Jan De Nul has completed its 2025 offshore campaign for TenneT at the DolWin kappa substation, transporting and installing three HVAC grid-connection power cables. Once the remaining works are done, the system will carry almost 660 MW of renewable electricity from two offshore wind farms, enough to serve 800,000 German homes.
Together, Jan De Nul and Hellenic Cables are handling the full scope for three HVAC export cables with a voltage rating of 155 kV and a combined length of 37 km. The cables form the grid link between the Nordseecluster 1 and 2 offshore wind farms and the DolWin kappa offshore converter station.
Cable-laying vessel Isaac Newton transported the three cables from Hellenic Cables’ vertically integrated submarine cable plant in Corinth, Greece, to the project area. The vessel then installed them between the DolWin kappa converter platform and the two Nordseecluster sites. Where the route crossed existing subsea infrastructure, Isaac Newton placed concrete mattresses on the seabed before continuing cable lay operations.
Multi-purpose vessel Adhémar de Saint-Venant followed to bury the cables along their full length using the UTV1200 trencher. Over the past two weeks, rock installation vessel Simon Stevin has placed about 25,000 tonnes of rock berms to protect the HVAC interconnector cables on the seabed. These activities bring the 2025 campaign at DolWin kappa to a close.
In spring 2026, final connection and testing work is planned, following the installation of the Nordseecluster 1 and 2 offshore stations.
The DolWin kappa substation forms part of TenneT’s HVDC DolWin6 project, which will transmit renewable electricity from the new Nordseecluster 1 and 2 wind farms and the existing Gode Wind 3 project in the German North Sea to the onshore grid. In total, these wind farms have a capacity of 900 MW and are expected to produce enough renewable energy to match the annual consumption of 1.1 million German households.
The DolWin kappa scope is one element of Jan De Nul’s long-term service portfolio for TenneT. Looking ahead, several export cable projects are planned to connect 2GW converter stations to the onshore German grid.
