For more than a century, Australians have looked to the waves pounding our southern shores as a potential resource for the generation of electricity. In 1909, Sorrento – the small town near the tip of the Mornington Peninsula south of Melbourne, Victoria – was without electricity. A frequent visitor to the town, Mr Robilliard believed he could harness the wave power on Ocean Beach to power the town, and the ‘electric ball’ was developed. Despite several attempts to operate the system, it was ultimately abandoned after the tethering chain broke in large seas and the ball washed up on the beach. It is reported that the electric ball powered one electric light globe for a time.
An international oil crisis in the 1970s lead to increased investment and effort in developing energy alternatives, particularly in the United Kingdom and Norway. While Australia was not directly involved, it came close to benefiting from the developments of these activities. In June 1989, an agreement was signed between the Tasmanian Hydro Electric Commission (HEC) and the Norwegian company Norwave to build and operate a tapered channel wave power station on the west coast of King Island – situated on the exposed western side of Bass Strait. In June 1991, it was anticipated that construction would commence towards the end of that year, with commissioning in January 1993. This wave power plant was never constructed.
Tidal power has also attracted interest over several decades. The 240megawatt (MW) La Rance tidal power station, located in Brittany, France, was opened in November 1966 as the world’s first full-scale tidal power station. In 1963, two French engineers involved with the building of the La Rance plant were called upon by the Western Australian State Government to advise on the feasibility of harnessing tides in the Kimberley region. A 1963 preliminary estimate of the tidal power potential of the whole northwest coast indicated a resource exceeding Australia’s total installed power capacity, and suggested it was of sufficient promise that a national body should be requested to investigate the size of resource in detail. In 2001, Derby Hydro Power proposed a 50 MW tidal barrage plant near Derby with support from the Australian Commonwealth. Following environmental concerns, a gas-fired generator was built instead. The potential for generating tidal power in the Kimberley continues to receive attention.
Australian ocean-power today
Recognition of the need to reduce carbon emissions to limit impacts of future climate change has put marine renewable energy (and all other renewables) back on the agenda, both in Australia and internationally. Some of Australia’s more advanced marine energy developers, Oceanlinx (founded as Energetech in 1997), Carnegie Wave Energy (who designed the CETO unit 1999), and United States based Ocean Power technologies (founded in 1994 by an Australian inventor) commenced operation during this period of strong growth in interest in marine renewables.
In December 2006, Oceanlinx completed the installation of Australia’s first successful demonstration wave-generated power station, with the deployment of its Mk1 500 kilowatt (kW) capacity oscillating water chamber (OWC) near Port Kembla, New South Wales. The Mk1 device has since been decommissioned, with Mk2 and Mk3 pre-commercial devices being deployed for short periods in a lead up to the 2010 release of its latest version shallow and deepwater OWC designs (the 1 MW greenWAVE and 2.5 MW blueWAVE units).
Carnegie Wave Energy deployed its first CETO 1 prototype wave energy unit in 2005. This was followed by the design and deployment of a 1/3 scale pre-commercial CETO II array off Fremantle in Western Australia, which successfully generated electricity and direct desalinated water. In April 2011, Carnegie successfully completed the design, manufacture and installation of their commercial-scale CETO 3 unit off Garden Island, Western Australia, with testing and operation ongoing. Carnegie aims to increase the number of units at this site to develop a small scale, grid-connected 5 MW commercial demonstration project. In 2011, more than 15 companies are actively developing marine renewable energy projects in Australia.
Mapping ocean power potential in Australia
A key step in the development of marine renewable energy projects is a comprehensive understanding of the characteristics of the resource. Here we consider three forms of ocean renewable energy in Australia – ocean current, tidal and wave energy.
Ocean current (non-tidal)
The East Australian Current flows southwards from Queensland into New South Wales, with a small fraction of its flow continuing past eastern Tasmania. While the current flows mostly as a fast narrow jet along the outer continental shelf between Fraser Island and northern New South Wales, from then onwards it is best characterised as a series of very large (hundreds of kilometres) swirling eddies. Off Brisbane, the flow speed has been observed to exceed 2 metres per second (m/s) but continuous measurements to document the frequency of this do not yet exist.
Analysing the 15-year data archive generated by the 0.1º×0.1º Resolution Ocean Model , the median value of the current speed is about 0.9 m/s, making this stretch of coast the most promising location in Australian waters for extracting energy from non-tidal currents. The power density at this velocity is very low so very large diameter devices are required in order to extract significant quantities of power. But even if a device extracts half the power of the upper 100 meters of the ocean, the power generation per linear meter is only 50 kilowatts per meter (kW/m).
The total width of the fast region of the current is about 20 km, giving an upper limit on the generated power of 1 gigawatt (GW) (8.8 terawatts hours per year [TWh/yr]) per line of 200 100 m diameter turbines. If five such lines of turbines were installed (at 100km intervals spanning the high-current stretch) of coastline, the total production would be 44 TWh/yr, or 17 per cent of Australia’s total present usage (254 TWh/yr). Any installation approaching this magnitude would, however, be likely to have a considerable effect on the physical properties of the East Australian Current, while also being a very significant hazard to navigation and possibly also to marine life.
Tidal energy
Initial interest in tidal power focused on impoundment systems, where natural bays are turned into reservoirs by the construction of a dam. More recently, attention is switching to free-stream turbines which are more like wind turbines than hydro-electric schemes. In the Australian context there exist just a few regions where tidal power is feasible, predominantly in the tropics (i.e the Kimberley, Darwin and Torres Strait).
An exception is the region between Flinders Island and the rest of Tasmania. The major passage here is Banks Strait, where tidal current speeds reach 2.6m/s (according to an unverified CSIRO computer model – the true value is possibly higher). The speed of the currents is not as high as some sites overseas but since Flinders Island uses diesel generation, tidal power is relatively attractive.
BioPower Systems has conducted preliminary investigations, site analysis and site design for a potential bioSTREAM pilot installation at this site. An upper limit on the power that could be generated in a year by an array of turbines across Banks Strait is probably in the vicinity of 125gigawatt hours (GWh). This is just 1 percent of Tasmania’s total power usage, implying that tidal power can only possibly have a niche role, regardless of the economics of extraction.
Wave energy
The southern ocean is well known for its large waves and this fact is recognised in global atlases of wave energy resource. Such global maps may be potentially misleading if used as an indicator of the resource available to a near-shore wave farm somewhere in southern Australia, unless attenuation of the deep ocean waves as they cross the continental shelf is taken into account.
Southern Ocean waves have been measured by buoys for many years at a few Australian locations. At a site of 100m in depth in the water off Cape Sorell on Tasmania’s west coast, the long-term average wave height, period and energy flux is significantly less than the World Energy Council estimate for the region, but nevertheless indicative of a very significant resource.
As a first step towards serving the needs of the wave energy sector, and to reconcile these various model and observed data sets, CSIRO has recently produced a wave energy atlas for southern Australia. This estimates the total amount of energy crossing the 25 m isobath between Geraldton, Western Australia and the southern tip of Tasmania as 1329TWh\yr (without attempting to correct for the possibility that the model slightly over-estimates the energy flux), or about five times the energy requirements of the whole nation.
Turning just 10 per cent of that into electricity would be a massive investment but it would provide half the country’s electricity. Clearly, it is the economics of energy extraction that will decide the future of wave energy, not the extent of the resource.
Summary
Over a hundred years after the resource was first identified as a potential source of electricity, a comprehensive national assessment of the full extent of Australia’s ocean renewable energy resources is still required. It is clear however, from the preliminary assessments which have been carried out, that the resource is not limited, and consequently it will be other factors (e.g economics, engineering, environmental, competing uses, and social impacts) which will determine its future exploitation. When these factors are overcome, Mr Robilliard’s vision of powering our townships with the energy harvested from the waves hitting our southern shores can be fulfilled.
