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Numerical and Experimental Study on Two-stage and Beam Splitting Systems Based on Solar Dish

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Tutor: LuoZhongZuo
School: Zhejiang University
Course: Thermal Power Engineering
Keywords: solar energy,thermal power,solar dish,beam down,beam splitter
CLC: TM615
Type: PhD thesis
Year:  2013
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Abstract:
There are three main challenges in solar energy utilization, for example lower energy density, changing with season, broad range solar spectrum and so on. Solar concentrating technology, thermal storage technology and beam splitting technology are some of the key technologies in solar power plant. Based on this, this thesis focuses on the development of solar dish systems. Experimental research and numerical simulation are carried out on the two-stage beam down system and the novel beam splitting system.The researches carried out in this paper include:¢Ùdiscuss and compare the performances and applications of five types of secondary mirrors.¢Úanalyze the3-D optical model of a beam-down system which employs the upper sheet of a hyperboloid as a secondary mirror.¢Ûestablish the experimental set up, the mirror scanning system and the flux density distribution measuring system; carry out the experiments indoor and outdoor.¢Üdesign a novel beam splitter and analyze the3-D optical model.¢İanalyze the performances of the two designed systems.In terms of numerical simulation, five types of two-stage reflection systems were analyzed and compared by ASAP software, of which the secondary mirror could be a planar, an ellipsoidal, a upper sheet of a hyperboloidal, a lower sheet of a hyperboloidal, or a paraboloidal type, respectively. The effect of the rim angle, numerical aperture of the secondary mirror and the relative position of the focus on the secondary mirror size, shading percentage, spot size and flu concentrator ratio are discussed. The system which employs an upper sheet of a hyperboloid as secondary mirror is discussed. A3-D optical model based on Monte Carlo method is established. The effect of the sun shape, the tracking errors and the alignment errors on the concentration ratio, the spot size and deviation are discussed.In terms of experiments, two experimental set ups are established. The shapes of both systems are scanned and compared with the design surfaces. The optical experiments are carried out indoor to verify the mirror scanning system. The flux density distribution measuring system is established and experiments are carried out outdoor. The experimental results show that the1000mm system has a good performance while the3000mm system needs to be improved. A novel beam splitter is designed and the3-D optical model is analyzed. The3D optical model of a beam splitting system is also established based on Monte Carlo method. The effect of the sun shape, the tracking error and the alignment error of the second mirror on the concentration ratio, the spot size and deviation are discussed.Finally, a two-stage beam down dish-Stirling power system with thermal storage and a hybrid system combining photovoltaic cells with a Stirling engine are analyzed. The comparison of the two systems is carried out based on the system analysis model we set up. The calculated efficiency of the two-stage beam down system is about21.3%. For the beam splitting system, the calculated efficiency is about25.9%when ¦Çther<21%or ¦Çther>30%, and it is not wise to employ the beam-splitting technology when21%<¦Çther<30%.The research in this thesis provides a theoretical basis for the research of two-stage beam down technology and beam splitting technology.
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