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Durability of Solar Reflective Materials with an Alumina Hard Coat Produced by Ion-Beam-Assisted Deposition: Preprint

Description: A promising low-cost reflector material for solar concentrating power (CSP) generation is a silvered substrate protected by an alumina coating several microns thick. The alumina hard coat is deposited under high vacuum by ion-beam-assisted-deposition (IBAD). Samples of this material have been produced both by batch and continuous roll-coating processes. The substrate materials investigated were polyethylene terephthalate (PET), PET laminated to stainless-steel foil, and chrome-plated carbon steel strip. The advantage of steel strip compared to PET is that it withstands a higher process temperature and lowers the final product installation costs. In this paper, we compare the durability of batch and roll-coated reflective materials with an alumina deposition rate as high as 10 nm/s. In general, the durability of the samples is found to be excellent. Comparisons between accelerated and outdoor exposure testing results indicate that these front-surface mirrors are more susceptible to weather conditions not simulated by accelerated tests (i.e., rain, sleet, snow, etc.) than other types of solar reflectors. For long-term durability, edge protection will be necessary, and durability could be improved by the addition of an adhesion-promoting layer between the silver and alumina.
Date: October 1, 2002
Creator: Kennedy, C. E. & Smilgys, R. V.
Partner: UNT Libraries Government Documents Department

Optical performance and durability of solar reflectors protected by an alumina coating

Description: Solar thermal electric power systems use large solar reflectors to concentrate sunlight to generate electricity. The economic viability of these systems depends on developing a durable, low-cost reflector. The goals for such a reflector are specular reflectance above 90% for at least 10 years under outdoor service conditions and a large-volume manufacturing cost of less than $10.8/m{sup 2} ($1.00/ft{sup 2}). Currently, the best candidate materials for solar reflectors are silver-coated, low-iron glass and silvered polymer films. Polymer reflectors are lighter in weight, offer greater system design flexibility, and have the potential for lower cost than glass reflectors. A promising low-cost reflector consists of a silvered polymer protected by an optically transparent alumina coating. The coating is deposited by an ion-beam-assisted physical vapor deposition (IBAD) technique. Samples of this reflector have maintained high optical performance in accelerated testing at the National Renewable Energy Laboratory for more than 3000 hours. Solar reflectors produced using this technique may represent an opportunity to bring solar power generation to reality.
Date: July 1, 1996
Creator: Kennedy, C.E.; Smilgys, R.V.; Kirkpatrick, D.A. & Ross, J.S.
Partner: UNT Libraries Government Documents Department

Progress toward achieving a commercially viable solar reflective material

Description: Solar thermal technologies use large mirrors to concentrate sunlight for renewable power generation. The development of advanced reflector materials is important to the viability of electricity production by solar thermal energy systems. The reflector materials must be low in cost and maintain high specular reflectance for extended lifetimes under severe outdoor environments. Production processes associated with candidate materials must be scalable to mass production techniques. A promising low-cost construction uses a stainless steel foil substrate with a silver reflective layer protected by an optically transparent oxide topcoat. Thick (2 to 4 micron), dense alumina coatings provide durable protective layers. The excellent performance of alumina-coated reflector materials in outdoor and accelerated testing suggests that a larger field trial of the material is warranted. The key to producing a greater quantity of material for field deployment and testing without incurring substantial capital is the use of a chilled drum coater. An existing chamber is being modified, and the deposition rate will be increased prior to the installation of a drum coater to produce 1-ft wide by 10-ft long strips of solar reflector material. The production and performance of these materials are discussed.
Date: June 1, 1998
Creator: Kennedy, C.E. & Smilgys, R.V.
Partner: UNT Libraries Government Documents Department