Floating offshore wind turbines are one of the big new ideas in the renewable energy field. They allow us to go far out to sea in deep water in which would be impossible, or vastly expensive, to install devices fixed to the sea-bed. They also avoid the environmental intrusion of sea bed foundations or monopiles.
There is a range of systems being tested, many of them owing much to experience with offshore oil and gas rigs. So perhaps it’s not surprising that the leaders in the field are the Norwegians. Statoil/Norsk Hydro have developed and tested a 2.3 MW Hywind system in water 220 metres deep off the coast of Norway, while Sway is developing a novel 10MW floating turbine. They both are essentially like the vertical bobbing floats used for fishing, with a long tail under the water providing buoyancy and supporting a conventional propeller-type wind turbine above the water line. They are kept vertical by sea-bed tethers, although the Sway system is designed to be able tilt by up to 8 degrees.
The Dutch have also developed a tension leg platform system, based on oil rig technology, called Blue H. http://www.bluehusa.com/
A prototype is being tested in the Mediterranean- in 108 meters waters at a distance of 10.6 nautical miles from the coast of Puglia in Southern Italy. France plans to install four floating offshore wind turbines and a 3.5 MW. Blue H is a candidate.
The UK is also in the race. Engineering firm Arup is working with an academic consortium backed by Rolls Royce, Shell and BP and linked to architects Grimshaw, on a 10MW “Aerogenerator X”, a novel V- shaped vertical axis floating offshore wind machine, measuring 300m from blade tip to tip. The first unit could be ready in 2013-14. See http://www.windpower.ltd.uk/ and http://vimeo.com/13654447
This grew out of the NOVA (Novel Offshore Vertical Axis) project, backed by the Energy Technology Institute (ETI) and involving Cranfield University, QinetiQ, Strathclyde University, Sheffield University. http://www.nova-project.co.uk/
The ETI has also funded development work on a concrete version of the Blue H design, with involvement from amongst others BAE Systems. In parallel US wind company Clipper, is planning to build the more conventional 7.5 MW “Britannia” deep-sea offshore turbine in north-east England in conjunction with NaREC, the New and Renewable Energy Centre.
The first in UK waters though could be a version of Hywind- Statoil is planning to build an offshore wind farm using 3 to 5 floating turbines developed for its HyWind project off the northeast coast of Scotland.
Feargal Brennan, head of offshore engineering at Cranfield University, where much of the Aerogenerator X development work has been carried out, told the Guardian (26/7/10) ‘There is a wonderful race on. It’s very tight and the prize is domination of the global offshore wind energy market. The UK has come late to the race, but with 40 years of oil and gas experience we have the chance to lead the world. The new [Aero-generator] turbine is based on semi-submersible oil platform technology and does not have the same weight constraints as a normal wind turbine. The radical new design is half the height of an equivalent [conventional] turbine.’ He added that the design could be expanded to produce turbines that generated 20MW or more.
Bigger machine have both advantages and problems. Doubling the diameter leads to four times as much power, but eight times as much weight and can also increase costs by a factor of eight. However vertical axis machines may be lighter, since they need no tower, and may also have the advantage of easier maintenance access and higher stability in high winds.
The USA, so far rather back-ward in developing off shore wind, has now also got into the race. One argument had been that, unlike the UK, which has shallow water offshore (with 1 GW of offshore wind now in place), US coastal waters were deep, so that offshore wind wasn’t very practical. There were also environmental and visual intrusion objections to location near-shore. For example the wind farm proposed for off Cape Cod has only just now been given the go ahead after 10 years of regulatory and legal battles. It will be the USA first offshore wind project. But deepwater floating turbines may change the game.
The US National Science Foundation, has now funded a 3 year project to see if the construction of floating wind turbines in the deep- ocean is a viable. And the State of Maine has just proposed a plan for installing up to 30MW of deepwater marine power, of which only 5MW can be tidal the rest being wind, which must be floating -and be expandable to 100MW or more. Hywind is said to be a candidate.
Back in the UK, the potential for floating offshore wind is very large.. The PIRC Offshore Valuation puts the practical potential at 870TWh/yr, with 660TWh/yr more beyond 100nm out. In all, that’s about four times UK electricity consumption. www.offshorevaluation.org
Of course location that far out will mean that the cost of the undersea grid links will be high, but deep sea wind seems likely to become increasingly attractive as a north sea supergrid network is established, with new UK- to-continental HVDC power grids linking in offshore wind farms across the area, helping the balance local and regional variations in wind availability.
For updates on renewable energy developments in the UK and elsewhere see : www.natta-renew.org