Anholt Offshore Wind Farm - Denmark's largest offshore wind farm

Anholt Wind Farm

Anholt Wind Farm


Peter Busch Nielsen

M.Sc., civil and structural eng., Head of Department, Structures, Denmark
Tel: +45 5161 7238

The Anholt Offshore Wind Farm, which was completed in 2013, is the world's third largest offshore wind farm. The 400 MW wind farm, placed in the Kattegat strait between Jutland and the island of Anholt, produces energy equivalent to the annual energy consumption of 400,000 households, or 4% of Denmark's total power consumption.

Ramboll made a significant contribution to the project delivering:

  • Detailed design for offshore substation
  • Detailed foundation design for 111 offshore wind turbines
  • Environmental studies
  • Maritime safety studies

DONG Energy is the developer and operator of the wind farm. The Danish transmission system operator,, was responsible for establishing the offshore substation, the export cable to shore and the connection to the main high-voltage power grid on land.

Detailed design for offshore substation

The substation of an offshore wind farm is one of the core elements in order to transform and transmit the energy from the wind turbines to the electrical grid on land. The three transformers at the Anholt substation change the voltage level from the wind turbines of 33 kV to 220 kV before the electricity is sent to the land-based connection point to the power transmission grid through a 25 km subsea AC-cable.

Ramboll provided the complete substation design, which included both topside and substructure. The design of the substructure was carried out as two solutions, which were both tendered for by the fabricators:

  • A traditional steel jacket solution (detailed design)
  • A combined concrete Gravity Based Structure (GBS) and a steel structure (tender design)

The GBS solution turned out to be the preferred solution as it combines the installation benefits of a floating concrete structure with that of a steel structure on top. One of the most significant benefits was that there was no need for heavy lift vessels with the GBS solution.

Detailed foundation design for 111 wind turbines

When DONG Energy laid out the plans for the design of the wind turbine foundations, Ramboll assisted in the first phase with definition of design interface, design basis part C and design briefs for certification. The second phase comprised:

  • Detailed design of primary steel structures, where each of the 111 foundations was designed individually considering soil conditions and water depth, in order to optimized the material consumption
  • Design of secondary steel structures, such as boat landings, platforms, ladders, corrosion protection etc.
  • Geotechnical design 
  • Assisting with tender material

Environmental and Maritime Safety Studies

Environmental studies

In order to keep the wind farm project on schedule and on budget, The Danish Ministry of Climate, Energy and Building decided to amend the existing tendering processes for offshore wind farms in Denmark. This meant that environmental assessments and other relevant studies had to be completed before tenders where submitted. selected Ramboll together with DHI to carry out the environmental studies for the area. It included an environmental impact assessment (EIA) for the wind farm and an environmental assessment of the submarine cable.

The job involved extensive studies and assessments of:

  • Birds and marine mammals
  • Geophysics and hydrography
  • Benthic flora
  • Fauna and fish patterns
  • Visualizing fishing, boating, mining and marine archaeology
Ramboll was awarded the project because of our coherent and broad knowledge within environmental assessments, regulatory procedures and the technical aspects of offshore wind project design.

Maritime safety studies

As part of the construction and operation of the wind farm, Ramboll carried out  risk analyses with the scope of identifying, analysing and evaluating the risks related to third party (human safety) and environment originating from ship collision. Ramboll assessed the maritime safety of the wind farm and the substation from an operational and construction point of view. The risk analyses followed the principles of IMOs format safety assessment (FSA). As part of the work, a number of risk reducing measures were assessed ending up with a number of recommendations.

The Ramboll SOW involved:

  • Hazard identification (HAZID) workshop
  • Detailed analysis of the ship traffic in the vicinity of the farm on the basis of historical automatic identification system (AIS) data
  • Modelling of ship-ship and ship-obstacle collisions (turbines and substation)
  • Frequency assessment
  • Consequence assessment
  • Risk evaluation
  • Evaluation of risk reducing measures including recommendations