IN Brief:
- Zingst and Darß topsides have been loaded out from yards in Schiedam and Vlissingen after completion of their jacket load-outs.
- Each offshore substation will handle about 450MW and transform Gennaker output to 220kV for export through 50Hertz’s OST-6-1 connection.
- Allseas will transport and install the structures as the 976.5MW wind farm progresses towards commercial operation by the end of 2028.
Smulders and engineering partner Iv have completed the load-out of the Zingst and Darß offshore substation topsides for the OST-6-1 grid connection serving Germany’s Gennaker offshore wind farm. The structures were transferred from yards in Schiedam and Vlissingen after the associated jacket foundations were loaded out earlier in September.
Each topside is designed to handle approximately 450MW. Together, Zingst and Darß form the offshore transformation stage of 50Hertz’s OST-6-1 connection, which has a maximum transmission capacity of 927MW and will link Gennaker with the transmission network in Mecklenburg-Western Pomerania.
The HSI joint venture is responsible for engineering, procurement, construction, transport, installation, and commissioning of the two offshore substations and their jacket foundations. Completion of the topside load-outs transfers another part of the programme from fabrication into the marine installation sequence.
Allseas is due to transport and install the structures using the heavy-lift vessel Pioneering Spirit. The handover from fabrication yard to offshore campaign places particular demands on structural tolerances, sea fastening, load distribution, lifting interfaces, and protection of installed electrical equipment during transport.
The substations will collect output from Gennaker and transform it to 220kV before electricity is exported towards the German coast. 50Hertz is constructing three 220kV alternating-current submarine cable systems as part of OST-6-1, with the connection running through the two offshore platforms to the Gnewitz substation.
The overall route extends for up to about 90km, including as much as 53km in the Baltic Sea and around 35km onshore. At Gnewitz, the 220kV export system will connect into the German extra-high-voltage network after transformation to 380kV.
Gennaker is being developed by Skyborn Renewables around 15km north of the Fischland-Darß-Zingst peninsula. The wind farm is designed for up to 976.5MW of installed generation, while the OST-6-1 connection limits maximum grid injection to 927MW.
The physical substation milestone follows Gennaker’s €2.1bn financial close earlier this month. Financing moved the wind farm into full execution; the load-out programme now shows the grid infrastructure advancing through a separate sequence of fabrication, marine transport, offshore installation, cable connection, and electrical commissioning.
Offshore substations concentrate some of the most critical electrical equipment in a wind project into a single structure. Transformers, high-voltage switchgear, protection systems, auxiliary supplies, communications, and control equipment all have to operate after the platform has been transported and installed offshore, where access for later modification is more difficult and expensive.
The Zingst topside measures approximately 48 metres long, 33 metres wide, and 17.5 metres high, with a mass of around 4,700 tonnes. Structures at that scale require temporary load paths and grillage systems capable of transferring weight safely through the quay, transport arrangement, and eventual heavy-lift operation without imposing unacceptable distortion on the platform or its installed systems.
Once offshore, the two substations become part of a longer electrical chain extending from turbine generators through the array network, transformation equipment, export circuits, landfall, underground cables, and the Gnewitz substation. Protection, communications, and control systems have to operate consistently across those interfaces as separate parts of the project are energised.
The use of a 220kV AC connection reflects Gennaker’s relatively short distance from shore compared with more remote North Sea projects increasingly connected through HVDC systems. AC avoids the need for offshore and onshore converter stations, but large-scale export requires multiple cable circuits and careful management of voltage and reactive power across the route.
Project sequencing is equally important. Wind turbines cannot deliver useful generation without the substations, export cables, onshore connection, and protection systems needed to carry power, while transmission infrastructure has to reach commissioning in step with the generating assets it is intended to serve.
With the jackets and topsides loaded out, the next stages are sail-away, offshore installation, cable integration, and commissioning. The wind farm is targeting commercial operation by the end of 2028, leaving the OST-6-1 programme to convert two completed steel platforms into operating high-voltage nodes in Germany’s Baltic transmission system.
