Under the ocean’s surface, tentacle-like stems of seaweed sway with the current, bending back and forth as they get tossed about by underwater waves. These movements are a physical representation of the invisible energy contained in waves, and researchers took inspiration from those motions to develop flexible generators that mimic seaweed to harvest wave energy.
Wave power could be a significant source of renewable energy, but harvesting that energy has been tricky. Wave turbines are often big, expensive, and float at the surface of the ocean. Seawater can also be corrosive, and the rigid form of these devices means they aren’t all that efficient at capturing energy from smaller, less frequent, underwater waves that don’t roil the ocean’s surface.
But those more gentle underwater waves can be an important source of energy, too, so researchers created a generator to mimic seaweed, which sways even in small waves or currents. The idea started when Minyi Xu, a professor in marine engineering at China’s Dallan Maritime University and visiting scholar to Georgia Institute of Technology, was speaking with Zhong Lin Wang, founding director of Georgia Tech’s Center on Nanoscience and Nanotechnology, about how to develop quiet, environmentally-friendly ocean energy harvesters.
“Professor Wang mentioned that seaweed vibrates softly in ocean flow and can live well even in huge waves,” Xu said over email, inspiring them to look into a way to develop a flexible generator. Using triboelectric nanogenerators, or TENGs—devices that generate electricity from the transfer of electrons between two surfaces, usually in how they rub together to produce static electricity—could address this need, since they can be made of flexible materials.
For four years, the researchers tested different materials and waterproofing methods. Their work was recently published in the journal ACS Nano. The device they made includes layers of FEP, a material often used for flexible tubing, and PET, coated in conductive inks. As the flexible devices are moved by waves, those internal layers make contact and then separate over and over, generating electricity.
When tested in a wave tank, 1.5-by-3-inch strips of the seaweed-like TENGS generated enough power to light up 30 LEDs. “With the large-scale installation underwater, high-power electrical appliances could be powered,” Xu said. And unlike other wave power devices, these may have less impact on marine life; they don’t produce sound or heat that could affect the environment. “A seaweed bush made of millions of flexible TENGs may be suitable for fish living,” he added.
Eventually, these generators could replace batteries for all the electronics in coastal zones, like sensors that monitor water quality, or help ships navigate. Dubbed the “marine internet of things,” this kind of equipment has grown lately, but these sensors are often powered by batteries that have to be replaced. “These seaweed-like TENG systems can be integrated with those ocean sensors to form a self-powered monitoring system,” said Xu.
The researchers are planning to develop a small-scale underwater power station made of these seaweed TENGS to test their performance in a real ocean. Millions of seaweed-like TENGs could also harvest ocean energy on a larger scale. Xu estimates that, if agitated two or three times per second, a network of these devices over an area equal to the size of Georgia could meet the entire world’s energy needs.