Use of flexible reflective surfaces for solar energy concentration Available to Purchase

Historically, many techniques for utilizing solar energy have suggested reflective optics, although usually with glass mirrors. The requirements of spacecraft and their associated thermal control problems provided the impetus to develop lightweight, flexible reflectors. Thin metallic vapor deposits such as aluminum and silver on a clear flexible film such as Teflon have been used to act in reflectances as high as 94%, with long−term stability even in a space environment. The high reflectance, coupled with present processing techniques, makes these materials candidates for solar energy concentrators. A flexible metalized film, stretched drum−head fashion, can form a mirror that can be oriented to direct sunlight to a central receiver. The use of taut membrane is being explored as part of a NSF/RANN grant studying feasibility of a large−scale solar thermal power plant. The evaluation of any reflector requires measurement of the spectral response, specularity, and over−all flatness. Integrating the spectral response to the energy distribution of sunlight gives the total reflected energy. Of equal importance is the specularity or divergence of the reflected beam. The combination of these factors will determine a candidate reflector’s suitability. A device for measuring the bi−directional reflectance−distribution function is described and data are presented. A discussion of membrane−reflector development and data from life tests are presented.