The Dudgeon Offshore Wind Farm development, off North Norfolk, England, is moving forward. In January, partners Statoil and Statkraft announced they awarded Siemens plc two contracts valued at US$848 million, covering the supply and service of 67 wind turbine generators (WTG).
The scope of the supply contract covers the engineering, procurement, assembly and offshore commissioning of the wind turbine generators (WTGs). Each turbine will have a 6MW capacity, and contain a tower section, nacelle, and three separate rotor blades. Statoil says the first group of turbines is expected to be complete for load out and installation in January 2017. Engineering started in January and will play a role in the design work for the foundations and electrical infrastructure.
The service contract will cover the operations and maintenance needed for the WTGs through the first two years after the installation is complete. It also covers the three years Siemens will provide technicians for Dudgeon and complete other agreed services. The Dudgeon Offshore Wind Farm is located in water depths ranging from 18-25m. After Warwick Energy reviewed the Dudgeon wind farm site and plans, the partners submitted proposed variations of the project to the UK Department of Energy and Climate Change (DECC), which were approved in September 2013.
The review discovered the presence of mobile sand waves and layers of chalk in the seabed, which could impact the stability of the turbines. The Dudgeon Offshore Wind Ltd. (DOWL) partners submitted an application to the DECC and the Marine Management Organisation (MMO) to extend the project’s red line boundary to increase the wind farm area in an attempt to prevent turbines from operating in areas that contain mobile sands. The document also discusses the need for new foundation concepts to stabilize the turbines, proposing either suction buckets or larger monopiles. The concept will be chosen at a later date.
Suction buckets are seen as a cost-effective alternative to steel monopiles or pylons by utilizing the sediment-rich sea floor as a foundation. Once suction is applied to the steel bucket, pressure swiftly sinks the structure in the quicksand it generates when the water from the bucket is dispersed into the seabed. Gravity takes over, and secures the bucket and the turbine. According to the variations document, the suction buckets will only penetrate the first few meters of the seabed, avoiding the chalk layer.
Monopiles are long steel tubes that can be driven deep into the seabed by a hydraulic piling hammer. DOWL submitted an application to the DECC and MMO to change the Marine License to enable use of larger, 8.5m-diameter monopiles over the 6.5m-diameter version. The larger design can increase surface friction and foundational stability in the chalk areas, while also permitting the on-site construction of 5-6MW turbines.The proposed variations document says that the wind farm has the potential to produce 560MW, but that a review of the project design caused the partners to reduce the total generating capacity to a maximum of 400MW. This downgrade was an attempt to curb the risk of the wake effects — or downwind effects — that occur when turbines operate too closely together. Furthermore, the total number of turbines was also reduced by 100 to a total of 78.
Once in operation, the Dudgeon wind farm is projected to reduce carbon emissions by 19 million tonnes over its 25 years lifetime. It is expected to supply electricity to about 400,000 homes in the UK market, which accounts for about 0.5% of the UK’s annual electricity demand.
DOWL holds the licenses and the consents that enable the wind farm’s construction. DOWL is operated by Statoil (70%) and Statkraft (30%). The final investment is scheduled for Q3 2014.
The Dudgeon Wind Farm is the Statoil-Statkraft partnership’s second offshore wind farm. The partnership owns and operates the Sheringham Shoal located off the Norfolk coast.