Dong installs first suction bucket

Danish developer Dong Energy has installed a pioneering three-legged offshore wind turbine foundation design at its Borkum Riffgrund 1 development off Germany.

The so-called suction-bucket jacket, fabricated at Bladt Industries' Aalborg yard, was lowered into place by Swire Blue Ocean's Pacific Orca jack-up in 24-metres of water off the island of Borkum, and is now ready to be topped out with an upscaled Siemens SWT-4.0-130 turbine as part of a technology demonstration project at the 312MW wind farm.

"We've now installed the very first suction-bucket jacket in the offshore wind industry," said Dong Energy vice-president Tove Feld."

"The reduction in cost of electricity and our ability to utilise some of the more challenging sites further from shore and in deeper water show some of the potential that this concept has."

The 850-tonne steel structure, which stands 57-metres tall, is fitted with cylindrical-shaped feet that are pulled down into the seabed by a system of high-pressure pumps.

Unlike conventional jackets, the suction-bucket concept, which was originally hatched under the UK Carbon Trust's Offshore Wind Accelerator (OWA) scheme, is not anchored to the seafloor with hammered-in piles, promising to make the offshore installation process quicker, less expensive and quieter.

"We believe innovative foundation designs, such as the suction jacket technology play an important role in our efforts to cut the cost of energy from offshore wind," said Carbon Trust chief executive Tom Delay.

"This foundation has been designed for serial fabrication and will save costs across design, fabrication, installation through to operation. Full-scale demonstrations are the last critical step before a new innovative design can be considered for commercial projects."

The Borkum Riffgrund suction-bucket jacket is kitted out with a comprehensive monitoring system that will feed data which is expected to inform thinking on the technology's use off Britain for OWA project partners E.ON, Mainstream Renewable Power, Iberdrola, Statkraft and Statoil.

The data will also be analysed under a separate joint research project between Leibniz University, German R&D centre BAM and Dong, which aims to have a design proven in time for the UK's Round 3 projects.

Suction bucket foundations are an import from the offshore oil industry, where the technology has seen widespread use for many years.

Several offshore wind designs, which are targeting the coming 6MW-plus turbines on projects in water depths of 30-60 metres, are under development, including Fred Olsen-backed Universal Foundation's, which has its flask-shaped concept piloted with met masts at Forewind's Dogger Bank mega-development.

The Borkum Riffgrund suction bucket jacket-based turbine will stand at the heart of the offshore wind farm, which is being built around 77 traditional monopile-based machines.

First power from the wind farm is slated to begin flowing later this year, with the development reaching full production in the first half of 2015.

A video of the installation can be viewed here.