Scientific American reports on new advances made by a team of Portuguese researchers toward getting electricity from the endless motion of the ocean:
Waves alone produce 32,000 terawatt-hours of natural energy per year—for reference, the entire world uses around 23,000 terawatt-hours annually. And there is also the power of currents, tides and thermal energy. But despite decades of research, the motion of the ocean has proved difficult to harness.
The team turned to so-called triboelectric nanogenerators, or TENGs, which convert motion into an electrical current using static electricity—the same principle as rubbing a balloon on a fuzzy sweater to generate charge. At each TENG’s core are two surfaces, just a few square centimeters in area, that can easily become positively or negatively charged. Atop these two stacked surfaces, the researchers placed 10 stainless steel balls, about 12 millimeters in diameter, that are free to move around. When their container tilts, the balls roll around and rub the two surfaces together. This builds up a static charge, which can be converted into electricity to power a battery.
“We developed these novel devices that convert rhythm and mechanical energy into electrical power,” says Cátia Rodrigues, a nanotechnology Ph.D. student at the University of Porto in Portugal.
Working in a hydraulics lab at the University of Porto, the team tested designs for TENGs embedded in a one-eighth-scale replica of an oceanic buoy. They placed the model in a wave pool and simulated the five most frequent wave patterns that occur in the seaport in nearby Figueira da Foz, Portugal.
TENGs were invented by a researcher at the Georgia Institute of Technology in 2012. The new study marked the first time they have been tested under such realistic wave conditions, Rodrigues says. And it was a success: the swimming-lane-esque TENG design produced a maximum output of 230 microwatts—enough to power small devices such as medical implants.
Based on the success of their wave pool trials, the researchers plan to modify their TENG prototype and install it in a full-scale buoy in Figueira da Foz.