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What is wave energy?

What is wave energy?Ocean waves are one the most powerful forces know to man. Even though almost 75% of the Earth’s surface is covered with water, waves are a largely unexplored source of energy.

Waves are caused by the wind blowing over the surface of the ocean. They can vary in size considerably, sometimes reaching the height of a 10 storey building!

Waves hold a lot of energy within their movement and we are now able to harness that energy to generate electricity.

Onshore waves

Waves behave very differently on the coastline compared to offshore. When a wave reaches the coast, the seabed underneath the wave gets shallower and shallower as it nears the shoreline. This causes the wave to rise up from the water and, if powerful enough, crash over the top of itself – something you’ve probably seen on most beaches.

Offshore waves

Out in the middle of the ocean, waves move in an up-and-down motion or swell. You’ve probably experienced the swell of waves that occur offshore if you’ve been on a ferry or ever felt seasick!

As the waves behave in very different ways depending on whether they occur on or offshore, they need two different approaches to successfully get energy from waves.

How does it work?

Onshore. Fixed devices are attached to the coastline and need the waves to break near them to generate electricity. They work by trapping a column of air inside a concrete chamber that is half submerged in the water.

As the wave moves into the chamber, air inside the chamber is pushed out, passing through a turbine which spins causing a generator to produce electricity. It also works the other way around – when the wave retreats from the chamber it sucks fresh air back through the turbine and into the chamber, generating even more electricity. This clever system can then repeat the process with each wave that passes into the chamber.

Offshore. Floating devices are found offshore and work in an entirely different way to fixed devices. The best way to visualise a floating device is like a giant snake that floats on the water. The floating device is made up of large metal tubes that are connected together by hinges. The group of tubes is attached to the sea bed using cables, so the device is fixed in one place.

As the swell passes underneath the snake, one tube will move upward and the tube that it is connected to will move downward. This movement is repeated down the snake of metal tubes as the wave passes underneath.

The hinges between the tubes are connected to a pump. This pumps oil through a hydraulic motor as the tubes move,which in turn generates electricity as it spins around.

The electricity generated can be taken to land via cables attached to the seabed.

Wave energy in the UK

The UK has some of the best wave power sites in the world due to being surrounded by water and exposed to extreme weather that often occurs out in the North Sea and Atlantic.

Currently there is a fixed device on the Scottish island of Islay called LIMPET or Land Installed Marine Powered Energy Transformer. This can generate enough electricity to power 350 homes and was the world’s first large wave power machine.

Another project in the UK is an offshore floating device called Pelamis. This was first tested near the Orkney Isles in Scotland and there are now plans to build 4 Pelamis machines to make the UK’s first wave farm.

The UK isn’t maximising its full potential wave energy at the moment, but it won’t be long until wave devices become a more popular way of generating sustainable energy in the UK.

Advantages of wave energy

  • Running and maintenance costs are very low
  • Wave energy machines emit no waste or pollution
  • Offshore devices have the potential to produce large amounts of energy

Disadvantages of wave energy

  • Offshore wave energy generation can interfere with shipping and wildlife
  • Waves need to be powerful to generate the maximum amount of electricity
  • Wave-energy generators can be noisy

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