Melding the old with the new can end up with some pretty green results. Take the classic antenna; by adapting it to a new fangled system, it may be possible to harness more power from the sun.
Solar devices, like calculators, only need a small panel of solar cells to function. But supplying enough power to meet all our daily needs would require enormous solar panels. At the same time, solar-powered energy collected by panels made of silicon, a semiconductor material, remains limited. After all, contemporary panel technology can only convert approximately seven percent of optical solar waves into electric current.
But that may soon change as there is a new solar panel under development at Tel Aviv University (TAU) composed of nano-antennas instead of semiconductors.
By adapting classic metallic antennas to absorb light waves at optical frequencies, a much higher conversion rate from light into useable energy is possible, said Professors Koby Scheuer, Yael Hanin and Amir Boag of Tel Aviv University (TAU) Department of Physical Electronics and its new Renewable Energy Center. That efficiency, combined with a lower material cost, would mean a cost-effective way to harvest and utilize “green” energy.
Radio and optical waves are electromagnetic energy, Scheuer said. When harvesting these waves, electrons generate that can convert into electric current. Traditionally, detectors based on semiconducting materials like silicon interface with light, while antennas capture radio waves.
For optimal absorption, the antenna dimensions must correspond to the light’s very short wavelength — a challenge in optical frequencies that plagued engineers in the past, but now they are able to fabricate antennas less than a micron in length. To test the efficacy of their antennas, Scheuer measured their ability to absorb and remit energy.
“In order to function, an antenna must form a circuit, receiving and transmitting,” Scheuer said, adding it is like a cell phone, whose small, hidden antenna receives and transmits radio waves in order to complete a call or send a message.
By illuminating the antennas, the researchers were able to measure the antennas’ ability to re-emit radiation efficiently, and determine how much power is lost in the circuit, a matter of measuring the wattage going in and coming back out. Initial tests indicate 95 percent of the wattage going into the antenna comes out, meaning they lose only five percent.
These “old school” antennas also have greater potential for solar energy because they can collect wavelengths across a much broader spectrum of light, Scheuer said. The solar spectrum is very broad, with UV or infrared rays ranging from ten microns to less than two hundred nanometers. No semiconductor can handle this broad a spectrum, and they absorb only a fraction of the available energy. A group of antennas, however, can be different lengths with the same materials and process, exploiting the entire available spectrum of light.
When finished, the team’s new solar panels will be large sheets of plastic which, with the use of a nano-imprinting lithography machine, will have varying lengths and shapes of metallic antennas.
The researchers have already constructed a model of a possible solar panel. The next step, Scheuer said, is to focus on the conversion process of how electromagnetic energy becomes electric current, and how they can improve the process.
The goal is not only to improve the efficiency of solar panels, but also to make the technology a viable option in terms of cost. Silicon is a relatively inexpensive semiconductor, but in order to obtain sufficient power from antennas, you need a very large panel — which becomes expensive.
Green energy sources have two main evaluation points. Not only do they need to contribute environmentally, they also need to be economically viable and have a positive return on investment.
“Our antenna is based on metal — aluminum and gold — in very small quantities,” Scheuer said. “It has the potential to be more efficient and less expensive.”