Optimization of dish solar collectors with and without secondary concentrators

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Abstract
Methods for optimizing parabolic dish solar collectors and the consequent effects of various optical, thermal, mechanical, and cost variables are examined in this report. The most important performance optimization is adjusting the receiver aperture to maximize collector efficiency. Other parameters than can be adjusted to optimize efficiency include focal length, and, if a heat engine is used, the receiver temperature. The efficiency maxima associated with focal length and receiver temperature are relatively broad; it may, accordingly, be desirable to design somewhat away from the maxima. Performance optimization is sensitive to the slope and specularity errors of the concentrator. Other optical and thermal variables affecting optimization are the reflectance and blocking factor of the concentrator, the absorptance and losses of the receiver, and, if a heat engine is used, the shape of the engine efficiency versus temperature curve. Performance may sometimes be improved by use of an additional optical element (a secondary concentrator) or a receiver window if the errors of the primary concentrator are large or the receiver temperature is high. Such factors as receiver temperature affect not only efficiency, but also maintenance, reliability, and availability. All of these affect the cost of the energy produced, as does, of course,more » the initial installed cost of the collector itself. Both collector costs and efficiency have strong effects upon the cost of the energy produced; trade-offs of system performance versus system cost are needed. « less

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