Wave power is the transport of energy by ocean surface waves, and the capture of that energy to do useful work — for example for electricity generation, desalination, or the pumping of water (into reservoirs). Wave power is a renewable energy source.
Though often co-
Physical concepts
Waves are generated by wind passing over the sea: as long as the waves propagate slower than the wind speed just above the waves, there is an energy transfer from the wind to the most energetic waves. Both air pressure differences between the upwind and the lee side of a wave crest, as well as friction on the water surface by the wind shear stress cause the growth of the waves. The wave height increases with increases in (see Ocean surface wave):
wind speed,
time duration of the wind blowing,
fetch — the distance of open water that the wind has blown over, and
water depth (in case of shallow water effects, for water depths less than half the wavelength).
In general, large waves are more powerful. Specifically, wave power is determined by wave height, wave speed, wavelength, and water density.
Wave size is determined by wind speed and fetch (the distance over which the wind excites the waves) and by the depth and topography of the seafloor (which can focus or disperse the energy of the waves). A given wind speed has a matching practical limit over which time or distance will not produce larger waves. This limit is called a "fully developed sea."
Oscillatory motion is highest at the surface and diminishes exponentially with depth. However, for standing waves (clapotis) near a reflecting coast, wave energy is also present as pressure oscillations at great depth, producing microseisms. These pressure fluctuations at greater depth are too small to be interesting from the point of view of wave power.
The waves propagate on the ocean surface, and the wave energy is also transported horizontally with the group velocity. The mean transport rate of the wave energy through a vertical plane of unit width, parallel to a wave crest, is called the wave energy flux (or wave power, which must not be confused with the actual power generated by a wave power device).
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-
In the United States, the Pacific Northwest Generating Cooperative is funding the building of a commercial wave-
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. The machine is long and narrow (snake-
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 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-
A device called CETO, currently being tested off Fremantle, Western Australia, 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 desalination.
Another type of wave buoys,using special polymeres, is being developed by SRI
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-
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.
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.
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.
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. One benefit of CETO is that the buoys that capture the wave motion are submersed and therefore, are not a visual pollutant. Furthermore, the underwater deployment makes them less prone to storm damage.
The waves and current of some places on earth are so strong that some researchers and scientist have focused primarily on them for for there renewable energy source.
The front of the Pelamis machine bursting through a wave at the Agucadoura Wave Park
The Anaconda prototype is 25cm in diameter and in varying lengths with a simulated power take-
Oscillating Water Column (OWC)
This method of generating power from the tide works by using a column of water as a piston to pump air and drive a turbine to generate power. This type of device can be fixed to the seabed or installed on shore.
In Scotland, the Government awarded three wave energy projects under the Scottish Renewables Obligation. Only one of these projects has been realised and is generating power in Scotland as this pack is being written, this is the LIMPET 500 on the Island of Islay of the west coast, enabling the Island to take a step towards becoming self sufficient in renewable energy.
