Asso.subsea Awarded Nearshore Cable Scope on TenneT 2GW Trio
The Greek subsea contractor will install the nearshore sections of the BalWin4, LanWin1 and LanWin5 525 kV HVDC bundles off Baltrum Island, working under main contractor Jan De Nul.
Asso.subsea has been awarded the nearshore cable installation scope for three of TenneT's 2GW Programme offshore grid connection systems — BalWin4, LanWin1 and LanWin5 — marking the start of a new collaboration with main contractor Jan De Nul, with TenneT as the end client.
The three landfall sites are located off the northwestern coast of Baltrum Island, in the German Wadden Sea region of Lower Saxony. Each link involves the transportation and nearshore installation of a four-cable bundle, comprising two 525 kV HVDC power cables, one metallic return cable and one fibre optic cable.
Installation campaigns are scheduled sequentially across three years, with BalWin4 in 2027, LanWin1 in 2028 and LanWin5 in 2029.
Asso.subsea's contracted scope includes cable transpooling from load-out ports in the Netherlands or Germany, nearshore installation operations, precision cable landing via beaching operations with spud cans, cable free-lay in intertidal zones, and wet storage of cable ends. The contractor has noted that the works are highly sensitive to tidal conditions in the Wadden Sea environment.
Operations will be carried out using the cable-laying vessel Atalanti, which will be specially modified to accommodate the four-cable bundle configuration required by the projects.
The three connections form part of TenneT's broader 2GW Programme, which comprises 14 offshore grid connection systems intended to bring clean energy from North Sea wind farms to the German and Dutch onshore grids at 525 kV DC.
The cable systems for BalWin4, LanWin1 and LanWin5 are being delivered by the consortium of LS Cable & System, Jan De Nul and Denys, under framework agreements signed with TenneT in 2023 covering cable design, engineering, production, delivery, project management and installation.
For the converter stations, BalWin4 and LanWin1 — both connecting to the onshore grid at Unterweser — are being delivered by the GE Vernova and McDermott consortium, while LanWin5, with its onshore connection point near Rastede, has been awarded to the Hitachi Energy and Petrofac consortium. According to McDermott, fabrication of the BalWin4 platform began in 2025, with commissioning targeted for 2029, while LanWin1 follows a year later for completion in 2030. Each platform will convert up to 2 GW of offshore wind generation from 66 kV AC to 525 kV DC for onward transmission to shore.
