A novel photovoltaic/thermal solar-assisted heat pump (PV/T-SAHP) system is described in this paper. A specially designed direct-expansion evaporator (PV evaporator), which is laminated with PV cells on the front surface of the thermal absorber, has been adopted in our system to acquire simultaneously thermal energy and electricity from solar radiation. A dynamic model of the PV evaporator based on the distributed parameter approach is also presented. Given the instantaneous solar irradiance and ambient temperature, the numerical model is able to output the spatial distributions of refrigerant conditions, including pressure, temperature, vapor quality and enthalpy. A two-dimensional temperature distribution of the evaporator body is also computed. Comparisons between the Simulation results and the experimental measurements show that the model is able to give satisfactory predictions. The results show that high electrical and thermal performance can be achieved. The PV efficiency and thermal efficiency are above 12% and 50% during the testing period. (C) 2008 Elsevier Ltd. All rights reserved.