Figure 63 Lifting of third blade during turbine installation, courtesy of Seajacks.
Function
The turbine installation vessel transports the turbine components to site and supports the erection of the turbine on the foundation. Similar jack-up vessels are used to those for foundation installation.
What it costs*
These costs are typically included in the turbine installation contract. A turbine installation vessel for a 1 GW wind farm costs about £98 million.
Who supplies them
Operators: A2Sea/GeoSea (DEME Group), Fred. Olsen WindCarrier, Jan de Nul, MPI Offshore, Seajacks, Swire Blue Ocean and Van Oord Offshore Wind.
Vessel manufacturers: generally in China, Korea, Singapore or the Arabian Peninsula.
Key facts
Recent turbine installation on commercial-scale projects to date has normally been undertaken with a self-propelled jack-up vessel designed primarily for the purpose, though in some cases, jack-up barges have been towed with tugs.
Vessel contracts are typically placed by the wind farm developer or the turbine supplier.
An example of specification for these vessels is:
- Length: 130 m, Beam 40 m, Draft 5 m
- Crew berths: 100
- Crane: 1,500 t
- Carrying capacity: 9,300 t
- Maximum transit speed: 12 knots
- Jack-up depth: 45 m
- Wind turbine component capacity: 5 sets
- Number of jack-up legs: 4-6
- Jack up speed: 1 m/min, and
- Dynamic positioning system (DP2).
Most of the vessels in operation have been used for both turbine and foundation installation. Increasingly the fleets are diverging. The increase in turbine capacity (and therefore rotor diameter) is associated with a higher hub height. At the same time, foundation mass is increasing and they can now be installed more rapidly from a floating vessel.
Investment in new vessels requires careful consideration due to:
- Developments in turbine size are associated with a declining vessel market because vessel carrying capacity in MW increases with turbine rating and installation time per MW drops
- Turbine ratings are likely to continue to increase, meaning that vessels become obsolete for installation, and
- Investment costs for a vessel suitable for turbine and foundation installation are high but lower cost vessels can only target one or other of the markets.
A number of vessel cranes have undergone modification but unless upgrades were considered in the original design, they can have an impact on other aspects of the vessels’ performance.
Feeder vessels could be used to limit the transit time of the main installation vessel but this is only likely to be cost effective if the transfer of turbine components from low cost floating feeder vessels can be achieved without increasing risk and if the feeder vessel has a considerably lower charter rate than the main installation vessel.
Floating vessels are considered a natural next step for turbine installation, offering theoretically faster installation than jack-ups. Hook height movements at 110 m or higher can be important, thereby limiting the operability of the vessel for installation work. A floating installation vessel could also be used efficiently for foundation installation thereby reducing investment risk.
Vessels no longer suitable for turbine installation in Europe could be further utilised in the service market and in new installation markets such as Asia, where turbine size has so far lagged behind that in Europe.
What’s in it
- Crane
- Auxiliary cranes
- Dynamic positioning system