What is... Wave Energy?

The energy associated with Waves and Tides comes in two forms, Kinetic and Potential. Ocean waves contain Kinetic energy through water motion, and potential energy due to the elevation of water as the waves crest. It is a similar situation for tidal energy, the question is, how do we harness this energy?

In this post, we are going to discuss Wave Technology:

Wave technologies can be fixed, submerged or floating. Some common technologies associated with wave energy are:

  • Attenuators

  • Point Absorbers

  • Oscillating Wave Surge Converters

  • Overtopping/Terminator Device

  • Rotating Mass


For an overview of both Wave Energy and Tidal Energy and where they fit in the Energy Transition, read our earlier blog: What is... Wave and Tidal Energy?

Attenuators

An Attenuator is effectively the opposite of an amplifier. This wave power device operates parallel to the wave direction and essentially rides up and down the crest of the wave. An example of this technology is the Pelamis Wave Energy Converter. Developed in Scotland, the Pelamis device was the first commercial scale machine to generate energy to the grid.



Point Absorbers

A point absorber is another surface/near surface device that floats up and down in motion with the passing waves. The base is fixed to the sea floor, while the top is buoyant moving up and down creating a piston like movement to create electrical energy. Of all these systems, the Point Absorber design has been the focus of most R&D over the past few years.



Oscillating Wave Surge Converters

These devices act like a submerged paddle, harnessing energy from the movement of the paddle (a float, flap or membrane), as waves pass by. Energy is collected as the paddle, pushed back and forth by the wave surge, moves relative to the fixed point. The moving paddle can either be used to pressurise a fluid, or more commonly, drive a generator.




Overtopping/Terminator Device

An Overtopping device simply collects waves as they break over a fixed level and into a reservoir, physically intercepting the waves. As the water flows over the point sometimes “collectors” are used to concentrate he wave energy. As the water flows into the reservoir, it passes down through a low head turbine before being returned back out to sea.

https://upload.wikimedia.org/wikipedia/commons/thumb/c/c1/WD_side_princip.JPG/400px-WD_side_princip.JPG

Rotating Mass

Perhaps the least common device, the rotating mass device uses the relative motion of the passing waves to spin an object inside the floating device. This object can either be an eccentric (off centred) mass or a gyroscope attached to electric generator also inside the device.






Whilst this list of wave energy devices is not exhaustive and others do exist (e.g. Pressure Differential Devices and Wave Rotors), this blog gives an idea of the range of technologies we can utilise to extract energy from the waves.


Read last weeks blog which described different technologies used in Tidal Energy: Read it Here
This article is part of a series explaining some of the key technologies that are enabling the energy transition. Click Here to see the full series.

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