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Offshore wind goes deep

For moment the EU leads the offshore wind field, with nearly 3GW in place, 1.3GW off the UK coast. The world’s largest offshore wind farm is currently the UK’s 300MW array at Thanet, in the North Sea. But the 500MW Greater Gabard project 23km off Suffolk is coming along and the 1GW London Array in the outer Thames estuary will top that, and many more are planned off the UK and also elsewhere, for example France is now looking for 30 sites for 3GW of offshore wind and wants 6GW by 2020. Overall, nearly 20GW has now been consented in EU waters. The longer term EU potential is put at maybe 150 GW, or much more, given newly emerging deep-water technology, allowing for location much further out in the North Sea and elsewhere, for example, off the coast of France, Spain and Portugal.

Although some projects are now emerging off New England, the US has been slow to develop offshore wind projects, in part since, unlike the UK and some other EU countries, it doesn’t have shallow water off its (east) coast. But deep-water technology solves that problem and, as in the EU, opens up a very large resource.

Deepwater Wind, a company based in Providence, Rhode Island, has drawn up plans for what could be the largest wind farm in U.S. waters – a 1GW Deepwater Wind Energy Center with 200 turbines off New England, which would cost $4–5bn. It would use 5MW turbines mounted on four legged platforms 18 to 27 miles off the Rhode Island coast at a depth of 52 meters: more than twice that of conventional steel ‘monopole’ wind turbine platforms.

As water depth increases, the diameter of monopoles must increase exponentially, making them uneconomical in water deeper than about 20 meters. By using a four-legged design, the company says they will be able to work in depths that were previously prohibitively expensive. And being far out to sea there should be fewer problems with objections over visual intrusion- a major issue so far in New England. More: www.dwwind.com

The basic deep-water technology, involving structures with multiple legs, was originally developed for oil and gas platforms and a version has already been used for some deep-water offshore wind turbines in the EU e.g. the Beatrice 2 x 5MW turbine project off Scotland. So-called ‘tension leg’ technology, with typically four semi-submersible piles tethered to the sea-bed, has been used. The 2.3 MW Dutch Blue H turbine, tested off Italy, used this concept. And in Portugal, EDP is developing a 2 MW WindFloat with three legs, while in France Nénuphar, Technip, and EDF are developing a novel Vertiwind device, with vertical axis wind turbine mounted on three legs. After work on a prototype, they hope to test a full scale 2MW device at sea in 2013.

If you want to go even further out and into deeper water then you need fully floating systems, like Norways Sway and HyWind, which, it’s claimed, can operate in depths of between 120 and 700 metres.
See my earlier blog.

Sway is about to start testing a scale prototype of its proposed 5MW floating turbine off the coast of Norway at site near Hordaland. The Sway turbine can tilt by 5–8 degrees from the vertical.

Although, a 2.3 MW version of HyWind has already been tested,10km off Norway, in general fully floating device technology is relatively undeveloped. But hopefully not for long. In addition to the work mentioned above, 19 partners from 8 EU countries, under the direction of the Fraunhofer IWES, have entered the conception phase for HiPRwind, the largest publicly funded research project for the development of enabling technology for deep-water offshore wind, with €11 m contributed to the €20 m 5-year project by the European Commission.

That’s in parallel with the EU’s £3m DeepWind Vertical axis Darrieus (‘egg beater’) type floating 10MW wind turbine project led by RISO in Denmark, Spain’s 50MW floating wind project 30km offshore in depths up to 100m, and the UK’s novel V-shaped vertical axis 10MWAerogenator X, developed out of the ETI’s Nova project.

China is also developing offshore wind technology. Its first offshore wind farm, a 102 MW array near Shanghai, is being followed by others Construction of a 1GW offshore wind farm in Bohai Bay, around three hours from Beijing, is expected to be complete by 2020. The Government has invested €1.6bn in the project, which is being managed by the state-owned China National Offshore Oil Corporation.

However, they are not currently looking far out to sea. As I reported in a previous Blog, they are looking at what they see as less risky and more commercially viable near-shore options: http://environmentalresearchweb.org/blog/2010/12/offshore-wind-costs.html.

In particular, with a potential 100 to 200GW being available in extensive tidal flats, the emphasis in China in the short term is on intertidal projects. There should be at least 10GW of installation by 2020 in Jiangsu province. A 30MW pilot project is under construction there and a 300-MW may follow, using 3.6MW turbines and a novel five pile support structure to cope with the tidal flat’s muddy seafloors and shifting sandbars.

www.technologyreview.com/energy/24978/?mod=related

It’s hard to know if deep-sea wind will prosper. If they can be developed successfully, floating wind turbines can be towed out to be located on station, and so can avoid some of the large deployment costs associated with drilling piles into the sea bed, and they can also be brought back to harbour for maintenance, avoiding the difficulty and cost of getting access at sea. But there are significant extra costs with longer undersea grid links. However, if and when a full North sea supergrid network is established, then some of these costs would be shared with other projects, and the system as a whole would earn more income by being able to transfer power between the UK and the other EU countries involved with the supergrid: see http://environmentalresearchweb.org/blog/2010/12/the-north-sea-supergrid.html.

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