Electrolysis system for electrochemical decomposition of water (W) to afford hydrogen (H2) and oxygen (O2) comprising: - at least one electrolyzer for electrochemical decomposition of water (W) to afford hydrogen (H2) and oxygen (O2), wherein the electrolyzer comprises a periphery which comprises conduits and a first heat exchanger , - a first gas separation apparatus for separation of oxygen (O2) and water (W) and a second gas separation apparatus for separation of hydrogen (H2) and water (W), wherein the gas separation apparatuses are at a height above the electrolyzer so that a natural circulation of the reactants and products in the electrolyzer is ensured solely as a result of the density differences arising in the electrolyzer , - a housing apparatus for receiving the electrolyzer , wherein the entire electrolyzer and the gas separation apparatuses are arranged in the housing apparatus and the housing apparatus is tightly sealed off from a first fluid (F1) surrounding the housing apparatus , wherein a first pressure inside the housing apparatus is higher than a second pressure outside the housing apparatus , - wherein the housing apparatus comprises a second heat exchanger for thermal equalization of the temperature in the housing apparatus and outside the housing apparatus , - and wherein the gas separation apparatuses are connected via a respective conduit to the first heat exchanger and via a respective conduit to the corresponding side of the anodic and the cathodic side of the electrolyzer , wherein the water circuits of the hydrogen and oxygen side are connected to one another via the first heat exchanger and the conduits respectively pass oxygen-water mixture to the first gas separation apparatus and hydrogen-water mixture to the second gas separation apparatus . - at least one electrolyzer for electrochemical decomposition of water (W) to afford hydrogen (H2) and oxygen (O2), wherein the electrolyzer comprises a periphery which comprises conduits and a first heat exchanger , - a first gas separation apparatus for separation of oxygen (O2) and water (W) and a second gas separation apparatus for separation of hydrogen (H2) and water (W), wherein the gas separation apparatuses are at a height above the electrolyzer so that a natural circulation of the reactants and products in the electrolyzer is ensured solely as a result of the density differences arising in the electrolyzer , - a housing apparatus for receiving the electrolyzer , wherein the entire electrolyzer and the gas separation apparatuses are arranged in the housing apparatus and the housing apparatus is tightly sealed off from a first fluid (F1) surrounding the housing apparatus , wherein a first pressure inside the housing apparatus is higher than a second pressure outside the housing apparatus , - wherein the housing apparatus comprises a second heat exchanger for thermal equalization of the temperature in the housing apparatus and outside the housing apparatus , - and wherein the gas separation apparatuses are connected via a respective conduit to the first heat exchanger and via a respective conduit to the corresponding side of the anodic and the cathodic side of the electrolyzer , wherein the water circuits of the hydrogen and oxygen side are connected to one another via the first heat exchanger and the conduits respectively pass oxygen-water mixture to the first gas separation apparatus and hydrogen-water mixture to the second gas separation apparatus . <EOS>