Wave power 

The wave star device relies on an array of floats, which pump fluid through a turbine as they rise and fall in the waves. Currently envisaged as being attached to a non-floating pier, the difference in response to waves between a small float and a 15m catamaran ...see www.wavestarenergy.com 

and from Wikipedia, the free encyclopedia:

Modern technology

Wave power devices are generally categorized by the method used to capture the energy of the waves. They can also be categorized by location and power take-off system. Method types are point absorber or buoy; surfacing following or attenuator; terminator, lining perpendicular to wave propagation; oscillating water column; and overtopping. Locations are shoreline, nearshore and offshore. Types of power take-off include: hydraulic ram, elastomeric hose pump, pump-to-shore, hydroelectric turbine, air turbine,^[13] and linear electrical generator. Some of these designs incorporate parabolic reflectors as a means of increasing the wave energy at the point of capture. These capture systems use the rise and fall motion of waves to capture energy.^[14]

These are descriptions of some wave power systems:

• In the United States, the Pacific Northwest Generating Cooperative is funding the building of a commercial wave-power park at Reedsport, Oregon.^[15] The project will utilize the PowerBuoy technology Ocean Power Technologies which consists of modular, ocean-going buoys. The rising and falling of the waves moves the buoy-like structure creating mechanical energy which is converted into electricity and transmitted to shore over a submerged transmission line. A 40 kW buoy has a diameter of 12 feet (4 m) and is 52 feet (16 m) long, with approximately 13 feet of the unit rising above the ocean surface. Using the three-point mooring system, they are designed to be installed one to five miles (8 km) offshore in water 100 to 200 feet (60 m) deep.
• An example of a surface following device is the Pelamis Wave Energy Converter. The sections of the device articulate with the movement of the waves, each resisting motion between it and the next section, creating pressurized oil to drive a hydraulic ram which drives a hydraulic motor.^[16] The machine is long and narrow (snake-like) and points into the waves; it attenuates the waves, gathering more energy than its narrow profile suggests. Its articulating sections drive internal hydraulic generators (through the use of pumps and accumulators).
• With the Wave Dragon wave energy converter large "arms" focus waves up a ramp into an offshore reservoir. The water returns to the ocean by the force of gravity via hydroelectric generators.
• The Anaconda Wave Energy Converter is in the early stages of development by UK company Checkmate SeaEnergy.^[17] The concept is a 200 metre long rubber tube which is tethered underwater. Passing waves will instigate a wave inside the tube, which will then propagates down its walls, driving a turbine at the far end^[18].
• The AquaBuOY, made by Finavera Renewables Inc., wave energy device: Energy transfer takes place by converting the vertical component of wave kinetic energy into pressurized seawater by means of two-stroke hose pumps. Pressurized seawater is directed into a conversion system consisting of a turbine driving an electrical generator. The power is transmitted to shore by means of a secure, undersea transmission line. A commercial wave power production facility utilizing the AquaBuOY technology is beginning initial construction in Portugal.^[19] The company has 250 MW of projects planned or under development on the west coast of North America.^[20]
• The SeaRaser, build by Alvin Smith; which uses a entirely new technique (pumping) for gathering the wave energy. ^[21]
• A device called CETO, currently being tested off Fremantle, Western Australia,^[22] consists of a single piston pump attached to the sea floor, with a float tethered to the piston. Waves cause the float to rise and fall, generating pressurized water, which is piped to an onshore facility to drive hydraulic generators or run reverse osmosis water desalination.^[23]
• Another type of wave buoys,using special polymeres, is being developed by SRI ^[24]
• Wavebob is an Irish Company who have conducted some ocean trials .
• The Oyster wave energy converter is a hydro-electric wave energy device, currently being developed by wave energy company, Aquamarine Power. The wave energy device captures the energy found in nearshore waves and converts it into clean usable electricity. The systems consists of a hinged mechanical flap connected to the seabed at around 10m depth. Each passing wave moves the flap which drives hydraulic pistons to deliver high pressure water via a pipeline to an onshore turbine which generates electricity. In Summer 2009, installation of the first full-scale demonstrator Oyster began at the European Marine Energy Centre (EMEC) on Orkney.^[25]
• Ocean Energy have developed the OE_bouy which has completed ( September 2009) a 2 year sea trial in one quarter scale form . The OE_bouy has only one moving part . ^[26]
• The Lysekil Project is based on a concept with a direct driven linear generator placed on the seabed. The generator is connected to a buoy at the surface via a line. The movements of the buoy will drive the translator in the generator. The advantage of this setup is a less complex mechanical system with potentially a smaller need for maintenance. One drawback is a more complicated electrical system. ^[27][28]
• An Australian firm is developing a deep-water technology to generate electricity from, ostensibly, easy-to-predict long-wavelength ocean swell oscillations. Oceanlinx recently began installation of a third and final demonstration-scale, grid-connected unit near Port Kembla, near Sydney, Australia, a 2.5 MW_e system that is expected to go online in early 2010, when its power will be connected to the Australian grid. The companies much smaller first-generation prototype unit, in operation since 2006, is now being disassembled.^[12]

Challenges

These are some of the challenges to deploying wave power devices:

• Capturing a reasonable fraction of the wave energy in irregular waves, in a wide range of sea states.
• Extremely large fluctuation of power in the waves. The peak absorption capacity needs to be much (more than 10 times) larger than the mean power. For wind power the ratio is typically 4.
• Efficiently converting wave motion into electricity; generally speaking, wave power is available in low-speed, high forces, and the motion of forces is not in a single direction. Most readily-available electric generators operate at higher speeds, and most readily-available turbines require a constant, steady flow.
• Constructing devices that can survive storm damage and saltwater corrosion; likely sources of failure include seized bearings, broken welds, and snapped mooring lines. Knowing this, designers may create prototypes that are so overbuilt that materials costs prohibit affordable production.
• High total cost of electricity; wave power will only be competitive when the total cost of generation is reduced (or the total cost of power generated from other sources increases). The total cost includes the primary converter, the power takeoff system, the mooring system, installation & maintenance cost, and electricity delivery costs.
• Impacts on the marine environment, such as noise pollution, could have negative impact if not monitored, although the noise and visible impact of each design varies greatly.^[7]
• In terms of socio-economic challenges, wave farms can result in displacement of commercial and recreational fishermen from productive fishing grounds, can change the pattern of beach sand nourishment, and may represent hazards to safe navigation.^[29]
• In the US, development of wave farms is currently hindered by a maze of state and federal regulatory hurdles and limited R&D funding.
• Waves generate about 2,700 gigawatts of power. Of that 2,700 gigawatts, we, with our current technology, are only able to capture about 500 gigawatts.^[14]

Wave farms

The world's first commercial wave farm opened in 2008 at the Aguçadora Wave Park near Póvoa de Varzim in Portugal. It uses three Pelamis P-750 machines with a total installed capacity of 2.25MW.^[3][30] However in November the units were removed from the water and in March 2009 the project was suspended indefinitely.^[31] A second phase of the project planned to increase the installed capacity to 21MW using a further 25 Pelamis machines^[32] is in doubt following Babcock's withdrawal from the project.

Funding for a 3MW wave farm in Scotland was announced on February 20, 2007 by the Scottish Executive, at a cost of over 4 million pounds, as part of a £13 million funding packages for marine power in Scotland. The farm will be the world's largest with a capacity of 3MW generated by four Pelamis machines.^[33]

Funding has also been announced for the development of a Wave hub off the north coast of Cornwall, England. The Wave hub will act as giant extension cable, allowing arrays of wave energy generating devices to be connected to the electricity grid. The Wave hub will initially allow 20MW of capacity to be connected with potential expansion to 40MW. Four device manufacturers have so far expressed interest in connecting to the Wave hub.^[34][35]

The scientists have calculated that wave energy gathered at Wave Hub will be enough to power up to 7,500 households. Savings that the Cornwall wave power generator will bring are significant: about 300,000 tons of carbon dioxide in the next 25 years.^[36]

A CETO wave farm of the coast of Western Australia has been operating to prove commercial viability and after preliminary environmental approval is poised for further development.^{[citation needed]} see http://www.ceto.com.au/home.php

Discussion of Salter's Duck

While historic references to the power of waves do exist, the modern scientific pursuit of wave energy was begun in the 1970s by Professor Stephen Salter of the University of Edinburgh, Scotland in response to the Oil Crisis. His 1974 invention became known as Salter's Duck or Nodding Duck, although it was officially referred to as the Edinburgh Duck. In small scale controlled tests, the Duck's curved cam-like body can stop 90% of wave motion and can convert 90% of that to electricity.^[37] The machine has never gone to sea.^{[citation needed]}

According to sworn testimony before the House of Parliament, The UK Wave Energy program was shut down on 1982-03-19, in a closed meeting,^[38] the details of which remain secret.

An analysis of Salter's Duck resulted in a miscalculation of the estimated cost of energy production by a factor of 10,^[39] an error which was only recently identified. Some wave power advocates believe that this error, combined with a general lack of enthusiasm for renewable energy in the 1980s (after oil prices fell), hindered the advancement of wave power technology.^[40]

Potential

Deep water wave power resources are truly enormous, between 1 TW and 10 TW, but it is not practical to capture all of this.^[41] The useful worldwide resource has been estimated to be greater than 2 TW.^[42][43] Locations with the most potential for wave power include; the western seaboard of Europe, the northern coast of the UK and the Pacific coastlines of North and South America, Southern Africa, Australia and New Zealand. The north and south temperate zones have the best sites for capturing wave power. The prevailing westerlies in these zones blow strongest in winter. Waves are very predictable. The waves that are caused by winds, can be predicted five days in advance. Tidal currents, caused by lunar positions, are known 100 years in advance. Water has a high power density which is 832 times greater than air's power density. That means that large amounts of energy can be obtained from relatively small devices. For example, it would require a wind turbine three times it size to generate the same amount of power than a regular-sized underwater turbine can.^[44]

Tidal currents in the seas affect the wave heights. This translates to greater energy captured by a wave motor. Studies by the Journal of Coastal Research show that the maximum wave height occurs 50-60 min after the tidal current flooding. These tidal currents have a speed of 0.7 m/s. ^[45]

The UK has an estimated recoverable resource of between 50–90TWh of electricity a year, this is roughly 15–25% of the current UK electricity demand.^[46]

Patents

• U.S. Patent 3,928,967 — Apparatus and method of extracting wave energy - The original "Salter's Duck" patent
• U.S. Patent 4,134,023 — Apparatus for use in the extraction of energy from waves on water - Salter's method for improving "duck" efficiency
• U.S. Patent 6,194,815 — Piezoelectric rotary electrical energy generator
• U.S. Patent Application 20040217597  — Wave energy converters utilizing pressure differences

Notes

1. ^ For a small-amplitude sinusoidal wave with wave amplitude the wave energy density per unit horizontal area is or using the wave height for sinusoidal waves. In terms of the variance of the surface elevation the energy density is . Turning to random waves, the last formulation of the wave energy equation in terms of is also valid (Holthuijsen, 2007, p. 40), due to Parseval's theorem. Further, the significant wave height is defined as , leading to the factor ¹⁄₁₆ in the wave energy density per unit horizontal area.
   
2. ^ For determining the group velocity the angular frequency ω is considered as a function of the wavenumber k, or equivalently, the period T as a function of the wavelength λ.

References

Further reading

• Cruz, Joao (2008), Ocean Wave Energy - Current Status and Future Prospects, Springer, ISBN 3540748946 , 431 pp.
• McCormick, Michael (2007), Ocean Wave Energy Conversion, Dover, ISBN 0486462455 , 256 pp.
• Twidell, John; Weir, Anthony D.; Weir, Tony (2006), Renewable Energy Resources, Taylor & Francis, ISBN 0419253300 , 601 pp.

News articles and compilations

• Kate Galbraith (September 22, 2008). "Power From the Restless Sea Stirs the Imagination". New York Times. http://www.nytimes.com/2008/09/23/business/23tidal.html?em. Retrieved 2008-10-09. 
• "Wave Power: The Coming Wave" from the Economist, June 5, 2008
• "Is wave power commercially viable?"
• "The untimely death of Salter's Duck"
• "Ocean Power Fights Current Thinking"
• "Wave energy in New Zealand"
• "How it works: Wave power station"
• Waves power future from the Corvallis Gazette Times, February 5, 2005
• EU Wavetrain project — A series of full-text, on-line scientific publications on physical concepts.
• Devices under test in the uk
• Make the Waves Operate a Motor-Boat Bilge-Pump, Popular Science monthly, February 1919, Unnumbered page, Scanned by Google Books: http://books.google.com/books?id=7igDAAAAMBAJ&pg=PT24
• Pelamis at Aguçadoura video

Wave climate and forecasts

• Information on the long-term statistics of ocean waves can be found at the KNMI wave atlas.
• The US National Oceanic and Atmospheric Administration provides imagery and forecasts of wave height on a global scale. On-line NOAA animation of a user-specified region-of-interest can be set to either wave height or wave period forecasts.
• Ireland's Wave Forecast