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Updated: Vestas joins floating offshore wind turbine project

Vestas has joined the WindFloat Project for floating offshore wind turbine platforms using a semi-submersible structure.

By Renewable Energy Focus staff - updated with comments from Anders Søe-Jensen, President Vestas Offshore.

Vestas will supply a V80 2 MW wind turbine to WindPlus, a joint venture led by the EDP Group with partners including Principle Power Inc.

Vestas will deliver, install and commission the wind turbine, which will be located off the shore of Portugal in 2011. Vestas will also support the integration of the wind turbine and the WindFloat platform.

WindFloat specifications

  • Power rating ≈ 3.6-10MW
  • Rotor diameter ≈ 120-150m
  • Turbine hub height ≈ 80-90 m
  • Turbine nacelle weight ≈ 225-315 tonne
  • Tower weight ≈ 180-315 tonne
  • Hull Weight ≈ 1080-1600 tonne
  • Total Displacement (w/ballast) < 5500 tonne
  • Hull Draft ≈ 20 m
  • Operational Water Depth > 50 m
  • Conventional mooring components (4 lines)
(Source: Principle Power)

The WindFloat semi-submersible floating structure for offshore wind turbines is said to dampen wave and turbine induced motion, enabling the siting of offshore wind turbines previously inaccessible where water depths exceed 50 m.

The system will be tested for at least one year focusing on performance, validation of the WindFloat and turbine control optimisation.

Anders Søe-Jensen, President Vestas Offshore, says: “Provided that the project outcome is successful, we believe that it can reinforce the already existing offshore wind industry and thereby help countries around the world increase their wind energy penetration levels and raise their energy independence.”

WindFloat

The floating offshore wind turbine platform is fitted with patented water entrapment (heave) plates at the base of each column, which dampens water effects.

Furthermore, WindFloat's closed-loop hull trim system mitigates mean wind-induced thrust forces, Principle Power says. This secondary system ensures optimal energy conversion efficiency following changes in wind velocity and direction.

The mooring system employs conventional components such as chain and polyester lines. Through the use of pre-laid drag embedded anchors, site preparation and impact is minimised, the company adds.

The Hywind project

Siemens together with Statoil of Norway are also working on floating offshore wind turbine platforms with their Hywind project. A prototype is currently located 12 km off the south east coast of Karmøy, Norway, at a water depth of about 220 m.

The floating structure consists of a steel floater with ballast. The floating element extends 100 m beneath the surface and is fastened to the seabed by three anchor wires. On top is a Siemens SWT 2.3 MW offshore wind turbine.

Hywind is designed to be suitable for water depths of 120-700 m.

Two very different concepts

Talking to Renewable Energy Focus, Søe-Jensen explains that the two concepts are very different despite both being floating foundations: "The Hywind is basically a buoy that the turbine is standing on top of. [Whereas] this is sort of a tripod that can also operate in shallower water.”

He adds: “This is early days for floating foundations. We have Hywind, we have our projects, and a number of other projects. We also have another cooperation with a Norwegian institute – a university. And you see something happen in Spain, you see something happen in Italy, you also have some other experiments. It’s definitely interesting, but it’s still early days.

“It’s the market that picks the winner and the winner hasn’t been picked yet.”

Asked whether WindFloat will cover a market of depths between jackts and Hywind, Søe-Jensen says: "Yes and no. With jackets [it depends on] what size turbine you are putting on the jacket, because if the turbine is heavy enough, you require a jacket for shallow water.

“[WindFloat] can compete on deeper water, but also on shallower water than the Hywind concept. The Hywind concept requires relatively deep water.” In comparison, WindFloat can also work in shallower water depths of 30-50 m.

Søe-Jensen declined to comment on project costs.

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