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Electronic Resource
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SAND Report: SAND77-0582, May 1977.
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Library's review
ABSTRACT:
An experimentally verified simple analytical model, based on classical optical aberrations, is derived and predicts the power reception of a central receiver solar facility. A laboratory simulation was made of a typical heliostat, and its images were photographed and measured at several
An experimentally verified simple analytical model, based on classical optical aberrations, is derived and predicts the power reception of a central receiver solar facility. A laboratory simulation was made of a typical heliostat, and its images were photographed and measured at several
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angles of incidence. The analytically predicted image size is in agreement with experiment to within less than '10% over an incident angle range of 60 degrees. Image size for several of the heliostats in the Sandia-ERDA Solar Thermal Test Facility array were calculated throughout a day and compared with ideal images and the size of the receiver. The optical parameters of the system and the motion of the sun were found to severely affect the design and optimization of any solar thermal facility. This analysis shows that it is the aberration astigmatism which governs the solar image size at the receiver. Image growth is minimal when heliostats are used at small angles of incidence, which usually corresponds to a limited operating time of two to three hours. However , image size is markedly increased at large angles of incidence which, unfortunately, occur when system operation is extended to a large fraction of a day over all seasons, as will be required for electric power producing facilities. There is no optically unique heliostat design, but sophistication of design must be tailored to heliostat location, size, and operational time interval as well as to receiver size. Obvious modifications to the optical surface which are intended to optimize performance are of only limited effectiveness and in fact can lead to images larger than those from a simple spherical surface at large angles of incidence. The principal result of this study is that the predominant sources of image enlargement are identified and measures for minimizing these enlargements are presented. This analysis considers only the idealized optical problem and does not consider the pragmatic errors associated with implementation and operation of a heliostat array. Show Less