies were performed to assess the importance of some design factors on the system performance and economy. Copyright (C) 1996 Elsevier Science Ltd.