Northland Power has confirmed it has halted work on installing two mono bucket foundations on the Deutsche Bucht offshore windfarm in Germany, throwing the future of the demonstration project into doubt
Reporting fourth quarter and full year 2019 results on 25 February 2020, Northland Power said installing two turbines with mono bucket foundations was paused in Q4 2019 following the identification of technical issues. Northland was granted a licence by the German authorities to install two turbines using mono buckets in 2018.
“A thorough evaluation of the cause of the technical issues is ongoing and there is a possibility the demonstrator project may not proceed,” the company said. As a result of the uncertainty, Northland recorded a non-cash impairment loss of US$98M for project costs incurred to date associated with the demo.
The first of two mono bucket foundations that were due to be installed at Deutsche Bucht left Bladt Industries in Lindoe, Denmark in November 2019.
The mono bucket – a cost-effective concept that combines the benefits of a gravity base foundation, suction bucket and monopile – was transported to the windfarm on Seajack’s offshore installation vessel Scylla.
Deutsche Bucht is the first commercial project to test the new foundation, which consists of a single steel cylinder – the suction bucket – upon which a shaft is mounted. A transition piece and a turbine are installed on the shaft.
It is installed using a patented installation process in which the pressure in the cavity between the foundation and the seabed generates water flow, which reduces resistance around the edge of the skirt of the foundation. This reduced resistance allows seabed penetration.
An installation control system controls vertical alignment, ensuring the foundation is installed within prescribed tolerances. Installation is almost completely noise free. For decommissioning, the foundation can be removed for reuse or recycling by reversing the suction process. This involves applying water pressure to the foundation skirt so that it can be lifted from the seabed.
The mono bucket concept has been in development at Universal Foundation since 2001, based on experience gained from the oil and gas industry, and was successfully used in applications such as the foundations for offshore met masts.
In the past Northland Power has said the mono bucket demonstration “could be of significant benefit for future offshore windfarms and enable Northland to construct projects more quickly and with lower costs.”
Deutsche Bucht is approximately 95 km to the northwest of the North Sea island of Borkum in Germany’s exclusive economic zone.
The rest of the 269-MW Deutsche Bucht project in the North Sea has progressed as planned, with installation of all 31 conventional monopile foundations and turbines ahead of schedule.