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31 October 1977 A Vacuum Solar Thermal Collector With Optimal Concentration
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Space heat, hot water, air conditioning and process heat utilize more than 40% of U. S. energy consumption. These uses provide the greatest opportunity for solar energy to contribute significantly to the U. S. and world energy needs. In order to compete economically with other energy sources for these uses and also achieve the higher operating temperatures required for air conditioning and process heat (up to - 200°C), a solar collector must have low energy loss and low cost. Low loss requires vacuum to eliminate conduction and convection losses, and concentration onto a selective absorber to minimize radiation loss. Optimum concentration, or minimum ratio of absorbing surface area to collecting area, requires Winston concentration. The apparent motion of the sun indicates the use of cylindrical concentration with axis east-west. A series of arguments leading to optimum performance at near minimum cost indicate the collector should be of all glass tubular construction. A mirror coating on side and bottom inside surfaces provides concentration onto an internal glass tube coated with selective absorber. The window is only slightly convex to withstand atmospheric pressure while keeping reflection losses low. Heat transfer calculations, which are used to minimize losses help fix the collector length and width. Radiation collection calculations determine the acceptance angle and other parameters.
© (1977) COPYRIGHT Society of Photo-Optical Instrumentation Engineers (SPIE). Downloading of the abstract is permitted for personal use only.
John D. Garrison "A Vacuum Solar Thermal Collector With Optimal Concentration", Proc. SPIE 0114, Optics Applied to Solar Energy Conversion, (31 October 1977);

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