Should CSP Mirrors Be Glass or Metal?

Glass or metal? That could become an increasingly important question for developers of concentrating solar power projects.
A growing number of companies, from 3M to Abengoa Solar, are working on mirrors made of metals and polymer that aim to be lightweight and cheaper than the glass variety. 3M is doing a pilot-stage launch of its Solar Mirror Film, and it’s planning for a full commercial launch by the end of the year, said Daniel Chen, business development manager of 3M’s renewable energy division.
“Saving time and material costs are the big advantages,” Chen said during a recent poster session at 3M’s headquarters in Minnesota. Metallic films “also are easier to transport – you can pack them densely and use aluminum locally” for project construction.
Like GE and other titans in their industries, 3M is keen on winning a fat slice of the growing renewable energy market. The use of metal film, which is then laminated onto an aluminum backing, isn’t a new concept, and 3M launched a similar product in the 1980s. It lasted for 4-5 years before the entire market disappeared, Chen said. The company restarted the research in this area about two years ago, when the solar industry began to revive in earnest.
Proponents say metal mirrors are suitable for all types of solar thermal power plant designs, including parabolic trough, power tower and stirling dish. But replacing glass, a durable and highly reflective material with a long history of surviving the outdoors, won’t be so easy. Investors and utilities tend to prefer well-proven technologies over novel ones. The largest solar thermal power complex in the world, the 354-megawatt solar field in the Mojave Desert, was built between 1984 and 1991 with glass mirrors.
“If you are going to finance these systems, banks want these things to last at least 20 years probably longer 30 years. Most glass products have some of that history,” said Mark Mehos, the program manager for concentrating solar power research at the National Renewable Energy Laboratory in Colorado.

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