If building wind farms at sea is difficult and expensive, installing turbines beneath the waves is far more so. Currents batter them; salt corrodes them. Yet Britain's coasts have become a playground for engineers and entrepreneurs intent on producing electricity from the tides. Their efforts are beginning to generate a buzz.
Most of the world's (at present puny) tidal power comes from barrages across estuaries. Yet long-mooted plans to wall up the River Severn, Britain's longest, have foundered because of high costs and worries about wildlife. Instead, scientists are focusing on two newer technologies, both of which could soon be tested in commercial schemes. This puts the country "completely at the forefront" of tidal technology, says Gareth Potter of Swansea University.
The first sort is found in the Pentland Firth, the fast-flowing strait between Orkney and the Scottish mainland. This year Atlantis Resources, a marine-power firm, plans to start installing turbines on the seabed--it hopes to plug in 260 by 2020, each about 18 metres in diameter.
That would create an underwater power plant with about the same oomph as a small gas-fired station. Researchers at Oxford University think the Pentland Firth could one day generate more than 40% of Scotland's power, if it were packed with similar gizmos.
The second project is in Swansea Bay in Wales. Entrepreneurs plan to create an artificial lagoon behind a six-mile-long sea wall. Turbines at its entrance would spin four times a day as the tide rises and falls, generating about as much power as an offshore wind farm.
Andy Field of Tidal Lagoon Power, the developer, says it would take three years to build; this could start as soon as next spring, if planners approve. His firm wants to rig up five more lagoons by 2023, making 8-10% of Britain's power.
Tidal power would, in theory, make decarbonising Britain much easier. Solar panels and wind farms produce electricity only when the weather allows, leading to unpredictable dips in supply that must be filled by burning fossil fuels. Tides, of course, are utterly predictable. Tim Cornelius of Atlantis Resources says that Britain's long, jagged coastline gives it unrivalled tidal resources.
Atlantis's turbines will be hidden many metres beneath the water, where even the fiercest NIMBYs could not object to them. Swansea's tidal lagoon could operate for more than a century; locals worried about spoiled views are promised opportunities for swimming, sailing and even farming oysters.
Both projects would be the largest of their type in the world, giving British firms a leg-up in a growing global market. Optimists claim this could increase from almost nothing to £50 billion ($84 billion) by 2050, as countries such as Canada, India, South Korea and China grow keen.
Yet these benefits, hoped-for and in the future, involve large spending now. Atlantis will spend £40m installing its first four turbines; the electricity they produce will be about twice as expensive as juice from offshore wind farms and roughly six times pricier than the wholesale price of power.
Investors will need to stump up £850m for Swansea's lagoon; its developers want the government to promise 35 years of subsidies, probably at a rate much higher than has been offered to a proposed new nuclear power plant in Somerset.
Those lofty sums explain why tidal firms are racing to test their designs at ever greater scale. Poyry, a consultancy, thinks Britain will need to build at least three tidal lagoons before they can produce power more cheaply than offshore wind farms; the Pentland Firth draws developers because its tidal streams run twice as fast as in other suitable sites.
Guy Houlsby at Oxford University worries that outsized ambitions could result in embarrassing failures. That has yet to stop the surge.
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