NOVELTY - The electrolyzer comprises a drying unit (3) in which a multi-circuit heat exchanger is provided with a first circuit for cooling hydrogen that is produced and a second circuit for cooling oxygen that is produced. The circuits of the multi-circuit heat exchanger have a common refrigeration circuit. The heat exchanger is designed or controlled so that a dew point of the dried oxygen is below the ambient temperature in a region arranged in an oxygen line sensor, and comprises radially extended tubes connected to each other so that flow-through passages are formed.    USE - The electrolyzer is useful for generating hydrogen and oxygen (claimed), and as a proton exchange membrane electrolyzer in a renewable energy generation system (from drawings).    ADVANTAGE - The electrolyzer efficiently generates the reusable hydrogen and oxygen with high yield and without any additional cost for security monitoring using sensors so that the electrolyzer is cost-effective.    DETAILED DESCRIPTION - The electrolyzer comprises a drying unit (3) in which a multi-circuit heat exchanger is provided with a first circuit for cooling hydrogen that is produced and a second circuit for cooling oxygen that is produced. The circuits of the multi-circuit heat exchanger have a common refrigeration circuit. The heat exchanger is designed or controlled so that a dew point of the dried oxygen is below the ambient temperature in a region arranged in an oxygen line sensor, and comprises radially extended tubes connected to each other so that flow-through passages are formed. The oxygen flows through a first channel, the hydrogen flows through a second channel, and a refrigerant of the refrigerant circuit flows through a third channel that is radially arranged between the first and second channels. The medium is performed with the high pressure through the innermost tube. The pressures decrease through the tubes from inside to outside. The electrolyzer further comprises a dryer for drying hydrogen arranged in the drying unit in downstream of the heat exchanger in a hydrogen line, water separator arranged in the drying unit in upstream of the heat exchanger in an oxygen line, and a hydrogen sensor arranged in downstream of the drying unit in the oxygen line. An INDEPENDENT CLAIM is included for a method for drying the prepared product gases of hydrogen and oxygen in an electrolytic process.    DESCRIPTION OF DRAWING(S) - The figure shows a schematic view of a renewable energy generation system.    Electrolysis unit (2)    Drying unit (3)    Hydrogen storage tank (4)    Fuel cell (5)    Power source. (6)