Application of Liquid Filters to Photothermal / Photoquantum Solar Energy Conversion

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Chendo, C.A.M
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University of Lagos
This thesis discusses the development, design, fabrication and testing of spectrally selective beamspliting absorption filters (AF-SSBS) which can decouple quantum and thermal convertors to improve conversion of the total solar spectrum to useful energy. These components separate the solar spectrum into regions or windows matched to the spectral response of the specific photoquantum process and the balance used for photothermal convertor. Higher conversion efficiencies can then be maintained in the photoquantum covertor while the other photons are directed to a thermally decoupled loop at an elevated temperature. Various AF-SSBS developed for hybrid photoquantum/photothermal systems employing silicon cells as the PQ convertors are discussed in terms of their applicability, flexibility and performance. By changing the filter medium concentration (for inorganic salts), optical path length and appropriate glass channel a variety of spectrally selective filters can be tailored to match system performance. Both simplified and detailed performance analyses using moderately concentrated solar radiation showed enhanced overall performance. Preliminary studies have had the following results: (1) 1. The AF-SSBS permits maximum possible PQ conversion efficiency while at the same time permitting high temperature thermal collection. This concept allows the optical quantum receiver to operate at the low temperatures with the greatest efficiency. (2) 2. Realistic performance evaluation requires the knowledge of the spectral distributions of the irradiance source at the time of measurement. There is also the need to spectrally characterize both the solar cell and the irradiance concentrating device. (3) 3. Parametric and design studies suggest that for good PQ/PT performance spectralirradiance measurements must be made at various geographical locations over extended periods. Such data will contribute to models that match PQ materials to different spectral profiles to maximize device performance. (4) 4. Knowledge of heat transfer mechanisms between the various AF-SSBS and PV cells/modules and the determination of optimum flow rates are necessary for optimization of the system performance. (5) Changes in the demand for electrical and thermal energy at design conditions can be met by varying the type of absorption filter, concentration, and photoquantum convertor. The result of the analysis suggests that cobalt sulfate in an appropriate glass channel could be ideal for low-temperature applications (< 1000C) while the heat transfer and related fluids in appropriate cells could serve as medium-temperature applications ( < 2000C) where high thermal energy output is required.
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Photothermal systems , Solar Energy
Chendo, C.A.M (1987), Application of Liquid Filters to Photothermal / Photoquantum Solar Energy Conversion. University of Lagos School of Postgraduate Studies PhD Thesis and Dissertation Abstracts, 186p.