Abstract: The invention relates to a fuel cell system (11, 111) comprising an anode chamber (13, 113) and a cathode chamber (14, 114) which are separated from each other by a proton conducting membrane (15, 115). When the fuel cell system is operated, fuel, in particular H2 or a water/methanol mixture, can be fed to the anode chamber and an oxidant, in particular oxygen, can be fed to the cathode chamber. In standby mode, the cathode chamber (14, 114) does not allow flow through and the oxidant and fuel are present in both the cathode chamber (14, 114) and the anode chamber (13, 113), respectively. The fuel cell system remains at operating temperature in the standby mode. This enables the fuel cell system (11) to be used as a combined interruption-free power supply unit and backup unit.

Abstract: An arrangement is disclosed for ensuring an uninterrupted current supply to at least one electrical consumer which draws energy from an alternating voltage network and is supplied with energy in the event of a network failure by a fuel cell. The fuel cell (8) is connected at its electrical outputs to at least one current inverter (7) whose output is connected to the minimum of one alternating voltage consumer (1, 2) and to a branch containing a switch (4) on the consumer side of the switch; the switch is connected to an alternating voltage network (6) and is opened in the event of the voltage in the alternating voltage network falling below a predetermined level and closed if the alternating voltage is above that threshold; and the fuel cell operates in stand-by mode if the network voltage is above the threshold, and, if voltage is below the threshold, in a mode in which the energy required by the consumer is supplied via the current inverter (7).