An energy storage system comprising a device for producing a first and a second secondary fluid by electrolysis of at least one primary fluid, and a storage device for secondary fluids in order to store the first and second secondary fluids separately, and a fuel cell for generating electrical energy by oxidation-reduction reaction between the first and second secondary fluids, the storage device for secondary fluids comprising at least two reservoir (30, 32) containing a pressurized fluid, the reservoirs (30, 32) being place inside an enclosure, the storage system also comprising an emptying system for emptying said reservoirs (30, 32), the emptying system comprising, for each reservoir (30, 32), a vent for discharging the fluid out of the reservoir (30, 32) and a discharge valve for connecting the reservoir (30, 32) to the vent, the discharge valve being movable between an open configuration, in which the discharge valve fluidly connects the reservoir (30, 32) to the vent, and a closed configuration, in which the reservoir (30, 32) and the vent are fluidly isolated from one another by the discharge valve, the emptying system further comprising, for each discharge valve, a return member for returning the discharge valve to the closed configuration, and a fluid control system for controlling the movement of each discharge valve to the open configuration by action of an operating fluid on the discharge valve, said control system comprising an operating station, and, for each discharge valve, a fluid pipe (60, 62) fluidly connecting the operating station to the discharge valve, each discharge valve of the emptying system being fluidly connected to a respective reservoir (30, 32) of the fluid storage device so as to be fluidly interposed between said reservoir (30, 32) and a vent of the emptying system, the operating station being placed outside the enclosure and comprising at least one reversible free connection for connecting to each fluid pipe (60, 62) of a supply device for supplying the control system with the operating fluid. the storage device for secondary fluids comprising at least two reservoir (30, 32) containing a pressurized fluid, the reservoirs (30, 32) being place inside an enclosure, the storage system also comprising an emptying system for emptying said reservoirs (30, 32), the emptying system comprising, for each reservoir (30, 32), a vent for discharging the fluid out of the reservoir (30, 32) and a discharge valve for connecting the reservoir (30, 32) to the vent, the discharge valve being movable between an open configuration, in which the discharge valve fluidly connects the reservoir (30, 32) to the vent, and a closed configuration, in which the reservoir (30, 32) and the vent are fluidly isolated from one another by the discharge valve, the emptying system further comprising, for each discharge valve, a return member for returning the discharge valve to the closed configuration, and a fluid control system for controlling the movement of each discharge valve to the open configuration by action of an operating fluid on the discharge valve, said control system comprising an operating station, and, for each discharge valve, a fluid pipe (60, 62) fluidly connecting the operating station to the discharge valve, each discharge valve of the emptying system being fluidly connected to a respective reservoir (30, 32) of the fluid storage device so as to be fluidly interposed between said reservoir (30, 32) and a vent of the emptying system, the operating station being placed outside the enclosure and comprising at least one reversible free connection for connecting to each fluid pipe (60, 62) of a supply device for supplying the control system with the operating fluid.