Researchers at the DoE’s Idaho National Laboratory have come up with an inexpensive way to use “nanoantennas” to collect heat energy produced by the sun and other sources. Flexible plastic sheets containing the nanoantennas could then be mass produced to creat flexible lightweight “skins” that could power everything from iPods to hybrid cars to buildings.
While lots more work needs to be done on methods to convert the energy absorbed into useful electricity, the nanoantennas, which collect “mid-infrared rays” would be able to produce energy not only during the day when the sun is shining like traditional PV solar cells, but also at night, when heat is still being radiated. Almost any industrial process radiates heat, meaning that these nanoantennas could be used almost anywhere.
These nanoantennas consist of tiny gold squares or spirals set in a specially treated form of polyethylene, which is a pretty cheap material. The researchers are finding that the nanoantennas absorb over 80% of the energy at the targeted infrared wavelengths. Traditional solar cells rely on chemical reactions that currently work for about 20% of the light that hits them. Higher efficiency cells have been created, but they have all been very complex and expensive.
Another possible use of these nanoantennas would be for cooling devices. The nanoantennas would absorb the heat (in the form of infrared radiation), and could be treated to re-emit the energy at a different wavelenght, for example as visible light.
The researchers note that lots of additional research needs to be done, including the biggie, which is to convert all the energy absorbed into electricity.
“The infrared rays create alternating currents in the nanoantennas that oscillate trillions of times per second, requiring a component called a rectifier to convert the alternating current to direct current. Today’s rectifiers can’t handle such high frequencies. “We need to design nanorectifiers that go with our nanoantennas,” says Kotter, noting that a nanoscale rectifier would need to be about 1,000 times smaller than current commercial devices and will require new manufacturing methods. Another possibility is to develop electrical circuitry that might slow down the current to usable frequencies.”