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Support structure concepts for offshore wind turbines

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Saturday 3. September 2011 - 0 comments on this article

Jacket structures on their way to site. Photo: Alpha Ventus

Jacket structures on their way to site. Photo: Alpha Ventus

No less than 104 different types of support structures competed when in 2009 the UK fund Carbon Trust set out to find the most cost effective. But even though the variety is large, support structure concepts are basically divided into two groups: Floating or Grounded.

Floating concepts imply that the support structure transfers loads and forces to the water, not the soil. Connection to the soil only ensures that the support structure stays in place.

Grounded concepts imply that the support structure transfers all loads and forces to the seabed.

The figure shows an overview of the types of structures and foundations. See the article 'What is the support structure' for more definitions, e.g. on the distinction between support structure and foundation.

The typology of support structures and foundations. Access articles about the different types via the menu to the left on this page

The different types of foundations and support structures for Offshore Wind Turbines (OWT). The overall dominant one is the monopile, which is both piled in foundation and support structure. Illustration: LORC

The two concepts have strong differences, which make them applicable for various environments. Speaking generally, the pros and cons of floating concepts are:

  • Pro: Large water depths – theoretically no limit
  • Pro: Floating structures allow full fabrication at shipyard and transport to site in one piece.
  • Con: Very expensive construction
  • Con: Commercially uninteresting for many countries with large areas of shallow water

The pros and cons of grounded concepts are:

  • Pro: Less expensive
  • Pro: Large potential with water depths up to 50 meters or even deeper.
  • Con: Expensive transportation and installation
  • Con:  Most types have only been installed in water < 25 meters.

Monopiles rule – so far
On the grounded concepts, the two major types used are the piled foundations and gravity-based foundations. The monopile is the most dominant, because of its simplicity in fabrication and installation. However, at large water depths the foundation is piled, but the support structure is more complex, i.e. a jacket or a tripod structure.

Gravity-based support structures are the second major type at the moment, but they lack the potential for large water depths. This is because when the water depth increases, the mass of the gravity-based foundation also has to increase, which leads to problems for transportation and installation.

However, the gravity-based foundations are simple to produce – although they require a large mass. Thereby they become very stable and experience no lifting between the seabed and the support structure.

For more details on each support structure concept, click the articles in the menu.

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Offshore Wind Statistics

Commissioned Sites by Developer/Owner

Operator Sites
DONG Energy 12
Vattenfall 7
E.ON 4

Comissioned Sites by turbine manufacturer

Turbine Manufacturer Sites
Vestas Wind Systems 16.83
Siemens Wind Power 14
Bonus Energy 4.83

Installed Capacity by Country

Country MW %
United Kingdom 1,858.4 49.73
Denmark 871.45 23.32
Netherlands 246.8 6.6

Installed Capacity by commissioned site

Site MW
Thanet 300
Horns Rev 2 209.3
Rodsand 2 207

Installed Capacity by Operator

Operator MW %
DONG Energy 1,163.25 31.13
Vattenfall 830.9 22.24
E.ON 451 12.07

Installed Capacity & Number of Turbines by turbine manufacturer

Manufacturer
Model
MW %
Siemens Wind Power
Siemens SWT-3.6-107
Siemens SWT-2.3-93
Siemens SWT-3.6-120
Siemens SWT-2.3-101
Siemens SWT-2.3-82 VS
1,553.1
730.8
575
194.4
50.6
2.3
41.56
19.56
15.39
5.2
1.35
0.06
Vestas Wind Systems
Vestas V90-3.0 MW
Vestas V80-2.0 MW
Vestas V39-500 kW
Vestas V66-2.0 MW (Offshore)
Vestas V47-660 kW
1,393.32
957
426
5
4
1.32
37.29
25.61
11.4
0.13
0.11
0.04
Bonus Energy
Bonus 2.3 MW/82
Bonus 2.0 MW/76
Bonus 450 kW/37
245.05
200.1
40
4.95
6.56
5.35
1.07
0.13
 

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