The seller is Erste Nordsee-Offshore-Holding, a joint subsidiary of Austrian construction firm Strabag and Etanax GmbH. The purchase price was not disclosed.
Gunnar Groebler, senior vice president and head of business area wind at Vattenfall, said the acquisition sent "a signal that we strongly believe in the German market".
The 79-turbine project is under development in the North Sea, 85km north of the island of Borkum. Its progress depends on a capacity contract being obtained in the forthcoming tendering process, with the first auction due in March 2017 and the second a year later.