Testing of the prototype facets for the stretched-membrane faceted dish

ABSTRACT:
The Faceted Stretched-Membrane Dish Program is part of a DOE-sponsored effort to develop a commercial 25 kWe dish/Stirling system employing a twelve-facet dish concentrator. The facets will utilize the stretched membrane technology originated in the heliostat development program. Each

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facet is constructed with a thin metal membrane stretched over both sides of a steel ring. When a small vacuum is induced between the membranes they assume a parabolic contour capable of concentrating sunlight at a predetermined focal length. A reflective polymer film is attached to the face of the facet to enhance the optical performance. During Phase II of the Faceted Stretched-Membrane Dish Program, Science Applications International Corp. and Solar Kinetics, Inc., constructed prototype 3.5-meter facets utilizing different design approaches to demonstrate their manufacturability and optical performance. Sandia engaged in a program to determine the on-sun performance of the facets (for f/Ds of 2.7 to 3.0). A uniformly distributed slope error was used as the basis for comparison. Flux arrays based on slope error from a computer model were compared to a measured flux array for each facet. The slope error for the facet was determined by the value that would produce a modeled array with the minimum mean square difference to the measured array. The facet produced by SAIC demonstrated uniform slope errors of 2.2 to 3,0 milliradians with peak flux intensities of 334 to 416 kW/m’, The SKI facet had slope errors of 1.6 to 1.9 milliradians with peak flux intensities of 543 to 1186 kW/m2,

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