Biologically-inspired flexible turbines could provide reliable, low-maintenance power from the world's oceans, says a researcher with the Okinawa Institute of Science and Technology Graduate University.

The project uses submerged turbines anchored to the sea floor through mooring cables that convert the kinetic energy of sustained natural currents into electricity, which is then delivered by cables to the land. The initial phase of the project was successful, according to researchers who now are searching for industry partners to continue into the next phase.

(Click to enlarge.) Diagram of ocean wave turbine. (Click to enlarge.) Diagram of ocean wave turbine. Large parts of the Japanese coastline are protected by concrete structures known as tretrapods. These are shaped like pyramids and are often placed along the coastline to weaken the force of incoming waves and protect the shore from erosion. Around 30 percent of the seashore in mainland Japan is covered with tetrapods and wave breakers, said Professor Tsumoru Shintake, who is leading the research. Replacing these with “intelligent” tetrapods and wave breakers, with turbines attached to or near them, could generate energy as well as help to protect the coasts.

“Using just 1% of the seashore of mainland Japan can [generate] about 10 gigawats [of energy], which is equivalent to 10 nuclear power plants,” Shintake said.

The university researchers launched the Wave Energy Converter (WEC) project in 2013. It involves placing turbines near tetrapods or among coral reefs, to generate energy. Each location allows the turbines to be exposed to wave conditions that allow them not only to generate renewable energy, but also to help protect the coasts from erosion while being affordable for those with limited funding and infrastructure.

The turbines are built to withstand harsh wave conditions as well as extreme weather, such as a typhoon. The blade design and materials are inspired by dolphin fins—they are flexible, and able to release stress rather than remain rigid and risk breaking.

The supporting structure is also flexible, “like a flower,” said Shintake. “The stem of a flower bends back against the wind,” and so, too, do the turbines bend along their anchoring axes. They are also built to be safe for surrounding marine life—the blades rotate slowly enough to allow creatures caught among them to escape.

The blades of this five-blade turbine are made of a soft material and they rotate on their axis when influenced by ocean waves—the diameter of the turbine is about 0.7 meters. The axis is attached to a permanent magnet electric generator, which is the part of the turbine that transforms the ocean wave energy into usable electricity. A ceramic mechanical seal protects the electrical components inside of the body from any saltwater leakage. This design allows the turbine to function for 10 years before replacing.