Energy And Economic Evaluation Of Solar Cogeneration Systems Based On Photovoltaic Thermal Collectors

With the rapid economic development and population growth,building energy consumption and carbon emission have been remarkably increased.In order to reduce building energy consumption,solar photovoltaic power generation systems have attracted much attention.However,photovoltaic modules can only convert less than 20%of solar energy into electricity,while nearly 80%of solar energy is dissipated to surroundings in the form of heat.In this regard,solar cogeneration systems based on photovoltaic thermal(PVT)collectors can significantly improve solar energy utilization efficiency,which is favorable for promoting energy conservation and emission reduction in buildings.The configuration of solar cogeneration systems has a significant effect on the operating temperature and the efficiency of PVT collectors,which is crucial for their energy and economic performance,as well as their application potential.Therefore,in this work,the theoretical models of different configurations of solar cogeneration systems are established by programming with Python.Based on the typical meteorological year of a tropical city,dynamic simulations are performed throughout the whole year,so as to comprehensively analyze the energy and economic performance of different systems and conduct an in-depth study for the influence of key design parameters.The results show that,with regard to solar cogeneration systems based on the parallel absorption-compression hybrid cooling configuration,their solar cooling efficiency and yearly electricity saving can be improved by substituting traditional single-effect absorption chillers with half-effect absorption chillers.Although the coefficient of performance(COP)of half-effect absorption chillers is 30%～50%lower than that of single-effect ones,the half-effect absorption chiller allows to greatly lower the operating temperature of PVT collectors,thereby,to a certain degree,improving their electrical and thermal efficiencies,as well as the yearly total electricity saving of the systems.Compared with the above-mentioned solar cogeneration system based on the parallel half-effect absorption-compression hybrid cooling configuration,a solar cogeneration system based on a single-effect absorption subcooled-compression hybrid cooling configuration not only achieves a higher COP of the absorption cooling cycle,but also avoids the excessively high operating temperature of PVT collectors,so that the higher electrical and thermal efficiencies of PVT collectors can be maintained,further improving the solar cooling performance and yearly total electricity saving.With a near-optimal design,the solar cooling efficiency of the solar cogeneration system can reach 0.214,and its yearly average collector electrical efficiency is 0.120,so its solar energy utilization efficiency is as high as 0.334,which is 2.2 times that of a comparable conventional photovoltaic system.Moreover,the yearly total electricity saving of this solar cogeneration system is 11%higher than that of the conventional photovoltaic system,with a payback period of 8.7 years.On the basis of the above-mentioned solar cogeneration system based on the single-effect absorption subcooled-compression hybrid cooling configuration,an operation strategy by cool energy storage can benefit from time-of-use electricity pricing,effectively improving the electricity cost saving of the system.In order to achieve a near-optimal yearly total electricity cost saving,a specific rated cooling capacity of 0.2 k W_c/m~2 is sufficient for absorption chiller design,while the specific volumes of 30 L/m~2 and 50 L/m~2 are recommended for the hot water storage tank and the cool water storage tank,respectively.Such a solar cogeneration system can achieve a yearly total electricity cost saving which is 19%higher than that of a comparable conventional photovoltaic system,with a payback period of 8.4 years.