Five-kilometre tunnel under the Elbe: SuedLink reaches another key milestone

The SuedLink backbone transmission project in Germany has reached another construction milestone with the completion of a more than five-kilometre tunnel beneath the Elbe. The ElbX river crossing project, which connected sections of the route between Schleswig-Holstein and Lower Saxony, is among the technically most complex parts of the 700-kilometre high-voltage direct-current link. From the end of 2028, it is set to strengthen electricity transmission capacity from northern to southern Germany.

TenneT, which operates part of the German transmission system, together with representatives of both federal states, symbolically marked the completion of tunnelling for the ElbX tunnel, which connects Wewelsfleth in Schleswig-Holstein with Wischhafen in Lower Saxony. The tunnel, approximately 5.2 kilometres long, now structurally connects the northern sections of the SuedLink route on both banks of the Elbe.

The tunnel-boring machine reached the receiving shaft in Wischhafen as early as June, meaning the breakthrough has now completed the underground construction phase of this section. The machine was launched from Wewelsfleth on 1 February 2025 and passed through variable sandy and clay sediment layers during excavation.

Cable installation to follow tunnelling

Following the recovery and dismantling of the tunnel-boring machine, preparations will begin for the subsequent installation of cables. A total of six cables will be laid in the tunnel: four as the main conductors of the SuedLink line and two additional cables as spares for future maintenance and to increase the connection's operational reliability.

SuedLink will comprise an approximately 700-kilometre high-voltage direct-current cable connection between the wind regions of northern Germany and regions with strong demand in Bavaria and Baden-Württemberg. The project is being implemented by transmission system operators TenneT and TransnetBW, with TenneT responsible for the northern part of the route and the converters in Schleswig-Holstein and Bavaria.

Construction of SuedLink began in summer 2023, and TenneT continues to expect the connection to enter operation at the end of 2028. Meeting this timetable will be important in particular for German plans to retire further conventional generation sources and to reduce redispatch costs between the wind-rich north and the country's industrial regions in the south. The original timetable envisaged completion of the line in 2022; however, the planned commissioning had already been postponed to 2025 10 years ago.

Completion of the tunnel beneath the Elbe does not in itself resolve the main challenges of Germany's energy transition, which lie primarily in the slow expansion of grids, lagging behind the growth of renewable generation capacity. However, it provides concrete evidence that some key projects are moving from the permitting and preparation phase into visibly advanced implementation.