Today, Switzerland covers around three quarters of its energy needs through imports. The upcoming energy transition is leading to uncertainty about future energy supplies and a desire to make greater use of domestic energy sources. However, renewable resources such as biomass are only available to a limited extent. Against this background, the project "Carbon Flows in the Energy Transition" was launched at the Institute for Energy Technology IET. Together with EPFL in Sion, the IET investigated the various energy and carbon sources in Switzerland. Among other things, the research project shows that CO2 levies of between 400 and 700 francs per tonne of CO2 are necessary to bring about a shift away from fossil to renewable energy sources.