Solar cells become ineffective when the sun goes down. At night, the earth radiates heat back toward the sky. Scientists at the U.S. Department of Energy's Idaho National Laboratory are working on a device to turn infrared radiation into electricity.
Billions of nanoantennas printed onto thin, inexpensive sheets will transform heat energy into electricity. The physics behind this conversion is the same as that of a radio antenna. The only difference between radiowaves and infrared light is wavelength. Antennas 1/25 the size of a human hair resonate when bombarded with heat radiation. If the resulting alternating current can be passed through a rectifier (one way valve) the current can charge up batteries. The infrared rays create alternating currents in the nanoantennas that oscillate trillions of times per second.
"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." Eureka Alert
If these technical hurdles can be overcome, nanoantennas have the potential to be a cheaper, more efficient alternative to solar cells. Computer models of nanoantennas predict up to 92% efficiency (compared to solar cells around 20%).