Wave Energy Devices
Ocean waves are created by the interaction of wind with the surface of the sea. The size of the waves is determined by the wind (speed, period and fetch), bathymetry of the seafloor (which can focus or disperse the energy of the waves) and currents. Waves have the potential to provide a completely sustainable source of energy which can be captured and converted into electricity by wave energy converter (WEC) machines. These WEC’S have been developed to extract energy from shoreline out to the deeper waters offshore.
We have identified six main types of WEC:
A) Attenuator
An attenuator is a floating device which works perpendicular to the wave direction and effectively rides the waves. Movements along its length can be selectively constrained to produce energy. It has a lower area parallel to the waves in comparison to a terminator, so the device experiences lower forces.
B)
Point absorber
A point absorber is a floating structure which absorbs energy in all directions
through its movements at/near the water surface. The power take-off system
may take a number of forms, depending on the configuration of displacers/reactors.
C) Oscillating Wave Surge Converter
This device extracts the energy caused by wave surges and the movement of water particles within them. The arm oscillates as a pendulum mounted on a pivoted joint in response to the movement of water in the waves.
D) Oscillating water column
An oscillating water column is a partially submerged, hollow structure. It is open to the sea below the water line, enclosing a column of air on top of a column of water. Waves cause the water column to rise and fall, which in turn compresses and decompresses the air column. This trapped air is allowed to flow to and from the atmosphere via a turbine, which usually has the ability to rotate regardless of the direction of the airflow. The rotation of the turbine is used to generate electricity.
E) Overtopping device
This type of device relies on physical capture of water from waves which is held in a reservoir above sea level, before being returned to the sea through conventional low-head turbines which generates power. An overtopping device may use collectors to concentrate the wave energy.
F) Submerged pressure differential
These devices are typically located nearshore and attached to the seabed. The motion of the waves causes the sea level to rise and fall above the device, inducing a pressure differential in the device. The alternating pressure can then pump fluid through a system to generate electricity.
G) Other
This covers those devices with a unique and very different design to the more well-established types of technology or if information on the device’s characteristics could not be determined. For example the Wave Rotor, is a form of turbine turned directly by the waves. Flexible structures have also been suggested, whereby a structure that changes shape/volume is part of the power take-off system.