Getting more wattage for the buck from silicon

 (12/23/2009)
http://www.eenews.net/climatewire/2009/12/23/4/

Saqib Rahim, E&E reporter
Government researchers have designed a solar cell a fraction of the width of a human hair, a breakthrough that could dramatically drop the cost of solar power.

The announcement yesterday by Sandia National Laboratories likened the minuscule cells to a "glitter" that could affix to buildings, even clothes, turning them into power plants.

Because the cells are so small, research scientist Greg Nielson said, their production process is far more efficient than that of conventional solar cells. They need thinner slices of silicon, leaving more material to make additional cells. They can be made from flatter, wider silicon pancakes that typical solar cells can't use.

They don't capture any less power -- their 15 percent efficiency roughly matches conventional cells -- but they use 100 times less silicon.

"We're right in the mix there with what is currently being sold, but we use much less silicon," Nielson said.

The cost of solar power has fallen over the decades, but it remains too expensive to compete against energy sources like coal and nuclear.

Critics point to vast research dollars, and solar's meager use in the national portfolio, as evidence that the technology can't get cheap enough to become a massive energy resource. The solar power industry has argued that with a climate policy and large-scale deployment, they will reduce costs enough to become competitive.

Part of what enabled the "glitter" cell -- and its cost improvement -- was working at the micro scale, where natural forces become distorted and strange.
Weirdness at the micro level
"At the micro-level things become weird in a several ways," Nielson said in an e-mail. Air thickens, becoming harder to move through. Light acts more like a wave, and it can even act as a forklift to carefully move particles around.

At this level, surfaces become stickier, making gravity less of a player. "If we were a hundred microns tall, walking around would be [a] different experience," he said. "We might actually have to physically pull our feet up off the floor because they have a stronger tendency to stick. It might be [like] walking on really sticky tape."

The instruments for getting silicon down to the micro level have been around for decades, usually for carving microscopic sensors out of silicon. These sensors could measure position, as in an iPhone that responds to being held sideways, or they could deflect light, to fine-tune the intensity of a laser.

Working at this level is Nielson's specialty, and he said it had rarely been applied to solar power. The "glitter" cell may have important effects on the cost of solar power, he added.

First, it can be built with the same widely used equipment that produces sensors for air bags, iPhones and other gadgets. The reduced silicon use means producers can get more cells -- producing the same amount of electricity -- for a fraction of the materials' cost.

And because of the mini-cells' wacky physical properties, he said, they might be a candidate to mat onto many kinds of oddly shaped surfaces and materials -- from hikers seeking to charge their mobile phones to the tent where those hikers snooze.