Energy nation

Tidal energy

Status: Renewable

What is it?

Tides are caused by the gravitational effects of the Sun and the Moon on our oceans. In the UK this creates a rise and fall in sea height, twice a day. Tidal steams are fast-moving currents that are caused by the movement of water between high and low tide. The amount of energy you can get depends of the size and speeds of the streams.

How is it used to generate electricity ?

There are several different ways to capture tidal energy: from trapping tides in lagoons or reservoirs to underwater turbines, like propellers, positioned in tidal streams. Here are three types of devices.

Artificial tidal lagoons or reservoirs trap water through turbines built into an artificial wall as the tide rises, generating electricity as they fill up. The water is released slowly through the turbines to generate power as the tide falls.

A tidal barrage can be built across an estuary. Like a lagoon, it holds water back to create a difference in tidal height. Water is then released through turbines to generate electricity.

Devices are placed directly into tidal streams and extract energy as water flows through and over blades, like a wind turbine.

Where can you find it?

It is found all over the world but the best places are where water cannot flow easily, around headlands or between islands. The UK has strong tidal streams and high tidal ranges.

Advantages and disadvantages of using tidal energy to generate electricity

Advantages

  • Tides are predictable
  • Once the plant is built, operating costs are very low, so the energy produced is very cheap
  • It does not produce carbon dioxide or waste
  • It needs no fuel

Disadvantages

  • The plants can only produce power when the tide is flowing in or out – around 20 hours a day
  • Barrages can be very expensive to build
  • There is no one leading tidal stream device at the moment 

How many stations in the UK?

There are dozens of devices under development.

The future?

The UK has some of the best locations for tidal energy - enough to make a significant contribution to the UK’s energy needs. The UK is fast developing the industry and hopes to be the world leader in tidal technology.