| Solar energy,as a sufficient clean and renewable energy,has been researched and utilized in recent years.Photovoltaic technology can convert solar energy into high-quality electric energy,and photovoltaic-thermal(PV/T)integration has gradually become one of the key technologies to improve the efficiency of photovoltaic power generation and enhance the utilization of solar energy.This paper is based on a plate-and-tube water-cooled PV/T-PCM system,which uses water and phase change material(PCM)as cooling means for the collector.It compares and analyzes the thermal-electric conversion efficiency and output power of the system,and discusses the impact of different component structural size designs,working fluid operating parameters,seasonal and climatic differences on the system’s thermal-electric performance.The specific research content includes:First,by establishing corresponding physical and numerical models,the computational fluid dynamics simulation results are compared with experimental data to verify the accuracy of the model.Then,the structural parameters of the plate-and-tube water-cooled PV/T system are optimized,with thermal-electric efficiency as the evaluation index,and the impact of the presence or absence of an air layer on the system performance is analyzed.Based on this,optimization analysis is conducted on the mass flow rate of the cooling fluid,the pipe diameter size of the cooling pipe,and the length-width ratio of the collector under the same design area.The results show that the presence of an air layer reduces the system’s photoelectric efficiency by 1.6%,while increasing the photothermal efficiency by 51%;the optimal working fluid flow rate occurs at m=0.02kg/s under the compared conditions;under the constant flow rate condition,increasing the pipe diameter to 0.015 m will result in a maximum photoelectric efficiency value,while the photothermal efficiency continues to decrease with increasing pipe diameter;increasing the length-width ratio of the collector from 1.07 to 3.75 will improve the lowest photoelectric efficiency value at 13:00 by 5.01%,the maximum output electric power by 5.06%,and the average photothermal efficiency by 2.8%,and the maximum output thermal power by 2.3%.Based on the optimized plate-and-tube water-cooled PV/T system,PCM is integrated into the underside of the absorber plate,and its thickness is optimized.The operational performance of the PV/T-PCM system and the PV/T system during the transitional season,summer,and winter are predicted.The results show that the suitable thickness of PCM is 0.04 m.In the transitional season,the photoelectric efficiency of the system with PCM increases by 2.3%,while in summer,due to higher irradiance,the photoelectric efficiency increases by 4.3%.Additionally,the presence of PCM has no significant impact on the thermal power output during the transitional season and summer.In winter,the photoelectric efficiency increases by 0.86%as the PCM does not reach the phase change temperature,but the average output thermal power decreases by 13.63 W compared to the system without PCM.Finally,the performance differences of a plate-and-tube water-cooled PV/T-PCM system are investigated for representative cities in different climatic regions of China during summer,transitional seasons,and winter.The results show that the system has advantages in cold regions and hot-summer/cold-winter regions of China.Among all seasons,the system has the best electric power output in Lhasa,representing cold regions,but its efficiency is relatively low compared to other cities.During transitional seasons and winter,the system’s heat output is relatively better in cold regions and hot-summer/cold-winter regions,but in hot-summer/coldwinter regions,the poor electric power output is not due to high levels of irradiation but rather benefited from the higher external temperature.Therefore,the electric power output of the system is relatively poor in Guangzhou,representing hot-summer/cold-winter regions.This study optimizes the system structure and analyzed the performance differences in seasonal climatic regions,providing a reference for the design and application selection of such systems. |
PDF Full Text Request