The DLR Institute of Networked Energy Systems in Oldenburg develops technologies and concepts for future energy supply based on renewable energy sources. The major challenge is how to form stable and efficient energy systems from weather-dependent decentralised production units. The research for this transformation process follows a D3 approach (D3 = Decarbonisation, Decentralisation, Digitalisation). The Institute's three departments, Urban and Residential Technologies, Energy Systems Technology and Energy Systems Analysis, work on system related issues for intelligent and efficient linking of the electricity, heating and transport sectors. Systems of all sizes and levels are being investigated, ranging from individual installations and "smart" buildings to networked residential districts and cities. The Institute also evaluates energy systems at national and international levels, using its own network structure models and technology assessment methods.