设施农业用槽式太阳能聚光电热联供系统性能分析与试验

Performance analysis and test for through concentrating photovoltaic/thermal system applied in facility agriculture

该文针对在设施农业中棚顶安装的光伏组件挡光导致棚间距离增加,提出一种可以用在设施农业中的槽式太阳能聚光电热联供系统,通过减少输出额定电功率所需光伏组件的数量以提高设施农业经济性,同时还可以在寒冷季节为作物生长提供热能。该文介绍了该聚光电热联供系统的工作原理,利用光学仿真软件对聚光器的聚光性能进行了仿真计算,搭建了聚光电热联供系统性能测试台,将电热联供系统组件与平板光伏组件工作温度进行了对比,通过改变换热介质流量,分析了系统综合性能效率随换热介质流量变化的规律。结果表明,在约2倍聚光条件下,换热介质质量流量为2.41 g/s,室外平均气温为2℃时,槽式聚光电热联供系统的输出电功率约是平板光伏组件的2倍,系统综合性能效率为69.88%,系统输出水温约为20℃左右。该研究可以为设施农业与太阳能光伏利用技术的高效耦合提供了参考。

With the increase of global urban population and development of agriculture science and technology, modern agriculture has increasingly become the focus of the urban planning and construction. Facility agriculture is an important mode of development in modern agriculture, which plays a key role in improving the micro-environment for growth of crops. But some environmental testing equipment and production facilities consume a lot of energy in the facility agriculture. In order to solve the problem of large fossil energy consumption in the facility agriculture, solar photovoltaic（PV） systems have been mounted based on configuration of the facility agriculture which does not need land space unlike PV systems. Facility agriculture integrated with photovoltaic systems can not only provide quality fresh agriculture products, but also fulfill the agriculture＇s electricity demand without negative impact on the environment. However, currently, photovoltaic ecological agriculture system increases the distance between the agricultural greenhouses and reduce the economic benefits of the facility agriculture in the unit land area because of the shielding of the solar photovoltaic modules arranged on the back wall of the greenhouse. Therefore, increasing the output power per the unit area of solar cell is imminent. For this reason, there is a growing interest in concentrating photovoltaic（CPV） technologies which are systems made of optical devices that focus light towards decreased area of photovoltaic materials. Thus a novel trough solar concentrating photovoltaic/thermal（CPVT） system in facility agriculture was proposed in this paper. The system had a compound parabolic concentrator（CPC）, photovoltaic/thermal（PV/T） system with steel heat exchanger sandwiched between two identical monocrystalline silicon batteries bonded with glue and tracking device. The two main advantages of the system were their ability to reduce the number of photovoltaic cells of rated electric power output required and to provide heat energy for the crops of the facility agriculture under cold weather conditions. The operational principle of trough type solar concentrating photovoltaic/thermal system was introduced. A 3D model of the concentrator supported with optical analysis software was used to analyze the tracking accuracy. Based on the simulation results, an experimental unit combined heating and power devices driven by solar trough type concentrator was constructed. The output electricity power and heat from the system were tested and analyzed. The results indicated that the tracking tolerance of the proposed trough concentrator held efficiencies of 98.56% to an incident angle of 3.0°, and then dropped to 90% at 3.5°. The maximum output power of the CPVT module on the sunny day was 3.85 W for a solar radiation input of 726 W/m2, which was two times higher than that for flat-plate module. The maximum output power produced by the CPVT system at the water mass flow rate of 2.41 g/s was higher than that of the system at the water mass flow rate of 6.65 g/s by 6.21%. For 2× and 2.41 g/s mass flow rate, the electrical efficiency of system was 7.42% and the overall performance efficiency was 69.88%, the water outlet temperature can reach about 20 ℃ when the ambient temperature is 2 ℃. Then solar energy can be efficiently utilized with the CPVT system and the electrical power output as well as electrical efficiency of the solar cell can be improved. The CPVT system could provide both the power and heat for the facility agriculture simultaneously.