Wind turbine installation
The installation of the 84 wind turbines required the use of one of the world's largest turbine installation vessels, the Swire Blue Ocean owned and operated 'Pacific Orca' jack-up vessel pictured.
Each turbine comprises of:
Three tower sections pre-assembled at the Nigg construction and marshalling facility on the Cromarty Firth - a combine weight of around 292 tonnes
One nacelle which contains the generator weighing around 350 tonnes
Three 75m blades, each weighing around 26 tonnes
The Pacific Orca was able to carry five full turbines worth of components.
Construction and marshalling
The construction and marshalling facility at Nigg was utilised during the turbine installation phase.
All of the turbine components were delivered here ahead of installation where they could be assembled and tested ahead of being loaded on to the Pacific Orca vessel as shown here.
In the case of the towers, they were pre-assembled with three sections required for each turbine.
The Pacific Orca would arrive and then jack up on its six 100m tall legs a before loading five turbines worth of components.
Once the Pacific Orca arrived at each turbine location, it would position itself alongside the jacket and jack up as this image shows.
This provided a stable platform from which to undertake the turbine installation work.
This image shows an installed tower section on a jacket. The bridge linking the Pacific Orca to the jacket meant that the installation teams could 'walk to work' easily to undertake their tasks.
The installation team bolt the tower to the jacket and connect the various electrical elements including the internal lift which takes the technicians around 80m up followed by a short ladder climb to the top of the nearly 88m tall structure.
Installing the nacelle
The 350 tonne nacelle contains the generator and much of the electrical control equipment.
It also contains the systems required to turn the nacelle so that the turbine blades are always facing in to the wind.
At the top of the nacelle is a platform area where technicians can be winched to and from the turbine when conditions prevent safe access by vessel.
At the front of the nacelle is the hub on to which the three blades are attached.
The turbine blades, each 75m long and weighing 26 tonnes are then lifted and attached to the hub by around 100 bolts.
Once the first is attached, the hub is rotated so that the next one can be attached on the horizontal and the third is attached in the same manner.
The weather plays an important part in all of the lifting activities - if the wind is too strong, the lifting does not start until safe conditions are available.
24 hour operation
With the weather potentially preventing installation, the Pacific Orca operated around the clock to ensure that operations could continue whenever favourable conditions were available.
This image shows the installation of a turbine blade underway at night.
Once a turbine was complete, the Pacific Orca would jack down to sea level and either mover to the next location to repeat the installation process or head back to Nigg to pick up another load of turbine components.
The last turbine was installed on 15 May 2019.