Here comes the sun

Michael Mackay, MSU professor of chemical engineering and materials science, is looking to the sky for solutions to the global energy crisis.

In the United States, each person requires about 97 watts of energy per day. In Michigan the sun provides, on average, a constant 150 watts of power, or about one to two light bulbs' worth, in every square meter.

"That's a reasonable amount," Mackay said. "We have this energy available to us -- we just need storage capacity."

The challenge is finding ways to cheaply channel the sun's energy. Silicon-based solar cells, the kind currently used, are expensive. Solar cells to fully power a home can cost more than $10,000.

Mackay's research focuses on developing polymer-based solar cells, which are potentially much less expensive than silicon-based cells. He works with nanoparticles, which are put in polymer films that are about 100 nanometers thick to absorb the sun's energy.

When the sun strikes a solar cell it puts the atoms into a higher energy state called an exciton. The challenge is that the exciton must be formed about 10 nanometers from the electrode to generate electricity before creating heat. The challenge is to create a film that is thick enough to absorb all the sun's energy but thin enough to let the exciton generate current. Mackay's approach is to let the nanoparticles assemble in the film to create pillars -- like the teeth in a comb -- yielding many sites for electricity generation.

The cells would need to harness about 10 percent of available energy to be economically feasible; so far researchers have managed to achieve 5 percent efficiency. Mackay said he's ready to test his structures; if he hits the 10 percent benchmark, the next step is patent approval for his process.

Mackay and his graduate students also are working on developing a solar paint, which would allow any surface to be made into a solar cell, and a solar fabric in which each fiber is a solar cell.

"You could weave the fiber into canvas or an umbrella - you could sit on the beach and keep your drinks cold," he said. "Or use the fiber to make a tent in your driveway to charge your electric-powered car during the day."