| The hybrid photovoltaic/thermal (PV/T) technology refers to a technology that integrates a PV module and a solar thermal collector into one unit. A hybrid PV/T system can simultaneously generate electrical and thermal energies; hence, the effective rate of solar energy utilization per unit collecting area can be increased in this PV/T system. In addition, heat carriers, such as water or air, take up the heat extracted from PV cells and cool them, thereby improving the yield of electricity. Moreover, the PV module and the solar thermal collector are integrated into a PV/T collector. Hence, they can readily be made in standardized and module product, and are quite fit for the integration with the building.According to type of the coolant, Hybrid PV/T systems are classified as the water-type and the air-type PV/T system. The previous investigations showed that, the water-type PV/T system can achieve higher total PV/T efficiency compared with that of the air-type PV/T system, and have an extensive future. However, a traditional water-type system is unsuitable to be used in the cold regions because of the freezing of the water, which will damage the PV/T collectors. Based on this account, a novel heat-pipe photovoltaic/thermal (HP-PV/T) system is presented here. In the HP-PV/T system, the heat pipes with very high thermal conduction are used to transfer the heat from the collectors to the water. As the heat pipe use the low boiling point refrigerant as its working fluid, thus freezing can be eliminated and corrosion can be reduced as well. Further more, a novel system named photovoltaic solar assisted heat pump/heat pipe (PV-SAHP/HP) system is also presented here. To focus on both actual demand and energy savings, the PV-SAHP/HP system is designed to be capable of operating in six different modes, namely, the heat-pipe solar water heating, solar-assisted heat pump water heating and space heating, air-source heat-pump water heating, space heating and cooling. According to the user’s demand and the ambient parameters (such as solar radiation and ambient temperature), the system operates in an optimal mode, hence it can be considered to be a significant technology for energy savings. In addition, an air-cooled heat exchanger was used as an auxiliary evaporator of the heat pump, on overcast or rainy days, when the solar radiation is weak, the system can absorb energy from ambient air, hence offsetting the weaknesses of the traditional solar system. The main works of this paper are summarized as follows:(1) A HP-PV/T system test rig was designed and constructed, and comparative tests were performed to study the performance of the system under different conditions, such as tube spaces of heat pipes at80mm and140mm, tilt angles of the collectors installed at32°and45°, and volume flow rate of the circulating water of3.7L/min and10.0L/min. Experimental results showed that, the daily thermal efficiency, daily electrical efficiency and total PV/T efficiency of the HP-PV/T system can reach45.8%,11.2%and52.3%, respectively; the total PV/T efficiency of the system can be improved by reducing the tube space of the heat pipes or increasing the water flow rate; the collector installed at a tilt angle of32°yielded a better results than the collector installed at45°for the HP-PV/T system used in Hefei, China.(2) A dynamic model was presented to predict the instantaneous performance of the HP-PV/T system. Experiments were also conducted to validate the simulation results, and the comparative result demonstrated that the simulated values agreed with the experimental results. Based on the validated model, the performances of the heat pipe PV/T system were studied under different parametric conditions, such as water flow rates, PV cell covering factor, tube space of heat pipes, and solar absorptive coatings materials of the absorber plate. Moreover, using this model, the annual electrical and thermal behavior of the HP-PV/T system used in three typical climate areas of China, namely, Hong Kong, Lhasa, and Beijing, were also predicted and analyzed.(3) A PV-SAHP/HP system test rig was designed and constructed. A series of experiments were conducted in Dongguan and Hong Kong to study the instantaneous system performance when this system was operated in the heat-pipe and the solar-assisted heat-pump modes. Moreover, energy and exergy analyses were used to investigate the total PV/T performance of the system and the optimum operation mode of the system.(4) A dynamic model of the PV-SAHP/HP system was presented. Using this model, the dynamic parameters of the PV/T collector/evaporator were predicted and analyzed under different intensities of solar irradiation. In addition, the instantaneous performances of the system were also simulated and studied. |
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