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20 Feb 2008 | United States
Harvesting the sun
A technology that could cost a few cents a yard to collect energy from the sun even after it has set and be imprinted on flexible materials is being developed by a team of researchers at the US Idaho National Laboratory, along with partners at Microcontinuum Inc. (Cambridge, MA) and Patrick Pinhero of the University of Missouri, USA.
A special manufacturing process is used to stamp tiny square spirals of conducting metal onto a sheet of plastic. Each interlocking spiral "nanoantenna" is as wide as 1/25 the diameter of a human hair.
The sun radiates a lot of infrared energy, some of which is soaked up by the earth and later released as radiation for hours after sunset. The nanoantennas take energy from both sunlight and the earth's heat with higher efficiency than conventional solar cells.
"I think these antennas really have the potential to replace traditional solar panels," says physicist Steven Novack.
The INL team hope the antennas might one day be produced like foil or plastic wrap on roll-to-roll machinery. So far, they have demonstrated the imprinting process with six-inch circular stamps, each holding more than 10 million antennas.
INL researcher Steven Novack holds a plastic sheet of nanoantenna arrays, created by embossing the antenna structure and depositing a conductive metal in the pattern. Each square contains roughly 260 million antennas.
Commercial solar panels usually transform less that 20 percent of the usable energy that strikes them into electricity. The team estimate that individual nanoantennas can absorb close to 80 percent of the available energy. The circuits themselves can be made of a number of different conducting metals, and the nanoantennas can be printed on thin, flexible materials like polyethylene, a plastic that's commonly used in bags and plastic wrap.
By focusing on readily available materials and rapid manufacturing from inception, Novack says, the aim is to make nanoantenna arrays as cheap as inexpensive carpet.
Double-sided panels could absorb energy from the sun during the day, while the other side might take in the narrow frequency of energy produced from the earth's radiated heat. It may be possible to charge portable battery packs, coat the roofs of homes and even be integrated into polyester fabric.
While the nanoantennas are easily manufactured the researchers still need to develop a process to create a way to store or transmit the electricity. Although infrared rays create an alternating current in the nanoantenna, the frequency of the current switches back and forth ten thousand billion times a second. That's much too fast for electrical appliances, which operate on currents that oscillate only 60 times a second. So the team is exploring ways to slow that cycling down, possibly by embedding energy conversion devices like tiny capacitors directly into the antenna structure as part of the nanoantenna imprinting process.
The next generation of solar energy collectors may only be a few years away say the scientists.
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