The storage of renewable energy is crucial for the substitution of fossil fuels with renewable energy. Hydrogen is the first step in the conversion of electricity from renewable sources to an energy carrier. However, hydrogen is technically and economically challenging to store, but can be converted with CO2 from the atmosphere or oceans to hydrocarbons. The heterogeneously catalyzed gas phase reaction and the electrochemical CO2 reduction are reviewed and the application of a new type of reactor is described. The mechanism of the gas phase CO2 reduction on a heterogeneous catalyst is shown in detail and the function of the supported catalyst is explained. Finally, an economic estimation on the cost of synthetic methane is presented which leads to a cost of 0.3 CHF/kWh in CH4.