Efficiency gain of the solar trough receiver using different optically active layers

Mohamed, Khaled Shehata Philippe
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The Parabolic Trough Collector (PTC) technology is the most widely used Concentrated Solar Power (CSP) technology. This is due to its maturity, promising cost-effective investments and the possibility to be hybridized with fossil fuels or other renewable power plants. Furthermore, it ensures the best land use among CSP technologies. The PTC receiver unit is the central component of the solar collecting plant, which is designed to absorb a large amount of the concentrated solar irradiation and minimize the thermal and optical losses. The research of finding an optimum design of the receiver unit that provides higher thermal and optical efficiency than the alternatives is a very active area of research in this field. The receiver unit with high efficiency will help to maximize electricity production and to reduce the cost of thermal storage due to a decrease in the requirements of the storage quantity. In addition, it will achieve optimum plant temperature within a shorter length, thus reducing the needed receiver unit length. The alternative optimized PTC receiver in this work is a novel design of a mirrored cavity receiver with a hot mirror application. The design incorporates different optically active layers in conjunction with a cavity absorber. The cavity geometry and a hot mirror coating at the aperture enable heightened retention of thermal radiation in the receiver. The design was analyzed numerically and studied experimentally. Novel aspects of the background theory for the design were presented and implemented in a simulation code. Three experimental setups, including the cavity receiver unit, were introduced. The experimental results were compared to our model and simulation results. It was seen that the correspondence between the experiments and simulation results was encouragingly close, and we proceeded to investigate simulations of the performance regarding the receiver design. The simulation results for receiver temperature profiles, heat transfer fluid temperature, and efficiencies were shown. It was seen that our proposed design had advantages in terms of thermal behavior over conventional designs in that it could exceed the heat transfer fluid temperature and the efficiency of existing alternatives.
A dissertation submitted for the fulfillment of the requirements of the degree of Doctor of Philosophy to the Faculty of Science, University of Witwatersrand, October 2019