Wind Power

Winding up to a crescendo

1 September 2007



The global wind energy scene is one of a rapidly increasing acceleration in new build, particularly in Europe and North America, and in proposals for much larger wind parks. There is also a significant shift towards exploiting offshore possibilities as a way of picking up more energy and avoiding NIMBY?related delays. These trends, and some of the technical innovations that are now emerging, are highlighted here.


Floating a good idea

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Artist’s impression of a field of Sway generators. Engineering of a pilot turbine is expected to begin this autumn. (Illustration: Sway)

Norway’s state owned oil major Statoil ASA is to invest 75 million NOK in Norwegian deep water technology company Sway. Statoil believes that Sway has 'developed promising solutions for floating wind turbines in deep water'. The Statoil investment is part of a 150 m NOK fund raising by Sway, with Norwegian firms Scatec, an investment company, the utility Lyse Energi and shipyard owner Rosenberg also coming on board as new major stock holders. The equity dilution is worth NOK 150 million.

No details were given on Sway's ownership structure following the fund raising, but Statoil said its investment is being made 'on the proviso that Sway is able to meet agreed target milestones'.

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Ballasting arangement of a Sway machine

Sway is expected to begin engineering of a sea going wind turbine pilot in the autumn. The first full-scale turbine is expected to be completed and installed between 2010 and 2012.

Statoil also acquired in June a 14% interest in ChapDrive, a technology company that has developed a patented system for hydraulic power transfer for wind and tidal turbines. ChapDrive has its origins in the Norwegian University of Science and Technology in Trondheim.

Statoil sees great potential in deep sea sited turbines, according to the CEO of its newly created energy business unit, which will benefit from the company’s strong foundation of offshore expertise. The investments in Sway and ChapDrive are its first direct investment in the development of wind power.

The Sway concept, which is covered by several patents, is based on achieving a centre of gravity well below the center of buoyancy of the tower by suspending ballast at the end of an elongated strut extending from the base of the tower far below the water surface. This confers on the tower sufficient stability to resist the wind loads and weight of the wind turbine placed on top of the tower.

The system is a floating foundation capable of supporting a 5 MW wind turbine in water depths from 80 m to more than 300 m in some of the world's roughest offshore locations. Motion at the top of the tower is confidently expected to be of sufficiently low amplitude to allow the wind turbine to function efficiently.

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Norsk Hydro's demonstration project is currently being planned to be based on windmills that reach 80 m above the surface and have a rotor diameter of 90 m

When the company’s patented ‘active thrust control system’ is added in, cost effective offshore floating wind turbines in the world's roughest locations should now be feasible.

The system has so far been designed to withstand the fatigue loadings of 25 years in service in rough deep-water areas. The system should also be able to withstand a single maximum 100 year wave height of above 30 m with stress levels below 60% of permissible and with small maximum accelerations.

The Sway system is not the first of its type to be modelled, nor the first conceptual design – so there is no shortage of skeptics among designers and academics, some of whom express doubts that tethering and stability will stand up to rough seas – but it may well be the first to proceed from investment project status to working large scale prototype. Another serious contender has been backed by Vorsk Hydro, who in 2005 announced plans for a prototype (illustration, above), called Hywind, that was intended as the foreruner of machines with a 660 foot tall tower, tethered to the sea floor, supporting 95 foot blades. A scaled-down 3 MW demo with 14 foot blades was planned for this year, leading eventually to parks of perhaps 200 windmills, in waters 700-2200 feet deep. In the autumn of 2005, Hydro tested its floater in different wind and wave conditions at Sintef Marintek’s sea laboratory. The results indicated that the concept can withstand extreme weather conditions, and Hydro therefore decided to proceed with the research project. But there is a final spin - since Hydro and Statoil are in the process of merging, it is at least possible that their technologies will merge also.

Hywind was awarded in September 2006 a concession from the Norwegian Water Resources and Energy Directorate allowing them to locate a floating windmill in the area of sea offshore Karmøy in order to carry out the extensive R & D that is still required for the concept to become commercially available. Hydro is still considering a possible full scale demonstration project.

The development by a joint venture of Arcadis, Deutsche Bank, GHF/Ventotec and Vestas of the Ventotec II site in 45 m of water off Rügen island in the Baltic may well be the first to prove this technology. The pilot site received offshore approval from the German Federal Office for Sea-going Vessels (BSH) in May and the consortium hopes to start construction in 2008. If the site, which will ultimately contain 80 units of output varying from 2 to 5 MW, goes well, a development to 600 MW will follow. The technology depends on floating foundations of an Arcadis/Vestas design that has been tested at a simulation plant and is, like the other designs, expected to halve the costs of foundation construction and significantly reduce O & M costs owing to complete on shore pre-production and the prospect of towing in to dry dock for repair work.

Turbines look like aircraft

Scottish Power’s renewables division, whose public image suffered somewhat last year when it applied to be granted compulsory purchase powers to acquire land for wind-farm schemes in Scotland, has awarded £330 million in contracts for wind turbines and civil engineering work for its Whitelee windfarm on Eaglesham Moor near Glasgow, the biggest project of its kind in Europe, to Morrison Construction and Balfour Kilpatrick for site infrastructure works including 90 km of access roads and turbine foundations. Siemens will build the 140 turbines for the 322 MW site.

The windfarm is scheduled to be built in 2009, but a stuttering permitting has been delaying matters and only speeded up when the company helped develop a novel solution to ease concerns about wind turbine interference with radar.

Airport operator BAA, which had held up the project for two years over air traffic control concerns, has now withdrawn its objection to the plan. BAA, working closely with National Air Traffic Services and ScottishPower, developed an innovative solution for the 21 square mile farm. BAA had opposed the plan over concerns that the 140 giant turbines could make planes coming in to land at Glasgow airport on a key approach 'disappear' from radar screens. The farm's wind turbines look like aircraft on the airport radar systems at Glasgow. But a solution has been found – an additional primary radar system costing about £5m will be built nearby to track aircraft directly above Whitelee. Data from Kincardine will be fed into a new radar display system at the airport where it will be merged with the data from the existing radar to provide an acceptable service for air traffic control. BAA says the system has been tested successfully in recent months and is thought to be the first of its kind to be implemented. It is believed it could offer a solution to similar problems elsewhere.

ScottishPower chief executive Philip Bowman said: “Whitelee is just the beginning. We also have large projects such as Harestanes (210 MW) and Arecleoch (180 MW) currently in planning and intend to spend £1 billion on onshore wind projects by 2010."

But the bullish attitude of UK companies conceals a deep lying dissatisfaction with the permitting process, which is causing months or years of what developers believe are unnecessary delays. The British Wind Energy Association meeting in October last year was treated to many such complaints. Philip Bowman, the chief executive, told the 1000-plus delegates that it took 50 months to win planning consents for Whitelee, and UK government promises to streamline planning consents have so far produced few tangible results.

Giant project in Texas (where else?)

Shell WindEnergy Inc. and Luminant, the recently renamed energy business subsidiary of TXU Corp, have signed a joint development agreement for a 3000 MW wind project in Briscoe County southeast of Amarillo in the Texas Panhandle region of the Texas High Plains. The deal commits both sides to work together on other renewable energy projects in the state.

Shell and Luminant will also explore the use of compressed air storage, by which excess power could be used to compress air underground for later use in generating electricity. This supply smoothing technology becomes more economical with large-scale projects such as that proposed for Briscoe County.

Recent testimony by Shell before the Public Utility Commission of Texas asserted that the Briscoe County project could deliver the lowest-cost wind energy for consumers, driven by excellent wind resources and the comparatively lower cost of bringing its power to market in the Panhandle region.

Briscoe County is not the only project being mooted for Texas, whose electricity regulators voted in July to designate suitable zones as the best sites for construction of new power lines to serve more than 25 GW of proposed new wind generation, 1500 MW of it scheduled to be completed this year. After evaluating the potential for wind-generation in about 25 areas in the state, the Texas Public Utility Commission agreed to designate eight areas as ‘Competitive Renewable Energy Zones’ or CREZ zones, said PUC spokesman Terry Hadley. Once finalised, the commission ruling will allow the state's electricity grid operator to begin studies of specific transmission routes for power lines to serve proposed wind farms to be built by other firms.

‘It is an astonishing testament to the wind resources available in our state to have aggregate expressions of interest in constructing 24 511 MW of wind generation’ PUC chairman Paul Hudson said in a memo. Texas supplanted California last year as the US state with, at more than 2300 MW, the most wind generation, but future development has been hampered by the lack of transmission lines to move power from the windy, western half of Texas to more populated areas in the eastern half of the state. The CREZ process will integrate transmission planning with new generation projects.

Flying windmills

There are companies in the US, Netherlands and Canada testing prototypes of what seems at first a far-fetched idea – flying windmills, tethered to the ground, that tap jet stream wind currents. The main advantages would seem to be fairly obvious – greater winds speeds, greater swept area, more constant source: and also the down side – the tether as a hazard, possible loss of control, the weight of the cable and rotor/generators. But if successfully developed, they could harness an enormous amount of power, although perhaps not as much as David Shepard, president of renewable energy startup Sky WindPower, in California, suggests. ‘If we were able to tap 1% of the wind energy at high altitude, that would be enough to supply all the world's energy needs’ he says.

The drawing (below) shows his concept. The ‘Flying Electric Generator’ takes off like a helicopter, powered by its electric cable tether, then feeds power back once it catches the wind at altitude.

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Running attitude of the Roberts Flying Electric Generator rated at 240 kW. (Preliminary working drawings by Ben Shepherd)

Shepard says he plans to begin building a 220 kW prototype later in 2007, and hopes to have it flying at 4500 m by the summer of 2009. The current prototype is based on an earlier model that was first flown in the 1980s by Sky WindPower's chief engineer, Bryan Roberts of Sydney’s University of Technology.

If the vision becomes reality, clusters of the devices will soon be flying at heights up to 9000 metres, providing renewable energy at a price that out-competes all other fuels, according to the inventors.

Renewable energy start-up Magenn Power says high-altitude jet stream currents are not worth the trouble, mainly because of the weight of the cable.. They are putting their faith in the plentiful wind power in the 180 to 300 metre range. The company uses a helium-filled balloon with curved fins that harnesses this lower altitude wind, causing the aircraft's midsection to spin, which runs generators at each end. The company’s first trial of its MARS project, a 3 x 7 m prototype, flew in 2006 but was too small to carry the weight of the generators. They now hopes to build a much larger balloon capable of lifting 1100 kg, and ultimately to target generating needs in remote areas, possibly working in conjunction with diesel sets.

Sandbank 24 - a warning

Sandbank 24 offshore wind farm in the North Sea off Germany is one of the most ambitious projects of its kind worldwide. It is being developed by the Oldenburg-based company Projekt GmbH and international financial investor Greenoak, in several phases starting with a pilot phase of 80 turbines of the 5 MW class and progressing in further development stages to a total of 980 turbines, nearly 5 GW. It was approved by the BSH (the German shipping authority) in August 2004, and preparatory construction work was set to start in 2008, with erection of the first turbines planned for 2009.

But in recent years, various factors have meant that the time plan for realisation of the giant project, has – like parks planned by others in the North and Baltic Seas – had to be adjusted to meet changed conditions.

Now the developer has stated that the framework conditions in Germany are not sufficiently helpful to make construction of offshore wind farms economically viable. Which means that although Sandbank 24 is well advanced in the complex permitting process, further progress depends on national policy developments. To help it along, wind energy planners and associations in October last year drew up a policy paper demanding a market incentive programme so that the ‘wind world champion’ does not fall behind internationally. With the German Energy law due for renewal soon, the industry awaits developments with bated breath.

Two firsts for Belgium
Thornton Bank, the first Belgian offshore project, achieved financial closure in May. The plant is being built by C-power and will consist of 60 x 5 MW turbines on the Thornton sandbank 28 km off the Belgian coast near Zeebrugge, in water ranging from 12 to 27 metres deep. A 37 km 150 kV sea cable will connect park to shore.

The farm is also believed to be the first non-recourse financed windfarm in the world. Allen & Overy LLP advised C-Power on a non-recourse r111 million senior and r20 million mezzanine facility for the financing of the first phase. The long term facilities are fully underwritten by Dexia, and are expected to be syndicated in the near future. The subordinated facility is provided by Rabobank.

The project, owned and developed by group companies of Dredging International, Ecotech Finance, EDF Energies Nouvelles, NUHMA and Socofe, is to be built by REpower Systems and Seawind (a consortium of Dredging and Fabricom GTI), with the 38.7 km 150 kV sub-sea cable supplied by ABB. Construction is starting in the spring and is expected to be completed by October 2008, for a total investment cost of r153 million.

Harbour front property

US maker Clipper is to supply seven of its Liberty 2.5 MW turbines to replace the nine currently sited at Blyth harbour in the UK. However, there will be a visable change. The new windmills are, at 125 m, three times as tall as the existing 42.5 m units, and much more powerful. The Clipper units are the largest units by capacity made in the USA and this is their first outing abroad. They are of a unique design, too. Each nacelle has four generators, and the windmill can continue to operate even if one generator breaks down.

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Clipper and BP last year entered into a strategic alliance for a long-term turbine supply agreement and the joint development of five of Clipper’s wind energy projects in the USA with an anticipated total generating capacity of 2015 MW in New York, Texas, and South Dakota. BP will order up to 2250 MW of additional Clipper turbines for its global wind portfolio.

UpWind progress

UpWind is an EU financed R&D effort to develop and verify substantially improved models of the principal wind turbine components, which the industry needs for the design and manufacture of wind turbines for future very large-scale applications – for example offshore wind farms of several hundred MW. The wind turbines needed will be very large (>8-10 MW and rotor diameter > 120 m), but present design methods and the available components and materials do not allow such up-scaling. In order to achieve the necessary up-scaling before 2020, full understanding of external design conditions, innovative materials with a sufficient strength to mass ratio, and advanced control and measuring systems are essential.

In 2003, European companies supplied 90% of the global market for wind power technology. UpWind will expect to help in maintaining that position and realising EU renewable electricity targets for 2010.

The project brings together the most advanced European specialists and experience. In the short year since work started in earnest significant new information and insights have been achieved. To give a few examples, it has been discovered that deflection of blades has a significant influence on aerodynamic behaviour, and that trailing edge deformation is an interesting option for blade control (see ‘Applying memory metal’, p24); it also provides a promising approach for more accurate modelling of wave loading. Individual blade control could reduce dynamic loads considerably, on blades between 10 and 30%, on hub and shaft by 20 to 40%.

Other areas of interest include investigation of what exactly causes the observed dramatic changes in output of individual wind turbines in response to very small changes in conditions; general work on large farms, both offshore and in complex terrain, which has been brought forward in response to the urgent needs of owners and operators; and two promising concepts for distributed aerodynamic control techniques, based on smart materials and structures (shape memory alloys and piezo-electric elements).




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