Technical and Cost Potential for Lightweight, Stretched-Membrane Heliostat Technology

This paper presents the background and rationale and describes the development effort of a potentially low-cost, concentrating reflector design. The proposed reflector design is called the stretched-membrane concept. In this concept a reflector film-which can be metal, polymeric, or of a composite construction-is stretched on a hollow torroidal frame that offers a structurally efficient andoptically accurate surface. Although the intent is to improve heliostat concentrator cost and performance for solar thermal applications, the collector design approach proposed here may well offer effective cost and performance opportunities for improving photovoltaic and solar daylighting applications as well. Some of the major advantages include a reflector, a support frame, and supportstructures that can be made extremely lightweight and low in cost because of the effective use of material with high average stress levels in the reflector and support frame; a 75% reduction in the weight of the reflector and support structure (down to the drive attachment) over the second-generation glass-and metal heliostat concept; a better than 50% cost reduction for the reflector assemblyand support structure compared to corresponding elements of the second-generation concept; and, finally, optical accuracies and an annual energy delivery potential close to those attainable with current glass-and-metal heliostats. In this paper we present results of initial design studies, performance predictions, and analysis, as well as results corresponding to subscale testing. We alsoinclude recommendations for further development and for resolving remaining issues.