Future structure of rural medium-voltage grids for sustainable energy supply

Due to the fundamental change of the legal framework in Germany [1] and the mandatory targets for renewable energy shares of final energy consumption set by the European Renewable Energy Council [2], the number of distributed renewable generation units in medium-voltage (MV) grids has strongly increased. Especially in rural areas an ongoing dynamic growth of integration of biomass and photovoltaic plants can be expected. In certain situations of injection, parts of rural grids will face overloads and can hardly be operated in line with the technical guidelines. This paper deals with the renewal effort of a rural 20 kV distribution grid with high proportion of renewable energy sources in the next 20 years. To analyze the future problems of voltage stability, scenarios of renewable energy injection of the years 2015 and 2030 have been created. Concrete recommendations for measures in the MV-grid have been developed. Furthermore general recommendations for planning guidelines of MV-grids with a high proportion of renewable energy sources have been derived.