Thermodynamic analysis of a novel solar photovoltaic thermal collector coupled with switchable air source heat pump system

Solar photovoltaic panel can only convert a small part of solar energy into electricity, and the remaining energy in the form of heat is discharged into the environment. In this paper, a novel solar photovoltaic thermal collector coupled with switchable air source heat pump system was introduced to improve the power generation of photovoltaic panels and effectively use the solar thermal energy, which can meet the requirements of the heating in winter and the cooling in summer. At first, the energy model and exergy model of the system were developed. Meanwhile, R134a, R290, R410A and R717 were selected as the candidate working fluids to remove the heat from the back of photovoltaic panel. Furthermore, a numerical simulation was implemented in MATLAB based on the energy and exergy models, and NIST REFPROP database was associated to obtain thermodynamic properties of the working fluids. And then, the thermodynamic performance of the system using different working fluids was investigated and compared. Finally, the optimal working fluid was determined based on the electrical efficiency, energy utilization coefficient, and exergy efficiency of the system. The results indicated that the electrical efficiency of cooled photovoltaic panel in the system was 4.1 %-13.7 % higher than that of uncooled photovoltaic panel in winter, and 1.1 % similar to 10.6 % in summer. The exergy destruction of the compressor and PVT collector accounts for a large percentage. Interestingly, R717 is the optimal working fluid of the proposed system, where the system has the highest annual energy utilization coefficient of 1.654 and the highest annual exergy efficiency of 0.251. Therefore, the application of the system has the potential for achieving the coupling of the annual photovoltaic cooling and the solar thermal energy utilization.

Automated summary

This study introduces a new method of combining solar photovoltaic thermal collector with switchable air source heat pump system to improve the power generation efficiency of photovoltaic panels and effectively utilize solar thermal energy. It is found that R717 is the optimal working fluid, and the system has a high annual energy utilization coefficient and exergy efficiency.