Abstract This paper defines two electric grids for the area of Jutland in Denmark, namely the existing grid versus a “nature protection grid”, in which all 400 kV AC overhead lines are replaced by 150 kV lines. According to official Danish policies for laying underground cables, such a replacement makes it economically feasible on a long-term basis to replace all overhead lines with underground cables. The two grids are then tested against different energy demand and supply systems in a load-flow analysis. It is found that the “nature protection grid” is well suited for the implementation of sustainable energy systems exploiting both CHP and renewable energy sources such as wind power if certain strategies for the technical regulation of decentralised CHP units are used.