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Oceans cover three-fourths of the earth's surface and hence are without any doubt a substantial ocean energy resource. There are two types of energy that derive from the ocean, mechanical and thermal energy. Waves and tides "produce" mechanical energy, whereas the sun is responsible for the thermal energy of the ocean. The ocean contains more than 5000 times the world's current power usage. The global wave power potential estimated at about 1-10 TW in water depeer than 100m and it can be found mainly on the western and southern coasts of South America, South Africa and Australia.
Even though there is abundant/high potential of/ ocean energy, little have been done for the utilization of this type of energy. The ocean energy industries are at an early stage, and only few have been commercialized so far. France and Canada are the only countries that have a developed ocean energy industry and their projects are on a commercial stage. More specifically, France has established the largest tidal power station in the world which generates 240MW whereas in Canada exists the Annapolis tidal generating station with a capacity of 20MW. Moreover, Republic of Korea has planned a 260MW tidal energy power plant to be built by 2010. In 2008, 0.5TWh of electricity was generated by those plants, representing only the 0.003 per cent of the world's electricity generation . However by 2030, ocean energy is projected to account for the 0.04 per cent of world's electricity generation.
Figure 1: The global tidal and wave resource 
Figure 2: Leading ocean developer's global focus 
Ocean energy in Australia
Australia has a high ocean energy potential. The western and southern coastline has wave energy potential especially in Tasmania, whereas the northwest coast of Western Australia is one of the best locations for tidal energy power. Furthermore, the Pacific ocean is a good source for thermal energy.
There has been observed limited progress in assessing Australia's ocean thermal energy resources, not least because of the greater prospectively of other renewable energy resources (WEC 2007)[?].There are some projects for electricity generation based on wave and tidal energy mainly. Carnegie Wave Energy Limited is one of the companies that generates green electricity using the Cylindrical Energy Transformation Oscillator (CETO) wave energy converter. CETO can produce a maximum of 1,623,473 GWh annually in the whole Australia.
Also another company , Oceanlinx, has had a 500Kw prototype oscillating water column wave power unit at Port Kembla, New South Wales since 2006[?] but the most recent project was installed by Atlantis Resources Corporation at Phillip Island in 2008.
Energy ( GJ/m2)
New South Wales
Victoria and Tasmania
Table 1: Total tide kinetic energy delivered annually on the continental shelf adjacent to each state 
Mean Energy ( GJ/m)
New South Wales
Victoria and Tasmania
Table 2: Total energy delivered annually in water depths equal to or less than 50m 
Wave energy in Sydney
As it is illustrated from the tables above, Sidney, which is the area of our interest, is a significant wave energy resource. In the coastlines of the New South Wales, the mean energy that is delivered annually is 391.04 GJ/m whereas the tidal mean energy is only 0.0011 GJ/m2. Therefore, it is necessary to determine an appropriate technology in order to estimate the potential scenarios so as to meet the future energy demand for the electric cars in Sydney which is 8.87 TWh/year. The wave technologie's comparison is represented in Table(? ) below.
Wave Energy Technology
Cost (cent per kWh)
Table 3: Comparison of wave energy technologies
The pelamis technology was chosen to be the most appropriate for the Sydney's case. It consists of 3 independent power conversion units and produces an overall power of 750kW while the annual output is 2.7GWh. The hydrostatic power limiting(limit?) is for more than a 7m wave height. It also has an overall length of 150m and a 3.5m diameter.
Calculations for Pelamis
Since the annual output is 2,7 GWh/year, a 40 pelamis farm on 1 kmÂ² will produce 108 GWh/kmÂ²/year.
If the total energy demand is derived 100% from wave energy we have:
8.87 TWh/ 108 GWh = 82.13 kmÂ² so 83 x 40 = 3320 Pelamis.
Thus, 985 Pelamis are needed in order to meet the total energy demand of 2.66 TWh if the
30% of energy would come from wave energy. Finally, the total area of the farm would be 24.6 km2.
Comparison with current technology
The equivalent gas turbine (produces) 600 tonnes of fuel per year and
2000 tonnes annually emissions of CO2 .
The optimal water depth is 50 - 150m, due to the typical wave resources at those depths. Hence the pelamis is usually installed within a number of miles offshore. In comparison with the offshore wind occupy (area occupancy),almost ~4-5 times less area is needed. For example one offshore wind farm site occupies 10km2 and typically has an output of 60-90MW. In the same space, albeit different locations would be 300MW [?].as it can be seen from Figure 3, the marine area with a mean depth of 60-80m which seems ideal for the Pelamis is in the middle of the South Pacific ocean. The exact location of the (proposed) farm is chosen taking into consideration the fact that the production cost is proportional to the distance from the shore while excluding the protected marine areas.
Figure 5 indicates the exact location of the plant which would be at 155 0o E, -33 0o S, approximately 450km from Sidney.
Figure 3: Mixed layer depth annual mean in the Australian jurisdiction 
Figure 4: Chosen area for the Pelamis farm[?]
Figure 5: Specific location of the Pelamis farm 
It would be difficult to provide an exact figure of the cost production of the Pelamis Wave Energy Converter as is still a relatively new technology. However, an approximation of the cost of the production could be estimated. The production costs of ocean energy technologies estimated by the IEA range from US$60 per kW to US$300 per kW (in 2005 dollars). Tidal barrage systems lie in the lower end of this range and tidal current and wave systems in the higher end. Thus, for the case where the highest cost is chosen the production cost for the Pelamis is ??
Pelamis has the following characteristics; it consists of a 3-phase system voltage and has 415/690Vac which is equivalent to 50/60Hz and a transformer of 950kVA. Therefore, a single subsea cable at high voltage of 33kV and a step up transformer on the machine to minimize losses would be the efficient transmission tools .
Figure 6: Existing Australian marine protected areas