Study On Parabolic Trough Solar Collectors And Its Water Heating Systems

With the shortage of conventional energy and the increasingly serious environmental pollution, solar energy has been more widely used. Parabolic trough solar collectors are able to concentrate and track the sun’s rays so that high temperature hot water can be produced. This type of solar collectors is mainly used in the field of solar power generation or other industrial areas, and the applications in the field of domestic hot water yet.According to the demands of domestic hot water and economic requirements, a kind of no-tracking parabolic trough solar collector hot water system was presented in this paper. Firstly, working principle and optical properties of the collector was analyzed, it was found that when the sun’s rays were perpendicular to the parabolic trough opening, the collector concentration ratio was in the range of 0.8 to 10. Secondly, an experimental platform was built to test performance of the collector. With studying the influence of inclination angle and azimuth, we found that the best inclination angle is 40°and the best azimuth is the south direction in Tianjin area. Meanwhile, instantaneous efficiency and daily collection efficiency were obtained with experimental tests.Furthermore, we studied the simulation and optimization of the solar hot water system using the software called TRNSYS. The results were showed that when the inclination angle of the collector was 40 °, it could get the maximum amount of solar radiation in a year. The collector efficiency and solar fraction per year of the solar hot water system increased with raising the ratio of the water tank volume and the collector area. However, when the ratio increased to a certain value, the above two aspects no longer changed. In addition, when the water temperature supplied to the users improved every 10℃, the collector efficiency would decrease by 1% and the solar fraction by 5% to 8% per year. And the users’ water consumption improved every 10 L, the solar fraction would decreased by 5% and the collector efficiency increased by 1.5%. When the pipe length increased from 5m to 25 m, the collector efficiency and solar fraction per year of the system decreased 5% and 6% respectively.Finally, a set of no-tracking parabolic trough solar collector hot water system was designed to apply in a practical heating engineering. Through experimental test, the result showed that the indoor temperature could hardly reach 18℃ in bitter cold periods while the indoor temperature could reach 18℃ from 12:00~16:00 every day at the end of the cold periods. The analysis of economic and environmental benefits was carried out and it was concluded that the no-tracking parabolic trough solar collector has some advantages compared to other types of ones.