Friday, January 20, 2012

Sunflowers Inspire Improved Solar Power Plant

The well-tuned geometry of the florets on the face of the sunflower head has inspired an improved layout for mirrors used to concentrate sunlight and generate electricity, according to new research.
In this file photo, a bee is pictured on a sunflower planted to help fight radiation the Fukushima nuclear power plant. Now, researchers are turning to sunflowers to improve the design of solar power plants.

The sunflower-inspired layout could reduce the footprint of concentrating solar power (CSP) plants by about 20 percent, which could be a boon for a technology that's limited, in part, by its massive land requirements.

CSP plants employ arrays of giant mirrors, each the size of half a tennis court, to beam the sun's rays up to heat a tube of fluid in the top of a tower. This hot fluid drives steam turbines that generate electricity.

In the traditional layout, the mirrors are arranged in rows of circles that ripple out from the central tower. Some, such as the Spain's Gemsolar power-generating array, take up 185 acres. That plant, when complete in 2013, will provide power for about 25,000 homes.

This voracious appetite for land sent Alexander Mitsos, a mechanical engineer at the Massachusetts Institute of Technology, and colleagues in search of an improved layout.

They started with a computer model that evaluates the efficiency of layouts and tested it on a CSP plant in Andalucia, Spain, called PS10. They found its arrangement of mirrors results in shading and blocking of sunlight that dampens the plant's efficiency.

In a bid to increase the efficiency, Mitsos and colleagues used some numerical optimizations to tinker with the layout. They came up with a design where the mirrors are closer together, reducing the amount of land required by 10 percent.

The pattern, a team member noticed, had some elements that resembled the spiraling pattern in sunflowers and suggested they mimic the florets.

"We started looking into it and it turns out that was an excellent idea," Mitsos told me Wednesday.

This "a ha" moment, in turn, led them to a simulated field of mirrors that even more closely resembles a sunflower, with each mirror angled at 137 degrees with respect to its neighboring mirror, as mathematicians had previously found each sunflower floret is turned.

The result was a layout that takes up 20 percent less space than the PS10 layout and is more efficient to boot, Mitsos said.

"It is very scary that we did all the [numerical optimization] work and then we go back to nature," he noted. "We could have started there."

While the finding is based on computer simulations, Mitsos has no doubts it is correct.

"The thing to realize is that a plant like [PS10] costs many millions of dollars and it takes some time to build, so it is not an experiment you can do in the lab," he said.

But he hopes that developers in the CSP industry will adopt his design, saving land and money in the process.


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