The UK’s massive offshore wind expansion is propelling the development of a new generation of offshore wind turbines rated at 6 MW and above, which are also bringing innovative solutions in engineering, finance, transmission and maintenance in their wake.

Piers Evans

This July, the unveiling of the UK’s long awaited Electricity Market Reform White Paper showed a green light for the next stage in offshore wind’s technological development.

Energy Minister Chris Huhne’s goal of 18 GW of offshore wind capacity by 2020 not only puts the UK at the heart of the sector’s development but also necessitates an overhaul of every aspect of the sector – design, construction, transmission, installation, maintenance and finance.

The step-change is possibly most dramatic in an emerging generation of giant wind turbines rated at 6 MW and above. Vestas is already promoting a turbine that nears the record capacity of Enercon’s 7.5 MW onshore E-126 turbine while braving the North Sea’s hostile meteorology. But a crowded field of rival designs are also testing constraints in the length of blades, the depths of foundations and the endurance of gearing systems.

CONTENDERS FOR THE DOMINANT DESIGN

The race to lead what has been described as Europe’s greatest current engineering undertaking has drawn both the sector’s longstanding leaders and less specialized power giants – with each contender in the technological beauty contest offering a subtly different conception of what constitutes the ideal giant offshore turbine.

Doosan has hinted its design may also leapfrog 6 MW – the median capacity for offshore wind’s new generation – although the company has yet to fully reveal the vital statistics of its contender in the pageant.

Sinovel, meanwhile, boasts that its 6 MW SL6000 turbine demonstrates how Chinese technology is ready to erode Europe’s dominance, offering a 128-metre rotor diameter along with an anti-corrosion system primed for tough offshore environments.

Alstom has pushed the boundaries in blade technology with its recent announcement on 15 June – ‘World Wind Day’ – that its 6 MW turbine will carry blades from LM Wind that stretch 73.5 metres to set a new record for length.

Testing a wind turbine blade at the UK’s Narec centre for researching renewable forms of generation
Testing a wind turbine blade at the UK’s Narec centre for researching renewable forms of generation

Siemens has set out its stall with an emphasis on aspects including weight. Its SWT-6.0-120 wind turbine, again rated at 6 MW, has a nacelle and rotor that together check in at under 350 tonnes. The turbine also reuses several technologies from the company’s 3.6 MW offshore model to enhance its reliability, including the same B58 blade, manufactured without glue joints.

Gamesa, which is aiming for pre-series runs of a 6–7 MW turbine by 2014, can offer cementing systems and platforms developed in collaboration with Newport News Shipbuilding. Their advantages include cost-effective civil engineering infrastructure – the biggest component in offshore developments, says Gamesa.

For its 6 MW N150/6000 Nordex vaunts a modular turbine concept intended to facilitate installation and service at sea. The company claims components can be replaced simply and rapidly, without dismantling the rotor.

Experience is a key battleground. REpower’s vice president of Offshore Development Norbert Giese stresses the extent of relevant experience gained with its 5 MW 5M turbines. “We see our advantages in coming from offshore wind projects far from shore – more than 30 km from the nearest harbour – and in depths of 20–60 metres,” he said.

“We were the first to install multi-megawatt turbines farshore and in deep water with the installation of the Beatrice project in the UK in 2006/2007 and since can look at a lot of experience with Thornton Bank in Belgium in 2008, Alpha Ventus in Germany in 2009, and recently Ormonde with 30 turbines.”

Yet experience also forms a central plank in the contrasting argument Finn Strøm Madsen, president for Vestas Technology, puts for developers entering this “very attractive but high risk field”. “Our customers say to us, ‘We want products with proven technology that reduce our risks and increase our business case certainty’.” In his view, only Vestas and Siemens – who between them can claim almost 90 per cent of Europe’s current installed offshore capacity – can offer such proven technology.

IS THE TIMELINE REALISTIC?

But, of course, neither utilities nor manufacturers can tread with full confidence in a field of technology that Dr Richard Court, technology specialist at the UK’s National Renewable Energy Centre (Narec), describes as “extremely embryonic”.

Two key issues were also left hanging in Chris Huhne’s white paper. First, the rate of support for wind generation is still unknown. Second, will the planned rollout of wind really go to plan? Given the turmoil convulsing most sectors of Europe’s power generation, this is surely a fair question. And Huhne’s vow to end “25 years of dithering” also came before the continent’s finances entered an even steeper nosedive.

The white paper unveiled on 12 July establishes feed-in tariff support for wind in the form of a ‘contract for difference’. A new government body will guarantee a fixed price for wind generated electricity to assure utilities a fixed rate of return. Meanwhile, a carbon price floor will raise the cost of running coal and gas plants. Under a ‘renewable energy roadmap’ launched alongside the white paper an industry-led committee, backed with £30 million ($50 million) of government cash would help offshore wind bring down its costs.

Yet the sheer scale of the UK’s offshore wind target could invite scepticism. Last month the European Wind Energy Association (EWEA) celebrated “solid growth” of 4.5 per cent for the first half of 2011 in new offshore wind turbines, which totalled 108 over six months. Round 3, the culmination of the UK’s offshore wind expansion, will call for as many as 5000 turbines by 2020.

Can it really be done? “It will have to happen,” says Dr Court. Indeed, the Narec centre at Blyth on England’s north east coast is gearing up to “de-risk” emerging offshore technology with a rapidly expanding set of facilities. By next spring Narec will accommodate blades as long as 100 metres. From 2013 it will test nacelles of up to 15 MW. The following year an offshore demo site will be home to up to 15 pre-commercial prototype turbines, totalling as much as 100 MW in capacity.

Jean-Michel Aubertin, chief executive of Doosan Power Systems, also expresses qualified faith in the timeline envisaged under the UK’s Round 3. “I think the start of the installations will be probably around the date that they have announced,” he said. “If you look at the number of companies in the various disciplines that are interested in providing the bits and pieces that you need, I think it’s going to happen more or less in the timeframe that they have said… Full implementation may take a bit longer than what is anticipated.”

But however upbeat the industry feels about the UK hitting its offshore wind target, it is far less certain about how. “We see there are a lot of investments in large installation vessels or harbour facilities. But we are also faced by some bottlenecks such as cabling,” said REpower’s Giese.

Narec’s director of electrical networks Alex Neumann sees another daunting challenge in getting the electricity from giant turbines between arrays and to shore. “One of the obvious challenges is that rather than laying more copper, voltage levels will have to go up. But where is the optimum level? How will the supply chain adapt?” he said.

While transmission and distribution manufacturers are eyeing offshore wind with interest, it fails to rank for them as “a massive global opportunity”. “They will try to adjust production as little as possible and use equipment developed for onshore,” he said. Even onshore, further hurdles must be overcome in getting power to homes. “You need massive corridors of connection – and how do you connect it to existing infrastructure without a heck of a lot more pylons? Some people somewhere will have to put up with big pylons,” he said. The effects of public hostility to such infrastructure can be seen in the prolonged delay to Scotland’s Beauly to Denny 440 kV overhead power line for connecting renewables to the grid.

For Vestas’s Madsen, an encouraging political backdrop also has yet to clear the bureaucratic hurdles from the path of offshore wind. “A lot of permitting still needs to be done,” he said. “Even in the UK it still needs to become clearer. The seabed is laid out and the initial planning of where cables will come to shore is being done. But formal due diligence and environmental impact report still needs to be done.”

Fig 1: A computer generated image of Alstom’s 6 MW contender for the offshore wind market
Fig 1: A computer generated image of Alstom’s 6 MW contender for the offshore wind market

A SHAKEOUT LOOMS

Such challenges are clearly no deterrent for turbine manufacturers, drawn by abundant opportunity and spurred by the race for an early lead – “It is very important to be first,” says Frédéric Hendrick, vice-president OffShore Alstom Wind.

Doosan sees room for many companies to enjoy success, said Aubertin. “The utilities have already recognized that they will not be going for one or two manufacturers,” he said. “Each of them will want to share their wind farms between two or three manufacturers. For sure no one manufacturer can take it all. We are aiming for 20 per cent of the market.”

In pursuit of this goal Doosan is among many companies – including General Electric, Vestas, Siemens, Mitsubishi and REpower – in planning to manufacture in the UK. The company hopes to eventually employ 500 staff in building turbines at Renfrew in Scotland.

Yet Round 3 will also thin the ranks of offshore wind contenders, says Dr Court. “There is still is a lot of variety but it will consolidate. We won’t have 20 machines in ten years’ time.” In his view, developers and utilities are also itching to narrow the field. “There is a contradiction inherent in what the industry wants. They want a dominant design so they can order hundreds – but they don’t want to put all their eggs in one basket.”

It is already possible to pick the winners? For Aubertin, the firms to come out on top will be ones with the financial clout back up their technological brilliance. “Financing is going to be very different and very demanding and unless you are part of a group with deep pockets, you will struggle,” he said. “I am rather convinced that by the end of the day you will have some consolidation and this consolidation will favour the groups and companies that have access to some serious finances.”

His opinion is echoed, in ringing terms, by Frédéric Hendrick, vice-president of offshore wind for Alstom: “Size matters: size of rotor and size of company. Investment is so big for customers that they want to deal with a supplier with a large balance sheet.” He sees an additional edge for Alstom as one of the few companies that provide both turbines and substations.

GEARS VS DIRECT DRIVE

In terms of turbine technology, though, the fiercest battle line is probably between geared and direct-drive solutions – a vital issue as data from existing farms suggests failures in drivetrains, generators and gearboxes are behind 39 per cent of downtime.

“The most simple design is a synchronous machine,” argues Hendrick. In his view, the priorities of being simple, robust and efficient demand a direct drive solution with permanent magnets. Siemens likewise places direct drive technology as a selling point for its SWT-6.0-120, the company’s third direct-drive turbine.

In the opposing corner, Vestas’s Madsen makes a vigorous case for gears. “Wind turbines with a geared solution have proven their worth – and the lost production factor is supporting this – we have seen a clear decrease in the downtime on our turbines with a geared solution over the last couple of years,” he said. Geared solutions also offer a higher efficiency than direct drives in terms of MWh per tonne, he claims.

“Thirdly, we do not develop technologies that depend on strategic raw materials. Direct drive technologies depend on substantial amounts of rare earths coming out of China. This dependency creates a risk of potential supply disruption that could interefere with normal repair and maintenance.”

Dr Court refuses to guess how close either firm’s design could be to the machines that will triumph in UK waters and take pole position for future contests over resources such as the USA’s East Coast. “We are honing in on a dominant design, but we don’t know how close we are yet – offshore wind hasn’t yet settled on a preferred solution, which is why you still have to build machines with a lifespan of only 20 to 25 years.”


CUTTING THE COST OF OFFSHORE WIND GENERATION

Offshore wind generation is doomed to carry heavy installation and transmission costs that will generally outweigh the advantages of superior offshore wind resources further from shore. Yet the industry is confident it can achieve a substantial drop in generation costs over the coming decade.

The UK’s recent electricity market reform white paper set a goal of slashing costs of wind generation from £190 ($310)/MWh to £100. An industry-led committee will be granted £30 million in innovation support to lead this effort.

In a recent report for the trade body RenewableUK, BVG Associates concluded that overall offshore wind costs will drop by 15 per cent between 2011 and 2022 under normal market conditions. A decrease of 33 per cent is forecast under favourable conditions.

The report concluded that the use of fewer, more reliable turbines would cut operational expenditure, despite their installation in deeper waters and further from shore. Energy yield is also predicted to climb by a fifth, driven by improved far-shore resources.

“Both capacity factor and load factor are much higher than for onshore wind turbines,” said Finn Strom Madsen of Vestas.

“These are now regarded as baseload. We are looking at a capacity factor of 80–90 per cent and a load factor of 40–50 per cent. Our assessment of how far we can go and still apply proven technology is that we can reduce the cost of electricity by 40 per cent from known products already on the market.”

His optimism is matched by his competitors and by Dr Court of the National Renewable Energy Centre (Narec). “Offshore’s always going to be more expensive but its costs will come down and the cost of gas will go up,” he says. “The cost of carbon will make renewable generation cheaper so that offshore will be able to compete with coal and gas in ten years’ time.”

Doosan’s Jean-Michel Aubertin expects offshore wind to become “closer and closer” to grid parity.

“I think there is no doubt about that. Gas is going to be more favourable, but you cannot have everything dependent on gas – so I deeply believe that offshore wind will be there,” he says.

For Frederic Hendrick of Alstom, though, the key will be establishing the volumes that justify serial production.

“It’s clear that offshore cannot be very high cost. We want to set up lean manufacturing to drive down the costs of generation. In the long term how does it compare to gas? I don’t know. Costs will come down substantially, but if you don’t have the volumes, then forget it.”


THE RISE IN WIND TURBINE CAPACITY

In offshore environments the advantages in raising wind turbine capacity up to 6 MW are obvious. “For the same water depth, with a 3 MW turbine you are paying twice for cable and maintenance,” said Frédéric Hendrick of Alstom.

Unsurprisingly, a steady rise in the capacity of offshore wind turbines is already a clear trend, says Julian Scola of EWEA. He forecasts that this year will bring a substantial rise in the average offshore wind turbine capacity of 2.6 MW recorded at the end of 2010.

“EWEA believes that average offshore turbine sizes are set to increase to over 4 MW in the coming years, due mainly to the more widespread use of 5 MW turbines,” he said. “Indeed the average turbine size of projects under construction at end 2010 was already 4.3 MW.”

He also expects turbine capacity to eventually far exceed that of the emerging generation of turbines rated about 6–7 MW. “One company has announced it will have a 10 MW prototype in 2012, with a least two others announcing even bigger prototypes in 2013,” he says.

Research is already underway into 15 MW designs while 20 MW wind turbines are feasible, according to a new report from the EU-funded UpWind project, he adds.

Yet pushing turbines past 7 MW confronts some basic technical constraints. “A fundamental challenge is getting the blade long enough, strong enough and stiff enough,” says Dr Richard Court of the UK’s Narec R&D and demonstration centre.

“People will have to use more carbon fibre. Fibreglass is an excellent material but not very stiff. You can design around this with downwind turbines, but upwind rotors run much more smoothly.”

Pre-bending is one method to design larger blades that can withstand high winds. Yet every extra metre requires adding to the root of the blade, where it is heaviest.

“These problems are mirrored at the generator,” says Alex Neumann, director of electrical networks at Narec. “The gearbox gets bigger and bigger. Is building for this heavier weight worth it?”

Offshore wind turbines are unlikely to have already reached their capacity limit. Yet the next growth spurt is still a way off.

“When we started development of turbines we looked at several sizes – 7 MW, 8 MW, 10 MW. We picked 6 MW because economically it was the optimum for conditions in the North Sea,” said Hendrick.

“In the future we could go for bigger machines, but that will be another generation. The equation is not that nice for machines of 10 MW. Even with new technologies, 10 MW not that appealing in the cost of electricity until we can get affordable and light blades above 100 metres long.”

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ROUND 3: THE UK’S LEAP IN SCALE FOR OFFSHORE WIND

The UK’s central role in the development of offshore wind was apparent in the latest installation figures from EWEA. Of 108 turbines installed in Europe during the first half of 2011, 101 were in UK waters.

But Round 3 projects will dramatically raise the British contribution to the sector. Through massive developments in nine zones, Round 3 is intended to deliver as much as a quarter of the UK’s electricity needs by 2020.

The initiative follows the completion since 2003 of 11 wind farms with a total capacity of 962 MW under Round 1 of the development of the Crown Estates’ offshore wind resources. A further 15 projects with a combined capacity of 7.2 GW were approved in December 2005 under Round 2. Another 2.5 GW was also approved as extensions to established project in Round 2.5.

The UK’s Crown Estate then launched a third round of site allocations in June 2008 on a much larger scale – with total capacity as high as 32.2 GW. Successful bidders for developments were announced in January 2010 and the first Round 3 projects are expected to start generating electricity by 2015.

While the wind resources set out in Round 3’s nine zones are vast – the largest, Dogger Bank, has potential for 9 GW – they are often in deep water and far from shore. Dogger Bank, for instance, has depths of between 18.6 metres and 63.5 metres. Its location also extends from between 125 and 195 km from shore.

A host of technical developments will be required to generate affordable electricity from such challenging locations. Built-in redundancy will enhance reliability as will sensors that monitor oil in gearboxes.

A fleet of vessels that can cope with challenging conditions of the North Sea will also be required. Round 3 turbines are also likely to be maintained by staff based permanently offshore under a “mothership” system.

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