Most of the technologies currently being explored to take advantage of the tides are what’s known as ‘tidal stream’ devices. There are dozens under development, and it may be many years before they reach commercial maturity. Tidal barrages, on the other hand, are a well-proven technology. However, they are highly capital intensive and need a significant degree of government support. They also have a number of environmental, social and economic impacts which need to be taken into consideration.

The largest and oldest tidal barrage in the world is at La Rance, France. This 240 MW barrage has been generating about 540 GWh per year since 1966. The second largest plant is the Annapolis Royal barrage on the Bay of Fundy in Nova Scotia, Canada. This 20 MW barrage came into operation in 1984. There are also some smaller barrages in China and Russia.

The Severn Barrage

Britain’s Severn Estuary has a tidal range of up to 14 metres (the second largest in the world) and the idea of building a barrage to harness the power of this surge (known as the ‘Severn bore’, and very popular with surfers) has been mooted for decades. A 16 kilometre barrage stretching across this waterway could potentially generate 8 GW of electricity, and supply around 4.4% of Britain’s energy needs. It could cost anything between £14 billion to £22 billion to build, and its construction would create around 18,000 jobs. Some environmentalists (and the Royal Society for the Protection of Birds) are opposed to one massive barrage because of the impact on vital habitats. Alternative ideas being mooted include smaller lagoons and barrages which would cause less environmental damage, but of course generate less power. In January 2009 the government issued its shortlist of five proposals, and feasibility studies are currently being undertaken by the Department for Business, Enterprise and Regulatory Reform (BERR). The engineering consultancy Atkins is calling for an even bigger barrage, stretching from Minehead to Aberthaw. This would cost some £30 billion to build, but would generate 50% more power than the current proposals, they say.

The Sustainable Development Commission has produced an in-depth report on tidal power in the UK which examines the proposition for a Severn Barrage and also the possible application of tidal range, tidal stream and tidal lagoon technologies at other sites around the UK. If fully exploited, tidal power has the potential to generate 10% of the UK's electricity, their report claims.