Generating power from the tides

Swansea Bay Tidal Lagoon is the world’s first energy generating tidal lagoon. The project offers a significant contribution to the UK’s industrial strategy, helping to solve the energy gap, deliver carbon savings and develop a world leading tidal energy industry.

A tidal lagoon is a ‘U’ shaped breakwater, built out from the coast which has a bank of hydro turbines in it. Water fills up and empties the man-made lagoon as the tides rise and fall. We generate electricity on both the incoming and outgoing tides, four times a day, every day.

Due to the incredible tides on the West Coast of Britain, by keeping the turbine gates shut for just three hours, there is already a 4m height difference in water between the inside and the outside of the lagoon. Power is then generated as the water rushes through 60m long draft tubes, rotating the 7.2m diameter hydro turbines.

Once built, it will provide clean energy for up to 155,000 homes. This could save up to 236,000 tonnes of carbon emissions each year. The lagoon will offer a boost to the local economy as well as providing protection again coastal erosion and the threat of flooding.

There are two main types of tidal power: tidal stream and tidal range.

Tidal stream

Tidal streams are currents in the sea that flow as the tide moves in and out. Tidal stream turbines are similar to wind turbines but use fast moving tidal streams instead of the wind to generate electricity. Sea water is 832 times denser than air and so a 5 knot ocean current has more kinetic energy than a 350 km/h wind.  As a result, ocean currents have a very high energy density and therefore tidal stream turbines tend to be smaller in size than wind turbines. Electricity is generated by the turning of a turbine and is brought to shore by a cable. An example of a tidal stream project is Atlantis Resources’ MeyGen scheme in Scotland, intended to become the largest tidal stream project in the world.  Following the deployment of a demonstration array of up to six turbines, a maximum of 86 turbines (86MW) will be deployed in phase one, with the project ultimately reaching up to 398MW of tidal stream capacity.

Tidal range

The difference between high tide and low tide is known as tidal range. The range in the Severn Estuary can be over 15 metres making it the second largest in the world. Until recently, the only way electricity has been harnessed from tidal range is through construction of tidal barrages containing turbines across the mouth of estuaries that have large tides. The first large tidal barrage to be built was La Rance in Brittany, France. This project began producing electricity in 1966 and is currently the second largest tidal power station in the world. Tidal lagoons work in a similar way to barrages by capturing a large volume of water behind a man-made structure, which is then released to drive turbines and generate electricity.  Unlike a barrage, where the structure spans an entire river estuary in a straight line, a tidal lagoon encloses an area of coastline with a high tidal range behind a breakwater, with a footprint carefully designed for the local environment.