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Floating Offshore Wind Power Taking Hold

Acknowledged as the leading nation in terms of offshore wind development, while it has failed to capitalize on opportunities for leadership in turbines, the UK has made efforts to avoid the same mistake when it comes to other aspects of offshore wind power. One area attracting considerable attention is floating offshore technology.

In July, the Crown Estate, the body which controls seabed licensing in UK territorial waters, called for expressions of interest in offshore wind off-grid projects as part of an offshore wind test and demonstration leasing program launched in June, including a leasing round for floating offshore wind.

Furthermore, the Estate also invited submissions for 'project variations'. It specifically notes: "Floating wind projects embedded within, or adjacent to, an existing project may be submitted as project variations."

In inviting industry to propose sites for the development of floating wind farms, a process expected take to up nine months, the Crown Estate said it hopes to facilitate early deployment of projects, which may allow some projects to commence construction as soon as 2017.

Successful projects will include arrays of up to fifteen machines, utilizing floating foundations and with less than 100 MW of installed capacity. The technologies involved must not have been previously deployed commercially and the projects must be used solely for test and demonstration purposes.

Commenting on the proposals, Martin Simpson, Head of New Energy and Technology at the Crown Estate said: "To unlock sustained growth in offshore wind we have to demonstrate that technological advancements can drive down costs."

He added: "Floating wind is included for the first time because of its future potential."

Of course, it's not just the UK that views the deep-water offshore sector as a notional gold mine of energy. While current commercial substructures are economically limited to maximum water depths of 40-50 meters, the European potential from relatively near-shore deep-water sites in the Atlantic, Mediterranean and deep North Sea waters is vast.

Indeed, a new report based on the work of the 'Deep offshore and new foundation concepts' Task Force, part of the European Wind Energy Association's (EWEA) Offshore Wind Industry Group, claims the energy produced from turbines in deep waters in the North Sea alone could meet the EU's electricity consumption four times over.

The document notes that deep offshore designs are competitive in terms of the levelized cost of energy (LCOE) with fixed foundations in more than 5O meters of water depth. And, though the technology is still at a very early stage of development if a number of technical, economic and political challenges are overcome; the first deep offshore wind farms could be installed and connected to the grid by 2017.

Floating Technology Development

According to EWEA, at the end of 2012 there were two full-scale grid-connected offshore wind turbines on floating substructures, Hywind and Windfloat, both in Europe. Hywind, developed by Statoil and installed in the North Sea off Norway in 2009, features a 2.3-MW Siemens turbine. Developed by Principle Power and EDP, Windfloat was installed in the Atlantic off Portugal in 2011 and uses a 2-MW machine from Vestas.

In addition, the report continues, seven experimental floating substructures have been or are under test. Those include SWAY, Blue H and Poseidon in Europe, Kabashima Island concept and WindLens in Japan and DeepCwind floating turbine in the U.S.

So far, deep-water offshore foundations have focused on three main types, adapted from the offshore oil and gas industry. The Spar Buoy, a cylindrical ballast-stabilized structure, as featured on Hywind concept; the Tension Leg Platform, in which a semi submerged buoyant structure is anchored to the seabed with tensioned mooring lines; and the Semi-submersible - used on the Wind-Float concept - which combines a semi-submerged structure with tension leg-type moorings.

One recent development in this area came from Glosten Associates, which completed scale-model testing of the PelaStar tension-leg platform (TLP) in June 2013. The next phase of the project will see the building and installation of a full-scale 6-MW floating turbine, explained William Hurley, PelaStar Director and Glosten program lead.

Overall, EWEA notes that in addition to the two full-scale deep offshore turbines, there are three grid-connected experimental floating substructures and thirty-five deep-water designs under development worldwide.

Of these 40 deep water wind projects identified by EWEA, more than 60 percent are located in Europe, in nine countries: Denmark, France, Germany, the Netherlands, Norway, Portugal, Spain, Sweden and the UK. A further four are in the U.S. and nine are in Japan.

Beyond European Seas

Despite the apparent disparity between Europe and those playing catch-up, there are encouraging signs from both the United States and Japan.

A consortium led by Marubeni Corporation, and including the University of Tokyo, Mitsubishi Corporation, Mitsubishi Heavy Industries, Japan Marine United Corporation and Hitachi, have been participating in an experimental offshore floating wind farm project sponsored by Japan's Ministry of Economy, Trade and Industry since March 2012.

Consisting of a 2-MW Hitachi-manufactured turbine and a four column Semi-submersible support structure, delivery to the Fukushima installation site - located about 12 miles (20 km) offshore in 400 feet (120 meters) of water - is underway, along with the world's first 66 kV floating sub-station and associated undersea cable.

The group is planning to install two more 7-MW turbines with the trade ministry earmarking some of Y22 billion ($232 million) for the five-year project.

Scheduled to begin operation from October 2013, delivery of the facility and its mooring operation in the testing area is due any day, as is the laying and burying of the riser cable at the testing area.

Further support for floating wind turbines seems likely in Japan, in January's Budget Request some Y9.5 billion ($95 million) of new money was requested to establish the technology with a full-fledged demonstration project.

Meanwhile, in the U.S, mid-June saw the deployment of the country's first ever grid-connected floating wind turbine off the coast of Maine.

The VolturnUS 1:8 machine is the product of the DeepCwind Consortium, led by the University of Maine and backed through a research initiative funded by the U.S. Department of Energy, the National Science Foundation, and others. The group responsible for floating turbine design, material selection, and lab testing includes organizations such as the Maine Maritime Academy, Technic, National Renewable Energy Laboratory and Sandia National Labs, among others.

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Christopher Long, Manager of Offshore and Siting Policy for the American Wind Energy Association (AWEA) described the development as "another signal of steady progress toward development of an American offshore wind industry."

With the support of a $12 million Energy Department investment over five years, at 65 feet (20 meters) the VolturnUS prototype is a 1:8th scale of the planned 6-MW commercial version.

It features a semi-submersible platform using a concrete foundation, claiming lower costs, in addition to a composite tower. As part of the five-year project, the Maine Maritime Academy helped test and conduct analysis on the design while Cianbro Corp. constructed the system.

Late last year, the University's Advanced Structures and Composites Center was also awarded $4 million by the DoE to support another deep-water floating offshore wind research project. The program, known as Aqua Ventus I, will be a 12-MW demonstration wind park using VolturnUS machines.

The $4 million will cover the first phase of a potential $93.2 million of DoE support and the Composites Center was one of seven projects selected to complete the engineering, design and permitting phase.

Up to three of these projects are expected to be selected in 2014 for follow-on phases that focus on siting, construction and installation, with the aim of achieving commercial operation by 2017. The projects will receive up to $47 million each over four years, subject to Congressional appropriations.

Several floating turbine concepts are among the seven projects chosen for the first phase of this six-year initiative. These include a project from Statoil North America, which plans to deploy four 3-MW wind turbines on floating spar buoy structures in the Gulf of Maine off Boothbay Harbor at a water depth of approximately 460 feet (140 meters), although that project was recently put on hold. On the Pacific Coast, Principle Power plans to install five semi-submersible floating foundations outfitted with 6-MW direct-drive offshore wind turbines in deep water 10 to 15 miles (16-23 km) from Coos Bay, Oregon. These projects join DeepCWind's plans to install a pilot project with two 6-MW direct-drive turbines on concrete semi-submersible foundations near Monhegan Island in the 2015-2017 timeframe.

Setting the Standard

If any clearer indication were required that floating wind turbine technology is rapidly maturing, DNV KEMA recently released its new standard for such structures.

This follows the September 2011 launch of a Joint Industry Project (JIP) focused on floater-specific design issues, such as station keeping, site conditions in relation to low frequency motion, simulation periods, higher order responses and design of structural components. DNV KEMA has been joined on the project by the likes of Statoil, Nippon Steel & Sumitomo Metal Corporation, Gamesa, Iberdrola, Alstom Wind, Glosten Associates and Principle Power.

Commenting on the new standard and effectively summarizing the evolution of deep water wind, Johan Sandberg, head of renewable energy at DNV KEMA in Norway, remarked: "As demand for wind energy increases, we predict offshore deployments will continue to move into deeper waters and, consequently, there's a need to establish design standards that will help ensure safety, reliability, and confidence in future wind turbines.

"Recent successful deployments of full-scale prototype configurations have demonstrated that floating wind turbines can be a viable alternative and the market is taking notice.

"It is now time to take the next step: standardization," he concluded.

Image: Hywind on location via Trude Refsahl, Statoil

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