Performance Comparison of the Glass Vacuum Tube and Flat Plat PV/T Heat Pump Systems

Many studies have found that the photovoltaic (PV) cell temperature plays an important impact on the solar-to-electricity conversion efficiency. Different cooling liquids like air and water have been introduced to pass across the PVs to reduce the cell temperature, and thus increase the electrical efficiency. In this paper, the refrigerant R134a is used as the cooling liquid and the PV/thermal (PV/T) panel is coupled with a heat pump system acting as the evaporator, which is expected to achieve a better cooling effect and energy performance due to its low boiling temperature. Two different kinds of PV/T panels, glass vacuum tube (GVT) type and flat plate (FP) type, are proposed for the study on the energy performance comparison. The results show that the GVT PV/T panel has an average thermal efficiency of 0.775 and an average electrical efficiency of 0.089 (based on the reference efficiency of 0.12), which is 73.4% and 1.1% higher than that of the FP PV/T panel respectively, with the solar radiation varying from 200 W/m² to 1000 W/m². The GVT PV/T heat pump system has an average COP of 5.6, 9.8% higher the FP PV/T heat pump system. The GVT PV/T heat pump system has a better energy performance than the FP PV/T heat pump system.