The achievement of more than 40 percent efficiency by a solar cell is most significant for the potential at which it hints, the developers say.
"These results are particularly encouraging since they were achieved using a new class of metamorphic semiconductor materials, allowing much greater freedom in multijunction cell design for optimal conversion of the solar spectrum," Richard R. King, the principal investigator of the high efficiency solar cell research and development effort, said in a Boeing statement.
In other words, the cells can use more of the sun's spectrum, which in turn creates more electricity.
"The excellent performance of these materials hints at still higher efficiency in future solar cells," King said. The exact efficiency rate the researchers recorded was 40.7 percent, a result verified by the U.S. Department of Energy's National Renewable Energy Laboratory in Golden, Colo.
Boeing's subsidiary Spectrolab passed the 40 percent mark -- a terrestrial world record -- last week while testing its new concentrator photovoltaic cells, the company said.
Photovoltaic cells turn regular sunlight into electricity using a chemical reaction. Concentrator PV cells convert stronger light; the models now on the market concentrate the light either with external, curved mirrors, or with special magnifying glass overlays called Frisell panels.
However, for testing purposes, Boeing uses special strong lights that have a concentration equal to 244 suns. This way, results can be easily replicated, Dave Garlick, a Boeing spokesman, told United Press International.
Conventional solar cells, whose main ingredient is multicrystalline silicon, have one layer of photovoltaic material, but the solar cell in question is a multijunction cell -- it has three layers of photovoltaic material, one on top of the other, Jeffrey A. Mazer, a photovoltaics engineer at the U.S. Department of Energy, told UPI.
"High efficiency multijunction cells have a significant advantage over conventional silicon cells in concentrator systems because fewer solar cells are required to achieve the same power output. This technology will continue to dramatically reduce the cost of generating electricity from solar energy as well as the cost of materials used in high-power space satellites and terrestrial applications," the Boeing statement said.
Many solar technologies were first developed for use in space.
Surpassing 40 percent efficiency was "like a door opening," Boeing's Garlick said. He said the achievement had been compared to humans finally succeeding in running a 4-minute mile.
However, Mazer said, passing the 40 percent mark isn't such big news. "Efficiency has been steadily increasing ... 40 percent efficiency is not a gigantic change qualitatively or quantitatively," he said.
Cells boasting 43 percent or 44 percent efficiency were always on the way, he said.
He said that this kind of cell was first developed by the NREL in the late 1980s and early 1990s, and that the laboratory still holds the original patents for this type of cell, which is known as a "multijunction III-V monolithic stack."
But even if breaking the threshold isn't an earth-shattering development, it puts the holy grail of solar energy -- cost effectiveness -- in reach, the Department of Energy's team leader for photovoltaic research and development, Richard J. King, told UPI.
Currently, using solar energy is only cost-effective in areas of the world where national or state governments provide subsidies, rebates and tax incentives to encourage the technology.
The Department of Energy's King -- not to be confused with Boeing's King -- said that as part of U.S. President Bush's Solar America Initiative, the government is working to help make solar energy cost effective on its own by 2015. This means solar energy will cost between 5 cents per kilowatt hour and 10 cents per kilowatt hour, he said.
The $148 million initiative is handed out to private companies, universities and laboratories on the basis of competitive solicitations, Richard J. King said, though Boeing has been working on this particular cell -- a 1-centimeter by 1-centimeter -- with the help of a Department of Energy contract that predates the Solar America Initiative, worth close to $3 million.
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