All eyes are on Borkum Riffgrund 1, the 78-turbine DONG Energy wind farm for which both A2SEA and CT Offshore have been busily preparing. Located 37 kilometres to the north of the island of Borkum, the first monopile foundation for Borkum Riffgrund 1 wind farm was installed on 21 January 2014. Now, with foundations and transition pieces in place, it’s time for the teams at A2SEA and CT Offshore to swing into action, executing plans that have been carefully laid over many months.

For A2SEA, the load-out port for the project is the Gemini quay at the Port of Esbjerg – part of the Siemens Wind Power extensions to harbour facilities. For Borkum Riffgrund 1, the quayside has received extra attention, with the construction of a stone bed upon which to jack up for loading, as soil conditions in the area vary greatly and the seabed isn’t strong enough to support a heavy installation vessel.

Borkum Riffgrund 1 is located 114 nautical miles from the Port of Esbjerg, or around 15 hours for the vessel, SEA INSTALLER, in a straight line. Getting there is plain sailing for her, but vessel project operating conditions, it seems, are a little more difficult.

Some of that difficulty centres around the fact that the site lies relatively far out to sea, in an area where there are no islands or reefs to break the pattern of the swells. So, even though the wind speed may be within the limit for the marine operations, wave heights or periods may still approach or exceed the maximum. In addition to this phenomenon, the risk of scour around the legs at the wind farm site will require more attention than usual.

Power upgrade

Originally, the plan was to install seventy-seven 3.6 MW Siemens Wind Power wind turbine generators (WTG). During the planning phase, performance of the turbines was boosted to be able to deliver the equivalent of 4 MW in effect, raising the wind farm’s power output to a total capacity of 312 MW. Also during this phase, transport and installation of the 78th turbine, which will serve as a sea trial for a new suction bucket foundation, was added to A2SEA’s scope. But more on that later.

Integrating lessons learned

Despite the slightly larger size of the upgraded turbines, few new challenges were presented for A2SEA in comparison with previous projects.

The deck layout for Borkum Riffgrund 1, for example, is based upon West of Duddon Sands, the project SEA INSTALLER finalised just prior to the Borkum project. During mobilisation, which was carried out in Frederikshavn, Denmark, during June and July, minor changes were made to the layout in order to accommodate both the increased weight of the larger turbines and the desired improvements. At the same time, some of the nacelle positions were relocated, and a new nacelle-lifting beam was installed, along with a new lifting yoke for the towers. The lifting yoke’s design is particularly interesting because it enables Siemens Wind Power technicians to perform fewer manual tasks, which promotes safety.

Sea fastenings, however, required almost no modifications, adding to the efficiencies created by increased emphasis on project-to-project standardisation. In fact, the fastening had originally been designed for use with no less than three separate projects.

“We’ve been able to re-use plenty of the learnings gathered from two earlier projects, in particular,” says Britta Finnich-Henningsen, A2SEA’s project manager for Borkum Riffgrund 1. “Of course, we’re working in German waters, so we are especially aware of German regulations and local issues. And we’re also paying careful attention to the rough weather we expect to encounter in the North Sea where the wind farm will be located.”

Helicopter transfers

Due to the often rough sea conditions, the client has decided to use helicopters to transport representatives, technicians and crew to and from the vessel. The helicopters will be provided by Germany’s HTM Helicopter Travel Munich, based at airfields in Emden and Norddeich.

Naturally, where you have a helicopter you also need a place to land. So the project has been hard at work installing a helipad on board SEA INSTALLER, mounted on the starboard side. A heli-lounge was also established just below the bridge.

“Extra training is required for our crew before they are allowed to fly to and from the vessel, so we’ve had them attending a HUET (Helicopter Underwater Evacuation Training) course,” says Britta. “And the officers on board were required to take an HLO (Helicopter Landing Officer) course to enable landing on an offshore helideck in the first place.”

When commissioned, Borkum Riffgrund 1 wind farm will be able to supply sustainable power annually for some 320,000 German households.

“The increased capacity of our wind farm will be another important step to secure the supply from renewable energy sources and therefore for the success of the German energy turnaround,” says Trine Borum Bojsen, Managing Director for the German offshore wind business of DONG Energy.

 

Innovation in a bucket

The 78th turbine to be installed at Borkum Riffgrund 1 is the result of development work being performed between DONG Energy and the UK’s Carbon Trust. Known from the oil and gas industry, the turbine rests on a three-legged jacket with bucket foundations, using a vacuum-assisted installation method that enables the installer to avoid jacking up entirely. In addition to time and cost efficiencies, the installation of this type of foundation is almost noiseless – comparatively speaking.

 

 

 

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