Optical Performance and Durability of Solar Reflectors Protected by an Alumina Coating

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/m2 ($1.00/ft2).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 isdeposited 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.