Tidal and Wave power

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Technology Overview

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Tidal power is, broadly speaking, electricity generation from the moving water due to tidal flow and is classified as renewable energy as the tides caused by the orbital mechanics of Earth, Sun and Moon are considered inexhaustible within a human timeframe. Tidal power has great potential for power generation due to the amount of energy potentially available and more significantly tidal power is very predictable (unlike wind).

Consequently a battery of tidal generation systems around (say) the UK coast means the low output times (at the high and low water points) would be staggered which would allow for backup power to made available as it is required (typically a main line power station take 30 minutes to get up to load, so it helps to know the requirement in advance!)

There are basically 2 different methods:

The first is the extraction of energy from currents arising because due to ebbing and flowing tides – these are often a way offshore and near the bottom. Generating energy from tidal currents is today considered more feasible than building tidal dams or barrages, with coastal sites worldwide being investigated for their suitability to produce tidal flow energy .

The second method requires generation from the difference in height between high and low tides.

The extraction of this potential energy involves building a dam (or barrage) and creating a tidal lagoon (or basin). Typically the dam traps water behind it on the flood tide and when the tide ebbs, the water is released via turbines. This is known as Ebb Generation and is not unlike typical hydroelectric schemes. You can generate on the Flood tide (Flood Generation), but this is less efficient as the volume of water in the “top half” of the area behind the dam is greater than the bottom half (because the basin sides are sloping). Also there is usually a river behind the dam, providing a further water supply.

You can generate in both directions, but 2 way turbines are less efficient and it is also possible to pump water, using turbines powered in reverse, into the basin – a form of pumped storage.

All of the above schemes will not produce energy continuously. Typically they would produce power for 6 - 12 hours each day. The tidal cycle is about 24.8 hours, so tides advance about 50 minutes a day. The demand for electricity does not coincide with the tides which means grid capacity needs to be available for the times the barrage is not generating. On the upside the tides can be predicted with an accuracy of about 5%, so alternate capacity can be scheduled much more easily than with other more variable generation sources.

A way around this issue is to have 2 basins behind the barrage. With 2 basins, one is filled at flood tide and the other is drained on the ebb tide, with turbines placed between the basins. This allows almost continuous generation. However, two-basin schemes can be expensive, as you need to build a lot more barrage.

With any of these schemes, the higher the tidal swell is, the more power you can develop.

Some Operating Tidal Power Schemes:

• The 240MW La Rance tidal power project in Brittany, France was commissioned in 1966. This plant (operated by Electricite de France) is equipped with 24 generators rated at 10MW. These machines were designed to generate energy on either the incoming or outgoing tide, to pump at periods of slack tide either into or out of the basin and to serve as orifices, passing water either into or out of the basin. The plant therefore could, and quite often did, operate as a single high-basin plant, generating energy on the outgoing tide. With the given versatility of its turbine generator equipment, the plant also operated equally well as a single low-basin plant, generating energy during the incoming tide. In addition, it operated at times as a single-basin double-effect plant, generating energy on both the incoming and outgoing tides.


• There is a 20MW tidal power plant, the Annapolis Royal Generating Station on the Bay of Fundy, Nova Scotia, Canada. This single high-basin tidal Power Plant was commissioned in 1984, has been in successful operation since. It has a single turbine.


• The is a small Tidal Power station in the Soviet Union at Kislaya Guba on the White Sea with a 0.5MW capacity.


• China has developed several small tidal power projects and one large facility in Jiangxia and is also developing a tidal lagoon, near the mouth of the Yalu.


• Some smaller tidal power plants are generating electricity in Norway. These exploit the strong tidal currents in narrow fjords using sub-surface water turbines.

Tidal and Wave power links

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Ocean Power Delivery Ltd. OPD Ltd is an Edinburgh based company set up in January 1998 to develop the Pelamis WEC concept. Interesting site.

Wavegen are a world leader in wave energy and wave power. They developed and operate Limpet, the world’s first commercial-scale wave energy device that generates wave energy for the grid. See below for details of this project.

Tidal Electric are a UK company who are developing a Tidal Lagoon based system which at first glance appears cheaper to build than traditional barrages and more environmmentally friendly. Their current UK project is the 60 MW system proposed for Swansea Bay measuring 5 square kilometers in area and about a mile offshore.

Swan Turbines are working on harnessing tidal streams relying on the same principles as a wind-turbine, in that a rotor spins to generate electricity. Instead of wind driving the rotor, a tidal stream turbine is mounted on the sea bed. This technology may have important advantages as a renewable energy: Low cost, Low visual impact, High predictability and Small environmental footprint.

Marine Current Turbines Ltd (MCT) is developing radically new technology, backed by the UK government, for exploiting tidal currents for large-scale power generation.

The world’s first tidal power station opened in the Kval Sound south of Hammerfest in northern Norway on 13 November 2003. This prototype facility delivers 300 kilowatts to Norway’s electricity grid.

Tidal and Wave power articles

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13th March 2006: The Engineer: Turning the Tide A renewable tidal energy technology which eliminates the need for moving parts and could prove more competitive than fossil fuel power has been developed at Imperial College London spin-out HydroVenturi.

28th February 2006: The Engineer: Pulling Power The energy stored in the oceans is vastly more than Man could possibly use. The oceans convert the gravitational forces from the celestial bodies into mechanical energy, felt by the sea as it bulges to form the ebb and flow tides.

28 January 2005: Western Morning News: £195,000 STAKE IN POWER OF THE WAVES A vital step has been made towards harnessing the energy of wave power off the Westcountry coast - giving hope that the region's landscape can be saved from the threat of wind turbines. Regen SW, the renewable energy agency for the South West of England, has received an award of £195,000 for a project to collect data on wave energy off the North Cornish coast. (Article reproduced by kind permission of the Western Morning News and This Is Devon).

28 January 2005: POWER FROM OUR WAVES It's the face of the future. An experimental wave buoy floats off the Westcountry coast in a pioneering bid to harness clean energy to power Britain. The buoy is to collect data to pave the way for the world's first wave farm, which experts say could be operating off the Westcountry within three years. The development was hailed by campaigners against windfarms. North Devon MP Nick Harvey, who is fighting plans for turbines in his constituency, said: "Wave power is the renewable energy contribution the Westcountry should be making." (Article reproduced by kind permission of the Western Morning News and This Is Devon).

22nd November 2004: British engineer works to secure cost effective tidal power A British engineer believes he can secure cost effective tidal power by innovatively placing existing turbine designs inside large bore underwater pipes. Don Cutler's view is that it's best to use everything that's standard. "You don't re-invent the wheel you improve it."

24th October 2004: Scotland on Sunday: Green energy scheme to connect Hebridean islands. THE wild Atlantic sound that divides the Hebridean islands of Harris and North Uist may be bridged for the first time by a £30m structure that harnesses the power of the waves to produce electricity. The revolutionary project is to be considered by the Western Isles Council as part of its plans to turn the Outer Hebrides into a renewable energy powerhouse. A series of tidal or wave-power generators would be linked to form a platform for a bridge across the four-mile Sound of Harris.

13th October 2004 News Wales: Swansea tidal energy project gets backing Plans for a pioneering tidal energy project in Swansea Bay have been detailed and confirmed by an independent report from leading engineering firm, WS Atkins Engineering. ..and will be the UK’s most competitive renewable power source producing electricity at 3.4p per kilowatt-hour from the relatively small (60 MW) Swansea Bay project.

13th October 2004 News Wales: Tidal lagoon power could give Wales a competitive edge Friends of the Earth Cymru says that significant quantities of low cost renewable electricity generated by tidal lagoons could give the south and north Wales economies a competitive edge by 2020.

23rd September 2004: Race is on to pioneer tidal electricity scheme AN INVESTIGATION into using Portland Race to generate electricity has been called for. The tidal energy could be used to supply the area with power in the next decade.

WAVEGEN's LIMPET (Land Installed Marine Powered Energy Transformer) is a shoreline energy converter sited on the island of Islay, off Scotland's west coast. The Islay Installation has a "nameplate rating" of 500kW. Also see the proposed Faroes wave power station.

24rd August 2004 The Guardian 'Wave power delivers electricity to grid'
The first wave-power machine to supply the national grid has been operating successfully for a week in Orkney at Emec...

A perfect place to make waves about renewable energy.Last year the world’s first offshore tidal energy turbine was built into the seabed about a mile from Lynmouth in north Devon.

3rd August 2004: '£50M to boost wave energy projects'
Projects to harness tidal power off the Westcountry coastline are to benefit from a share of a £50 million cash fund, the Government announced yesterday. (Article reproduced by kind permission of the Western Morning News and This Is Devon).

27th July 2004: 'Wave Power comes closer to reality' The prospect of generating electricity from the waves off the coast of Cornwall came closer yesterday with the announcement of a major study to work out how to feed the power back to shore. (Article reproduced by kind permission of the Western Morning News and This Is Devon).