Skip to content


In the DolWin5 project, TenneT is installing an offshore grid connection system in the North Sea with a capacity of 900 MW using extra-high voltage direct current transmission technology.

Niedersachsen, Nordsee
  • DolWin5

About the project

130 kilometre long and 900 megawatt strong direct current connection


The three-phase alternating current generated by the wind farms at sea is converted into direct current on the offshore platform DolWin epsilon and transported south to Hamswehrum near the river Ems in East Frisia via a 100-kilometre-long submarine cable. From there, a 30 kilometre long land cable leads to the converter station in Emden/East. Here, the direct current is converted back into three-phase alternating current and fed into the extra-high voltage grid on land.


Connecting concept

DolWin5 is one of the offshore grid connection systems, which TenneT connects directly to the corresponding wind turbines via 66 kilovolts three-phase alternating current (AC) cables. Hence, a transformer station that was previously necessary in each wind farm is no longer needed. Furthermore, 155 kV AC cables are no longer required to connect TenneT's offshore platform to that of the wind farm. This means that the electricity generated at sea is directly fed into the TenneT converter platform. The conversion of AC into direct current (DC) takes place at the converter station. The electricity is transported by submarine cable to shore and then by underground cable to the onshore converter station, where it is converted back into AC and fed into the extra-high voltage grid. Economically speaking, this innovative technology leads to enormous cost savings.



  • DolWin5 DW epsilon

    Computer illustration of the future offshore platform DolWin epsilon. In addition to the converter plant, the platform will provide accommodation for 50 people, a helipad, a crane and a lifeboat.

  • Time capsule

    Groundbreaking ceremony of DolWin5: Michiel Cadenau, right, TenneT's overall Technical Project Manager of DolWin5, and Evaldas Semelis, Hitachi Energy’s DolWin5 site manager, fill the time capsule with coins, a regional newspaper and construction plans.

  • DolWin5

    The steel structure of one part of the converter hall is already in place (on the right of the picture), the foundation for the second area is currently being prepared (reinforcement). On the far left of the picture you can see the preparations for the future switchgear field as part of the transformer station. This is where the electricity converted from direct current to three-phase alternating current in the converter is fed into the extra-high voltage grid.

  • Pile foundation

    The pile foundation marks the official start of construction of the DolWin5 land station in Emden/East. Over an area of around 25,000 square metres, a good 600 piles with a length of 24 metres were drilled into the ground to achieve a sufficiently load-bearing soil layer.

  • Pile foundation

    Following Dutch tradition, coins from each country involved in the project were placed in the first borehole during the pile foundation: a Euro coin, a German mark, a Dutch guilder and a Swedish and Norwegian krone. The coins are not only supposed to bring luck to the project, but above all to appease evil earth demons.

  • DolWin epsilon steelcut

    The "first steel cut" in December 2020 marked the start of construction of the DolWin epsilon offshore converter platform in Singapore. After completion, the steel structure will be approx. 80 metres long, 70 metres wide and 80 metres high.


cornelia junge.jpg

Cornelia Junge

Spokesperson - Project Communication Offshore

Further information