EWE has initially acquired a 40% stake in Borkum 2 phase 2 from full owner Trianel, with the option to acquire more next year.
This leaves Trianel with a 60% stake in the second part of Borkum 2. Utility Stadtwerke Bochum said in May that it was in favour of acquiring a 10% share in the second phase.
Borkum West 2 is located 45km off the German coast. The first phase of Borkum West 2, also 200MW, was completed in July this year. It uses 40 Areva (now Adwen) M5000 5MW turbines.
The first phase is owned by 33 municipal and regional energy companies in Germany, Netherlands, Austria and Switzerland as well as Trianel. It cost around €1 billion. Investment in the second 200MW phase is expected to amount to €800 milion, according to the joint statement.
Construction of phase 2 is expected to start in 2017.
EWE chief operating officer Ines Kolmsee said the second phase is in an "excellent starting position" as the project will already have much of the infrastructure in place from the first phase including a substation.
"EWE brings expertise from the development and operation of the first German offshore wind farm Alpha Ventus and the first commercial offshore wind farm Riffgat," said Kolmsee.
Installation of phase one's turbines and cabling was completed in August 2014, but Trianel said the "multiple displacement" of the transmission system meant a delay in the connection.