See also:

• Wave Power Physical Concepts


• Modern Wave Power Technology and Wave Farms

Water Power
Hydroelectricity Micro Hydro Wave Power Tidal Power OTEC Deep Lake Cooling Blue Energy

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.

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, 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.^[27] 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,^[28] 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^[29] 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.^[30]

For more information see the following links:

• Wave Power Physical Concepts


• Modern Wave Power Technology and Wave Farms

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 - Assignee: Ocean Power Technologies
• U.S. Patent Application 20040217597  -- Wave energy converters utilizing pressure differences - PowerBuoy Video

References

Sources and external articles

Institutional links

• Ocean Renewable Energy Coalition
• European Ocean Energy Association
• The European Marine Energy Centre Ltd.
• MIT Underwater Energy Research Group
• Danish Wave Energy Society
• IEA - Ocean Energy Systems

News articles and compilations

• "Is wave power commercially viable?"
• "A Swedish Wave Power project that has come very far"
• Forskningsprojekt
• "The untimely death of Salter's Duck"
• "Ocean Power Fights Current Thinking"
• "Wave energy in New Zealand"
• "How it works: Wave power station"
• An Ocean Wave Energy Converter Using Rotors
• Oceanography: Waves
• "Waves"
• Corvallis Gazette Times
• List of most wave energy devices
• 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.

Demonstration of physical concepts

• The interplay between kinetic and potential energy in pendula and waves is demonstrated by this apparatus at Arizona State University.

Company and institutional links with technology descriptions

• Indian wave energy device --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 in turn connected to gearbox and generator. see animation in webpage.
• 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 Power Technologies (PowerBuoy) -- A mostly-submerged buoy connects to a generator on the sea floor.
• Kneider's Sea Wave Energy Propulsion Technology -- (This device is not suitable for electricity generation.) Wave action on flexible flippers forces a boat through the water.
• 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 Navitas (Aegir Dynamo Wave Energy Converter) -- The point attenuating device converts the linear (rise and fall) motion of ocean waves and swells into rotation energy in one phase with an efficiency of 93%. This rotational energy is passed through standard permanent magnet alternators (as used in modern wind turbines)to create grid compliant electrical energy. The efficiency of the mechanical dynamo enables the technology to be scalable and can be deployed in various scenarios.
• 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.
• Sea Electrical Generators Ltd -- A wave power device is made of polyethylene tubes. Details are not specified.
• 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.
• 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".)
• 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.
• 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.