A Path to Cheaper Solar Energy: Big Mirrors by Alcoa

industry.bnet.com
Mar 19, 2010

Over the past few months, there has been a lot of talk about how to make a certain kind of solar energy, called solar thermal, cheaper. The big cost in solar thermal comes from the price of the mirrors used to reflect sunlight onto an enclosed liquid - often water - which boils to drive turbines. Mirrors, it turns out, only seem cheap until you need to buy a few hundred thousand of them.

A number of companies have been working to make mirrors cheaper - including some you wouldn't expect. Back in February, I wrote about Google's bid to drive down the cost of mirrors, the search company's first serious foray into materials technology. Google's motivation is its investments in two solar thermal companies, BrightSource Energy and eSolar.

Google hopes to put its cheaper mirrors on the market within a few years. But it has just had its thunder stolen by another unexpected entrant: Alcoa, one of the world's biggest aluminum makers. It turns out that a bit of spit and shoeshine can make aluminum highly reflective.

You can see Alcoa's take on a parabolic trough in the image above. The trough design is pretty typical in solar thermal; its advantage is that the curved design focuses a lot of sunlight to one point. What you can't see are the parts behind the mirror. Alcoa's money-saving idea is not only to eliminate the glass in mirrors, but also to fabricate the trough as a single piece - the support structure is built into the mirror.

Alcoa's mirror is in testing now, but the company expects the design to knock 20% off the cost of a solar thermal installation. An Alcoa exec spoke to the New York Times about the design:

"If you go out and look behind large parabolic troughs, you'll find an elaborate truss structure," said Rick Winter, a technology executive with Alcoa. "From our understanding of aerospace structures, we said if we can modify the wing box design used in aircraft and integrate a parabolic reflector, it would give us a light and stiff structure that would fundamentally affect the cost equation."

Clearly, Alcoa is no stranger to unusual fabrication techniques. Apart from working on aircraft, it also does work for the automotive, construction, defense, and oil industries, among others.

What remains to be seen is whether the products that Alcoa, Google or anyone else manufactures actually fit the needs of the solar thermal companies. But if the cost reductions are anything on the order of what's claimed, it will be great news for the solar thermal industry - so much so that cheap mirrors could potentially put solar power on an even footing with traditional sources of energy, like natural gas.