Numerical Simulation Of Hybrid Photovoltaic/Thermal Solar Energy System

Hybrid photovoltaic/thermal (PV/T) solar energy system, combining solar cell module with thermal solar collector, can simultaneously provide electricity and heat and raise the total solar energy utilization efficiency. Compared with separate photovoltaic solar system or thermal solar collecting system, hybrid photovoltaic/thermal solar energy system can share some components, decrease system cost, and reduce installation area. Moreover, in such kind of equipment, there is only one component in appearance visible, which makes the building much beautiful and more effective in solar energy utilization. So far, the research on hybrid PV/T system concentrates into the thermal collectors, which are mainly tube-plate type and flow-channel type. Moreover, most of flow-channel type collectors are straight channel, few of collector is multiple serpentine flow-channels.In this paper, a three-dimensional steady model of solar collector with multiple serpentine flow-channels used for PV/T system is presented. Numerical calculation is conducted to simulate the characteristics of the collector considering the variations of solar radiation intensity, operating parameters and the external conditions. To understand the dynamic performance of the output of the PV/T system, a two-dimensional dynamic model of the water subsystem of the PV/T system is also established here. The simulating results give out the characteristics of system output and electric and thermal efficiencies with the variation of solar daily or annual radiation and climate conditions. Some critical conclusions are listed below.â‘ The fluid temperature at the outlet of collector decreases with the increase of coolant mass flux, while electrical and thermal efficiency increase with the mass flux. Temperature gradient on the solar cell surface decreases with the increase of the mass flux. For the serpentine flow-channel type collector, the optimum value of mass flux is 40 kg/m2, with higher electrical and thermal efficiencies and lower pressure drop in the flow channels.â‘¡Adding solar concentrator to hybrid PV/T collector will decrease the electrical efficiency, rise thermal efficiency, and reduce total efficiency. However, the concentrator significantly improves the system output with slight cost increase. The increase of surrounding wind velocity will obviously decrease thermal efficiency, with little impact on the electrical efficiency. Adding glass cover can improve fluid temperature and thermal efficiency, but has little influence on the electrical efficiency.â‘¢Output power changes along with the change of solar radiation intensity. The higher the solar radiation, the higher the output power, And vice versa. Water temperature rises along with the increase of daily radiation intensity. Electrical and thermal efficiencies of system decline along with the increase of daily radiation intensity. Annual variation of the water temperature and output power is the same as the annual variation tendency of solar radiation intensity. In hazy day, the fluctuation of system's output power is obvious. However, the instantaneous changes of the water temperature and output power are not obvious.Finally, according to simulation results of PV/T collector and natural-circulation water system, a design method of household hybrid PV/T system is proposed. The new designed PV/T system can satisfy both the thermal and electrical requirement of the residential user. And the system performance is also analyzed.