Energy world

Tidal

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 where tidal height differs. The amount of energy available depends of the size and speed of the flowing stream. Because we know how the Sun and the Moon move around our planet, it is possible to forecast fairly accurately the amount of energy that can be captured.

It is predicted that tidal energy across the world is capable of generating over 3000 gigawatts (GW), but only about 3% of that is in places where it would be easy to capture .

How is it used to generate electricity?

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

Artificial tidal lagoons or reservoirs trap water through turbines built into an articifical 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.

Tidal barrages can be built across an estuary. Like lagoons, they hold water back and create a difference in tidal height. Water is then released through turbines to generate electricity.

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

Where can you find it?

Almost anywhere in the world but the best places are where water cannot flow easily like lagoons, 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 produces 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 systems in the UK?

There are dozens of devices under development.

How much does it cost to produce?

No reliable figures are available at present.

What is the carbon cost?

Tidal power does not produce any carbon dioxide.

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 a world leader in tidal technology.