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 oriented parallel to the direction of wave propagation;
terminator, oriented perpendicular to the direction of 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 capture systems use
the rise and fall motion of waves to capture energy. Once the wave
energy is captured at a wave source, power must be carried to the
point of use or to a connection to the electrical grid by transmission power
cables.
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 Ocean Power Technologies which consists of modular, ocean-going
buoys. The rising and falling of the waves moves hydraulic fluid with the buoy;
this motion is used to spin a generator, and the electricity is transmitted to
shore over a submerged transmission line. A 150 kW buoy has a diameter of 36 feet
(11 m) and is 145 feet (44 m) tall, with approximately 30 feet of the unit
rising above the ocean surface. Using a 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. 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. 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.
● The AquaBuOY is made by Finavera
Renewables Inc. 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. This
technology seems to be on-hold as of February 2009. Finavera Renewables
surrendered wave energy permits from FERC.
● The SeaRaser, built by Alvin Smith, uses
an entirely new technique (pumping) for gathering the wave energy.
● 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 water
desalination.
● Another type of wave buoys, using
special polymeres, is being developed by SRI
● 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 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 November
2009, the first full-scale demonstrator Oyster began producing power when it
was launched at the European Marine Energy Centre (EMEC) on Orkney.
● Ocean Energy have developed the OE buoy
which has completed (September 2009) a 2-year sea trial in one quarter scale
form. The OE buoy has only one moving part.
● 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.
● An Australian firm, Oceanlinx, 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 MWe 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.
● An Israeli firm, SDE ENERGY LTD., has
developed a breakwater-based wave energy converter. This device is close to the
shore and utilizes the vertical motion of buoys for creating an hydraulic
pressure, which in turn operates the system's generators. S.D.E. is currently
building a new 250 kWh model in the port of Jaffa, Tel Aviv and preparing to
construct it's standing orders for a 100mWh power plants in the islands of
Zanzibar and Kosrae, Micronesia.
● Another Australian company BioPower
Systems uses the biomimicry of the floats of swaying sea plants in the presence
of ocean waves in its BioWave system.
● A Portuguese company, Martifer, is
developing an attenuator and offshore device, FLOW.