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Electronic Resource
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Publication
SAND Report: SAND84-7011, September 1984.
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Library's review
ABSTRACT:
A Cassegrainian point focus solar concentrator system has been analyzed and a conceptual design developed. In this system, the receiver is located at the vertex of the primary mirror eliminating limitations of receiver size and weight associated with standard parabolic dish collectors.
A Cassegrainian point focus solar concentrator system has been analyzed and a conceptual design developed. In this system, the receiver is located at the vertex of the primary mirror eliminating limitations of receiver size and weight associated with standard parabolic dish collectors.
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Disadvantages include increased reflection loss at the secondary mirror and increased beam spread associated with the longer focal length. A non-imaging, trumpet shaped tertiary reflector located at the receiver aperture increases the system efficiency by 15 to 20 percent. Because the secondary mirror may reach very high temperatures, a reflective film cannot be used as a mirror surface. Recommended instead is thin polished stainless steel stamped into shape and used as the mirror substrate with vacuum deposited silver used for the reflecting surface. A transparent coating is then required to protect the silver. Both the secondary and primary mirrors require radial supports on the back surface to minimize deflection under wind loading. The Cassegrainian system is more efficient than the standard dish only at high operation temperatures and for large receivers. However, the cost per kilowatt into the receiver aperture is less for the Cassegrainian, due primarily to the high cost of piping and insulation running to the receiver of the standard dish. Further efforts in the analysis and design of the Cassegrainian concept appear warranted. Show Less