IN Brief:
- Allseas installed the Darß and Zingst jackets and topsides during one offshore campaign.
- The substations will transform collected turbine power from 66kV to 220kV.
- 50Hertz lists a provisional July 2028 grid connection completion date, subject to an appeal.
Skyborn Renewables has confirmed the offshore installation of the Darß and Zingst substations in the German Baltic Sea, completing a substantial marine construction phase of the Gennaker wind farm connection. Allseas placed the jackets and topsides during a single installation campaign using its heavy lifting vessel Pioneering Spirit. The two platforms will form part of 50Hertz’s OST-6-1 connection, but neither the installation milestone nor the platforms’ physical completion means electricity is already being delivered through them.
The installation follows the structures’ departure from Dutch fabrication yards earlier in October. Zingst sailed from Schiedam and Darß from Vlissingen; IN Power reported that transport milestone separately on 12 October. Their subsequent placement offshore advances the project to the stage where electrical integration and commissioning work can proceed. The operating equipment, turbine array circuits and export cables still need to be connected and tested before power can flow to the transmission network.
Skyborn’s October project announcement puts the planned Gennaker wind farm at 976.5MW, comprising 63 turbines in the 15MW class. A separate 50Hertz project information page describes an approximately 900MW grid connection; its figures should not be silently equated with installed turbine capacity. Smulders, the substation contractor, also refers to a 927MW wind farm in its installation update. These are different published descriptions, and the material reviewed does not establish 927MW as the final certified export rating. The wind farm lies about 15km north of the Fischland-Darß-Zingst peninsula.
Power from the turbines will be collected at a nominal 66kV and transformed at the offshore substations to the 220kV alternating current level used by the export connection. Raising the voltage allows a given amount of power to be transmitted at lower current, reducing resistive losses in the cable conductors and changing the design requirements for switchgear, transformers and associated protection systems. It also increases the electrical insulation and equipment ratings required within the substations.
The offshore structures perform several electrical functions in addition to voltage transformation. Circuits from groups of turbines must be combined through collection switchgear, monitored and protected so that faults can be identified and isolated. Transformers transfer the electricity to the export voltage, while auxiliary systems support the operation of cooling, control, communications and safety equipment. The precise final arrangements and installed equipment ratings must be established through the project’s commissioning documentation rather than inferred from the platforms’ external appearance.
50Hertz describes three 220kV alternating current submarine cable systems running from the offshore substations towards the coast. Its public project documentation gives a route of roughly 90km to an inland connection in the Sanitz/Gnewitz/Dettmannsdorf/Marlow area, including approximately 54km at sea and 35km on land. A planned cable corridor is not a statement that the cables have already been installed. The operator’s published overview describes the intended connection and route; final construction and commissioning status must be judged from the newer project milestones.
Separating power collection offshore from the inland point of connection requires coordination of cable installation, joints, termination equipment, protection settings and operational control interfaces. A subsea export cable has to withstand mechanical loads during laying and its operating thermal environment after burial or protection. Once the circuits are installed, electrical testing must establish their insulation integrity and the correct performance of switchgear and protective equipment before routine service can begin.
The installation contractor, Allseas, used the Pioneering Spirit, a vessel designed for heavy offshore lifts. Skyborn cites dimensions of 382m by 124m and a lifting capability of up to 60,000 tonnes. Those figures describe the ship’s overall capability, not the mass of either Gennaker structure. Positioning the jackets and topsides offshore nevertheless requires coordination of foundation placement, lifting and marine operations, including allowances for vessel movement, weather and equipment tolerances.
The structures have been developed through the HSI joint venture of Smulders HSM and engineering business Iv. Its contract covers engineering, procurement, construction, transport, installation and commissioning of the two substations. Combining the fabrication and electrical integration responsibilities provides one contractual route through several interdependent stages, although mechanical completion at sea remains distinct from the handover of an operational transmission asset.
Responsibility for the export system rests with 50Hertz. Its project information identifies 1 July 2028 as an expected completion date for the connection under German energy legislation, while explicitly warning that the date is not final because appeal proceedings are pending. An older planning overview on the same page should not be taken as definitive confirmation of every current permit or construction status. This latest announcement concerns offshore structural installation, leaving cable works, equipment integration, testing and operational acceptance still to follow.
OST-6-1 is described as an alternating current connection, rather than the high voltage direct current configuration used for some longer offshore routes. The arrangement requires the turbine collection circuits, offshore transformers, three export systems and the eventual onshore substation to function together. The voltage is raised offshore from 66kV to 220kV, and the onshore point of connection is intended to transform it again for the higher voltage transmission network. The electrical design must also account for reactive power arising from long AC cable circuits, alongside thermal limits and protection coordination.
The two installed platforms provide the physical locations where the collection and export systems will be joined, but their operational role depends on the remaining installation and commissioning programme. The next project disclosures will need to distinguish completed cable installation, successful electrical testing and the eventual ability to export power. Until those conditions are met, Darß and Zingst are installed offshore substations awaiting integration, not an energised connection delivering Gennaker generation to the German grid.
