The ongoing penetration of large amounts of wind power capacities in Germany has strong impacts on the necessary promotion volumes (direct costs of Renewable Energy Source (RES) promotion) but also on necessary grid extensions, the future need for regulating and reserve power capacities, the thermal power plant system and the electricity price for end-consumers (indirect effects). On behalf of the German Energy Agency (Dena) and with a contribution of the affected parties such as wind power associations, TSOs, politics and science, a consortium consisting of DEWI/EWI/E.ON Net/ RWE Transportnetz Strom and VE Transmission analysed these economical end technological effects of the planned extension of wind power capacities onshore and offshore in Germany until 2020. This paper illustrates and summarises the main results of the study.