Solar energy is abundant, but diffuse. The cost-effective concentration of solar energy to higher energy levels permits a wider array of applications, such as thermal power via traditional or organic Rankin cycles, Sterling dish/engine systems, concentrating photovoltaics, etc. While the projected cost of traditional carbon-based energy sources is expected to continue rising, the cost of delivered solar energy must also decrease for active solar applications to achieve widespread economic success. A Better Focus Co. has manufactured 4' diameter stretched membrane dishes for cooking applications since 2004, and has recently scaled this design up to an 8' diameter, envisioned for use as a facet component in a tracking point focus concentrating system. The stretched membrane concept utilizes reflective polymer film, stretched across a rigid, round frame. A vacuum is applied inside to induce a concave shape to the film for the purposes of focusing solar radiation to a concentrated spot. The stretched membrane concept is not new, so a literature review was conducted of past research. Past papers were not always illuminating as to the shortcomings of individual designs, so comment was solicited from participants in past stretched membrane investigations..The design and scaling problems addressed with this specific dish design are discussed in detail. The resulting design delivers 350 suns concentration to a 4-6" spot, with static temperatures of over 900C with solar insolation of 950 w/m~2. A second prototype was constructed with weatherable film, and has been mounted outdoors on a weathervane mount since December 06. Long-term outdoor testing continues. Finally, a primary design goal is to reliably achieve maximum concentrating capability with the lowest cost of materials. Actual materials costs recorded is $ 57/M~2 with weatherable materials in research quantities and at retail pricing levels.
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