| In response to climate change,China clearly put forward the Emission peak and Carbon neutrality goals in 2020.At present,China’s total energy consumption and carbon emissions are in the rising stage.Increasing the proportion of renewable energy use is an important way to accelerate the process of China’s Double Carbon Goals.New opportunities and challenges are emerging in the field of solar energy technology.Among them,Comprehensive utilization technology of solar photovoltaic and solar heat to realize cogeneration of heat and power has extensive research significance and application prospect.Since the traditional copper tube-water PV/T system has the problem of low temperature freezing during operation,it is not conducive to popularization and application in cold regions.The heat pipe PV/T system can stably provide electricity and thermal energy without seasonal obstacles,and the heat pipe is an efficient heat conduction body with the characteristics of antifreeze,constant temperature heat transfer and high performance.Therefore,this paper adopts the method of experimental research and takes the heat pipe PV/T system as the research object to study its thermoelectric performance and influencing factors,mainly including the following contents.This paper first introduces and summarizes the working principle and research status of micro heat pipe and solar photovoltaic photothermal.A lot of numerical simulation and experimental studies have been carried out on the geometrical parameters such as the size and shape of the fluid channel,the length ratio of the evaporation and condensation section,and the operating parameters of the evaporation section,such as heat flux density,liquid filling rate and sloped Angle.In this paper,the rectangular cross section and trapezoidal cross section micro heat pipes are combined with monocrystalline silicon photovoltaic modules to produce the MHP-PV/T modules respectively.R141b is used as the heat pipe filling medium,and the liquid filling rate is 25%.The module can effectively reduce the operating temperature of photovoltaic modules,improve the efficiency of photoelectric conversion,increase the power generation.At the same time,the micro heat pipe was fully pasted to reduce the contact thermal resistance and increase the heat conduction,which significantly improved the comprehensive utilization efficiency of solar energy.Secondly,this paper carries on the heat transfer theory analysis to the heat pipe,carries on the energy analysis to the MHP-PV/T component.Then two sets of the same MHP-PV/T system performance test platform are designed and built.Firstly,the performances of PV/T modules with rectangular cross-section and trapezoidal cross-section under 45°,40°and 35°sloped angle are compare and analyze.Then,we compare and analyze the thermoelectric output performance of PV/T module with rectangular cross-section micro-heat pipe at different sloped angle of 30°and 45°,35°and 45°,40°and 45°,30°and 40°,35°and 40°,30°and 35°.Finally,the effects of circulating water flow and initial circulating water temperature on the performance of PV/T of rectangular cross-section micro-heat pipe are experimentally studied,and the effects of solar radiation intensity and ambient temperature on the performance of PV/T of rectangular cross-section micro-heat pipe are analyzed.The results showed that:(1)During the test period,the thermoelectric output performance of the two sets of MHP-PV/T system is calculated and analyzed.The results show that the comprehensive performance of the rectangular cross section micro heat pipe PV/T at45°,40°,35°sloped angle is better than that of the trapezoidal cross section micro heat pipe PV/T.The photoelectric efficiency of the rectangular plate micro heat pipe PV/T module is larger at 30°installation sloped Angle,and the total energy power and total energy efficiency of the system are the largest at 40°sloped angle.The relationship between the total energy power and total energy efficiency at other sloped angles is as follows:45°>35°>30°.(2)By calculating the average value of each parameter in the effective data under different solar radiation intensities and outdoor environment temperatures,and processing and analysis,we can obtain:when the solar radiation intensity increased from 629.6 W/m~2 to 976.8 W/m~2,the thermal efficiency of R-MHP-PV/T system increased from 10.6%to 19.5%,the total energy efficiency increased from 24.1%to30.5%,and the electrical efficiency decreased from 14.2%to 10.9%.When the ambient temperature increased from-1.5°C to 7.0°C,the thermal efficiency of R-MHP-PV/T system increased from 10.8%to 21.8%,the total energy efficiency increased from 23.7%to 33.9%,and the electrical efficiency decreased from 12.9%to 12.1%.(3)The thermal performance and electrical performance of rectangular micro-heat pipe PV/T with circulating water flow rate of 6 L/min and 8 L/min was compared and analyzed.During the test period,the average total energy power and average total energy efficiency of PV/T system with circulating water flow rate of 8 L/min were253.8W and 26.3%,respectively.Compared with the system with the circulating flow of 6 L/min,the average total energy power and average total energy efficiency were35.2W and 2.9%higher,and the average electric power and efficiency were 2.1W and0.2%higher,respectively.The tank temperature curves corresponding to different circulating water flows have almost the same variation trend with time,but the difference lies in the different increase rates.(4)The thermal performance and electrical performance of rectangular cross section micro heat pipe at the initial temperature of PV/T cycle is compared and analyzed when the water temperature is 5℃and 13.5℃respectively.During the test period,the average total energy power and average total energy efficiency of PV/T system with the initial temperature of 5℃are 343.9W and 28.5%respectively.Compared with the PV/T system with water temperature of 13.5℃at the beginning of the cycle,the average total energy power and average total energy efficiency are 60.8W and 4.8%higher,and the average electric power and efficiency are 2.2W and 0.2%higher,respectively.The experimental results of this paper show that:in Lanzhou area in winter,the rectangular and trapezoidal flow section micro heat pipe PV/T system with filling medium R141b and liquid filling rate of 25%can be started and work normally during the test period,and the rectangular flow section micro heat pipe PV/T performance is better.It has certain reference value for the popularization and application of heat pipe PV/T system in cold area. |
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