PERCHED on the deck of a little fishing trawler 8 kilometres off the north Wales coast, Mike Carter surveys his team’s handiwork. In his 24 years in the energy business Carter has built gas, coal and even nuclear power stations. But nothing has made him as proud as building the UK’s first large-scale offshore wind farm at North Hoyle. He says it is one of the most important projects he has worked on. “My kids finally think I’m cool.”
Last month North Hoyle’s 30 turbines each began pumping, 2 megawatts of power into the national electricity grid, marking the UK’s entry into the exclusive club of countries operating large-scale offshore wind farms. The other members are Denmark, Sweden and Ireland (see Map). North Hoyle represents a fundamental shift in attitude about the potential of offshore wind in the UK, and follows the inauguration last year of the world’s biggest offshore wind farm at Horns Rev, where 80 turbines, 2 megawatts each, stand 14 kilometres off the coast of Denmark.
Europe is leading the march of wind power offshore. If local communities, politicians and businesses can be persuaded to play ball, Europeans will soon be getting a substantial slice of their energy from the wind. Bigger, more efficient turbines and cheaper techniques for building wind farms offshore all play their part. One new design could even open up huge, hitherto inaccessible areas of the sea for the wind farms of the future, making offshore wind farms viable for countries such as the US and Japan. Analysts say that if the price of producing electricity from wind offshore continues its downward trend, by 2010 it could become as cheap as producing electricity from gas. But in spite of positive news from wind enthusiasts, protests against wind farms remain high. The question is: will offshore wind power win over its critics and succeed where onshore farms have failed?
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North Hoyle has certainly got the UK’s offshore wind farm movement off to a good start. Built to schedule, and within budget, it even has the general support of the local community back on shore in the town of Rhyl. Local residents’ only serious complaints against its developers, National Power, arose from the pounding of the piledrivers hammering in the turbines’ foundations. “Starting at 2 am on a Sunday wasn’t exactly the best planning,” Carter admits.
Companies trying to develop offshore wind farms face many obstacles. The first hurdle for a developer in the UK, as in most other countries, is to bid for a licence from the government to build power-generating turbines on a site already earmarked for the purpose. The second hurdle, which is usually tougher, is to gain planning consent from several central government departments responsible for offshore territories. The planning process takes into account objections from any individual or body that thinks it may be adversely affected, and must consider the project’s environmental impact. The process takes about three or four years in total.
While permission for North Hoyle was granted smoothly, plans for some other wind farms round the UK are getting a rougher ride. A development at Scarweather Sands off the south Wales coast near Swansea, for example, has triggered massive protests from locals. Fishermen argue it will stop them trawling in 10 square kilometres of sea, and local residents are angry in case it ruins the view and harms tourism. “It’s going to be a landmark case,” says Alison Hill of the British Wind Energy Association (BWEA). If the decision, expected in the new year, goes against the developers, it will set a worrying precedent for the UK’s whole offshore wind project.
The only proposed offshore wind farm in the US, in Nantucket Sound near Cape Cod, Massachusetts, has already come under attack from owners of waterfront homes, who say it will spoil their view. The approvals process there has another 12 months to run.
But in the UK, where the coastal waters have perhaps some of the best potential for wind farms in all Europe, more often than not it is the Ministry of Defence (MoD) and civilian air traffic controllers who pose the biggest obstacle. They often object because of the effect wind turbines can have on radar systems (see “A blip on the screen”). According to the BWEA, the MoD objected to 34 per cent of applications to build land-based wind farms in the UK in 2002, and to 48 per cent this year. Offshore sites have fared somewhat better. The MoD objected to five of the 18 sites announced in April 2001, allowing 13 (including North Hoyle) through without objection. By contrast, Danish air traffic controllers have not raised a single objection on the grounds of radar interference. “It seems to be a uniquely British problem,” says Jakob Holst, an economist at the Danish wind energy association. But despite all these obstacles, Britain and Europe stand at the forefront of the offshore wind power revolution.
One of the key reasons for the huge change in attitude among politicians and energy companies to offshore wind has been the increased power output of turbines. Since 1991, when Vindeby, the world’s first offshore wind farm, was built near the island of Lolland in southern Denmark, the power available from turbines has increased tenfold. Wind farm builders have realised that they can slash their installation and maintenance costs by using a few large turbines instead of several small ones. The 450-kilowatt turbines – 11 of them – installed at Vindeby are now dwarfed by the latest designs. Arklow Sands in Ireland uses General Electric’s 3.6-megawatt turbines, and North Hoyle uses 2-megawatt turbines made by Danish manufacturer Vestas whose blades rise 110 metres above the sea.
Basic mechanics has driven this evolution. A turbine’s power output is proportional to the square of the length of the turbine’s blades, so a small increase in blade length yields a significant rise in output. Some manufacturers use lightweight carbon fibre to reinforce bigger blades, allowing the blades to withstand the increased stresses that they are subjected to.
In September, German turbine manufacturer RePower, based in Hamburg, announced plans to test the world’s biggest turbine, a huge 5-megawatt machine 180 metres tall whose blades are a record-breaking 61.5 metres long. A single turbine would stretch tip to tip across an entire football pitch. “I do not see any technical boundary to the size of the blades,” says Peter Quell, technical director at RePower. “It is just a matter of how big can you go and stay economically viable.”
Other experts agree. “It should be possible to build turbines with blades 70 to 75 metres long within five years,” says Ole Gunneskov, director of R&D at Danish turbine manufacturer NEG Micon. Steen Broust Nielsen of blade manufacturer LM Glasfiber, also in Denmark, says 6-megawatt machines are already in the early stages of design. “I can’t see any technological barriers to offshore blades reaching 100 metres in the next few years,” he adds. “That would take output up to around 10 megawatts.”
It is not only the turbine designs that have acted in Europe’s favour. Countries bordering the North, Baltic and Irish Seas have a huge asset to help them: large sandbanks that stretch several kilometres out to sea. One proposed German wind farm, called Sandbank 24, is 120 kilometres from the coast, yet the water in which its 120 generators will stand, each producing 3 megawatts, is no more than 35 metres deep. Japan and the US don’t have that luxury. Even 5 kilometres into the Atlantic off the US’s eastern seaboard, for example, the seabed plunges to depths of hundreds of metres. At sites like these, fixing masts for the turbines to the seafloor is out of the question.
But there may soon be an alternative. Walt Musial, a senior engineer at the US Department of Energy’s National Renewable Energies Laboratory in Golden, Colorado, is particularly keen on the development of floating offshore wind turbines, a concept long discussed but never yet put into practice. One of the leading contenders is being developed by Dan Hannevig of Sure Engineering in Dublin, Ireland, and David Bone of Ocean Energy and Resource in Chepstow, Monmouthshire, in the UK. “We’re the only ones with such a floating turbine system,” Hannevig claims.
Out of sight, out of mind
Most wind turbines are mounted on monopiles: tall, thin towers that are held in place by a single pile driven 25 metres into the seafloor. The sideways forces exerted by waves and currents rule out the use of monopiles in water deeper than about 30 metres, though there are other fixed designs that that can go a little deeper. But for really deep water, floating platforms are the only option. “We are very interested in pursuing floating turbines, because around the US there isn’t as much shallow water as there is in Europe,” says Musial. “Going 8 kilometres off the coast would largely rule out monopile foundations.” Even in Europe, floating turbines have a lot to offer. They could be built in water far offshore where no one would worry about their visual impact and radar reflections are likely to be less of a problem. And sites could be chosen for optimum wind conditions rather than ease of construction or depth of water.
Hannevig and Bone have wave-tank tested a 1:50 scale model of a floating turbine designed to operate over depths of 60 to 200 metres. The turbine would be assembled onshore, towed out to sea and tethered at the desired site to a concrete anchor. The blades would be attached to a telescopic mast, designed to be jacked up once the structure is fixed in position. The developers are currently awaiting approval from the Irish government to install a prototype in the Irish Sea. Once approved, the turbine will take 18 months to build, the developers say.
In the US, floating turbines would allow big wind farms to be built near large population centres, but far enough out at sea to avoid any protests from air traffic control authorities or local residents. “There’s a lot of new interest in building offshore wind farms,” says Musial.
Andrew Henderson, an independent consultant who has been studying floating turbine designs for over six years, is cautiously enthusiastic, though he thinks Hannevig and Bone’s design is still a long way from becoming widespread. Even the cheapest floating rigs for the oil and gas industry cost several million dollars. For the companies that build them, switching to high-volume, low-margin floating turbines would require a big change in approach. Hannevig and Bone “have got the technical details done”, says Henderson. “But my feeling is that these things are going to be difficult to do cheaply in the short term.” He thinks the technique is unlikely to be used widely for at least another six or seven years.
The unpredictable nature of wind makes it desirable to store the power generated when there is plenty of wind and low demand. One way to do this is with huge batteries. Regenesys Technologies of Harwell, Oxfordshire, in the UK is developing banks of high-capacity batteries that could be attached to power plants such as wind farms to store charge. The scale of these installations would be huge. For example, a bank of batteries capable of storing 100 megawatt-hours of energy would occupy a site of around 1 hectare.
What’s more, this technique would only store electricity for a few hours, or a day at best. An alternative approach is being developed by a company called Wind Hydrogen based in Anglesey, a few kilometres along the coast from North Hoyle. It uses the excess electricity to produce hydrogen by electrolysing water. The idea is to produce hydrogen at times when demand is low but the wind is strong, and then burn it to produce electricity at times of peak demand, when it can be sold at a premium. Critics of this approach point out that 75 per cent of the energy generated from the wind is lost in the process of converting it into hydrogen and back again.
But Declan Pritchard, director of Wind Hydrogen, says the ultimate goal is not to compete with Regenesys’s batteries, but rather to build infrastructure for the hydrogen economy. “That’s where hydrogen from wind makes the most sense.” Ultimately he hopes it will be possible to sell the hydrogen directly as a fuel. “We can produce a litre of hydrogen for about 20p, the same price as the tax-free price of a litre of petrol,” he says. If Amory Lovins, a pro-hydrogen campaigner at the Rocky Mountain Institute in Colorado, is to be believed, then Pritchard is ahead of the game. Lovins predicts that a commercial market for hydrogen will develop within seven years. “Towards the end of this decade we will start to see the rapid emergence of hydrogen for transport,” he says.
Meanwhile, back in North Hoyle, Carter is winding up the construction project. Later this month the British government will announce the winning bidders for the latest round of licences to build offshore wind farms with a maximum output of 6 gigawatts on a windy day, which would be enough to meet more than 15 per cent of the UK’s household demand for electricity. Would he like to be involved in building the next round of offshore wind farms? “Absolutely,” he says. “Only next time I think we will start the piledriving a little later than 2 am on a Sunday morning.”
A blip on the screen
Objections from the Ministry of Defence and the civil air traffic control authorities have scuppered more wind farm developments in the UK than anything else. The problem is that on a radar screen, turbines can look very much like planes. They may also produce a large area of radar “clutter” that obscures planes in the vicinity and, according to the aviation authorities, compromises safety. “The bottom line is that we have to protect the safety of our personnel,” says Julian Chaffer of Defence Estates, an agency which maintains land owned by the MoD.
But many in the wind industry feel that aviation authorities could do more to overcome the problems (żěè¶ĚĘÓƵ, 27 April 2002, p 8). The Ministry of Defence and National Air Traffic Services (NATS), which is responsible for civilian air traffic control in the UK, counter that they are overwhelmed by the number of proposed developments they have to scrutinise.
Air traffic control radar works by releasing a radio wave “ping” and listening out for reflections from objects in its path. The strength of the return signal depends on the size, shape and composition of the object. Large, metallic, sharp-edged objects give the strongest returns, called the radar cross section (RCS).
This means that a single turbine can show up as brightly on a radar operator’s screen as a jumbo jet. To make things worse, the blades rotate, which means that the techniques used to filter out other stationary objects, such as tall buildings, won’t work for wind farms. The filters detect whether the frequency of the return signal is different from that of the outbound signal, a change known as a Doppler shift. If the frequencies are the same, the object must be stationary and so can be safely ignored.
Also, each turbine is only visible on roughly one in six radar sweeps, making the area occupied by the wind farm appear as a twinkling mass. To the radar operator, planes flying over the turbines seem to disappear in the clutter. Another problem is that a row of rotating blades could, by chance, appear in linear succession. That would look like a plane flying across a radar’s field of view.
To avoid the problem, air traffic controllers in Denmark use software that instructs the radar to ignore tracks that start within the wind farm. But on land, that can prevent the radar from detecting planes that are obscured by terrain until they are over the wind farm.
Last month, a team at the British defence research company Qinetiq released a computer model designed to help assess the radar interference from wind turbines. Given a turbine’s design and proximity to the radar, the model tells you what the proposed development would look like on a radar screen. It should help to challenge objections that are likely to prove unjustified. Andy Beck, who led the team, claims that it will allow turbine manufacturers to test designs with lower RCS more cheaply. He also suggests making blades out of “stealthy” materials which absorb the radar pulse. The results of Qinetiq’s research on “stealth blades” are expected next year (żěè¶ĚĘÓƵ, 9 August, p 6). Radar manufacturer AMS is working on a new system, called the Advanced Digital Tracker, that filters out signals from turbines.
But the wind industry fears that whatever it does will never be enough. Without a target for the acceptable size of the signature of a wind farm on a radar screen, air traffic controllers could continue to move the goal posts. NATS doesn’t want to set a target. It argues that each situation depends on the number of turbines, their proximity to the radar installation and the type of terrain.
“There is no easy answer,” says David Hilton, head of air traffic services at Glasgow Airport in Scotland. “Each development needs to be considered on its own merits.”
James Randerson
