How is hydroelectricity generated?

  1. As water flows downhill (e.g. from mountains), a hydroelectric dam will trap the water in a man made lake (known as a reservoir).
  2. Whenever water is released through the dam, it spins turbines which are connected to generators, and so produces electricity.
  3. The water can then return to the river on the downstream/lower side of the dam.

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How do tidal barrages generate electricity?

  1. As the tide comes in, a tidal barrage (basically a dam) will trap the water upstream.
  2. Once the tide has gone back out, water is released through the dam which spins turbines connected to generators, and so produces electricity.
  3. The water can then return to the river on the downstream side of the tidal barrage.

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What energy transfer takes place in hydroelectric dams and tidal barrages?

Gravitational potential energy ➔ kinetic energy ➔ electrical energy.   


In both cases the water on the higher side contains lots of gravitational potential energy. This energy is transferred to kinetic energy as the water rushes down to the lower side.  As the waters moves past turbines, some of its kinetic energy is transferred to the turbines, causing them to start spinning. The generators use this energy to generate electrical power.

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Give 3 advantages of hydroelectricity.

  1. It is renewable.
  2. It can increase or decrease energy output to match demand.
  3. It is cheap to run once set up.

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Give 3 disadvantages of hydroelectricity.

  1. Large environmental impact on the area upstream, as the reservoir can disrupt the natural habitats.
  2. Expensive to build initially.
  3. Only possible in regions with the right kinds of rivers. 

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What is wave power?

The water in the sea rises and falls because of waves on the surface. Wave machines use the kinetic energy of this motion to drive electricity generators.

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Give 3 advantages of wave power.

  1. It is a renewable energy resource.
  2. It is cheap to run.
  3. No harmful polluting gases are produced.

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Give 2 disadvantages of wave power.

  1. It is difficult to scale up the designs for wave machines to produce large amounts of electricity.
  2. Having many wave machines can negatively affect wildlife.

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