The challenge
Seeking alternative renewable energy options
The ocean provides an abundant source of renewable energy. However, as a new technology there are challenges in understanding the sustainable level at which ocean energy resources could be used for energy supply, and whether they can be competitive with other energy technologies.
Our response
Predictability and availability of ocean energy
One of the benefits ocean energy has over other renewable energy sources is its greater predictability and availability. Tides are predictable over all time-frames, and waves have a forecast horizon up to three times more than wind.
Ocean energy technologies include:
Wave
Waves are generated by the wind as it blows across the sea surface. Energy is transferred from the wind to the waves. Wave energy converters (or WECs) are able to capture this energy to do useful work such as electricity generation or water desalination.
The design of WECs have not yet converged on a common system. There are several classes of WECs in development which harness the power of the waves through different methods.
Our preliminary estimates suggest Australia has an abundant and attractive wave energy resource, and could potentially contribute 11 per cent of Australia's energy needs by 2050. Given this potential contribution, CSIRO has focussed on refining its estimates of Australia's wave energy resource. To do this, we've considered the temporal and spatial variability of the resource and the spatial constraints for WEC deployments (owing to alternative uses of the marine domain), while also looking at potential environmental effects of wave energy extraction on the marine and coastal environment.
Tidal
Tidal power, or tidal energy, is a form of hydropower that converts the energy of the tides into electricity. Modern tidal turbine technologies extract energy from the tidal currents, or streams. Tidal streams are caused due to the gravitational pull of the moon and sun, and consequently entirely predictable. During rising tide, water will flow past the turbines in one direction, and this flow will be reversed during the ebb, or falling tide. Turbines can be located individually or in an open fence configuration. These technologies do not restrict the flow of water, which reduces the environmental impact.
Preliminary assessments of Australia's tidal resource shows energy availability is less wide-spread than Australia's wave resource. There are several localised regions which exhibit possible resource potential, however the magnitude of this resource has not been sufficiently quantified.
Thermal
Ocean thermal energy conversion (OTEC) operates by using warm sea water to vaporise a working fluid, so that the relatively high pressure vapour can turn a turbine. It is also possible to use warm sea water as the working fluid, and this is known as an open cycle system. A fraction of the warm sea water is evaporated by passing it through jets into a chamber with lower pressure than the saturation pressure for the sea water temperature.
Australia's OTEC resource is limited to the coast of Far North Queensland. Given the limited resource for Australia, and unproven nature of this technology, further assessments of OTEC viability for Australia are of lower priority.
Currents
Ocean water is in continuous motion, driven by the surface winds, and spatial gradients in temperature and salinity of the world's oceans. The energy associated with these flows can be captured much like the capturing of wind currents with turbines. Technologies used to extract energy from ocean currents would be similar to those used for extracting tidal energy, i.e. turbine-type devices.
Ocean currents off the East coast of Australia offer a potential large energy resource, but the extraction of ocean current energy is in the very early stages of development, and still face a number of technological and oceanographic challenges.