How Harvesting Wasted Heat Could Power Electronics
A new nanowire converts wasted heat energy into electricity.
CREDIT: Nano Letters
The vast amounts of energy wasted as heat each year could get harvested to power electronics with the aid of microscopic wires made of a common cosmetics additive, researchers say.
The device harnesses an effect first described by the Greek philosopher Theophrastus in 314 B.C. He noticed the gemstone tourmaline generated static electricity and attracted bits of straw when heated. This phenomenon, called the pyroelectric effect, occurs when warming and cooling rearranges the molecular structure of certain materials, including tourmaline, creating an imbalance of electrons that generates an electric current.
In this way, scientists want to convert heat into electricity, much as solar power converts sunlight into electricity. They specifically want to focus on heat released as the byproduct of everything from computers to cars to long-distance electric transmission lines.
"Wasted heat is a rich source of energy that could be harvested,"researcher Zhong Lin Wang, a nanotechnologist at the Georgia Institute of Technology, in Atlanta, told InnovationNewsDaily. "In 2010, for example, more than 50 percent of the energy generated from all sources in the U.S. is lost mainly in the form of wasted heat."
Wang and his colleagues harnessed the pyroelectric effect by creating nanogenerators — generators whose heart are components only nanometers, or billionths of a meter, in size. They created nanowires of zinc oxide, a compound often added to cosmetics, paints, electronics and even food. The nanowires were each about 200 nanometers wide, or about half the wavelength of violet light, and about 2 micrometers, or millionths of a meter, long, or approximately one-fiftieth the width of a human hair.
An array of these nanowires standing on end like bristles on a brush generated electricity when heated or cooled.
"This is a first demonstration of a pyroelectric nanogenerator," Wang said.
For each watt of heat every 10.7 square feet (1 square meter) of the nanogenerators receive, they generate up to about 0.08 volts. For comparison, the average amount of solar radiation the Earth receives is about 126 watts per square foot (1,361 watts per square meter). If this energy came only in the form of heat, 10.7 square feet (1 square meter) of the nanogenerators would produce about 108 volts.
Potential applications for these nanogenerators might include powering wireless sensors and personal microelectronics, Wang said. Still, the researchers point out a lot of work is needed to boost the performance of the nanogenerators for use in larger-scale applications; for instance, by controlling defects and improving the properties of the materials used.
"Readers need to be ready to wait some time before this technique can be used for driving practical small electronics," Wang said.
The scientists detailed their findings in the June 13 issue of the journal Nano Letters.