The use of a heat pump as an auxiliary energy source for solar domestic hot water systems can achieve significant energy savings, due to the remarkable potential of heat pumps on the efficient provision of thermal energy. In this work, the performance of a combined solar thermal heat pump hot water system is investigated. A component based simulation model for the whole system was experimentally validated. Emphasis was paid on the formulation of a simple and efficient approach for the modeling of the heat-pump. The performance of the system on an annual basis is investigated, with regard to the methodology used in solar domestic hot water systems testing. According to the results of the analysis, the system achieves significant auxiliary energy savings, which can present a value in the order of 70% for the climatic data of Athens. The temperature set-point for the activation of the heat pump proves to be an important parameter for the performance of the system, noting that the higher the value of the set-point, the lower the efficiency of the heat pump. (C) 2013 Elsevier Ltd. All rights reserved.