A Sustainable Concept for the Supply of Pure CO2 as a Carbon Source for Solar Fuels - Synergies of Biochar and Biogas In times of the German energy transition (Energiewende) chemical storage technologies achieve an increasing interest because only with their help the energy of the excess electricity from wind- and solar plants can be stored in huge quantities in form of hydrocarbons. The hydrogen generated by water electrolysis can be converted with carbon dioxide to hydrocarbons. In addition, pure CO2 must be available at a reasonable price. For this CO2 supply a sustainable concept is presented.