Jan De Nul, Hellenic Cables link German offshore wind farm site with DolWin kappa platform

December 15, 2025, by Adrijana Buljan

Jan De Nul has installed three HVAC subsea cables, delivered by Hellenic Cables, between TenneT’s offshore converter station DolWin kappa and Nordseecluster 1 and 2 sites, the two locations in the German North Sea making up the 660 MW Nordseecluster A offshore wind farm, which itself is part of a bigger, two-phased Nordseecluster project.

CLV Isaac Newton at DolWin kappa; Source: Jan De Nul

With the cables and cable protection now installed, the company has concluded the 2025 transport and installation campaign for the project.

Using its cable-laying vessel (CLV) Isaac Newton, Jan De Nul transported the three 155 kV cables from Hellenic Cables’ factory in Corinth, Greece, and installed them along their respective routes from the wind farm sites to the offshore converter platform. At crossings with other subsea infrastructure, the vessel installed concrete mattresses, and the multi-purpose vessel Adhémar de Saint-Venant buried the cables along the cable routes using the trencher UTV1200.

During late November and early December, the rock installation vessel Simon Stevin installed about 25,000 tonnes of rock berms to ensure the protection of the HVAC interconnector cables on the seabed, which concluded the 2025 campaign at DolWin kappa, according to Jan De Nul.

The last connection and testing works are planned to be carried out in the spring of 2026, after the installation of the Nordseecluster 1 and 2 substations.

TenneT’s HVDC DolWin6 offshore grid connection, with DolWin kappa at the heart of the project, connects the new 660 MW Nordseecluster A and the existing 250 MW Gode Wind 3 offshore wind farm to the German onshore grid.

Gode Wind 3, built by Ørsted, was fully commissioned earlier this year and is already supplying electricity to the German grid.

Nordseecluster A, the first phase of the 1.6 GW Nordseecluster offshore wind development in Germany, owned by RWE and Norges Bank Investment Management, is currently under construction.

The 660 MW, first phase of the project, Nordseecluster A, is planned to be fully commissioned in 2027. Nordseecluster B, which will contribute an additional 900 MW and also consists of two locations, is planned to be operational in 2029.