NOVELTY - Biogas plant comprises at least one fermenter (1) and two storage tanks, which are connected together in a communicative manner. The storage tanks are formed as gas storages (2) and respectively have a filling level sensor, where one of the gas storage is defined as primary gas storage and the other gas storage is defined as the secondary gas storage. The secondary gas storage is formed as a double membrane gas storage having an inner membrane (7) and an outer membrane (8). A control device is connected with filling level sensor of the gas storage and fan of the double membrane gas storage.    USE - Used as biogas plant.    ADVANTAGE - The biogas plant utilizes available storage capacity in a simple manner, and fills biogas in all gas storages in a uniform manner.    DETAILED DESCRIPTION - Biogas plant comprises at least one fermenter (1) and two storage tanks, which are connected together in a communicative manner. The storage tanks are formed as gas storages (2) and respectively have a filling level sensor, where one of the gas storage is defined as primary gas storage and the other gas storage is defined as the secondary gas storage. The secondary gas storage is formed as a double membrane gas storage having an inner membrane (7) and an outer membrane (8), where a fan is provided for adjusting supporting air pressure between the two membranes. A control device is connected with the filling level sensor of the gas storage and the fan of the double membrane gas storage, and is formed such that the supporting air pressure is adjusted and the filling level in the secondary gas storage corresponds to the filling level in the primary gas storage. An INDEPENDENT CLAIM is also included for operating the biogas plant, comprising producing biogas in the fermenter, supplying the biogas to one of the two gas storages, detecting the filling level in both gas storages and adjusting the supporting air pressure.    DESCRIPTION OF DRAWING(S) - The figure shows a schematic representation of the biogas plant having two fermenters and three gas storages.    Fermenter (1)    Gas storage (2)    Inner membrane (7)    Outer membrane (8)    Cogeneration plant (15)