You may have learned at school that the ocean’s tides are caused by the Moon’s gravitational force pulling water towards it as it orbits the Earth, while waves are caused by wind blowing across the ocean’s surface. All that movement means ocean waters contain a huge amount of kinetic energy.

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Tidal energy can be harnessed using underwater turbines, which are similar to wind turbines but with shorter, stronger blades. Water flowing through the turbine turns the blades, which turns a generator, producing electricity.

Tidal turbines work best in narrow passages of water, which naturally channel tidal energy through the turbines. For example, one of the world’s largest collections of tidal turbines can be found between the Scottish mainland and the Island of Stroma, capturing the tides flowing between the Atlantic Ocean and the North Sea.

Another approach is to use natural or artificial barriers to trap water at high tide and redirect the flow through turbine-filled channels as the water returns to the ocean.

In contrast, wave energy converters can be placed on the shoreline or in the open ocean, and often use floats that rise and fall with the waves to compress a hydraulic piston, turning a generator. Alternatively, shoreline devices can direct incoming waves into a narrow column, forcing air through a turbine to generate electricity. There are still technological challenges to overcome, but the oceans could one day provide huge amounts of reliable, renewable energy.

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Asked by: Kyla Ball, via email

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Authors

Dr Claire Asher is a science journalist and has a PhD in Genetics, Ecology, and Evolution (GEE) at the University of Leeds. She also works part time as Manager of the UK Robotics and Autonomous Systems (RAS) Network, based at Imperial College London. Asher is also the author of Brave Green World: How Science Can Save Our Planet.

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