Kriegers Flak Combined Grid Solution

Less than 30 km of sea separates the Danish Kriegers Flak wind farm from the German Baltic 2 farm. The Combined Grid Solution bridged that gap with cable, so that the export lines each farm already needed for its own country could also carry trade between the two. The result was the world’s first interconnector built from the national grid connections of offshore wind farms, as 50Hertz describes it.

The wind farms are Kriegers Flak at 600 MW on the Danish side and Baltic 1 at 48 MW and Baltic 2 at 288 MW on the German side. When the turbines are running, the cables carry their output ashore; when they are not, the spare capacity is free for trade. Cross-border flows began on 15 December 2020, with a trade capacity of 400 MW.

The offshore network runs on alternating current. The direct current part is on land, at Bentwisch near Rostock, where a back-to-back converter turns AC from the Nordic system into DC and immediately back into AC adapted to the Continental European grid. Eastern Denmark and Germany are in different synchronous areas, and 50Hertz notes that their frequencies run at a slightly different phase, so the two cannot simply be joined. Hitachi Energy, which supplied the converter, lists it as a voltage-source unit rated at 410 MW and in operation from 2019.

Construction ran from January 2017 to the first quarter of 2020, and commissioning followed in December 2020. The project was supported by the European Energy Programme for Recovery and is listed as a Project of Common Interest. Energinet and 50Hertz own and operate it.

For the next generation of hybrid links, which put the converter at sea and scale up to gigawatts, see Bornholm Energy Island and the guide to energy islands. Bentwisch, where the converter stands, is also the German end of Kontek.