Floating wind turbine
Floating wind parks are wind farms that site several floating wind turbines closely together to take advantage of common infrastructure such as power transmission facilities.
History
The concept for "large-scale offshore floating wind turbines was introduced by Professor William E. Heronemus at the University of Massachusetts in 1972. [I]t was not until the mid 1990’s, after the commercial wind industry was well established, that the topic was taken up again by the mainstream research community."[1] As of 2003, existing offshore fixed-bottom wind turbine technology deployments had been limited to water depths of 30-meters. Worldwide deep-water wind resources are extremely abundant in subsea areas with depths up to 600 meters, which are thought to best facilitate transmission of the generated electric power to shore communities.[1]
Operational deep-water platforms
As of 2009, there have been only two operational floating wind turbines used to farm wind energy over deep-water.
Blue H deployed the first floating wind turbine 113 kilometres (70 mi) off of the coast of Italy in December, 2007. It was then decommissioned at the end of 2008 after completing a planned test year of gathering operational data.[5]
The first large-capacity, 2.3 megawatt floating wind turbine is Hywind, which became operational in the North Sea off of Norway in September 2009,[6] and is still operational as of October 2010.[7]
Blue H Technologies
Blue H Technologies of the Netherlands operated the first floating wind turbine,[7] a prototype deep-water platform with an 80-kilowatt turbine off of Puglia, southeast Italy in 2008.[8] Installed 21 km off the coast in waters 113 meters deep in order to gather test data on wind and sea conditions, the small prototype unit was decommissioned at the end of 2008. Blue H has successfully decommissioned the unit as it embarks on plans to build a 38-unit deepwater wind farm at the same location.[5]
The Blue H technology utilizes a tension-leg platform design and a two-bladed turbine. The two-bladed design can have a "much larger chord, which allows a higher tip speed than those of three-bladers. The resulting increased background noise of the two-blade rotor is not a limiting factor for offshore sites."[5]
As of 2009, Blue H is building the first full-scale commercial 2.4 MWe unit in Brindisi, Italy which it expects to deploy at the same site of the prototype in the southern Adriatic Sea in 2010. This is the first unit in the planned 90 MW Tricase offshore wind farm, located more than 20 km off the Puglia coast line.[5]
Hywind
The world's first operational deep-water floating large-capacity wind turbine is the Hywind, in the North Sea off of Norway.[6][9] The Hywind was towed out to sea in early June 2009.[10] The 2.3 megawatt turbine was constructed by Siemens Wind Power and mounted on a floating tower with a 100 metre deep draft. The float tower was constructed by Technip, and Nowitech contributed to the design.[11][verification needed] Nowitech (Norwegian Research Centre for Offshore Wind Technology) is a consortium of 30 members, including SINTEF and the Norwegian University of Science and Technology at Trondheim.[12] Statoil says that floating wind turbines are still immature and commercialization is distant.[11][13]
The installation is owned by Statoil and will be tested for two years. After assembly in the calmer waters of Åmøy Fjord near Stavanger, Norway, the 120-meter-tall tower with a 2.3 MW turbine was towed 10 km offshore into 220-meter-deep water, 10 km southwest of Karmøy, on 6 June 2009 for a two year test deployment."[8] Alexandra Beck Gjorv of Statoil said, "[The experiment] should help move offshore wind farms out of sight ... The global market for such turbines is potentially enormous, depending on how low we can press costs."[14] The unit became operational in the summer of 2009.[6] Hywind was inaugurated on 8 September 2009.[15][16] As of October 2010, after a full year of operation, the Hywind turbine is still operating and generating electricity for the Norwegian grid.[7]
The turbine cost 400 million kroner (around US$62 million) to build and deploy.[17][18] The 13-kilometer (8-mile) long submarine power transmission cable was installed in July, 2009 and system test including rotor blades and initial power transmission was conducted shortly thereafter.[19] The installation is expected to generate about 9 GW•h of electricity annually.[20] The SWATH (Small Waterplane Area Twin Hull), a new class of offshore wind turbine service boat, will be tested at Hywind.[21]
Topologies
Platform topologies can be classified into:
• single-turbine-floater (one wind turbine mounted on a floating structure)
• multiple turbine floaters (multiple wind turbines mounted on a floating structure)
Engineering considerations
Undersea mooring of floating wind turbines are accomplished with three principal mooring systems. Two common types of engineered design for anchoring floating structures include tension-leg and catenary loose mooring systems. Tension leg mooring systems have vertical tethers under tension providing large restoring moments in pitch and roll. Catenary mooring systems provide station keeping for an offshore structure yet provide little stiffness at low tensions."[22] A third form of mooring system is the ballasted catenary configuration, created by adding multiple-tonne weights hanging from the midsection of each anchor cable in order to provide additional cable tension and therefore increase stiffness of the above-water floating structure.[22]
Economics
"Technically, the [theoretical] feasibility of deepwater [floating] wind turbines is not questioned as long-term survivability of floating structures has already been successfully demonstrated by the marine and offshore oil industries over many decades. However, the economics that allowed the deployment of thousands of offshore oil rigs have yet to be demonstrated for floating wind turbine platforms. For deepwater wind turbines, a floating structure will replace pile-driven monopoles or conventional concrete bases that are commonly used as foundations for shallow water and land-based turbines. The floating structure must provide enough buoyancy to support the weight of the turbine and to restrain pitch, roll and heave motions within acceptable limits. The capital costs for the wind turbine itself will not be significantly higher than current marinized turbine costs in shallow water. Therefore, the economics of deepwater wind turbines will be determined primarily by the additional costs of the floating structure and power distribution system, which are offset by higher offshore winds and close proximity to large load centers (e.g. shorter transmission runs)."[1]
As of 2009 however, the economic feasibility of shallow-water offshore wind technologies is more completely understood. With empirical data obtained from fixed-bottom installations off many countries for over a decade now, representative costs are well understood. Shallow-water turbines cost between 2.4 and 3 million United States dollars per megawatt to install, according to the World Energy Council.[8]
As of 2009, the practical feasibility and per-unit economics of deep-water, floating-turbine offshore wind is yet to be seen. Initial deployment of single full-capacity turbines in deep-water locations began only in 2009.[8]
As of October 2010, new feasibility studies are supporting that floating turbines are becoming both technically and economically viable in the UK and global energy markets. "The higher up-front costs associated with developing floating wind turbines would be offset by the fact that they would be able to access areas of deep water off the coastlne of the UK where winds are stronger and reliable." [23]
The recent Offshore Valuation study conducted in the UK has confirmed that using just one third of the UK's wind, wave and tidal resource could generate energy equivalent to 1 billion barrels of oil per year; the same as North Sea oil and gas production. Some of the primary challenges are the coordination needed to develop transmission lines.[24]
Proposals
Floating wind farms
The US State of Maine solicited proposals in September 2010 to build the world's first floating, commercial wind farm. The RFP is seeking proposals for 25 MW of deep-water offshore wind capacity to supply power for 20-year long-term contract period via grid-connected floating wind turbines in the Gulf of Maine. Successful bidders must enter into long-term power supply contracts with either Central Maine Power Company (CMP), Bangor Hydro-Electric Company (BHE), or Maine Public Service Company (MPS). Proposals are due by May 2011.[25] [26]
Some vendors who could bid on the proposed project have expressed concerns about dealing with the United States regulatory environment. Since the proposed site is in Federal waters, developers would need a permit from the Minerals Management Service, "which took more than seven years to approve a yet-to-be-built, shallow-water wind project off Cape Cod," and is also the agency under fire in June 2010 for lax oversight of deepwater oil drilling in Federal waters. "Uncertainty over regulatory hurdles in the United States ... is 'the Achilles heel' for Maine's ambitions for deepwater wind."[26]
Floating design concepts
WindFloat
WindFloat is a patent pending floating foundation for offshore wind turbines aimed at improving dynamic stability. The WindFloat design is intended to dampen wave and turbine induced motion utilizing a tri-column triangular platform with the wind turbine positioned on only one of the three columns. The triangular platform is then "moored with 6 lines, 4 of which are connected to the column stabilizing the turbine, thus creating an asymmetric" mooring to increase stability and reduce motion.[27] This technology could allow wind turbines to be sited in offshore areas that were previously considered inaccessible, areas having water depth exceeding 50 meters and more powerful wind resources than shallow-water offshore wind farms typically encounter.[28]
As of 2010, Principle Power and electricity provider Energias de Portugal is utilizing the WindFloat design to construct a "three-legged floating foundation designed to accommodate any 5 MW turbine." Completion of construction and installation off of Portugal is expected by the end of summer 2012. Construction cost is expected to be below $30 million.[7]
Nautica Windpower
Nautica Windpower uses a patented technology aimed at reducing system weight, complexity and costs for deep water sites. Scale model tests in open water have been conducted and structural dynamics modeling is under development for a multi-megawatt design.[29] Nautica Windpower's Asymmetric Floating Tower (AFT) uses a single mooring line and a downwind two-bladed rotor configuration that is deflection tolerant and aligns itself with the wind without an active yaw system. Two-bladed, downwind turbine designs that can accommodate flexibility in the blades will potentially prolong blade lifetime, diminish structural system loads and reduce offshore maintenance needs, yielding lower lifecycle costs. [30]
OC3-Hywind
The European Wind Energy Association (EWEA), under the auspices of their Offshore Code Comparison Collaboration (OC3) initiative, has completed high-level design and simulation modeling of the OC-3 Hywind system, a 5-MW wind turbine installed on a floating spar buoy, moored with catenary mooring lines, in water depth of 320 meters. The spar buoy platform would extend 120 meters below the surface and the mass of such a system, including ballast would exceed 7.4 million kg. [31]
DeepWind
Rise and 11 international partners started a 4-year program called DeepWind in October 2010 to create and test economical floating Vertical Axis Wind Turbines up to 20MW. The program is supported with €3m through EUs Seventh Framework Programme.[32][33] Partners include TUDelft, SINTEF, Statoil and United States National Renewable Energy Laboratory
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