Marine energy uses the movement of water to generate electricity from tides, waves or ocean currents. Australia's long, surf-swept coastline is a massive potential source of marine energy.

Types of marine energy

Tidal energy
Tides cause movements in ocean waters, and constrained topology near coastlines can accelerate these movements. Tidal energy generates electricity using the regular local flows of the tidal cycle.

The Kimberley and Pilbara coasts of northern Western Australia see the largest tides in Australia. Other potential sources of tide power are the Torres Strait off the coast of Darwin, Broad Sound in Queensland and Bass Strait in Tasmania.

Wave energy
Waves are created by wind passing over the surface of the ocean. Wave power plants can harvest the energy in the up and down motion of waves and convert it into electricity.

Wave energy is strongest where there are trade winds and ocean swells. In Australia, our wave energy resources are greatest along the southern coastline.

Ocean thermal energy
Ocean thermal uses temperature variations in the ocean to generate electricity.

As sea water becomes colder with depth, the temperature difference between water near the surface and water at a depth of 1000 m can be up to 20 degrees in tropical regions. Ocean thermal can extract energy from these regions using a heat exchange process.

Marine energy technologies

Carnegie Wave Energy Research Facility, Fremantle

Carnegie Wave Energy Research Facility, Fremantle

The ocean's energy can be harnessed using a variety of technologies and methods. Generally, floating buoys, platforms or submerged devices are placed in the water and use hydraulic systems coupled to an electrical generator.

Common wave energy devices

  • Attenuator devices – these are usually long, floating structures placed parallel to the direction of waves in order to absorb them. The device's motion can be selectively damped to produce energy.
  • Overtopping devices – a wave surge/focusing system that contains a ramp over which waves travel into a raised storage reservoir.
  • Oscillating water column (OWC) – a column of water moves up and down with the wave motion. The water column acts as a piston, compressing and decompressing air which is then ducted through an air turbine.
  • Point absorber – these floating structures can absorb energy from all wave directions due to their small size compared to the wave length.
  • Oscillating wave surge converter (OWSC) – OWSCs extract energy from the surge motion of waves. They are generally seabed-mounted devices located close to shore.

Common tidal energy devices

  • Horizontal or vertical axis turbines – these consist of two or three blades mounted on a horizontal or vertical shaft to form a rotor. The motion of the water current creates lift on the blades, causing the rotor to turn and drive an electrical generator.
  • Oscillating hydrofoil – these operate in a similar way to an aeroplane wing. Control systems alter the hydrofoils' angle relative to the water current, creating lift and drag forces that cause the device to oscillate. The physical motion from this oscillation feeds into a power conversion system.
  • Tidal barrages – these dam-like structures can be built across a narrow bay or river mouth. As the tide flows in and out, it creates uneven water levels on opposite sides of the barrage. Water flows from the high side to the low side through turbines to generate electricity.

Marine energy in Australia: 2017 in focus

The Australian Wave Energy Atlas, an initiative of CSIRO, delivered a searchable, free and publicly available online web atlas of Australia's national wave energy resource and marine management uses in 2018. It also provided best practice guidelines on physical impact assessments for wave energy developments in Australia's marine domain.

Similarly, Tidal Energy in Australia, a joint research project of CSIRO, the Australian Maritime College at the University of Tasmania, the University of Queensland and industry partners will develop a hydrodynamic tidal model to map the scale and distribution of the nation's tidal energy resources to the nearest 500 m.

In other marine developments, Sydney company Wave Swell Energy has created a prototype to harness the power of waves, effectively acting as an artificial blowhole. The company will build a $7 million large-scale unit on the seabed near the coast of King Island that will feed into Hydro Tasmania's grid, and at peak times will provide up to half the island's power.

Sources:

  • An International Vision for Ocean Energy (Ocean Energy Systems)
  • Clean Energy Council Renewable Energy Database
  • Clean Energy Australia Report 2018