The power of the sea: How Britain could harness its greatest natural resource

Hannah Strange and Alex Monro write... In this small grey isle, solar power on a commercial scale was always going to be a non-starter, while onshore wind has stumbled in the face of rural opposition. But now Britain is turning back to the one resource that has for centuries ensured its survival and prosperity. Lashed by some of the roughest seas in the world and with high tidal ranges, Britons could one day see wave and tidal power providing at least one-fifth of its energy needs, with some experts predicting an even greater role.

After years of relative inactivity in the field, Britain is now once again focusing on the power of the ocean wave as a sustainable energy source that could plug the gap left by dwindling North Sea oil and gas stocks. With the world's first commercial tide turbine installed in Northern Ireland earlier this year and a wave farm developed in Edinburgh to take another world first when installed off the coast of Portugal in the autumn, Britain is poised to become the global leader in marine energy. Here we take a look at the best projects under development.

Tidal power

The Severn Barrage

Despite having toyed with the idea since the mid 1900s, plans to harness the tides of the Severn Estuary remain firmly on the drawing board, largely due to environmental and political concerns. In September last year, the Government announced a feasibility study for a 8.6 GW hydro-electric barrier that would generate five percent of Britain's energy needs. The study is due to culminate in a full public consultation in 2010, but opposition by environmental groups and local residents could well hinder progress further.

Strangford Lough

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The world's first commercial tide turbine makes use of tidal stream technology, viewed by many experts as preferable to barrages because of the reduced environmental impact and lower costs. Though one Seagen turbine generates just 1.2 MW - enough to power around 1,000 homes, their relatively small size means that several could be deployed at one site, while the depth and slow movement of the blade should leave wildlife unaffected. The company behind the generator, Marine Current Turbines, is to begin work with nPower on larger scale power stations, with sites in Pentland Firth, Anglesey and the Isle of Wight under consideration. Professor Stephen Salter of Edinburgh University says the Pentland Firth site alone could meet up to a quarter of Britain's energy needs, making this narrow strip of water the "Saudi Arabia of tidal energy".

Wave power

Pelamis Wave

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Described by the World Energy Council as "the UK's leading device", the Pelamis Wave, developed in Edinburgh, is soon to be installed at Aguçadoura wave farm off the Portuguese coast. Three units, generating a total of 2.25 MW, are to make up the world's first wave power station, while a further 20MW of capacity will be installed in the second phase of the project. Back in its native Britain, Pelamis is set to be deployed at a seven-unit power station off the Cornish coast and at the European Marine Energy Centre in the Orkneys, where four units are to be installed as part of the Orcadian Wave Farm.

Resembling a water-snake bobbing on the surface of the water, the Pelamis is made up of jointed sections which move up and down with the waves, the motion driving electricity generators. Crucially, the units are semi-submerged and can be located far offshore, making them virtually invisible from the shoreline. Currently, the Pelamis Wave is also the most economically viable design in the wave energy field. Click here to see it in action.

The Limpet

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The Limpet, developed in 2000 by Wavegen and installed on the Isle of Islay in Scotland, is the world's first commercial wave energy device to be connected to the National Grid. Sitting close by the shoreline, it comprises a hood-shaped shell that contains an oscillating water column. This column is made up of a vertical concrete tube with an opening below the water level. The rise and fall of the sea's water-level is mimicked within the tube, causing the air trapped above to compress and decompress in turn. This pressure makes the air flow backwards and forwards through two turbines, which convert the pneumatic energy into electrical energy. One unit generates up to 500 kW - enough to power more than four hundred homes - with plans underway for a 4MW commercial facility in conjunction with nPower on the Isle of Lewis in Scotland.

C-Wave

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The C-Wave was invented in 2002 and the Southampton-based company that invented it plans to connect it to a grid for the first time in 2009. Projects are to be situated around 10-12 miles offshore, virtually eradicating any visual impact. The C-Wave looks like a raft, with two metal "walls" placed at right angles to the water, joined by a submerged steel frame. The walls, which sit parallel to one another but both face the oncoming waves, pivot on axels and move in different directions as a wave reaches them, since they are designed to be a half-wave apart. As the walls pivot from their axels at one end, at the other their movement feeds directly into power generators to create electrical energy.