As predictable as the tides
Tidal range technology uses the same principles as hydropower and requires a dam or barrier to impound a large body of water. The difference between the tide height inside and outside the impounded area causes water to be discharged from one side to the other. This water is forced through turbines inside the structure, which creates energy.
Since tidal energy production is not influenced by weather conditions but only by well-known cycles of the moon, sun and earth, it is entirely predictable.
Tried and tested technology
Tidal range power generation is not new, with several tidal barrage schemes in existence worldwide. For example, the 240MW La Rance Tidal Barrage has been operated by EDF since 1966. This was the largest of its type until Sihwa Lake Tidal Power Station opened in South Korea in 2011 with a capacity of 254MW.
Tidal barrages typically utilise bulb turbines, which have been used for decades in river-run hydropower schemes. The hydro turbines are mounted inside concrete turbine housings along a harbour wall and are permanently submerged.
Recent projects have centered on tidal lagoons, structures which utilise the same turbine technology but do not span an estuary. They avoid impacts on the environment or sea other users and use less marine space.
Tidal lagoon schemes can be land-connected, with a ring-shaped harbour wall housing a section of hydro turbines, such as has been proposed for a 320MW scheme in Swansea Bay, Wales. They can also be located entirely offshore.