With enough sunlight falling on home roofs to supply at least half of America's electricity, scientists today described advances toward the less-expensive solar energy technology needed to roof many of those homes with shingles that generate electricity.
Shingles that generate electricity from the sun, and can be installed like traditional roofing, already are a commercial reality. But the advance ― a new world performance record for solar cells made with "earth-abundant" materials ― could make them more affordable and ease the integration of photovoltaics into other parts of buildings, the scientists said.
Their report was part of a symposium on sustainability at the 244th National Meeting & Exposition of the American Chemical Society, the world's largest scientific society, being held in Philadelphia this week. Abstracts of other presentations appear below.
"Sustainability involves developing technology that can be productive over the long-term, using resources in ways that meet today's needs without jeopardizing the ability of future generations to meet their needs," said Harry A. Atwater, Ph.D., one of the speakers. "That's exactly what we are doing with these new solar-energy conversion devices."
The new photovoltaic technology uses abundant, less-expensive materials like copper and zinc ― "earth-abundant materials" ― instead of indium, gallium and other so-called "rare earth" elements. These substances not only are scarce, but are supplied largely by foreign countries, with China mining more than 90 percent of the rare earths needed for batteries in hybrid cars, magnets, electronics and other high-tech products. Atwater and James C. Stevens, Ph.D., described successful efforts to replace rare earth and other costly metals in photovoltaic devices with materials that are less-expensive and more sustainable.
Atwater, a physicist at the California Institute of Technology, and Stevens, a chemist with The Dow Chemical Company, lead a partnership between their institutions to develop new electronic materials suitable for use in solar-energy-conversion devices.
Atwater and Stevens described development and testing of new devices made with zinc phosphide and copper oxide that broke records for both electrical current and voltage achieved by existing so-called thin-film solar energy conversion devices made with zinc and copper. The advance adds to evidence that materials like zinc phosphide and copper oxide should be capable of achieving very high efficiencies, producing electricity at a cost approaching that of coal-fired power plants. That milestone could come within 20 years, Atwater said.
Stevens helped develop Dow's PowerHouse Solar Shingle, introduced in October 2011, which generates electricity and nevertheless can be installed like traditional roofing. The shingles use copper indium gallium diselenide photovoltaic technology. His team now is eyeing incorporation of sustainable earth-abundant materials into PowerHouse shingles, making them more widely available.
"The United States alone has about 69 billion square feet of appropriate residential rooftops that could be generating electricity from the sun," Stevens said. "The sunlight falling on those roofs could generate at least 50 percent of the nation's electricity, and some estimates put that number closer to 100 percent. With earth-abundant technology, that energy could be harvested, at an enormous benefit to consumers and the environment."
Other presentations at the symposium included:
- Efforts by the mining company Molycorp to expand and modernize its Mountain Pass, Colo. facilities to increase United States production of rare earth elements with greener and less costly technology.
- An overview of the challenges to maintaining a sustainable supply of critical materials ranging from rare earth elements to more abundant metals like copper.
- A new material for recovering rare metals from the 800 billion gallons of wastewater produced by mining and oil and gas drilling every year.
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