NOVELTY - Power supply system comprises an electric power supply (1), at least one electrolyzer (5) for generating hydrogen and oxygen, at least one chemical reactor (7) for catalytically converting carbon dioxide and the hydrogen generated by electrolysis into a long-term storable first chemical compound with a high energy density, at least one tank (10) for temporarily storing carbon dioxide and the chemical compound, and at least one converter (9) for generating heat and/or electricity. The electric power supply is a local electric power supply which is associated solely with power supply system.    USE - The power supply system is useful in building technology.    ADVANTAGE - The power supply system is highly efficient, decentralized, self-sufficient and highly carbon dioxide-neutral.    DETAILED DESCRIPTION - Power supply system comprises an electric power supply (1), at least one electrolyzer (5) for generating hydrogen and oxygen, at least one chemical reactor (7) for catalytically converting carbon dioxide and the hydrogen generated by electrolysis into a long-term storable first chemical compound with a high energy density, at least one tank (10) for temporarily storing carbon dioxide and chemical compound, and at least one converter (9) for generating heat and/or electricity. The electric power supply is a local electric power supply which is associated solely with the power supply system. The local electric power supply is associated with an electric short-term store as a buffer store. At least one gas separator is provided, which separates carbon dioxide from the air and/or from the exhaust gases of the converter and/or from metal oxides which absorb carbon dioxide, and at least one gas separator is connected to the local tank via a line. An INDEPENDENT CLAIM is also included for operating the power supply system, comprising recovering and reusing carbon dioxide required for the preparation of the first chemical compound from the combustion and decomposition processes, producing the first chemical compound including methane, formic acid, carbonates and/or bicarbonates in the circulated missing part of the carbon dioxide by separation of carbon dioxide from the air and/or combustion or fermentation processes of biomass and/or from alcohol including methanol and ethanol, or natural gas.    DESCRIPTION OF DRAWING(S) - The figure shows a schematic representation of the power supply system.    Electric power supply (1)    Electrolyzer (5)    Chemical reactor (7)    Converter (9)    Tank (10)