The impacts of renewable energy production and German nuclear phase-out on the electricity transmission systems in Central Europe is investigated with focus on the disparity between the growth of renewable production and the pace at which new electricity transmission lines have been built, especially in Germany. This imbalance endangers the system stability and reliability in the whole region. The assessment of these impacts on the transmission grid is analysed by the direct current load flow model ELMOD. Two scenarios for the year 2025 are evaluated from different perspectives. The distribution of loads in the grids is shown. Hourly patterns are analysed. Geographical decomposition is made, and problematic regions are identified. The high solar or wind power generation decrease the periods of very low transmission load and increase the mid- and high load on the transmission lines. High solar feed-in has less detrimental impacts on the transmission grid than high wind feed-in. High wind feed-in burdens the transmission lines in the north-south direction in Germany and water-pump-storage areas in Austria.