FAQs
Ocean waves are generated by wind that blows over the surface of the ocean. The water particles are pushed up by the wind and then fall back. This leads to the subsurface circular motion that WaveRoller harnesses. To learn more and find some videos and other useful information please see our story of the ocean wave.
WaveRoller is a bottom hinged, oscillating wave surge converter developed by AW-Energy. It converts kinetic energy of the ocean waves into electrical energy. WaveRollers are installed on the seabed as single units or wave farms. The device consists of three main parts: foundation, panel, and power take-off unit.
WaveRollers are installed in the nearshore surge area where the water is moving continuously. The panel of the WaveRoller unit oscillates back and forth with the movement of the waves. This motion is transmitted through a drivetrain to the PTO which houses a hydraulic circuit and electrical generators that convert the torque into electrical power. The produced electricity is transported via a subsea cable to an onshore substation and to further use.
WaveRoller can be deployed in nearshore areas at depths of approximately 6 – 20 meters. The depth range depends on the total height of the unit.
Most ocean waves are slow moving and most of the time people can run faster than the wave as it surges up the beach. Faster waves do occur, but these are longer and less frequent. The time between these waves is roughly 10sec. Thus, if you compare this to the speed of a combustion engine the engine cylinder is moving up and down more than 300 times faster than a wave. This is the challenge for any wave energy converter, how to transform slow motion and high force levels into useful electricity.
Sir Christopher Cockerell, inventor of the hovercraft and the Cockerell Raft wave energy converter, described the benefits of using hydraulic systems in his paper “The development of the wave-contouring raft” at the Wave Energy Conference, Heathrow, 22-23 November 1978. This was one of the first conferences on wave energy and since that time the advances in control engineering have further strengthened the case for hydraulic systems
Similar to the Cockerell Raft, the WaveRoller panel captures energy as it moves. In typical waves this motion is less than ± 30 degrees. As the panel slows down to change direction at the end of its stroke, the panel counter torque is also actively controlled to keep the oscillation in the same phase with the waves. For a directly connected generator high currents are needed to create a high counter torque and this leads to resistive losses at low speed. A gearbox could be used to increase the speed, but this leads to high mechanical inertia loading, difficulties in controlling the generator and fatigue damage.
Thus, after thorough study we have selected hydraulic systems as they give higher yields and longer operational life for our WaveRoller power take off.
A roman numeral for the panel counter torque, in ton-meters, is used in the naming of WaveRoller family members. For example, WaveRoller-C panel counter torque is approximately 100 ton-meters. When the panel moves at 0.5 radian per second the power take off takes 500kW from the panel.
WaveRoller uses the same corrosion protection methods as other offshore technology, such as offshore wind or oil and gas installations.
- the structures are designed and built for seawater environments using standards such as DNV-OS-C101 and C401.
- approved painting systems are used that are designed for extended operation in salty water.
- cathodic protection is fitted that follows the recommended practice DNV-RP-B401. DNV-RP-B101 is used for the combination of coating system and cathodic protection.
These standards and recommended practice have been developed to enable decades of safe operation in a saltwater environment.
To verify that these codes have been correctly followed the design and manufacture have been certified by Lloyd’s Register.
WaveRoller’s panel follows the movement of the water and the power take off system is fully sealed inside the hull, which makes more friendly to the surrounding marine life.
WaveRoller does not produce any emissions during operation. The technology has been thoroughly assessed for environmental impact across its development. In all cases, it has been found to have either no or minimal disturbance on the natural environment.
The units can be removed after decommissioning, allowing the seabed to return to its natural state. Devices have previously been safely deployed inside a Natura 2000 park in Portugal.