Wave power encyclopedia topics

Wave power

Wave power refers to the energy of ocean surface waves and the capture of that energy to do useful work — including electricity generation, desalination, and the pumping of water (into reservoirs). Wave power is a form of renewable energy. Though often co-mingled, wave power is distinct from the diurnal flux of tidal power and the steady gyre of ocean currents. Wave power generation is not currently a widely employed commercial technology although there have been attempts at using it since at least 1890.

The world's first commercial wave farm is based in Portugal, at the Aguçadora Wave Park, which consists of three 750 kilowatt Pelamis devices.

The north and south temperate zones have the best sites for capturing wave power. The prevailing westerlies in these zones blow strongest in winter.

Physical concepts

See Energy, Power and Work for more information on these important 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).

Wave power formula

In deep water, if the water depth is larger than half the wavelength, the wave energy flux is

P = frac{rho g^2}{64pi} H_{m0}^2 T approx left(0.5 frac{text{kW}}{text{m}^3 cdot text{s}} right) H_{m0}^2; T,

where

P the wave energy flux per unit wave crest length (kW/m);
H_m0 is the significant wave height (meter), as measured by wave buoys and predicted by wave forecast models. By definition, H_m0 is four times the standard deviation of the water surface elevation;
T is the wave period (second);
ρ is the mass density of the water (kg/m³), and
g is the acceleration by gravity (m/s²).

The above formula states that wave power is proportional to the wave period and to the square of the wave height. When the significant wave height is given in meters, and the wave period in seconds, the result is the wave power in kilowatts (kW) per meter wavefront length.

Example: Consider moderate ocean swells, in deep water, a few kilometers off a coastline, with a wave height of 3 meters and a wave period of 8 seconds. Using the formula to solve for power, we get

P approx 0.5 frac{text{kW}}{text{m}^3 cdot text{s}} (3 cdot text{m})^2 (8 cdot text{s}) approx 36 frac{text{kW}}{text{m}},

meaning there are 36 kilowatts of power potential per meter of coastline.

In major storms, the largest waves offshore are about 15 meters high and have a period of about 15 seconds. According to the above formula, such waves carry about 1.7 MW/m of power across each meter of wavefront.

An effective wave power device captures as much as possible of the wave energy flux. As a result the waves will be of lower height in the region behind the wave power device.

Wave energy and wave energy flux

In a sea state, the energy density per unit area of gravity waves on the water surface is proportional to the wave height squared, according to linear wave theory:

E=frac{1}{16}rho g H_{m0}^2,

where E is the mean wave energy density per unit horizontal area (J/m²), the sum of kinetic and potential energy density per unit horizontal area. The potential energy density is equal to the kinetic energy, both contributing half to the wave energy density E, as can be expected from the equipartition theorem. In ocean waves, surface tension effects are negligible for wavelengths above a few decimetres.

As the waves propagate, their energy is transported. The energy transport velocity is the group velocity. As a result, the wave energy flux, through a vertical plane of unit width perpendicular to the wave propagation direction, is equal to:

P = E, c_g, ,

with c_g the group velocity (m/s). Due to the dispersion relation for water waves under the action of gravity, the group velocity depends on the wavelength λ, or equivalently, on the wave period T. Further, the dispersion relation is a function of the water depth h. As a result, the group velocity behaves differently in the limits of deep and shallow water, and at intermediate depths:

Properties of gravity waves on the surface of deep water, shallow water and at intermediate depth, according to linear wave theory
quantity	symbol	units	deep water (h > ½ λ )	shallow water (h < 0.05 λ )	intermediate depth (all λ and h )
phase velocity	$displaystyle c_p=frac{lambda}{T}=frac{omega}{k}$	m / s	$frac{g}{2pi} T$	$sqrt{g h}$	$sqrt{frac{glambda}{2pi}tanhleft(frac{2pi h}{lambda}right)}$
group velocity	$displaystyle c_g= c_p^2 frac{partialleft(lambda/c_pright)}{partiallambda}=frac{partialomega}{partial k}$	m / s	$frac{g}{4pi} T$	$sqrt{g h}$	$frac{1}{2} c_p left(1 + frac{4pi h}{lambda}frac{1}{sinhleft(displaystyle frac{4pi h}{lambda}right)} right)$
ratio	$displaystyle frac{c_g}{c_p}$	-	$displaystylefrac{1}{2}$	$displaystyle 1$	$frac{1}{2} left(1 + frac{4pi h}{lambda}frac{1}{sinhleft(displaystyle frac{4pi h}{lambda}right)} right)$
wavelength	$displaystylelambda$	m	$frac{g}{2pi} T^2$	$T sqrt{g h}$	for given period T, the solution of: $displaystyle left(frac{2pi}{T}right)^2=frac{2pi g}{lambda}tanhleft(frac{2pi h}{lambda}right)$
general
wave energy density	$displaystyle E$	J / m²	$frac{1}{16} rho g H_{m0}^2$
wave energy flux	$displaystyle P$	W / m	$displaystyle E;c_g$
angular frequency	$displaystyle omega$	rad / s	$frac{2pi}{T}$
wavenumber	$displaystyle k$	rad / m	$frac{2pi}{lambda}$

Deep water corresponds with a water depth larger than half the wavelength, which is the common situation in the sea and ocean. In deep water, longer period waves propagate faster and transport their energy faster. The deep-water group velocity is half the phase velocity. In shallow water, for wavelengths larger than twenty times the water depth, as found quite often near the coast, the group velocity is equal to the phase velocity.

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 attenuate; 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, 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 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. The project will utilize the PowerBuoy technology 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 and is 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 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.
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-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. The company has 250 MW of projects planned or under development on the west coast of North America.
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.

Challenges

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

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. The total cost includes the primary converter, the power takeoff system, the mooring system, installation & maintenance cost, and electricity delivery costs.

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. A second phase of the project is now planned to increase the installed capacity to 21MW using a further 25 Pelamis machines.

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.

Potential

Good wave power locations have a flux of about 50 kilowatts per metre of shoreline. Capturing 20 percent of this, or 10 kilowatts per metre, is plausible. Assuming very large scale deployment of (and investment in) wave power technology, coverage of 5000 kilometres of shoreline (worldwide) is plausible. Therefore, the potential for shoreline-based wave power is about 50 gigawatts. Deep water wave power resources are truly enormous, between 1 TW and 10 TW, but perhaps impractical to capture.

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 invention became known as Salter's 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. The machine has never gone to sea, primarily because its complex hydraulic system is not well suited to incremental implementation, and the costs and risks of a full-scale test would be high. Most of the designs being tested currently absorb far less of the available wave power, and as a result their Specific Power remain far away from the theoretical maximum.

According to sworn testimony before the House of Parliament, The UK Wave Energy program was shut down on March 19, 1982, in a closed meeting, the details of which remain secret. The members of the meeting were recruited largely from the nuclear and fossil fuels industries, and the wave programme manager, Clive Grove-Palmer, was excluded.

An analysis of Salter's Duck resulted in a miscalculation of the estimated cost of energy production by a factor of 10, 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.

Patents

— Apparatus and method of extracting wave energy - The original "Salter's Duck" patent
— Apparatus for use in the extraction of energy from waves on water - Salter's method for improving "duck" efficiency
— Piezoelectric rotary electrical energy generator - Assignee: Ocean Power Technologies
— Wave energy converters utilizing pressure differences - PowerBuoy Video

References

, 601 pp.
Notes

External links

Institutional links
News articles and compilations
- Kate Galbraith Power From the Restless Sea Stirs the Imagination. New York Times. Retrieved on 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"
- " Oceanography: Waves Theory and principles of waves, how they work and what causes them", at Seafriends, New Zealand
- "Waves"
- 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.
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.

Wikipedia, the free encyclopedia © 2001-2006 Wikipedia contributors (Disclaimer)
This article is licensed under the GNU Free Documentation License.
Last updated on Saturday October 11, 2008 at 12:58:30 PDT (GMT -0700)
View this article at Wikipedia.org - Edit this article at Wikipedia.org - Donate to the Wikimedia Foundation

Wave power

Wave power refers to the energy of ocean surface waves and the capture of that energy to do useful work — including electricity generation, desalination, and the pumping of water (into reservoirs). Wave power is a form of renewable energy. Though often co-mingled, wave power is distinct from the diurnal flux of tidal power and the steady gyre of ocean currents. Wave power generation is not currently a widely employed commercial technology although there have been attempts at using it since at least 1890.

The world's first commercial wave farm is based in Portugal, at the Aguçadora Wave Park, which consists of three 750 kilowatt Pelamis devices.

The north and south temperate zones have the best sites for capturing wave power. The prevailing westerlies in these zones blow strongest in winter.

Physical concepts

See Energy, Power and Work for more information on these important 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).

Wave power formula

In deep water, if the water depth is larger than half the wavelength, the wave energy flux is

P = frac{rho g^2}{64pi} H_{m0}^2 T approx left(0.5 frac{text{kW}}{text{m}^3 cdot text{s}} right) H_{m0}^2; T,

where

P the wave energy flux per unit wave crest length (kW/m);
H_m0 is the significant wave height (meter), as measured by wave buoys and predicted by wave forecast models. By definition, H_m0 is four times the standard deviation of the water surface elevation;
T is the wave period (second);
ρ is the mass density of the water (kg/m³), and
g is the acceleration by gravity (m/s²).

The above formula states that wave power is proportional to the wave period and to the square of the wave height. When the significant wave height is given in meters, and the wave period in seconds, the result is the wave power in kilowatts (kW) per meter wavefront length.

Example: Consider moderate ocean swells, in deep water, a few kilometers off a coastline, with a wave height of 3 meters and a wave period of 8 seconds. Using the formula to solve for power, we get

P approx 0.5 frac{text{kW}}{text{m}^3 cdot text{s}} (3 cdot text{m})^2 (8 cdot text{s}) approx 36 frac{text{kW}}{text{m}},

meaning there are 36 kilowatts of power potential per meter of coastline.

In major storms, the largest waves offshore are about 15 meters high and have a period of about 15 seconds. According to the above formula, such waves carry about 1.7 MW/m of power across each meter of wavefront.

An effective wave power device captures as much as possible of the wave energy flux. As a result the waves will be of lower height in the region behind the wave power device.

Wave energy and wave energy flux

In a sea state, the energy density per unit area of gravity waves on the water surface is proportional to the wave height squared, according to linear wave theory:

E=frac{1}{16}rho g H_{m0}^2,

where E is the mean wave energy density per unit horizontal area (J/m²), the sum of kinetic and potential energy density per unit horizontal area. The potential energy density is equal to the kinetic energy, both contributing half to the wave energy density E, as can be expected from the equipartition theorem. In ocean waves, surface tension effects are negligible for wavelengths above a few decimetres.

As the waves propagate, their energy is transported. The energy transport velocity is the group velocity. As a result, the wave energy flux, through a vertical plane of unit width perpendicular to the wave propagation direction, is equal to:

P = E, c_g, ,

with c_g the group velocity (m/s). Due to the dispersion relation for water waves under the action of gravity, the group velocity depends on the wavelength λ, or equivalently, on the wave period T. Further, the dispersion relation is a function of the water depth h. As a result, the group velocity behaves differently in the limits of deep and shallow water, and at intermediate depths:

Properties of gravity waves on the surface of deep water, shallow water and at intermediate depth, according to linear wave theory
quantity	symbol	units	deep water (h > ½ λ )	shallow water (h < 0.05 λ )	intermediate depth (all λ and h )
phase velocity	$displaystyle c_p=frac{lambda}{T}=frac{omega}{k}$	m / s	$frac{g}{2pi} T$	$sqrt{g h}$	$sqrt{frac{glambda}{2pi}tanhleft(frac{2pi h}{lambda}right)}$
group velocity	$displaystyle c_g= c_p^2 frac{partialleft(lambda/c_pright)}{partiallambda}=frac{partialomega}{partial k}$	m / s	$frac{g}{4pi} T$	$sqrt{g h}$	$frac{1}{2} c_p left(1 + frac{4pi h}{lambda}frac{1}{sinhleft(displaystyle frac{4pi h}{lambda}right)} right)$
ratio	$displaystyle frac{c_g}{c_p}$	-	$displaystylefrac{1}{2}$	$displaystyle 1$	$frac{1}{2} left(1 + frac{4pi h}{lambda}frac{1}{sinhleft(displaystyle frac{4pi h}{lambda}right)} right)$
wavelength	$displaystylelambda$	m	$frac{g}{2pi} T^2$	$T sqrt{g h}$	for given period T, the solution of: $displaystyle left(frac{2pi}{T}right)^2=frac{2pi g}{lambda}tanhleft(frac{2pi h}{lambda}right)$
general
wave energy density	$displaystyle E$	J / m²	$frac{1}{16} rho g H_{m0}^2$
wave energy flux	$displaystyle P$	W / m	$displaystyle E;c_g$
angular frequency	$displaystyle omega$	rad / s	$frac{2pi}{T}$
wavenumber	$displaystyle k$	rad / m	$frac{2pi}{lambda}$

Deep water corresponds with a water depth larger than half the wavelength, which is the common situation in the sea and ocean. In deep water, longer period waves propagate faster and transport their energy faster. The deep-water group velocity is half the phase velocity. In shallow water, for wavelengths larger than twenty times the water depth, as found quite often near the coast, the group velocity is equal to the phase velocity.

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 attenuate; 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, 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 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. The project will utilize the PowerBuoy technology 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 and is 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 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.
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-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. The company has 250 MW of projects planned or under development on the west coast of North America.
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.

Challenges

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

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. The total cost includes the primary converter, the power takeoff system, the mooring system, installation & maintenance cost, and electricity delivery costs.

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. A second phase of the project is now planned to increase the installed capacity to 21MW using a further 25 Pelamis machines.

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.

Potential

Good wave power locations have a flux of about 50 kilowatts per metre of shoreline. Capturing 20 percent of this, or 10 kilowatts per metre, is plausible. Assuming very large scale deployment of (and investment in) wave power technology, coverage of 5000 kilometres of shoreline (worldwide) is plausible. Therefore, the potential for shoreline-based wave power is about 50 gigawatts. Deep water wave power resources are truly enormous, between 1 TW and 10 TW, but perhaps impractical to capture.

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 invention became known as Salter's 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. The machine has never gone to sea, primarily because its complex hydraulic system is not well suited to incremental implementation, and the costs and risks of a full-scale test would be high. Most of the designs being tested currently absorb far less of the available wave power, and as a result their Specific Power remain far away from the theoretical maximum.

According to sworn testimony before the House of Parliament, The UK Wave Energy program was shut down on March 19, 1982, in a closed meeting, the details of which remain secret. The members of the meeting were recruited largely from the nuclear and fossil fuels industries, and the wave programme manager, Clive Grove-Palmer, was excluded.

An analysis of Salter's Duck resulted in a miscalculation of the estimated cost of energy production by a factor of 10, 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.

Patents

— Apparatus and method of extracting wave energy - The original "Salter's Duck" patent
— Apparatus for use in the extraction of energy from waves on water - Salter's method for improving "duck" efficiency
— Piezoelectric rotary electrical energy generator - Assignee: Ocean Power Technologies
— Wave energy converters utilizing pressure differences - PowerBuoy Video

References

, 601 pp.
Notes

External links

Institutional links
News articles and compilations
- Kate Galbraith Power From the Restless Sea Stirs the Imagination. New York Times. Retrieved on 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"
- " Oceanography: Waves Theory and principles of waves, how they work and what causes them", at Seafriends, New Zealand
- "Waves"
- 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.
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.

Wikipedia, the free encyclopedia © 2001-2006 Wikipedia contributors (Disclaimer)
This article is licensed under the GNU Free Documentation License.
Last updated on Saturday October 11, 2008 at 12:58:30 PDT (GMT -0700)
View this article at Wikipedia.org - Edit this article at Wikipedia.org - Donate to the Wikimedia Foundation

Physical concepts

Wave power formula

Wave energy and wave energy flux

Modern technology

Challenges

Wave farms

Potential

Discussion of Salter's Duck

See also

Renewable energy

Ocean energy

Other renewable energy

Other

Patents

References

Notes

External links

Institutional links

News articles and compilations

Wave climate and forecasts

Physical concepts

Wave power formula

Wave energy and wave energy flux

Modern technology

Challenges

Wave farms

Potential

Discussion of Salter's Duck

See also

Renewable energy

Ocean energy

Other renewable energy

Other

Patents

References

Notes

External links

Institutional links

News articles and compilations

Wave climate and forecasts