Counter-spinning turbine design draws double the energy from ocean waves
Scientists at Australia's RMIT investigating the massive untapped potential of wave energy have come up with a novel design for a convertor they say operates with far greater efficiency than comparable solutions, and which they hope could open the door to widespread commercial use of the technology. The team's prototype employs a novel dual-turbine design that sidesteps some common technical issues, and proved capable of harvesting twice the energy from waves as current designs in early experiments.
The idea of capturing energy from ocean waves has been around for centuries, and recently we're starting to see modern machines designed for these purposes take to the seas in some interesting forms. This includes rotating systems that extract power from vertical and horizontal movement, blowhole-like generators that capture energy as waves push water and air through concrete chambers, and squid-like generators with buoyant arms that rise and fall with the motion of the waves.
One of the more common approaches to harnessing wave energy is known as a point absorber buoy, which consists of a flotation device on the surface that is tethered to the seabed. As the buoy moves up and down with the passing waves, it drives an energy converter mechanism built onto the tether partway below the surface. This might be a geared drivetrain that uses the linear motion to spin a flywheel and generate power, as seen in some experimental designs.
The RMIT scientists used the point absorber buoy as a jumping off point for their novel generator, which they say addresses a couple of problems with conventional designs. To efficiently harvest energy, point absorber buoys typically need to use sensors, actuators and other electronics to precisely synchronize themselves with the incoming waves, but this leaves them open to maintenance and reliability issues.
In what they call a world-first design, the scientists eschewed all these synchronization sensors and electronics and went with a passive approach that has the device float up and down naturally with the swell. Two turbine wheels that are stacked close together down below rotate in opposite directions, and combine to amplify the energy being relayed to the generator.
This generator is housed inside a buoy above the surface to protect it from corrosion, and is connected to the spinning turbines via shafts and a belt-pulley drive transmission. Testing of this prototype in the lab showed that it could draw twice as much power from ocean waves as other point absorber designs, while promising a simpler and cost-effective path forward.
“By always staying in synch with the movement of the waves, we can maximize the energy that’s harvested,” says lead researcher Professor Xu Wang. “Combined with our unique counter-rotating dual turbine wheels, this prototype can double the output power harvested from ocean waves, compared with other experimental point absorber technologies.”
The scientists now hope to build on their successful laboratory testing by studying the performance of a full-scale version in tanks and, eventually, the ocean.
“Our prototype technology overcomes some of the key technical challenges that have been holding back the wave energy industry from large-scale deployment," says Wang. “With further development, we hope this technology could be the foundation for a thriving new renewable energy industry delivering massive environmental and economic benefits.”
The research was published in the journal Applied Energy.