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Wave and tidal power - which will win?

Wave power and tidal current turbine technology, if successfully developed, could supply the UK with about 20% the electricity it needs and possibly much more. The UK has one of the world’s best resources, but there are also significant potentials elsewhere. For example it has been claimed that the US could generate 10% of its electricity from wave and tidal schemes.

Wave power was the initial leader – the UK launched a R&D programme in the 1970, with some scale model devices being tested in open water. However we then lost a couple of decades following the withdrawl of government funding for most of the work in 1982 and for the remainder in 1994. Work on Tidal power was also halted – the emphasis at that time being on large tidal barrages across estuaries. Now however, all three options, wave, tidal-current turbines and tidal barrages, are back on the agenda, with the UK still being in the lead, just.

Tidal current turbines seem to have the edge in many ways. Whereas with wave energy you are trying to extract energy from a chaotic interface between water and air with multiple energy vectors, with tidal flows, a few metres under the sources, you have nice laminar flow and a more stable environment. And whereas with barrages you are in effect blocking an entire estuary, with freestanding tidal turbines you are only intercepting parts of the flow, so the environmental impact is much lower.

It’s perhaps not surprising then that there are reputedly 150 or so tidal projects at various scales under tests around the UK. Most are small lab tests but some full-scale systems are now in place – notably the 1.2 MW Seagen tidal turbine in Strangford Loch, Northern Ireland. That has now been signed up to received Renewable Obligation Certificates for the power it feeds the grid. A 10 MW tidal farm is now planned off Anglesey. Next in line is the novel “Open Hydro” open-centred turbine device, the Pulse Tidal oscillating hydrofoil system, the “Lunar Energy” ducted rotor device and Neptune’s vertical-axis “Proteus” ducted rotor.

There are many others under test – for example TidalStream Ltd reports that their unique tidal-turbine platform design – Triton – has successfully undergone validation testing at the deep-water test basin at Ifremer in Brittany, France. Meanwhile Swanturbine’s Cygnet device is being be assembled at Swanturbine’s facilities in South Wales ready for deployment at the European Marine Energy Centre Tidal Test Site (EMEC) in Orkney. A 1.8 MW full-scale machine is under development. And ScotRenewables, located on the Orkney Islands, has raised £6.2 m to build a working prototype of its floating tidal turbine. An 8-metre long prototype will, it’s hoped, go into the water at the EMEC in 2010. Commercial versions would weigh 250 tonnes, and have generation capacity of 1.2 MW.

There are many more projects emerging elsewhere in the world, such as Clean Current’s ducted rotor and Verdant Power’s propeller units, as well as some novel ideas like Indigo Pearl Marine’s open centre “Mer” Vertical Axis Turbine tidal device, while Atlantis, who had already developed a ducted rotor system, have just announced details of a new double-rotor propeller unit, with contra-rotating blades.

But wave energy is not out of the race. The leader is the UK developed Pelamis wave snake system – a 2.2 MW version of which was installed in Portugal. There have however been minor hitches with this system as you’d expect with any new technology – and money for new projects is tight. But new ideas for wave energy are emerging. Cornish wave power developer Orecon has won a contact to install three of its 1.5&nnbsp;MW wave devices off Portugal. Meanwhile a 350 KW version of Aquamarine’s Oyster sea bed mounted “hinged flap” inshore system has been under test in the UK. Next will be a 2 MW demonstration unit, to be expanded if all goes well to 10 MW in 2012. Cardiff-based Tidal Energy Ltd meanwhile is about to test its DeltaStream wave device.

A clever new idea is the 500 kW Wave Treader (developed by Aberdeen-based Green Ocean Energy), which is a new wave unit designed to be attached to an offshore wind-turbine tower, adding to its energy output while sharing the infrastructure costs of cabling and foundations. And Web Engineering in Wiltshire have developed and patented a Sea Wave Energy Accumulator Barge, a novel variation to the “overtopping” reservoir wave-energy concept, but fixed to the sea bed, unlike the floating Danish “Wave Dragon” system.

Progress is also being made on the novel Danish Waveplane concept, which has a series of slots, in three rows, with the higher waves reaching the top row of slots, the rest going into the lower ones. The captured water is let tangentially into a horizontal pipe in such a way as to create a spinning vortex of water, which drives a turbine. Even so it’s certainly not always straight forward to develop new ideas. For example, the UK’s Trident Energy has been deploying its novel linear motor based wave device for testing off the Suffolk coast at Southwold, but its 20 kW demonstration device sank when being taken out to sea. Moreover, while small wave and tidal systems may be interesting, there is still inevitably a major focus on large tidal barrages, if nothing else because of their scale-like 11-mile long 8.6 GW barrage proposed for the Severn estuary. A new round of consultation on that and its rivals is planned and interest is still being shown in smaller barrages elsewhere in the UK, including the Mersey, Solway Firth, the Wash and the Humber.

The UK maybe at the forefront in tidal power and also wave power but the potential elsewhere is also large – especially for tidal. For example, Tidal Today’s second annual Tidal Summit held in London in November was told that South Korea’s theoretical tidal resource was up 1000 GW, and they have some ambitious projects underway or planned, including nearly 2 GW of tidal range projects and 100 MW of tidal current turbines.

That’s not to say that wave power is out of the running – there are many projects underway around the world, including a range of tethered buoy systems, and in the UK work is in now underway on the £42 m Wave Hub project 10 miles off the coast of North Cornwall. The seabed “socket” can take up to four devices at any one time for field testing, without the need for them to build additional grid links. That could speed up the development wave power.

For updates on these and other renewable energy projects, visit www.natta-renew.org.

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Posted by Dave Elliott on December 19, 2009 12:54 PM |

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Comments (48)

  • 1 Anonymous December 20, 2009 12:43 PM

    What a terrible article.

    "Wave and tidal power -which will win?"
    Win what?

  • 2 dave elliott December 20, 2009 1:02 PM

    OK, maybe the title was too journalistic- we need all the renewables we can get. But there is something of a race underway and not all the projects will succeed.

  • 3 Rick Sellers December 20, 2009 8:03 PM

    To present the commercialization of two very distinct and different renewable resources as a competition with only one winner is to totally miss the point - all forms of renewable energy are needed if we are to provide power to keep our societies progressing without destroying the planet. The fact is that all renewable forms have their own strengths and weaknesses, and their own pathways to commercial success. It is phoney sensationalism to present it the way the author does - and it neither informs the reader nor illuminates the important issues. Why not, for example, describe the complementarities created by having two forms of variable output ocean energy that produce on different cycles, and, together with offshore wind, reduce the cost of the transmission systems necessary to transport these reliable, ultimately low cost energies to load centers? Please, can we have less of this kind of shock journalism and more honest reporting?

  • 4 dave elliott December 20, 2009 9:02 PM

    Whoever said there would be only one winner? I think there could and should be many, and they could complement each other. Even so, for good or ill, with money inevitably being limited there may be a need to decide which to invest initially, or what mix to try e.g. in the tidal field, barrages, lagoons and tidal current turbines, each have their positives and negatives, economically, technically and environmentally and in terms of the various wave and tidal options, some will develop faster than others and attract more financial support.

    However the potential complentarity benefits ought to be taken seriously. I would certainly like to explore that aspect- looking for example at the British Wind Energy Association's Redpoint study of the extent to which diversification away from wind to wave and tidal power could help reduce grid balancing costs and excess wind spillage. Wave energy is in effect stored/delayed wind energy and so is less sensitive to wind variations, while tides, though cyclic, are unrelated to wind. The study suggests that to get the best from these different time correlations, the optimum mix might be around a 70%/30% wind to wave and tidal current mix, or, if tidal range projects were included along with tidal current systems, a 60/40 wind/marine mix. The former ratio could reduce the need for backup by 2.15 GW, the later by 2.3GW and the overall carbon savings could be increased by up to 6% and wholesale costs reduced by up to 3.3%. Very interesting.