Comparative Study On The Performance Of Micro-heat Pipe Photovoltaic Thermal System Inside And Outside The Solar Greenhouse In Summer

The combination of solar energy and modern solar greenhouses is an application method for distributed utilization of new energy,which has great potential for solving the energy crisis and the deterioration of the global climate and environment.Most traditional solar greenhouses use natural ventilation to cool the greenhouse,so there is a problem that crop growth will stagnate or even wither when the high temperature in summer,and the installation and application of photovoltaic(PV)modules in solar greenhouses and the effective photosynthesis of greenhouse crops have sunlight exploit the problem of conflict.There are many studies on the combination of PV and greenhouses at home and abroad,but the photovoltaic solar thermal modules based on micro heat pipes are installed inside and outside the solar greenhouse,and the micro-heat pipe photovoltaic/thermal(Micro-Heat Pipe Photovoltaic/Thermal,MHP-PV/T).The output characteristics of MHP-PV/T in summer when the modules are at different working inclination angles and the insulation layer are rarely reported.In this paper,taking MHP-PV/T and PV as the research object and the solar greenhouse as the application background,two sets of experimental systems are designed and built,which are placed inside and outside the solar greenhouse,and the inclination angle of MHP-PV/T and PV is changed by a motor.First of all,a study of the photoelectric power,photoelectric efficiency,photothermal power,photothermal efficiency,solar comprehensive income and comprehensive utilization rate of solar energy of MHP-PV/T and PV under different inclination angles(30°,45°,60°,75°,90°)inside and outside the summer solar greenhouse were compared.Secondly,a comparative study of the working performance of the MHP-PV/T system before and after heat preservation under a 30° inclination angle inside the summer solar greenhouse,and on the basis of the experimental results,the two sets of MHP-PV/T were placed inside the summer solar greenhouse after heat preservation,respectively different inclination angles(30°-45°,30°-60°,30°-75°,30°-90°,45°-60°,45°-75°,45°-90°,60°-75°,60°-90°,75°-90°),which a comparative study of the photoelectric power,photoelectric efficiency,photothermal power,photothermal efficiency and comprehensive performance of MHP-PV/T system.MHP-PV/T is combined with the production of solar greenhouse to convert solar radiation into electric energy and heat energy,and promote the efficient production of solar greenhouse.Through the transformed electric energy and heat energy,the problems of single energy supply,poor thermal insulation performance and high indoor temperature affecting crop quality and yield in traditional greenhouse can be solved.Therefore,this experiment can provide theoretical guidance for the combined application of MHP-PV/T and solar greenhouse in summer.Through research,it is concluded that the performance difference of MHP-PV/T is mainly affected by the wind speed,temperature and solar radiation inside and outside the solar greenhouse.The main research conclusions of this paper are as follows:(1)A comparative study of the performance of the MHP-PV/T system inside and outside the solar greenhouse in summer found that the photothermal power,photothermal efficiency,solar comprehensive income,comprehensive utilization rate of solar energy and heat collection time of the MHP-PV/T system in the solar greenhouse under the conditions of 30°,45°,60°,75°,and 90° inclination angles are better than MHP-PV/T system outside sunlight greenhouse,while photovoltaic power and photovoltaic efficiency are just the opposite.At an inclination angle of 45°,the all-day average photoelectric efficiency of O-MHP-PV/T(Outdoor MHP-PV/T)is 8.07%,and the all-day average photoelectric efficiency of O-PV(Outdoor PV)is 7.48%.Efficiency increased by 0.59%;I-MHP-PV/T(Indoor MHP-PV/T)all-day average photoelectric efficiency is 5.05%,I-PV(Indoor PV)all-day average photoelectric efficiency is 4.93%,compared with the two,the photoelectric efficiency has increased by 0.12%.(2)At an inclination angle of 45°,I-MHP-PV/T(Indoor MHP-PV/T)all-day average solar thermal efficiency and solar comprehensive utilization rate are 17.13% and 23.02%,respectively.O-MHP-PV/T(Outdoor MHP-PV/T)average solar thermal efficiency and comprehensive utilization rate of solar energy are 10.03% and 20.17%,respectively.Compared with the average solar thermal efficiency and solar comprehensive utilization rate,the two have increased by 7.10% and 2.85% respectively.(3)The summer coverage ratio is 5.4%(the ratio of the PV area to the solar greenhouse film).Under the condition of opening the greenhouse with natural ventilation,the influence of the MHP-PV/T system on the temperature and humidity in the greenhouse at different inclination angles was studied.The average temperature of the experimental greenhouse was0.6°C lower than that of the control greenhouse at a tilt angle of 30°,and the average relative humidity of the experimental greenhouse was 5.6% lower than that of the control greenhouse.MHP-PV/T played a role in shading.(4)The average photoelectric efficiency of MHP-PV/T before and after heat preservation is 3.67% and 3.28% in the summer solar greenhouse at an inclination of 30°,respectively.Compared with before insulation the average photoelectric efficiency decreased by 0.39% in the whole day.The average solar thermal efficiencies are 9.06% and 17.47% respectively,which are 8.41% higher than the average solar thermal efficiency in the whole day after insulation;the comprehensive utilization rate of solar energy before and after insulation is13.21% and 21.22% respectively.Compared with insulation the average comprehensive utilization rate of solar energy increased by 8.01% in the whole day.(5)The photoelectric power and photoelectric efficiency of the system after the MHP-PV/T heat preservation in the solar greenhouse in summer are the largest at an inclination angle of 30°,and the maximum photoelectric efficiency is 12.44%,followed by an inclination angle of 45°;the average light and heat efficiency of 45° and 60° throughout the day the difference between the comprehensive utilization rate of solar energy and solar energy is only 1.59% and 0.85%,and the photoelectric efficiency of the 45° tilt angle system is greater than the 60° tilt angle.Therefore,considering the system’s photothermal performance,photoelectric performance and comprehensive performance,the MHP-PV/T in the summer solar greenhouse is obtained.The system performance is optimal when the inclination angle is 45° after heat preservation.