Can Solar Power Be Efficient?

Solar power has always been considered an environmentally friendly energy source. Duke University research could make the strategy not only green but also cost-efficient.

Atop Duke's Pratt School of Engineering, assistant professor Nico Hotz is constructing a test-model hybrid solar cell to capture sunlight and use it to heat a water-methanol combination.

The system creates hydrogen that can be stored and used to power fuel cells later.

"With a hybrid system in the summer, we can turn 28.5 percent of the energy produced into something else - that's 10 percent more than with a conventional system," Hotz said.

He's testing whether his system can work at a large scale.

"In the winter, the increase is the same: 15 percent versus 5 percent. It's a more efficient system."

Hotz compared the hybrid to three existing systems: one that directly converts sunlight to electricity and splits water into hydrogen and oxygen, one that stores converted sunlight in different types of batteries, and one that is simpler, though similar, to Hotz's. The hybrid is the least expensive, he said, with installation costs totaling $7,900. Conventional installations can cost as much as $40,000.

The hybrid mimics conventional solar cells by collecting sunlight. It is different, however, because it runs a water-methanol mixture through vacuum-sealed copper tubes coated with aluminum and aluminum oxide. This structure allows the water to heat up to at least 200 degrees Celsius (392 Fahrenheit). The heat is necessary to produce hydrogen. Hotz said standard solar cells reach only 60 to 70 degrees Celsius (140-158 Fahrenheit).

At the appropriate temperature, Hotz's team infuses small amounts of catalyst to kick off hydrogen production.

"This reaction produces hydrogen efficiently," Hotz said. "It can be used immediately or stored in a tank to be used later, perhaps by homeowners who want it in the winter months to supplement their other energy sources."

However, according to Clemson University engineering professor Rajendra Singh, a commercial application of Hotz's research is unlikely.

"This is great basic research, but it won't change the world." Singh said. "There's not a single system in existence that can economically produce hydrogen."

SOURCE: http://www.charlotteobserver.com/2011/11/28/2809554/can-solar-power-be-cost-efficient.html