The German energy supply shall be changed from a fossil-fuel and nuclear energy based to a regenerative energy based supply. For a successful implementation of the energy turnaround, the repowering of existing wind farms is deemed one of the major cornerstones. Due to shrinking numbers of suitable locations for Greenfield projects, the Renewable Energy Sources Act provides repowering incentives in the form of a repowering-bonus to promote the replacement of inefficient wind turbines, commissioned prior to 1 January 2002, by state-of-the-art technology. Despite repowering incentives and increased efficiency of modern wind turbines, the feasibility of repowering projects is not necessarily guaranteed. On the basis of two case studies on existing wind farms in northern Germany, the thesis demonstrates that numerous factors have an impact on the realisation of repowering projects. A repowering of an existing wind farm inevitably changes the original conception of the underlying wind energy fund and can negatively affect the rights of the actual investors. Both case studies show that potential repowering decisions lead to additional financial burdens for the repowering projects due to necessary compensation payments to the existing investors. Using consistent financial parameters within the framework of profit and loss forecasts, as well as applying accepted methods of financial mathematics, the feasibility studies on two different types of wind turbines allow for meaningful evaluations by comparing financial ratios. The study reveals that the realisation of both repowering projects strongly depends on the type of installation. Especially at the stronger wind location Sustrum, the entitlement to the repowering-bonus is not the key factor for the feasibility of the project. Rather, the potential annual energy production at the respective project site in combination with the level of investment costs per wind turbine is the crucial factor for a successful implementation.