Breaking ocean waves

Prototype tech extracts twice the power from ocean waves

Image credit: Dreamstime

Researchers from the Royal Melbourne Institute of Technology (RMIT) in Australia have developed prototype technology that can double the power harvested from ocean waves. The advance marks a step towards making ocean waves a viable source of renewable energy.

The energy potential of ocean waves is vast; estimates put the combined power of coastal waves at approximately the same as global power generation. However, the challenges of creating technologies to extract that natural source of energy efficient while withstanding the ocean environment has held back this category of renewables at the experimental stages.

The RMIT University’s dual-turbine wave energy converter, however, is twice as efficient at harvesting power as any similar technologies developed so far. Professor Xu Wang, who led the research, explained that wave energy is among the most promising sources of clean, reliable and renewable power.

“While wind and solar dominate the renewable market, they are available only 20 to 30 per cent of the time,” Wang said. “Wave energy is available 90 per cent of the time on average and the potential power contained in offshore waves is immense.

“Our prototype technology overcomes some of the key technical challenges that have been holding back the wave energy industry from large-scale deployment. With further development, we hope this technology could be the foundation for a thriving new renewable energy industry delivering massive environmental and economic benefits.”

One of the most common experimental approaches involves harvesting wave energy via a buoy-type converter (a “point absorber”) which harvests energy from the vertical movement of ocean waves. This is cost-effective to manufacture and install, and ideal for offshore locations. A point absorber harvests energy from the vertical movement of ocean waves. Despite its promise, it must be precisely synchronised with incoming waves to harvest the energy efficiently, using an array of sensors, actuators, and control processors. Adding such complexity undermines the cheapness and simplicity of the system, potentially causing underperformance, unreliability and maintenance issues.

The prototype developed by the RMIT researchers – in collaboration with Beihang University in China – requires none of this technology to synchronise with the waves, as the device floats naturally up and down with the ocean waves: “By always staying in sync with the movement of the waves, we can maximise the energy that’s harvested,” said 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.”

Two turbine wheels stacked one atop the other and rotating in opposite directions are connected to a generator through shafts and a belt-pulley driven transmission system. The generator is placed inside a buoy above the waterline to keep it out of corrosive seawater, extending the lifespan of the device.

So far, the prototype has been tested at lab scale. Next, the researchers plan to collaborate with industry to test a full-scale model and work towards commercialisation.

“We know it works in our labs, so the next steps are to scale this technology up and test it in a tank or in real-life ocean conditions,” Wang said. “Tapping into our wave energy resource could not only help us cut carbon emissions and create new green energy jobs, it also has great potential for addressing other environmental problems.

“For example, as the frequency of drought increases, wave energy could be used to power carbon-neutral desalination plants and supply fresh water for the agriculture industry: a smart adaptation to the challenge of a changing climate.”

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