Researchers develop efficient solar power devices

Will Dunham, Reuters 10 Jul 08;

WASHINGTON (Reuters) - Using sheets of glass covered with organic dyes, scientists have devised an efficient and practical solar power device that they believe can help make this clean, renewable energy source more affordable.

Experts eager for energy sources that do not involve the burning of fossil fuels often point to the promise of solar energy -- harnessing sunlight to make electricity. But solar power so far has proven costlier than standard energy sources.

Writing on Thursday in the journal Science, Massachusetts Institute of Technology researchers describe the development of a new type of "solar concentrator" that may provide a better way to extract energy from the sun.

They used glass sheets coated in organic dyes to concentrate light hitting the panes. The dyes absorbed the light, then emitted it into the glass, which carried the light to the edges of the pane much as fiber-optic cables transport light over distances, the researchers said.

At the edges of the glass are located small solar cells that then transform the light into electricity.

"It consists of just a piece of glass with a layer of paint on top of it," MIT electrical engineering professor Marc Baldo, who led the research, said in a telephone interview.

"The idea is the light comes in and hits the paint. The paint then bounces the light out to the edges of the glass. All you need is the solar cells on the edges. So we think we can use this to reduce the cost of solar electricity," added said.

MIT researcher Jonathan Mapel, who also worked on the study, said the hope is that the use of this sort of technology can help bring the cost of solar power closer to the cost of conventional fossil fuel power sources such as coal.

"One of the challenges with solar (energy) in general is that it's just too high in cost. And what you'd like to do is reduce the price of solar electricity," Mapel said.

Solar concentrators collect sunlight over a large area -- in this case the panes of glass -- and concentrate it into a small solar cell that turns the light into electricity.

Existing solar concentrators use mirrors or lenses to concentrate the light. The sheets used in this research are flat and light, thus can be utilized in solar panels placed on roofs or even used as windows that could generate power.

The new system, unlike some concentrators, does not have to move to track the progression of the sun across the sky in order to provide a continuous power source, Baldo said.

The researchers think their system could be available within three years and even could be added onto existing solar-panel systems to increase their efficiency.

"This accomplishment demonstrates the critical importance of innovative basic research in bringing about revolutionary advances in solar energy utilization in a cost-effective manner," Aravinda Kini of the U.S. Department of Energy's Office of Science, a sponsor of the work, said in a statement.

Some of the MIT researchers are forming a company, Covalent Solar, based in Boston to develop and market the technology.

(Editing by Anthony Boadle)

More Efficient Solar Energy Collectors Attach to Windows
Andrea Thompson, LiveScience.com Yahoo News 10 Jul 08;

A new, compact way to collect sunlight from windows and focus it to generate more electricity could make those multiple expensive rooftop solar panels a thing of the past.

The solar panels that cover the tops of some buildings today contain photovoltaic cells that convert sunlight into electricity. Unlike burning coal, collecting and converting solar energy releases no greenhouse gases, which warm the atmosphere. Limited efficiency and high construction costs have kept solar from producing more than about 0.07 percent of U.S. energy needs in 2007, according to figures from the U.S. Department of Energy.

Solar concentrators can be used to increase the electrical power obtained from the photovoltaic cells. But most concentrators in use today "track the sun to generate high optical intensities, often by using large mobile mirrors that are expensive to deploy and maintain," said MIT's Marc A. Baldo, who led the team that created the new type of solar concentrator.

New approach

Instead of covering a large area with solar cells, the new method only requires locating cells around the edges of a flat glass panel.

The MIT solar concentrator involves a mixture of two or more dyes painted onto a pane of glass or plastic. The dyes absorb light across a range of wavelengths, reemit it at a different wavelength and transport it across the pane to the solar cells at the edges.

"Light is collected over a large area [like a window] and gathered, or concentrated, at the edges," Baldo said.

Focusing the light like this increases the electrical power generated by each solar cell "by a factor of 40," he added.

The work was funded by the National Science Foundation and the U.S. Department of Energy's Office of Science.

Old idea

Scientists had tried using similar solar concentrators in the 1970s, but abandoned the idea when not enough of the collected light reached the edges of the concentrator. The MIT engineers revamped the idea by using a mixture of dyes in specific ratios, which allows some level of control over how the light is transmitted.

"We made it so the light can travel a much longer distance," said study team member Jon Mapel, an MIT graduate student. "We were able to substantially reduce light transport losses, resulting in a tenfold increase in the amount of power converted by the solar cells."

Because the system, detailed in the July 11 issue of the journal Science, is simple to manufacture, the team thinks that it can be implemented within three years. It could also be added on to existing solar-panel systems, increasing their efficiency and reducing the cost of solar energy.