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, Energinet.dk, 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