Riffgrund up to 312MW, bucket trial

Danish developer Dong Energy will pioneer a new suction bucket foundation concept at its Borkum Riffgrund 1 wind farm, currently under construction off Germany – as well as boosting its capacity to 312MW by using 4MW Siemens turbines.

The innovative technology – a tripod jacket that uses a vacuum-assisted installation method rather than piles to fix the foundation to the seabed – will occupy a single spot on the outskirts of the development, which otherwise employs conventional monopiles.

The suction-bucket design, being fabricated by Bladt Industries for installation later this year along with the first of the monopile-based turbines, could be moved into serial production by 2017 for UK Round 3 projects.

Borkum Riffgrund 1 was originally down to use Siemens 3.6MW machines.

“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 of Dong’s German offshore wind business.

Dong sees the suction bucket tripod – which marries a welded tubular space frame with a suction caisson concept commonly used to fix North Sea oil platforms to the seabed – as a key technology in meeting its target of cutting the cost of energy from offshore wind power projects by 40% by 2020.

“Having more developers utilising the suction bucket jacket will benefit optimisation of design, fabrication process and installation logistics and thereby help to drive down the cost,” says Dong Energy vice president Tove Feld.

Borkum Riffgrund 1 was chosen for prototype trials due to its sandy soil conditions, seen as a“highly suitable” test for the new foundation concept. The flagship suction bucket jacket will be fitted with a state-of-the-art measurement system to feed-back data for performance verification.

E.ON, Mainstream Renewable Power, ScottishPower Renewables, Statkraft and Statoil – which all partnered early development of the design through the Carbon Trust’s cost-cutting Offshore Wind Accelerator scheme – will be given open access to the collected data and “full visibility” of the fabrication and installation of the new foundation design to help in evaluation of the technology for use off Europe.

Suction bucket foundation designs, which are targeting the coming market for 6MW-plus wind turbines on projects in water depths of 30-60 metres, are under development at a number of companies, including Fred Olsen-backed Universal Foundation, which has had its flask-shaped concept piloted as a foundation for two met-masts at consortium Forewind’s Dogger Bank development.

Borkum Riffgrund 1 is owned by Dong Energy (50%) and Lego-owner KIRKBI Invest A/S and William Demant Holding A/S (together 50%).