Study On Comprehensive Efficiency Of Photovoltaic/Thermal-phase Change System

In today’s world,the development of human society is accelerating.Whether in industry,agriculture,or tertiary industry services,high-tech industries are among the fastest growing stages in human history.The development of society has improved the living standards of human beings,greatly enhanced social productivity,and the demand and use of energy has also increased significantly.Therefore,the development of renewable energy such as solar energy,wind energy and geothermal energy is an important direction for achieving sustainable development.Among them,due to China’s vast land and abundant solar energy resources,the development of solar energy utilization technology has become the top priority of renewable energy applications.The main heat and electricity utilization methods of solar energy in buildings are: solar water heating,solar air heating,solar photovoltaic power generation and so on.The solar photovoltaic/thermal comprehensive utilization technology is one of the research hotspots in the field of solar energy and building energy conservation in recent years.It can simultaneously provide the output of electric energy and thermal energy,and effectively improve the comprehensive utilization efficiency of solar energy.The phase change material can realize the transfer of energy in time and space,which makes it attract attention in many fields such as low temperature refrigeration,textile heat preservation,waste heat waste heat recovery,building energy conservation,and solar heat storage.Especially in today’s vigorous development of renewable energy applications,there are many ways to couple solar energy applications with phase change thermal management.Therefore,this paper couples the phase change material with the solar photovoltaic/thermal collector,and proposes a solar photovoltaic/thermal collector based on phase change heat management.The solar photovoltaic/thermal collector based on phase change thermal management adds a phase change layer to the conventional water-cooled solar photovoltaic/thermal collector,and uses the latent heat and sensible heat of the phase change material to thermally manage the collector.Thereby improving system efficiency.The research content as follow:(1)A comparison test bench with a conventional water-cooled solar photovoltaic/thermal collector was built indoors,and five phase change materials with different phase transition temperatures were prepared according to system requirements,and one of them was applied to the system to study the phase change material pair.Enhance the impact of phase change thermal management on the performance of solar photovoltaic/thermal systems.The results show that the addition of the phase change layer effectively reduces the temperature of the photovoltaic panel.Under the same solar radiation illumination,the maximum photovoltaic panel temperature difference is 15.8 °C;the phase change thermal management solar photovoltaic/thermal system generates more water than the solar cooled solar energy system.The photovoltaic thermal system has been significantly improved.The cumulative power generation efficiency of the two systems is 8.16% and 6.98%,respectively.The heat collection of the two systems is 12050.63 kJ and 9996.04 kJ,and the thermal efficiency is 70.34% and 58.35%,respectively.For the photovoltaic/thermal comprehensive performance efficiency,they are 87.5% and 73%,respectively.It can be seen that the addition of phase change materials can effectively improve the system efficiency,and the phase change thermal management solar photovoltaic/thermal system has practical application value.(2)In order to reduce the time and break the limitations of experimental equipment,and to study the phase change thermal management solar photovoltaic/thermal system more deeply,this paper establishes the mathematical model of the system based on the experiment,and combines the operation mode of the experiment to the system.Dynamic simulation and comparison of the results with experimental data.The results show that for the temperature of the photovoltaic panel,the experiment and the simulation agree well,and the final temperature is about 57 °C.For the system heat collection,the relative error of the water tank temperature is between-0.1% and-3.4%.The average relative error is 4.7%.The theoretical simulation and experimental results are basically consistent.The established mathematical model can accurately predict the performance of the phase change thermal management solar photovoltaic/thermal collector.(3)Using the single factor analysis method,using the validated mathematical model,the system comprehensive performance and the fire efficiency as the target parameters,focusing on the factors such as battery coverage factor,tube spacing,Reynolds number,solar irradiance,phase change material and so on.The law of influence of efficiency.The results show that the battery coverage factor can obtain high photovoltaic/thermal comprehensive performance efficiency at around 0.8;considering the cost and system output efficiency,the tube spacing of 80 mm is suitable;when the Reynolds number is increased within 7500,the system efficiency is Increased rapid rate;in the case of increasing solar irradiance,reasonable increase in heat collection and power generation efficiency can more efficiently use the heat collected by the collector;use the same acid(phase transition temperature 30.1 ° C)to obtain the highest photovoltaic/thermal comprehensive performance efficiency,the highest exergy efficiency can be obtained by CA-MA(phase transition temperature 20.24 °C).(4)Using the orthogonal test method,the influences of key parameters and their interactions on the four system target parameters of heat collection efficiency,photoelectric efficiency,system comprehensive efficiency and system fire efficiency are studied respectively,and the target parameters are also proposed.System optimization combination.Multi-objective optimization design of PV/T-PCM system using game analysis method.The multi-objective optimization design game analysis of the system under the Nash equilibrium strategy is studied.The multi-objective optimization problem of the system is transformed into the game problem,and the game equilibrium solution is obtained through game analysis,that is,the optimal solution of multi-objective optimization.