Heerma Marine Contractors heavy-lift behemoth Sleipnir has installed the 49-meter-high, 2,100-tonne jacket for the Hollandse Kust (west Beta) transformer platform over the past weekend. 

Dutch grid operator TenneT said that this critical infrastructure component lays the foundation for a future offshore wind farm connection.

Seabed preparation and secure anchoring

Prior to installation, TenneT conducted thorough seabed surveys to ensure optimal placement and stability. This included a comprehensive check for potential World War II explosives and the creation of a solid foundation using a bed of large stones.

The jacket boasts four corner points firmly anchored with piles driven over 50 metres deep into the seabed. These piles are encased in 10-metre tubes welded to the jacket’s base, creating a secure connection that can withstand even the most severe North Sea storms. Additionally, grouting, a process of filling the space between the piles and tubes with cement, further reinforces the structure’s stability.

Sleipnir’s lifting capabilities were instrumental in placing the jacket onto its prepared seabed location, approximately 53 kilometres off the coast of Egmond aan Zee. Special equipment installed on the jacket will monitor any potential misalignment after placement, ensuring a level platform for the future installation of the topside containing transformers.

Socket at sea

From the beach at Velsen, contractor NBOS (Boskalis / Orient Cable) is currently installing the sea cables that will connect the socket to the electricity grid in 2025. These cables (220 kilovolts) are laid at a safe depth and connected to the land cables behind the dunes. Through this connection, the electricity ultimately ends up in the high-voltage grid at the correct voltage (380 kilovolts) via the transformer station in Wijk aan Zee.

TenneT’s socket is intended for the wind farm that RWE/OranjeWind will have built at sea in the coming years. The jacket (undercarriage) and the topside (superstructure) are built by the contractor combination Equans / Smulders. The grid operator will soon bring the green energy ashore at Velsen via the 700-megawatt grid connection. This will make approximately 3.3 terawatt hours of sustainable electricity available. This approximately corresponds to the annual consumption of 1 million households.