Energy

Counter-spinning turbine design draws double the energy from ocean waves

Counter-spinning turbine desig...
Scientists hope to use innovative converters to tap in to the huge potential of wave energy
Scientists hope to use innovative converters to tap in to the huge potential of wave energy
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Scientists hope to use innovative converters to tap in to the huge potential of wave energy
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Scientists hope to use innovative converters to tap in to the huge potential of wave energy
Diagram depicting the features of a novel wave energy convertor design
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Diagram depicting the features of a novel wave energy convertor design
Scientists at RMIT have developed a prototype wave energy convertor with great potential
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Scientists at RMIT have developed a prototype wave energy convertor with great potential
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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.

Scientists at RMIT have developed a prototype wave energy convertor with great potential
Scientists at RMIT have developed a prototype wave energy convertor with great potential

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.

Diagram depicting the features of a novel wave energy convertor design
Diagram depicting the features of a novel wave energy convertor design

“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.

Source: RMIT

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12 comments
12 comments
Simon Redford
What appears to be missing in the text above is that the blades of the turbines can rotate radially such that the set directly facing the flow engage in position to generate torque whereas the second set do not impede flow. I suspect that only one set of blades at any one time is recovering energy from the water flow. The advantage is that the shafts always rotate in the same direction. However, the reliability of the blade rotation mechanism may be a weak point in this design when compared to electronic control of (say) a permanent magnet generator on a single shaft which rotates in either direction taking power through an inverter with optimum power transfer control.
guzmanchinky
It does seem like there is almost endless energy to be had in the motions of the oceans. Very cool...
Bob Flint
Am I missing something here? without being tethered to take advantage of the natural lateral current, it's not going to rotate but just boob along freely, with little or no rotation.
Tim Read
The novel thing here is that with the two shafts rotating in opposite directions the buoy itself will not rotate. Both sets of blades capture energy with every up & down motion - the blades look to rotate about their connection to those shafts to "flip" based on flow direction. Looks simple but rotating shafts and blades in seawater....
Holger
@Bob Flint: The vertical motion of the ocean water doesn't propagate down that far. If the shaft is long enough they'll be in water that doesn't go up and down with the waves.
Trylon
@Simon Redford, you're wrong. Both shafts rotate in opposite directions at the same time, doubling the generator RPM. That's the gist of the concept. Like if you twist a jar and its lid in opposing directions at once, you'll get it screwed off in half the turns compared to if you hold the jar stationary and just twist the lid. The shafts do not always rotate in the same direction. They don't have clutches. They rotate in one direction as the buoy rises and reverse as the buoy drops, but they always oppose each other. And I'm sure they are using permanent magnet generators, along with rectifiers to convert it to DC for transmission to shore, where inverters would convert it to AC.
Aermaco
I like a device that floats while tethered like traditional buoys and possibly having that double function of marking navigational areas.
Importantly once the DC is created it can convert H20 to H2 & O for storage and use in fuel cells for most of the future of civilization that is in need of electricity.
James Craig
I give 2-3 days before it is fouled up on its anchor line!
having sailed around the world, I wonder if, in fact, these students have actually spent any time in the oceans experiencing actual swell and waves. A far cry from a test tank with acrylic sides, and a nicely generated wave.
ljaques
They would have to channel and house the two turbines separately to provide any useful output. Hmm, no, that would be for tidal flow, but this floats. The device as shown is absolutely useless (unless they're talking milliwatts or watts instead of kilowatts or megawatts output.) Hey, RMIT, is this all theoretical at this point? I can't see how blocking interference and/or severe turbulence wouldn't negate the other turbine's power.
jsopr
While both rotors clearly collect energy at the same time, SR is right that the blades also rotate radially, as can be seen by the fact that the rotor rotation direction is the same in both figures and the flaps point down in the first and up in the second. It's a nice design since there is no need to add power or timing to the flaps, which presumably just freely flap back and forth 45 degrees depending on the flow direction.
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