'''Wave power''' refers to the energy of ocean surface waves and the capture of that energy to do useful [[Mechanical work|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 a widely employed technology, and no commercial [[wave farm]] has yet been established.
'''Wave power''' refers to the energy of ocean surface waves and the capture of that energy to do useful [[Mechanical work|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 a widely employed technology, and no commercial [[wave farm]] has yet been established.
On December 18, 2007, [[wgfgwgfgwgfgwgfgwgfgwgfgwgfgwghfgtyerpfcoast of Northern California<ref>{{cite news |first=Matt |last=Nauman |title=PG&E to invest in wave energy |url= http://www.siliconvalley.com/news/ci_7749450 |publisher=[[San Jose Mercury News]] |date= 2007-12-18 |accessdate=2007-12-18 }}</ref>. The plant will consist of eight buoys, 2 1/2 miles offshore, each buoy generating electricity as it rises and falls with the waves. The plant is scheduled to begin operating in 2012, generating a maximum of 2 megawatts of electricity. Each megawatt can power about 750 homes.
On December 18, 2007, [[Pacific Gas and Electric Company]] announced its support for plans to build [[America]]'s first commercial wave power plant off the coast of Northern California<ref>{{cite news |first=Matt |last=Nauman |title=PG&E to invest in wave energy |url= http://www.siliconvalley.com/news/ci_7749450 |publisher=[[San Jose Mercury News]] |date= 2007-12-18 |accessdate=2007-12-18 }}</ref>. The plant will consist of eight buoys, 2 1/2 miles offshore, each buoy generating electricity as it rises and falls with the waves. The plant is scheduled to begin operating in 2012, generating a maximum of 2 megawatts of electricity. Each megawatt can power about 750 homes.
Plans to install three 750 kW [[Pelamis wave energy converter|Pelamis]] devices at the Aguçadora Wave Park in [[Portugal]] in 2006 have been delayed and no installation had taken place by August 2007. Other plans for wave farms include a 3MW array of four 750 kW Pelamis devices in the [[Orkneys]], off northern [[Scotland]], and the 20MW [[Wave hub]] development off the north coast of [[Cornwall]], [[England]].
Plans to install three 750 kW [[Pelamis wave energy converter|Pelamis]] devices at the Aguçadora Wave Park in [[Portugal]] in 2006 have been delayed and no installation had taken place by August 2007. Other plans for wave farms include a 3MW array of four 750 kW Pelamis devices in the [[Orkneys]], off northern [[Scotland]], and the 20MW [[Wave hub]] development off the north coast of [[Cornwall]], [[England]].
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 a widely employed technology, and no commercial wave farm has yet been established.
On December 18, 2007, Pacific Gas and Electric Company announced its support for plans to build America's first commercial wave power plant off the coast of Northern California[1]. The plant will consist of eight buoys, 2 1/2 miles offshore, each buoy generating electricity as it rises and falls with the waves. The plant is scheduled to begin operating in 2012, generating a maximum of 2 megawatts of electricity. Each megawatt can power about 750 homes.
Plans to install three 750 kW Pelamis devices at the Aguçadora Wave Park in Portugal in 2006 have been delayed and no installation had taken place by August 2007. Other plans for wave farms include a 3MW array of four 750 kW Pelamis devices in the Orkneys, off northern Scotland, and the 20MW Wave hub development off the north coast of Cornwall, England.
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
When an object bobs up and down on a ripple in a pond, it experiences an elliptical trajectory.
Waves are generated by wind passing over the sea: organized waves form from disorganized turbulence because wind pressure pushes down wave troughs and lifts up wave crests, the later due to Bernoulli's principle. See Ocean surface wave.
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."
Wave motion is highest at the surface and diminishes exponentially with depth; however, wave energy is also present as pressure waves in deeper water.
The potential energy of a set of waves is proportional to wave height squared times wave period (the time between wave crests). Longer period waves have relatively longer wavelengths and move faster. The potential energy is equal to the kinetic energy (that can be expended). Wave power is expressed in kilowatts per meter (at a location such as a shoreline).
The formula below shows how wave power can be calculated. Excluding waves created by major storms, the largest waves are about 15 meters high and have a period of about 15 seconds. According to the formula, such waves carry about 1700 kilowatts of potential power across each meter of wavefront. A good wave power location will have an average flux much less than this: perhaps about 50 kW/m.
Formula: Power (in kW/m) = k H² T ~ 0.5 H² T,
where k = constant, H = wave height (crest to trough) in meters, and T = wave period (crest to crest) in seconds.[2][3]
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[4], 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[5] is funding the building of a commercial wave-power park at Reedsport, Oregon.[6] The project will utilize the PowerBuoy[7] 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 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. Two commecial projects utilizing Pelamis technology are under construction, one in Portugal the Aguçadora Wave Park near Póvoa de Varzim which will initially use three Pelamis P-750 machines generating 2.25 MW. [8]. Funding for a 3 MW wave farm in Scotland was announced on February 20, 2007 and is projected to use four Pelamis machines.[9].
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[10] 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 faciity utilizing the AquaBuOY technology is beginning initial construction in Portugal. [11]
A device installed near Wollongong, New South Wales, uses a parabolic reflector to concentrate wave energy into an oscillating water column which drives air through a Denniss-Auld turbine, designed to rotate in a constant direction in the oscillating airflow.[12][13].
File:AeroDynamicTHUMB.PNGA device called Neo-AeroDynamic[14]: It is an airfoil base design to harness kinetic power of the fluid flow via an artificial current around its center. The device differentiates from others by its capability to directly transfer wave power into rotational torque to drive a generator without moving part. As the result of its high efficiency; it's not only applicable to wind but also to the variety of hydro electric including free-flow (rivers, creeks), tidal, oceanic currents and wave via ocean wave surface currents.
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.
Portugal continues to plan the world's first commercial wave farm, the Aguçadora Wave Park near Póvoa de Varzim, though efforts to install three Pelamis P-750 machines generating 2.25 MW have yet to come to fruition.[15][16] Initial costs are put at 8.5 million euro. Subject to successful operation, a further 70 million euro is likely to be invested before 2009 on a further 28 machines to generate 72.5 MW.[17]
Funding for a 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.[18].
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 by this generator 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. [19]
Potential
Good wave power locations have a flux of about 50 kilowatts per meter of shoreline. Capturing 20 percent of this, or 10 kilowatts per meter, is plausible. Assuming very large scale deployment of (and investment in) wave power technology, coverage of 5000 kilometers 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, 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, Salter's Edinburgh Duck, continues to be the machine against which all others are measured. 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.[citation needed] While it continues to represent the most efficient use of available material and wave resources, 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 Mass to Power Ratios 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[20], 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[21] 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.[22]
European Ocean Energy Association The European Ocean Energy Association has been established to strengthen the development of the markets and technology for ocean energy in the European Union.
The European Marine Energy Centre Ltd. -- EMEC was established to help the evolution of marine energy devices from the prototype stage into the commercial market place.
Company and institutional links (with technology descriptions)
Indian wave energy device - patented --Near shore floating device facing incoming waves.The rise and fall of the waves is converted to mechanical motion by heavy buoyant piston driving an overhead crankshaft that is inturn connected to gearbox and generator. see animation in webpage.
Aerovironment -- A buoy is attached to a cable, and the buoy sits several meters underwater. The buoy rises and falls in response to pressure changes from waves passing overhead. (Although the buoy's design is unclear, it probably includes a flexible, gas-filled bladder.) The bottom of the cable is connected (through an unspecified mechanism) to a generator on the seabed.
AW-Energy -- The company has made a near shore machine called "WaveRoller" which operates on utilising the ‘bottom wave’ phenomenon. An underwater wing is attached to a hydraulic arm and uses the backwards and forwards underwater pressures produced by surface waves as they enter shallower waters.
AWS Ocean Energy -- Submerged (about 50 meters underwater) free-floating buoys are filled with gas and are partly open at the bottom. Each free-floating buoy fits (like a sleeve) over a stationary buoy, and it rises and falls due to pressure changes from waves passing overhead. Power take-off is linear magnetic generator.
Finavera Renewables Inc.(AquaBuOYs) -- A buoy is attached to a long piston, which pumps water to a common (shared by a number of buoys) hydroelectric generator on the seabed. Electricity is transmitted ashore.
BioPower Systems -- Oscillating flexible arms, based on kelp fronds, drive an electrical generator via a proprietary gear system.
Brooke Ocean Technology Ltd (SeaHorse -- Wave-Powered Moored Ocean Profiler) -- (This device is not suitable for electricity generation.) A suitcase-sized ocean sensor is attached to a rope between a buoy and a seabed anchor. It uses the motion of waves to power a ratchet mechanism. This mechanism drives the device up and down the rope to programmed depths. Water density, temperature, and turpidity data is gathered.
C-Wave Ltd -- Two or more vertical plates sit underwater and normal to the direction of wave propagation. Wave forces cause the plates to be alternately drawn together and forced apart. Hydraulic pistons utilize these forces.
Oceanlinx (formerly Energetec) -- A parabolic face focuses waves into an inverted basin, and the rising and falling of the water moves an air column. The air column drives a special air turbine generator, one whose vanes rotate to maintain generator direction when the air column reverses.
Gyro-Gen, developed by Aaron Goldin -- The device includes a spinning gyroscope and a power generator inside a buoy. As the buoy travels over a wave, it tilts, first one way and then the other, and this motion causes the gyro to undergo precession. The gyro resists the rocking motion, not by tilting in the opposite direction, but by turning on the axis of the tilting force. This action is harnessed to move a crank that turns a generator.
Ing Arvid Nesheim (Oscillating device) -- A floating column is fitted into a sleeve (to enable sliding) and through a large hole in the center of a buoy. The sleeve is attached to the buoy by means of a universal joint, which enables more active (adaptive) up-and-down movement of the buoy. The movement powers an hydraulic electrical generator. (The column has a sea anchor attached to its bottom to reduce vertical movement.)
Independent Natural Resources Inc (SEADOG Pump) -- A buoyancy block moves up and down in a buoyancy chamber, which rests on a water tank on the seabed. Movement of the buoyancy block drives a piston, which pumps pressurized water into the tank and from there to a reservoir onshore. Water from the reservoir runs through hydroelectric turbines and back into the sea.
Japan Agency for Marine-Earth Science and Technology (JAMSTEC) (Mighty Whale) -- A large steel raft has a work deck aft and a vertical grill that faces the waves. The device uses an oscillating water column to move air in each of three pneumatic chambers. The turbines that convert the pneumatic energy to electrical energy are self-reciprocating. Specifically, the vanes are fixed pitch and have reflective symmetry normal to the direction of airflow, creating bidirectional equivalent lift and drag. (See image of "Wells Turbine".)
Neo-AeroDynamic: A rotating turbine made of airfoils harnesses kinetic energy of the wave surface current.
Ocean Motion International -- Buoys are suspended from a platform (like a fixed oil platform) and are able to move up and down. The buoys are quite heavy (even though buoyant), and they work (pumping water) as they descend into wave troughs. The pressurized water is intended for hydroelectric use or water purification.
Ocean Power Delivery (Pelamis Wave Energy Converter) -- 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).
Ocean Renewable Energy Group (OREG) -- This Canadian association studies wave and tidal energy development and maintains an extensive online library of ocean energy information.
OWECO Ocean Wave Energy Company -- The Ocean Wave Energy Converter (OWEC®) is a system of quick-connectable modules that form neutrally-buoyant arrays stabilized and sea-anchored by damper sheets. The system may be slack-moored. Large wave-following buoys convert reciprocal motion to counter-rotating, direct-drive electrical generators located in submerged chambers. Sensors control ballast volume and generator resistance. Electricity from multiple modules is combined through linking tubes to output terminals. Major components are shaped to permit volume manufacturing, shipping, and deployment. The electricity produced can be used to desalt water or produce hydrogen.
Ocean Wave Energy Conversion System (SARA) -- A surfboard-shaped buoy is attached to a long rod. The rod is embedded with magnets, and it moves up and down within a linear generator housing, which is stabilized by an anchored damping plate. A ballast is connected to the bottom of the rod, to pull the rod down after each wave.
Renewable Energy Holdings Plc (CETO) -- A gas-filled tank has rigid sides and base and a flexible (bellows-like) top. The center of the top, which is attached to a lever, rises and falls in response to pressure changes from the waves passing (about 10 m) overhead. The lever drives pistons, which pump pressurized water ashore, for hydroelectricity or reverse osmosis.
S.D.E. (Sea Wave Power Plant) -- A buoyant metal plate is attached at one side to a concrete seawall. Waves press the plate up (in a cantilever action) and drive an hydraulic ram. The hydraulic system is connected to a hydroelectric system.
Seabased AB -- A buoy pulls on a rope attached to a linear electromagnetic generator on the seabed. Permanent magnets (NdFeB) are used. The device is claimed ideal for calmer seas. The mechanism for adjusting the generator housing in sympathy with tidal sea levels is not specified.
Seavolt (Wave Rider) -- A cam shaped buoy rolls with the passing of waves. The rolling action drives hydraulics, which run a hydroelectric generator.
Sperboy (Embley Energy) -- A large cylinder contains an oscillating water column. The cylinder is kept in place by buoyancy and ballasts tanks and by about 12 vertical anchor lines. The water column drives air in and out of 4 horizontal ducts that radiate out from the top of the main cylinder. The ducts contain self-reciprocating turbines that convert the pneumatic energy to electrical energy.
SyncWave Energy -- Two buoys of different buoyancy are connected by a mechanical power take-off. Electronics control the mechanical resistance of this connection.
Vortex Oscillation Technology -- Claims involve discussion of theoretical hydrodynamic concepts. Details are not specified.
Wavebob The device is a point absorber that is designed for rough, winter conditions. The top of the unit rests at or just below the surface. The incorporated linear generator uses adaptive electronics to match the wave conditions.
Wave Dragon -- A parabolic face focuses waves onto a ramp. Waves overtop the ramp and spill into a low dam. Water from the low dam flows through hydroelectric turbines into the sea beneath the floating structure. See also Wave Dragon.
WAVEenergy AS (Seawave Slot-Cone Generator) -- Waves wash up a slotted ramp (over swept-back louvers) into tiered basins, which drain into a multi-stage hydroelectric system.
Wavegen (Limpet) -- A shore-side inverted basin contains an oscillating water column, which moves an air column. The turbines that convert the pneumatic energy to electrical energy are self-reciprocating. Specifically, the vanes are fixed pitch and have reflective symmetry normal to the direction of airflow, creating bidirectional equivalent lift and drag. (See image of "Wells Turbine".)
Wavemill Energy Corp -- Water flows up a ramp, which is on a modular concrete structure. A system of valves captures the water and uses it hydroelectrically.
WavePlane Production A/S -- A raft shaped like an obtuse angle is anchored (by chain or cable) in the middle. The point of the angle is designed to self-orient into the waves. Horizontal damping plates reduce vertical movement. Waves spill into guide vanes ("funnels"), which direct water towards a cylindrical tube. The water enters the tube tangential to the curved surface, creating a spinning cylinder of water ("fly wheel tube"). The type of turbine appropriate for utilizing that spinning energy is not specified.
Wave Star Energy -- A long truss is mounted on steel piles. Articulating arms are attached to the truss, and buoys are attached to the ends of the arms. Movement of the arms forces fluid into a central hydraulic accumulator and through a generator turbine.
A.W.S. BV (Wave Swing) -- A large buoyant cylinder is open at the bottom. The cylinder surrounds and slides up and down on a cylindrical framework, which is attached to a platform on the seabed. The cylinder is mostly full of gas, and it rises and falls as the gas pressure equalizes with the sea pressure, which changes as the wave peaks and troughs pass overhead. The whole assembly is a linear electrical generator.
Waveberg -- A central float is connected to 3 bent lattice arms, each of which has another float on its outer end. Vertical movement of the outer floats drives hydraulic rams, which pump high-pressure water to shore. This high-pressure water can then be used for hydroelectric generation.
