Renewable Energy
Floating wind farms
The technology used in offshore oil and gas extraction is now making wind power installation in deeper waters possible.
O
ffshore sites are seen as the best option for wind farms. Not only is wind virtually guaranteed 24/7, but also installations out at sea alleviate any concerns about noise pollution and
damage to the beauty of the countryside. Until now offshore wind turbines have had to be firmly rooted on the seabed with large and costly subsea structures. Tings are changing, however, with the advent of Statoil’s innovative new offshore floating Hywind wind turbine, the first of which is now successfully moored in the North Sea off the Norwegian coast. Te Hywind turbine incorporates Trelleborg’s
syntactic foam (hollow glass microspheres embedded in a binder) buoyancy technology.
For Hywind, Trelleborg designed and supplied 45 polymer-coated syntactic foam distributed buoyancy modules (DBMs), which supply buoyancy support for a three-ton, 100-metre section of cable as it exits the turbine spar and descends to the seabed 220 meters below the surface. Te buoyancy modules include an internal clamp
for secure fastening and precise positioning on the cable. Te cable is supported mid-water in what is known as a ‘lazy wave’ configuration, featuring gentle, long radius curves that minimise stress on the cable while accommodating natural movement created by wind and waves. Trelleborg’s DBMs were originally developed for
deepwater support of umbilicals and risers in the oil and gas industry. “It is subsea technology that has already been
extensively proven,” says Howland. “People see the tower and turbine but forget that the expertise in designing the subsea portion is also critical, as ultimately it keeps the whole turbine afloat. We have seen many of the technical challenges before in the offshore oil and gas arena, so our engineers can quickly adapt proven solutions for use in offshore wind power generation. Tis will greatly reduce project risk and make development of the industry quicker and less costly.”
Keeping afloat For optimum buoyancy under different sea conditions, the precise position of Trelleborg’s 45 polymer-coated syntactic foam distributed buoyancy modules (DBMs) on the cable from the Statoil’s Hywind floating wind turbine is precalculated.
Fig. 1.Until now offshore wind turbines have had to be rooted on the seabed. Things are changing with the Statoil’s offshore floating Hywind wind turbine..
“It’s like the proverbial iceberg,” says Gary Howland, Renewables Sales Manager for Trelleborg Offshore. “Te mass floating below the surface ensures the stability of the wind turbine on the sea’s surface.” Without the support of properly designed buoyancy
the structure would be much less able to resist the extremes of the offshore environment, and the cable that anchors the turbine to the seabed could suffer premature damage.
Te positions must be maintained, despite stresses during launch and in operation. Te clamp is crucial; the design, material selection and manufacturing technique are critical in ensuring that the finished clamp maintains the buoyancy module position during cable contraction and expansion over the 20-year lifetime of the project. “Trelleborg has substantial expertise in operating
in deepwater marine and subsea environments, and a track record acknowledged by leading offshore engineering companies around the world,” says Trelleborg’s Gary Howland. “Te company has significant experience in the supply of DBMs, with more than 35 000 modules in service. Tis experience will be invaluable in the rapid establishment of the far- offshore renewables industry.” ●
For more information, visit
www.trelleborg.com www.engineerlive.com 55
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