Figure 62 Installation vessel Seajacks Scylla, courtesy of Seajacks.
Function
Turbine installation involves transportation of the turbine components from the Construction port [I.7] and installation of the turbine components onto the foundation.
What it costs*
About £132 million for a 1 GW wind farm.
Who supplies them
A2Sea/GeoSea (DEME Group), Fred. Olsen WindCarrier, Jan de Nul, MPI Offshore, Newwaves Solutions, Seajacks, Statkraft UK, Swire Blue Ocean and Van Oord Offshore Wind.
Key facts
Installation methods vary depending on the turbine supplier and the relative size of turbine and vessel. Installation methodologies aim to reduce as far as practical offshore operations. Typically, the turbine tower is pre-assembled onshore and transported with the nacelle and blades for final assembly offshore.
Three variations in the rotor installation process have been used repeatedly:
- Placing the nacelle on the tower then lifting the pre-assembled rotor in one piece to mate with the nacelle (a single rotor lift)
- Mounting the hub and two blades on the nacelle “bunny ears” at port, before mounting the nacelle on the tower onsite and then fitting the final blade, and
- Placing the nacelle plus hub on the tower then lifting individual blades to mate with the hub, turning the rotor each time to repeat the same lift three times.
The third method is current preferred practice, even though this involves more offshore operations.
Tower sections are typically preassembled onshore with any internal components and the completed structure is transported vertically to site for installation. Offshore turbine installation is undertaken by jack-up vessels due to the need for a stable platform to perform offshore lifting operations and mating of components at height.
The installation of a turbine from positioning the vessel at the site to departure takes about 24 hours, depending on location and weather conditions. The cycle time is between 1.5 and 4 days, depending on the project (factoring in mobilisation, demobilisation, loading and waiting on weather).
A constraint during transportation and installation is the acceleration limit defined by the turbine supplier to avoid damaging the turbines and invalidating warranties. This is typically about 0.5g.
Blade installation is constrained not only by the operating range of the vessel but also the wind speeds, and the limit has been gradually increased with innovations in blade lifting equipment. The current maximum is normally 13 m/s at hub height and any increases beyond this may be limited by health and safety risks.
Turbine installation is beginning to be explored through the use of floating vessels for turbine component installation, which aims to shorten installation times further. The movements of the lifting hook at hub heights greater than 110 m on a floating vessel have the potential to be substantial, however. Progress on floating installation methodologies will depend on collaboration between turbine suppliers and installation contractors.
Turbine installation is undertaken jointly by the turbine supplier technicians and the installation contractor. The turbine supplier is usually responsible for the lifts along with mechanical and electrical completion.