In this paper, concept of a passive photovoltaic-thermal system (PVT) means the combination of a photovoltaic (PV) panel and an integrated collector-storage solar water heater (ICSSWH) for cogeneration of heat and electricity. In this work, the four different absorber types of passive PVT systems have been simulated and compared. To compare, the aluminum with fin, the aluminum without fin, the Tedlar and the black painted glazing absorbers were selected. In the case of finned absorber, it is assumed that parallel fins have been installed longitudinally back of the absorber plate in the direction of the natural flow of the water to enhance the heat transfer rate and efficiency. Both the height (L-fin) and the numbers effects of fins on the collector performance have been studied. The simulation results show that the aluminum with fin absorber has the highest both the electrical and the thermal efficiencies from other absorber types. Fins reduce the cell temperature and increase the total efficiency (eta(pvt)) about 12%. (C) 2014 Elsevier Ltd. All rights reserved.