The order is for 30 Siemens 3.6MW turbines and includes installation and maintenance for five years.
Riffgat is located 15km northwest of the north Frisian island of Borkum and a preliminary license for the development has been issued. EWE and Enova hope to receive construction approval in the later half of this year. The project is expected to be online by 2012 with initial work set to commence next year.
EWE has been involved in development of the project since 2004. In 2008, EWE teamed up with Enova develop the wind farm.
Riffgat will be the second offshore project for EWE, following on from the 60MW Alpha Ventus wind farm. Alpha Ventus became Germany's first operational offshore wind farm when it launched last year.
Speaking about the project René Umlauft, CEO of the Renewable Energy Division of Siemens Energy said: "Offshore wind power is now finally picking up impetus in Germany too.
"Riffgat will be one of the first commercial wind farms in German waters. Together with EWE and ENOVA we're bringing Germany a big step forward in establishing ecofriendly, sustainable power supply."