A “crazy idea”: Tiny solar mirrors controlled by actuators

Written on:March 27, 2012
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The solar mirrors that BrightSource Energy is mounting on trackers in California’s Mojave Desert run 7.2 meters by 10.5 meters. That’s hundreds of times larger than a new kind of tiny solar mirror that energy tinkerer Saul Griffith is working on, which stretches no bigger than 5 centimeters by 5 centimeters and is meant to sit on little tubular trackers that are no taller than a toothpick.

Griffith showed off this solar mirror and tracker concept at the Cleantech Forum in San Francisco Tuesday, and at first glance it is hard to imagine how the concept will translate into a marketable solar energy system later. The idea is in such an early stage of development that Griffith, an inventor who is working on several cleantech ideas through his Otherlab incubator, sounded a tad regretful when I pressed him for details after his talk: “I shouldn’t have shown it.”

Griffith and a couple members of his team are exploring how to reduce the cost of generating solar electricity by shrinking the size of the reflector system and figuring out ways to make them with cheaper materials and production processes. It’s the same goal for many academic researchers and solar companies today. In fact, Google also experimented with using small mirrors and trackers in its quest to engineer a more productive system and cheaper electricity, but the company abandoned the project last year.

The job of solar mirrors is to concentrate and direct sunlight onto solar cells (to produce electricity) or onto a container of water or other fluid to create steam, which is then piped to drive a turbine and generator to produce electricity. Griffith says he’s focusing on the design of the mirrors and trackers that will tilt and move the mirrors to follow the sun’s movement throughout the day and reflect the sunlight onto a target as precisely as possible. Whether the system will be used with solar cells or steam production equipment will depend on who become the investors and customers.

What makes Griffith’s idea intriguing and unusual, though, is how tiny each mirror-and-tracker system is. The 5 cm x 5 cm mirrors and the tiny trackers are about the actual size that he thinks will work as a system that can be deployed in the field, though he says the size and dimension of the system could very well change later as he develops the concept further (his website mentions a 100 cm mirror).

The mirrors can be glass or plastic, but the key is to have the mirrors small and light weight, which reduces the need for hefty trackers to prop them up. Small and low-profile mirrors also are less susceptible to strong wind, Griffith says. Strong wind could knock the mirrors out of alignment and do a poor job of reflecting a precise beam of light. He’s designing this system for large-scale solar power projects, and for those projects it would involve having to use thousands and thousands more mirrors.

The solution then – and the core technology of Griffith’s design – lies in the tracker, which is really an actuator that doesn’t rely on an electrical system to run. Instead, Griffith is borrowing microfluidic technology to design the mechanics of the tracker, which has to move the mirror in a precisely calibrated path that can best capture and reflect light. Griffith says he wants to borrow manufacturing methods from the toy industry to use, say, the injection molding process to make what he calls “single, monolithic actuators.”

Griffith has raised an angel round to fund the research, though he declines to disclose the amount. He’s hoping to get funding from ARPA-E, the federal program for early-stage cleantech technology. His solar mirrors did make an appearance at the recent ARPA-E conference, and you can check out a photo of the mirrors and other cool ideas here.

“It’s a crazy idea, but we have to try it,” he says.

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