This article focuses on the influence of increased wind and solar power production on the transmission networks in Central Europe. The German Energiewende policy together with insufficient transmission capacity between northern and southern Germany as well as the existence of the German-Austrian bidding zone heavily contribute to congestion in the Central European transmission system. To assess the exact impact on the transmission grid, the direct current load flow model ELMOD is employed. Two development scenarios for the year 2025 are evaluated on the basis of four representative weeks. The first scenario focuses on the effect of Energiewende on the transmission networks, the second one drops out nuclear phase-out and thus assesses isolated effect of increased feed-in. The results indicate that higher feed-in of solar and wind power increases the exchange balance and total transport of electricity between transmission system operator areas as well as the average load of lines and volatility of flows. Solar power is identified as a key contributor to the volatility increase, wind power is identified as a key loop-flow contributor. Eventually, it is concluded that German nuclear phase-out does not significantly exacerbate mentioned problems.