Reversible fuel cell system and method for operating the same

Abstract

To provide a reversible fuel cell system that can be simplified in the system configuration and enables prevention of excessive consumption of hydrogen required for system operation.SOLUTION: A reversible fuel cell system is provided, including: a solid oxide reversible fuel cell which has an anode, a cathode, and a solid electrolyte, and can reversibly perform water electrolysis and electric power generation; a fuel supply portion that supplies fuel gas including hydrogen and / or water vapor to the anode; an oxygen supply portion that supplies gas containing oxygen to the cathode; and a control portion that switches between a water electrolysis mode and an electric power generation mode, and the fuel supply portion includes a fuel storage device, first fuel piping, and second fuel piping, and the flow direction of the fuel gas is the same in both the water electrolysis mode and the electric power generation mode.SELECTED DRAWING: Figure 2

Description

[Technical Field]

[0001] The present invention relates to a reversible fuel cell system and a method for operating the same. [Background technology]

[0002] The reversible solid oxide fuel cell (hereinafter sometimes referred to as "r-SOC") system is an energy system that can reversibly produce hydrogen and generate electricity. The reversible solid oxide fuel cell system reversibly combines the power generation technology of solid oxide fuel cells (SOFC) and the hydrogen production technology of solid oxide steam electrolyzers (SOEC) in a single device, and is attracting attention as a next-generation energy system that can not only generate electricity using hydrogen as fuel, but also store energy using the hydrogen produced by steam electrolysis.

[0003] When incorporating a reversible solid oxide fuel cell (r-SOC) into a system, it is important to manage hydrogen and water (water vapor), which involves switching between power generation (fuel cell operation), an exothermic reaction, and water electrolysis (water electrolysis), an endothermic reaction. For example, Patent Document 1 discloses a system using a reversible fuel cell (reversible cell) that achieves high round-trip efficiency (charge / discharge efficiency). This system recovers and stores the hydrogen produced at the fuel electrode and the oxygen produced at the air electrode during water electrolysis (charging), and can generate electricity using the stored hydrogen and oxygen. The temperature of the reversible fuel cell cell can also be controlled, creating a highly efficient system.

[0004] Patent Document 2 discloses a system (energy storage device) using a reversible fuel cell that can stably store energy obtained by water electrolysis (charging) for a long period of time. This system recovers and stores hydrogen produced at the fuel electrode during water electrolysis (charging), and stores water (water vapor) produced at the fuel electrode while generating electricity using the stored hydrogen, allowing the stored water to be used during water electrolysis. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] Patent No. 7306651 [Patent Document 2] Patent Publication No. 2021-34131 Summary of the Invention [Problem to be solved by the invention]

[0006] Incidentally, a reversible fuel cell is a device with two functions: power generation and water electrolysis, and in order to operate the two functions of a reversible coulometric cell, the configuration of the reversible fuel cell system has tended to be complicated. Furthermore, while reversible fuel cell systems have been developed from the perspective of energy efficiency, such as round-trip efficiency, sufficient consideration has not been given to operational aspects such as the excessive consumption (and depletion) of hydrogen required for power generation.

[0007] The present invention has been made in consideration of the above-mentioned problems, and aims to provide a reversible fuel cell system and an operating method thereof that can simplify the system configuration and prevent excess (and depletion) of hydrogen required for system operation. [Means for solving the problem]

[0008] The present inventors have conducted extensive research to solve the above problems, and as a result have found that the following invention meets the above object, thereby completing the present invention.

[0009] That is, the present invention relates to the following inventions. <1> 1. A reversible fuel cell system, comprising: a reversible solid oxide fuel cell having an anode, an cathode, and a solid electrolyte disposed between the anode and the cathode, and capable of reversibly performing water electrolysis and power generation; a fuel supply unit that supplies a fuel gas containing hydrogen and / or water vapor to the fuel electrode; an oxygen supply unit that supplies an oxygen-containing gas to the air electrode; a control unit that switches between a water electrolysis mode in which power is received from an external source and water is electrolyzed by the reversible fuel cell, and a power generation mode in which hydrogen and oxygen are used to generate power by the reversible fuel cell; and the fuel supply unit includes a fuel storage device that stores the fuel gas, a hydrogen storage amount measuring device that measures the amount of hydrogen stored in the fuel storage device, a first fuel pipe that connects the fuel storage device to the fuel electrode and distributes the fuel gas from the fuel storage device to the fuel electrode, and a second fuel pipe that connects the fuel storage device to the fuel electrode and distributes the fuel gas from the fuel electrode to the fuel storage device, The reversible fuel cell system has the same flow direction of the fuel gas in the first fuel pipe and the second fuel pipe in both the water electrolysis mode and the power generation mode. <2> A bypass pipe is provided to connect the first fuel pipe and the second fuel pipe. <1> 1. A reversible fuel cell system according to claim 1. <3> The fuel storage device has a hydrogen storage alloy. <1> or <2> 1. A reversible fuel cell system according to claim 1. <4> The fuel storage device includes a pressurized tank. <1> from <3> 1. A reversible fuel cell system according to any one of the preceding claims. <5> <1> from <4> A method for operating a reversible fuel cell system according to any one of the above, in the water electrolysis mode, a fuel gas containing water vapor is supplied to the anode via a first pipe to perform water electrolysis, and the fuel gas with an increased hydrogen content is discharged to a second pipe, and a portion of the fuel gas with an increased hydrogen content is recycled to the first pipe via the bypass pipe; A method for operating a reversible fuel cell system, in which, in the power generation mode, fuel gas containing hydrogen is supplied to the anode via a first pipe to generate power, and the fuel gas with an increased amount of water vapor is discharged to a second pipe, and a portion of the fuel gas with an increased amount of water vapor is recycled to the first pipe via the bypass pipe. <6> determining a recycling amount of the hydrogen-rich fuel gas that has passed through the anode based on the amount of hydrogen produced in the water electrolysis mode; determining a recycling amount of the fuel gas having a large amount of water vapor that has passed through the anode based on the amount of hydrogen consumed in the power generation mode; <5> A method for operating a reversible fuel cell system according to claim 1. <7> The hydrogen stored in water electrolysis mode is used up in power generation mode within a specified period. <5> or <6> A method for operating a reversible fuel cell system according to claim 1. <8> The predetermined period is 0.5 days or more and 7 days or less <7> A method for operating a reversible fuel cell system according to claim 1. <9> Set the operating times of the water electrolysis mode and power generation mode so that the system efficiency of the reversible fuel cell system is 50% or more. <5> from <8> 2. A method for operating a reversible fuel cell system according to claim 1, wherein:

[0010] <1a> <1> from <4> A method for operating a reversible fuel cell system according to any one of the above, A step (P1) of setting a first power generation stop hydrogen amount; a step (P2) of measuring the amount of hydrogen consumed in the power generation mode after the step (P1), and stopping the power generation mode when the amount of hydrogen consumed exceeds the first power generation stop hydrogen amount; A method for operating a reversible fuel cell system comprising: <2a> A method for operating a reversible fuel cell system according to <1a>, comprising a step (Q1) of measuring the amount of hydrogen stored in the power generation mode and stopping the power generation mode when the amount of hydrogen stored falls below a second power generation stop hydrogen amount. <3a> The method for operating a reversible fuel cell system according to <1a> or <2a>, wherein the operation times of the water electrolysis mode and the power generation mode are set so that the system efficiency of the reversible fuel cell system is 50% or more.

[0011] <1b> The reversible fuel cell system further includes a waste heat supply unit that can supply waste heat from the solid oxide reversible fuel cell in the power generation mode to the fuel storage device, and in the power generation mode, hydrogen is extracted from the fuel storage device using the waste heat from the solid oxide reversible fuel cell that is supplied by the waste heat supply unit to generate power. <1> from <4> 1. A reversible fuel cell system according to any one of the preceding claims. <2b> The pressure tank is kept warm by a heat insulating material so that the water does not condense in the pressure tank. <4> 1. A reversible fuel cell system according to claim 1. <3b> The fuel storage device further stores carbon dioxide, the fuel supply unit has a methanation catalyst device that produces methane from hydrogen and carbon dioxide, and the fuel supply unit stores the high-energy-density gas containing methane produced in the methanation catalyst device in the fuel storage device. <4> Or a reversible fuel cell system as described in <2b>. <4b> The reversible fuel cell system according to <3b>, wherein the methanation catalyst device is installed inside the fuel storage device and / or upstream of the fuel storage device. [Effects of the Invention]

[0012] According to the present invention, it is possible to provide a reversible fuel cell system and an operating method thereof that can simplify the system configuration and prevent excess or depletion of hydrogen required for system operation. [Brief explanation of the drawings]

[0013] [Figure 1] 1 is a conceptual diagram of a reversible fuel cell system of the present invention. [Figure 2] 1 is a schematic diagram showing a reversible fuel cell system according to a first embodiment of the present invention. [Figure 3] FIG. 2 is a control flow diagram of a first embodiment of a method for operating a reversible fuel cell system according to the present invention. [Figure 4] FIG. 2 is a control flow diagram of a second embodiment of the method for operating a reversible fuel cell system of the present invention. [Figure 5]FIG. 4 is a control flow diagram of a third embodiment of the method for operating a reversible fuel cell system of the present invention. [Figure 6] This shows the simulation results of the relationship between operation time and system efficiency in water electrolysis (SOEC) mode. [Figure 7] This shows the simulation results of the relationship between operation time and output ratio in water electrolysis (SOEC) mode. [Figure 8] FIG. 4 is a schematic diagram showing a reversible fuel cell system according to a second embodiment of the present invention. [Figure 9] FIG. 10 is a schematic diagram showing a reversible fuel cell system according to a third embodiment of the present invention. DETAILED DESCRIPTION OF THE INVENTION

[0014] The present invention will be described in detail below with reference to examples, but the present invention is not limited to the examples below and can be practiced with any modifications within the scope of the gist of the present invention. In this specification, the symbol "to" is used as an expression including the numerical value or physical quantity before and after it.

[0015] (Definition of terms) In this specification, the term "reversible fuel cell" means a "reversible solid oxide fuel cell (sometimes referred to as "r-SOC")." In addition, in this specification, the term "reversible fuel cell system" refers to a system that includes a reversible fuel cell that performs, within a single fuel cell, the reaction of hydrogen and oxygen to obtain water and electricity (power generation), and the reverse reaction of water electrolysis to obtain hydrogen and oxygen (water electrolysis).

[0016] <1. Reversible fuel cell (r-SOC) system> The reversible fuel cell system of the present invention is a reversible fuel cell system comprising: a solid oxide reversible fuel cell having a fuel electrode, an air electrode, and a solid electrolyte provided between the fuel electrode and the air electrode, and capable of reversibly performing water electrolysis and power generation; a fuel supply unit that supplies a fuel gas containing hydrogen and / or water vapor to the fuel electrode; an oxygen supply unit that supplies a gas containing oxygen to the air electrode; and a control unit that switches between a water electrolysis mode in which power is received from an external source and water is electrolyzed by the reversible fuel cell, and a power generation mode in which hydrogen and oxygen are used to generate power by the reversible fuel cell, The fuel supply unit includes a fuel storage device that stores the fuel gas, a hydrogen storage amount measuring device that measures the amount of hydrogen stored in the fuel storage device, a first fuel pipe that connects the fuel storage device to the fuel electrode and distributes the fuel gas from the fuel storage device to the fuel electrode, and a second fuel pipe that connects the fuel storage device to the fuel electrode and distributes the fuel gas from the fuel electrode to the fuel storage device, and the flow direction of the fuel gas in the first fuel pipe and the second fuel pipe is the same in both the water electrolysis mode and the power generation mode.

[0017] In one aspect of the reversible fuel cell system of the present invention, there is a bypass pipe connecting the first fuel pipe and the second fuel pipe. In another aspect of the reversible fuel cell system of the present invention, the fuel storage device includes a hydrogen storage alloy. In another aspect of the reversible fuel cell system of the present invention, the fuel storage device includes a pressurized tank.

[0018] A method for operating a reversible fuel cell system of the present invention uses the reversible fuel cell system of the present invention, and in the water electrolysis mode, supplies fuel gas containing water vapor to the anode via a first pipe to perform water electrolysis, thereby discharging the fuel gas with an increased hydrogen content to the second pipe, and recycles a portion of the fuel gas with an increased hydrogen content to the first pipe via the bypass pipe; and in the power generation mode, supplies fuel gas containing hydrogen to the anode via the first pipe to perform power generation, thereby discharging the fuel gas with an increased water vapor content to the second pipe, and recycles a portion of the fuel gas with an increased water vapor content to the first pipe via the bypass pipe.

[0019] The method for operating a reversible fuel cell system of the present invention is characterized in that it uses the reversible fuel cell system of the present invention and includes the steps of: (P1) setting a first power generation stop hydrogen amount; and (P2) measuring the amount of hydrogen consumed in the power generation mode after step (P1) and stopping the power generation mode when the amount of hydrogen consumed exceeds the first power generation stop hydrogen amount. In this case, the method may also include the step (Q1) of measuring the amount of hydrogen stored in the power generation mode and stopping the power generation mode when the amount of hydrogen stored falls below a second power generation stop hydrogen amount set to prevent excessive consumption of the stored hydrogen.

[0020] FIG. 1 shows a conceptual diagram of a reversible fuel cell system of the present invention. As shown in FIG. 1, the reversible fuel cell system of the present invention supplies a fuel gas containing hydrogen and water (water vapor) stored in a storage tank (fuel storage device) to the fuel electrode of the reversible fuel cell. The reversible fuel cell (r-SOC) according to the present invention is composed of an anode, an cathode, a cathode, and a solid electrolyte, and generates oxide ions (O 2- This reversible fuel cell uses hydrogen as a carrier. By switching the direction of the current, it is possible to select between water electrolysis mode (SOEC mode) and power generation mode (SOFC mode), and the flow of fuel gas (hydrogen and water (steam)) is the same in either mode.

[0021] In water electrolysis mode (SOEC mode), fuel gas containing water vapor is supplied from a storage tank to the fuel electrode. Hydrogen is produced from the water vapor at the fuel electrode, and this fuel gas, which contains a larger amount of hydrogen than the fuel gas supplied to the fuel electrode, is returned from the fuel electrode to the storage tank. As a result, the amount of hydrogen in the storage tank increases and the amount of water vapor decreases. On the other hand, in power generation mode (SOFC mode), fuel gas containing hydrogen is supplied from a storage tank to the fuel electrode. Water vapor (water) is produced from the hydrogen at the fuel electrode, and this fuel gas, which contains a larger amount of water vapor than the fuel gas supplied to the fuel electrode, is returned from the fuel electrode to the storage tank. As a result, the amount of hydrogen in the storage tank decreases and the amount of water vapor increases. The reversible fuel cell system of the present invention can continue to operate while repeatedly switching between a water electrolysis mode and a power generation mode, while maintaining the same flow direction of the fuel gas.

[0022] In the reversible fuel cell system of the present invention, in both the water electrolysis mode and the power generation mode, fuel gas containing hydrogen and / or water vapor is circulated through the fuel storage device, the first fuel pipe, the fuel electrode of the r-SOC, and the second fuel pipe in that order, and is then stored again in the fuel storage device (e.g., a hydrogen storage alloy or a pressurized tank) and can be reused as fuel gas.

[0023] As such, the reversible fuel cell system of the present invention does not require changing the flow direction of the fuel gas, and therefore does not require flow paths (piping) for changing the flow direction, or equipment (opening / closing valves, etc.) and controls for switching flow paths, thereby simplifying the system configuration.

[0024] One aspect of the reversible fuel cell system of the present invention is characterized by the inclusion of a bypass pipe connecting the first fuel pipe and the second fuel pipe, through which a portion of the fuel gas with an increased amount of hydrogen can be recycled in the water electrolysis mode, and a portion of the fuel gas with an increased amount of water vapor can be recycled and reused in the power generation mode. By recycling and reusing a portion of the fuel gas in this way, the efficiency of the reversible fuel cell system can be improved.

[0025] When the reversible fuel cell system of the present invention is operated by recycling a portion of the fuel gas as described above, it is preferable to determine the amount of the hydrogen-rich fuel gas that has passed through the anode and is recycled based on the amount of hydrogen produced in the water electrolysis mode, and to determine the amount of the water vapor-rich fuel gas that has passed through the anode and is recycled based on the amount of hydrogen consumed in the power generation mode. In this case, hydrogen is produced at the fuel electrode in the water electrolysis mode, and the fuel gas that passes through the fuel electrode contains a large amount of hydrogen (a small amount of water vapor). If the amount of hydrogen produced is large, the amount of recycled fuel gas that has a large amount of hydrogen that passes through the fuel electrode can be reduced, and if the amount of hydrogen produced is small, the amount of recycled fuel gas can be increased. In addition, in the method of operating the reversible fuel cell system of the present invention, hydrogen is consumed at the fuel electrode in the power generation mode, and the fuel gas that passes through the fuel electrode contains a large amount of water vapor (a small amount of hydrogen). If the amount of hydrogen consumed is large, the amount of recycled fuel gas that contains a large amount of water vapor that passes through the fuel electrode can be reduced, and if the amount of hydrogen consumed is small, the amount of recycled fuel gas can be increased. Therefore, the amount of hydrogen and water vapor supplied to the fuel electrode can be adjusted according to the amount of hydrogen produced in the water electrolysis mode and the amount of hydrogen consumed in the power generation mode, thereby improving the efficiency of the reversible fuel cell system.

[0026] Furthermore, the reversible fuel cell system of the present invention may be operated so that the hydrogen stored in the water electrolysis mode is used up in the power generation mode within a predetermined period of time. By using up the hydrogen stored in water electrolysis mode in power generation mode within a specified period, the reversible fuel cell system can be operated highly efficiently and water electrolysis and power generation can be made the most effective.

[0027] There is no particular restriction on the specified period, and it can be, for example, between 0.5 days (12 hours) and 7 days (84 hours). In particular, by setting the specified period to 1 day (24 hours), it becomes possible to operate the reversible fuel cell system according to a daily cycle. For example, during the day, electricity generated by solar power generation can be used to produce and store hydrogen in water electrolysis mode, and at night, the stored hydrogen can be used to generate electricity in power generation mode, making it possible to make effective use of electricity derived from natural energy sources. In the reversible fuel cell of the present invention, it is preferable to set the operation times of the water electrolysis mode and the power generation mode so that the system efficiency is 50% or more, and preferably 60% or more.

[0028] In the reversible fuel cell system of the present invention, there is no limitation on the ratio of the operation time in the power generation mode to the operation time in the water electrolysis mode, but it can be set to, for example, 1:0.1 or more and 1:10 or less.

[0029] Preferred embodiments of the present invention will now be described with reference to the drawings. The present invention is not limited to the following embodiments, and can be implemented with any modifications within the scope of the present invention. The dimensions, materials, and other specific numerical values ​​shown in the embodiments are merely examples to facilitate understanding of the invention, and do not limit the present invention unless otherwise specified. Furthermore, in all drawings, similar components are given similar reference numerals, and descriptions thereof will be omitted as appropriate.

[0030] FIG. 2 is a schematic diagram showing a reversible fuel cell system according to an embodiment of the present invention (first embodiment). The reversible fuel cell system 100 includes a reversible fuel cell 110 , a fuel supply unit 120 , an oxygen supply unit 130 , a control unit 140 , and a hydrogen measurement unit 150 .

[0031] [1-1. Reversible fuel cell] The reversible fuel cell 110 has an anode 112, an cathode 114, and a solid electrolyte 116 provided between the anode 112 and the cathode 114, and is capable of reversibly electrolyzing water and generating electricity. The reversible fuel cell 110 uses oxide ions (O 2- ) and the reversible fuel cell system of the present invention can be used to repeatedly perform water electrolysis (steam electrolysis) and power generation in a high temperature range (for example, 300°C or higher and 1000°C or lower).

[0032] (1-1-1.Solid electrolyte) The solid electrolyte 116 is selected from among known solid electrolytes for conventional SOFCs and SOECs, taking into consideration its reactivity with the constituent materials of the anode and cathode during manufacture and operation, its long-term stability in the power generation environment of the SOFC and the steam electrolysis environment of the SOEC, and other factors. For example, zirconia-based oxides doped with scandium or yttrium (ScSZ and YSZ, respectively), ceria-based oxides doped with gadolinium or samarium (GDC and SDC, respectively), lanthanum gallate-based oxides doped with strontium or magnesium, etc. can be used as the solid electrolyte 116. Among these, ScSZ, which has high ionic conductivity and high stability, and YSZ, which is inexpensive and highly stable, are preferred. The thickness of the solid electrolyte 116 may be adjusted appropriately according to the required conductivity and strength. For example, in the case of an electrolyte-supported cell, a thickness of 5 to 500 μm or less is preferably used for ScSZ.

[0033] (1-1-2. Air electrode) The material of the air electrode 114 is appropriately selected taking into consideration factors such as reactivity with the solid electrolyte during manufacturing and operation. For the air electrode 114, for example, a metal oxide such as a perovskite-type oxide can be used. More specific examples include (Sm,Sr)CoO3, (La,Sr)MnO3, (La,Sr)CoO3, (La,Sr)(Fe,Co)O3, and (La,Sr)(Fe,Co,Ni)O3. The thickness of the air electrode 114 varies depending on the form and purpose of the reversible fuel cell, but is, for example, about 10 to 300 μm.

[0034] (1-1-3.Fuel electrode) The anode 112 is appropriately selected taking into consideration factors such as reactivity with the solid electrolyte during manufacture and operation. The anode 112 may be composed of, for example, a cermet material containing Ni and / or a Ni compound (e.g., NiO), or may be composed of an electronically conductive oxide and an ionically conductive oxide. Here, the electronically conductive oxide may be a Ti-containing perovskite-type oxide represented by the composition formula ABO3, in which the A site is at least one selected from the group consisting of Ca, Sr, Ba, and La, and the B site is Ti. The ionically conductive oxide may also be a Ce-based oxide (Gd2O3-doped CeO2 or Sm2O3-doped CeO2). The thickness of the fuel electrode 112 varies depending on the form and purpose of the reversible fuel cell, but is, for example, about 10 to 300 μm.

[0035] [1-2.Fuel supply section] The fuel supply unit 120 supplies a fuel gas containing hydrogen and / or water vapor to the fuel electrode 112 . The fuel supply unit 120 includes a fuel storage device 121 that stores fuel gas, a hydrogen storage amount measuring device 124 that measures the amount of hydrogen stored in the fuel storage device, a first fuel pipe 122 that connects the fuel storage device 121 to the fuel electrode 112 and distributes fuel gas from the fuel storage device 121 to the fuel electrode 112, a second fuel pipe 123 that connects the fuel storage device 121 to the fuel electrode 112 and distributes fuel gas from the fuel electrode 112 to the fuel storage device 121, and a bypass pipe 126 that connects the first fuel pipe and the second fuel pipe.

[0036] The fuel supply unit 120 has a blower (not shown), and in either the water electrolysis mode or the power generation mode, the fuel gas can be circulated through the fuel storage device 121, the first fuel pipe 122, the fuel electrode 112, and the second fuel pipe 123 in that order, and then stored again in the fuel storage device 121. Therefore, the reversible fuel cell system 100 does not need to change the flow direction of the fuel gas, and does not require a flow path (pipe) for changing the flow direction, or equipment (such as an on-off valve) or control for switching the flow path, thereby simplifying the system configuration.

[0037] Furthermore, since the fuel supply unit 120 has the hydrogen storage amount measuring device 124, the reversible fuel cell system 100 can grasp the amount of hydrogen stored in the fuel storage device 121, that is, the amount of hydrogen stored. The hydrogen storage amount measuring device 124 may be any measuring device (for example, a pressure gauge) as long as it can measure the amount of hydrogen storage.

[0038] Furthermore, since the fuel supply unit 120 has the bypass pipe 126, a portion of the fuel gas that has passed through the anode 112 can be recycled and supplied again to the anode 112. The amount of recycled gas flowing through the bypass pipe 126 can be adjusted by any means. For example, by providing a flow control valve (not shown) in the bypass pipe 126 and adjusting the opening of the flow control valve, the amount of recycled fuel gas that has passed through the anode 112 can be adjusted. Adjustment of the recycled amount will be described later.

[0039] [1-3. Oxygen supply unit] The oxygen supply unit 130 supplies a gas containing oxygen to the air electrode 114 . The oxygen supply unit 130 has a blower (not shown) and, in the power generation mode, circulates a gas containing oxygen (e.g., air) from an oxygen-containing gas supply source to the air electrode 114 and discharges unreacted air from the air electrode 114. In addition, in the water electrolysis mode, the oxygen supply unit 130 discharges an oxygen-containing gas containing oxygen produced at the air electrode 114 from the air electrode 114.

[0040] [1-4. Control Unit] The control unit 140 can switch between a water electrolysis mode in which power is received from an external source and water is electrolyzed by the reversible fuel cell, and a power generation mode in which hydrogen and oxygen are used to generate power by the reversible fuel cell. The control unit 140 is composed of a semiconductor integrated circuit including a CPU (Central Processing Unit). The control unit 140 reads programs and parameters for operating the CPU itself from the ROM. The control unit 140 manages and controls the entire reversible fuel cell system 100 in cooperation with RAM as a work area and other electronic circuits. The water electrolysis mode and the power generation mode will be described below.

[0041] (1-4-1. Water electrolysis mode) The water electrolysis mode is an operation mode of the reversible fuel cell system 100 in which power is received from an external source and the reversible fuel cell 110 electrolyzes water (water vapor).

[0042] In the water electrolysis mode, the control unit 140 drives the fuel supply unit 120 and the oxygen supply unit 130. Specifically, the control unit 140 causes fuel gas containing water vapor to flow (supply) from the fuel storage device 121 to the fuel electrode 112 through the first fuel pipe 122, and causes fuel gas containing unreacted water vapor and generated hydrogen at the fuel electrode 112 to flow (return) from the fuel electrode 112 to the fuel storage device 121 through the second fuel pipe 123. The control unit 140 also discharges the oxygen-containing gas containing oxygen generated at the air electrode 114 from the air electrode 114. The control unit 140 also controls the charge / discharge unit 160 to supply power to the reversible fuel cell 110. That is, the control unit 140 controls the power supply between the reversible fuel cell 110 and the charge / discharge unit 160. The charge / discharge unit 160 may be connected to a power generation device that uses renewable energy, such as a solar power generation device, a hydroelectric power generation device, or a wind power generation device.

[0043] As a result, water vapor is supplied to the fuel electrode 112, and the reaction shown in formula (1) below proceeds due to the received power. H2O + 2e - → H2+ O 2- ...Equation (1)

[0044] And oxide ions (O 2- ) is conducted (moves) through the solid electrolyte 116, and the reaction shown in formula (2) below proceeds in the air electrode 114. O 2- → 1 / 2O2+ 2e - ...Equation (2)

[0045] Thus, in the water electrolysis mode, water (water vapor) is electrolyzed at the fuel electrode 112 to generate hydrogen (the above formula (1)). Note that the fuel gas containing unreacted water vapor and generated hydrogen at the fuel electrode 112 flows (returns) from the fuel electrode 112 to the fuel storage device 121 through the second fuel pipe 123.

[0046] In the water electrolysis mode, oxygen is generated at the air electrode 114 (the above formula (2)). The oxygen generated at the air electrode 114 is discharged from the air electrode 114.

[0047] The temperature of the reversible fuel cell 110 in the water electrolysis mode is determined taking into consideration the components and size of the reversible fuel cell 110, the required steam electrolysis reaction rate, etc., and is, for example, 300°C or higher and 1000°C or lower, or 500°C or higher and 900°C or lower.

[0048] (1-4-2. Power generation mode) The power generation mode is an operation mode of the reversible fuel cell system 100 in which hydrogen and oxygen are used by the reversible fuel cell 110 to generate electricity.

[0049] In the power generation mode, the control unit 140 drives the fuel supply unit 120 and the oxygen supply unit 130. Specifically, the control unit 140 distributes (supplies) fuel gas containing hydrogen from the fuel storage device 121 to the fuel electrode 112 through the first fuel pipe 122, and distributes (returns) fuel gas containing unreacted hydrogen and generated water vapor (water) at the fuel electrode 112 from the fuel electrode 112 to the fuel storage device 121 through the second fuel pipe 123. The control unit 140 also supplies air from an oxygen-containing gas supply source to the air electrode 114, and discharges the oxygen-containing gas containing unreacted oxygen at the air electrode 114 from the air electrode 114. Furthermore, the control unit 140 connects the charge / discharge unit 160 to an external load (not shown).

[0050] As a result, fuel gas is supplied to the fuel electrode 112, and the reaction shown in the following formula (3) proceeds. H2+ O 2- → H2O + 2e - ...Equation (3)

[0051] Furthermore, an oxygen-containing gas is supplied to the air electrode 114, and the reaction shown in the following formula (4) proceeds. 1 / 2O2+ 2e - → O 2- ...Equation (4) And oxide ions (O 2- ) conducts (moves) through the solid electrolyte 116, causing the reversible fuel cell 110 to generate electricity. The generated electricity is supplied to an external load via the charge / discharge unit 160.

[0052] In the power generation mode, water (water vapor) is generated at the fuel electrode 112 (see formula (3) above). The fuel gas containing the water vapor generated at the fuel electrode 112 and unreacted hydrogen is circulated (returned) from the fuel electrode 112 to the fuel storage device 121 through the second fuel pipe 123. The fuel gas is stored in the fuel storage device 121 and is reused in the water electrolysis mode or the power generation mode.

[0053] In the power generation mode, air is supplied from an oxygen-containing gas supply source to the air electrode 114, and oxygen reacts and is consumed (see formula (4) above). The oxygen-containing gas containing unreacted oxygen at the air electrode 114 is discharged from the air electrode 114.

[0054] The temperature of the reversible fuel cell 110 in power generation mode is determined taking into consideration the components and size of the reversible fuel cell 110, the required reaction speed, etc., and is, for example, 300°C or higher and 1000°C or lower, or 500°C or higher and 900°C or lower.

[0055] [1-5. Hydrogen measurement section] The hydrogen measurement unit 150 measures the amount of hydrogen produced in the water electrolysis mode and the amount of hydrogen consumed in the power generation mode. The hydrogen measurement unit 150 also transmits signals related to the measured amounts of hydrogen produced and consumed to the control unit 140. Any measuring device capable of measuring the amount of hydrogen produced and the amount of hydrogen consumed can be used for the hydrogen measurement unit 150. A typical example of the hydrogen measurement unit 150 is an ammeter. When an ammeter is used as the hydrogen measurement unit 150, the amount of hydrogen produced can be calculated from the water electrolysis current (integrated value) in the water electrolysis mode, and the amount of hydrogen consumed can be calculated from the power generation current (integrated value) in the power generation mode.

[0056] <2. Operation method of reversible fuel cell> The method for operating a reversible fuel cell of the present invention can reversibly perform water electrolysis and power generation in the reversible fuel cell of the present invention using the above-mentioned reversible fuel cell system. The method for operating a reversible fuel cell according to the present invention will be described below with reference to the drawings. FIG. 3 shows a control flow diagram of a first embodiment of the method for operating a reversible fuel cell of the present invention, FIG. 4 shows a control flow diagram of a second embodiment of the method for operating a reversible fuel cell of the present invention, and FIG. 5 shows a control flow diagram of a third embodiment of the method for operating a reversible fuel cell of the present invention. In addition, explanations that overlap with the above content may be omitted as appropriate.

[0057] [2-1. Reversible Fuel Cell Operation Method - First Aspect] A first aspect of the method for operating a reversible fuel cell according to the present invention determines the amount of fuel gas recycled via a fuel electrode 112 containing a larger amount of hydrogen than the fuel gas supplied to the fuel electrode 112 based on the amount of hydrogen produced in the water electrolysis mode, and determines the amount of fuel gas recycled via a fuel electrode 112 containing a larger amount of water vapor than the fuel gas supplied to the fuel electrode 112 based on the amount of hydrogen consumed in the power generation mode.

[0058] By adopting such a configuration, the first aspect of the method for operating a reversible fuel cell system of the present invention can reduce the amount of fuel gas recycled that contains a large amount of hydrogen via the anode 112 when the amount of hydrogen produced in the water electrolysis mode is large, and can increase the amount recycled when the amount of hydrogen produced is small. Furthermore, the first aspect of the method for operating a reversible fuel cell system of the present invention can reduce the amount of fuel gas recycled that contains a large amount of water vapor via the anode 112 when the amount of hydrogen consumed in the power generation mode is large, and can increase the amount recycled when the amount of hydrogen consumed is small. Therefore, the amounts of hydrogen and water vapor supplied to the anode can be adjusted according to the amount of hydrogen produced in the water electrolysis mode and the amount of hydrogen consumed in the power generation mode, thereby improving the efficiency of the reversible fuel cell system.

[0059] Furthermore, the first aspect of the method for operating a reversible fuel cell system according to the present invention makes it possible to use up the hydrogen stored in the water electrolysis mode in the power generation mode within a predetermined period of time. By using up the hydrogen stored in water electrolysis mode in power generation mode within a specified period, the reversible fuel cell system can be operated highly efficiently and water electrolysis and power generation can be made the most effective.

[0060] There is no particular limitation on the predetermined period, and it can be, for example, from 0.5 days (12 hours) to 7 days (84 hours). In particular, by setting the predetermined period to 1 day (24 hours), it becomes possible to operate the reversible fuel cell system according to a daily cycle.

[0061] [2-2. Reversible Fuel Cell Operation Method - Second Aspect] A second aspect of the method for operating a reversible fuel cell according to the present invention includes a step (P1) of measuring the amount of hydrogen produced in the water electrolysis mode and setting a first power generation stop hydrogen amount based on the amount of hydrogen produced, and a step (P2) of measuring the amount of hydrogen consumed in the power generation mode after step (P1) and stopping the power generation mode when the amount of hydrogen consumed exceeds the first power generation stop hydrogen amount.

[0062] With this configuration, when the amount of hydrogen consumed in the power generation mode exceeds the first power generation stop hydrogen amount that is set based on the amount of hydrogen produced in the water electrolysis mode, the power generation mode of the reversible fuel cell system 100 can be stopped. This prevents the amount of hydrogen consumed in the power generation mode from exceeding the amount of hydrogen produced in the water electrolysis mode, and the reversible fuel cell system 100 can prevent excessive consumption (and depletion) of hydrogen contained in the reversible fuel cell system 100.

[0063] Here, the first power generation stop hydrogen amount is a variable used to control the operation of the reversible fuel cell system 100, and is a variable that is compared with the hydrogen consumption amount in the power generation mode and is used to control the power generation mode to stop when the hydrogen consumption amount exceeds the first power generation stop hydrogen amount. The first power generation stop hydrogen amount is set based on the amount of hydrogen produced in the water electrolysis mode, but the first power generation stop hydrogen amount may be the same as the amount of hydrogen produced, or may be a value smaller than the amount of hydrogen produced. If the first power generation stop hydrogen amount is the same as the amount of hydrogen produced, the stored hydrogen can be used to the maximum extent while avoiding excessive hydrogen consumption. If the first power generation stop hydrogen amount is a value smaller than the amount of hydrogen produced, a surplus of stored hydrogen can be secured, and excessive hydrogen consumption can be more effectively prevented. The hydrogen production amount used to set the first power generation stop hydrogen amount may be the hydrogen production amount in the immediately preceding water electrolysis mode only, or may be the hydrogen production amount obtained by integrating the amounts of hydrogen produced in multiple prior water electrolysis modes, or may be the hydrogen production amount obtained by averaging the amounts of hydrogen produced in multiple prior water electrolysis modes per water electrolysis mode.

[0064] 3, when the power generation mode is started (S100), a first power generation stop hydrogen amount is set based on the amount of hydrogen produced in the water electrolysis mode (S110, step (P1)). Subsequently, the amount of hydrogen consumed in the power generation mode after step (P1) is measured (S120), and the power generation mode is continued while the hydrogen consumption amount is below the first power generation stop hydrogen amount, and the power generation mode is stopped when the hydrogen consumption amount exceeds the first power generation stop hydrogen amount (S130, S140, step (P2)).

[0065] [2-3. Reversible Fuel Cell Operation Method - Third Aspect] A third aspect of the method for operating a reversible fuel cell system according to the present invention includes a step (Q1) of measuring the amount of hydrogen stored in a power generation mode and stopping the power generation mode when the amount of hydrogen stored falls below a second power generation stop hydrogen amount set to prevent excessive consumption of the stored hydrogen.

[0066] With this configuration, when the amount of hydrogen consumed in the power generation mode falls below the second power generation stop hydrogen amount set to prevent excessive consumption of the stored hydrogen, the power generation mode of the reversible fuel cell system 100 can be stopped. Therefore, the reversible fuel cell system 100 does not consume excessive hydrogen in the power generation mode while measuring the amount of hydrogen stored (amount of hydrogen held) in the reversible fuel cell system 100, thereby preventing problems with the operation of the reversible fuel cell system 100 due to a decrease in the stored hydrogen amount.

[0067] Here, the second power generation stop hydrogen amount is a variable used to control the operation of the reversible fuel cell system, and is a variable that is compared with the hydrogen storage amount in the power generation mode and is used to control the power generation mode to stop when the hydrogen storage amount falls below the second power generation stop hydrogen amount. The second power generation stop hydrogen amount is set to prevent excessive consumption (and depletion) of the stored hydrogen amount. The second power generation stop hydrogen amount can be set so that an amount of hydrogen that does not interfere with the operation of the reversible fuel cell system 100 is left (stored) in the fuel storage device 121. For example, the second power generation stop hydrogen amount may be the sum of the amount of hydrogen required for the shutdown process of the power generation mode and the amount of hydrogen required for temperature rise, etc. until hydrogen can be produced in the subsequent water electrolysis mode, or a value greater than this sum. If the second power generation stop hydrogen amount is the same as the sum of these (the amount of hydrogen required for shutdown process and the amount of hydrogen required for temperature rise, etc.), the stored hydrogen can be used to the maximum extent while avoiding excessive hydrogen consumption. If the second power generation stop hydrogen amount is greater than this sum, a surplus of stored hydrogen can be secured, more effectively preventing excessive hydrogen consumption.

[0068] 4, when the power generation mode is started (S200), the amount of hydrogen stored in the fuel storage device is measured (S210). Thereafter, the power generation mode is continued while the amount of hydrogen stored exceeds the second power generation stop amount, and when the amount of hydrogen stored falls below the second power generation stop amount, the power generation mode is stopped (S220, S230, step (Q1)).

[0069] [2-3. Reversible Fuel Cell Operation Method - Third Aspect] In a third embodiment of the method for operating a reversible fuel cell system according to the present invention, the reversible fuel cell system 100 has a ratio of the operation time in the power generation mode to the operation time in the water electrolysis mode of 1:0.1 or more and 1:10 or less.

[0070] By adopting such a configuration, the reversible fuel cell system 100 can determine whether to stop the power generation mode based on the operating time of the power generation mode and the operating time of the water electrolysis mode, and the reversible fuel cell system 100 does not require a measuring instrument for determining whether to stop the power generation mode, thereby simplifying the system configuration.

[0071] Here, the ratio of the operation time in the power generation mode to the operation time in the water electrolysis mode can be set within a range that prevents the reversible fuel cell system 100 from excessively consuming (and depleting) hydrogen. If the ratio of the operation time in the water electrolysis mode to the operation time in the power generation mode is large, hydrogen can be sufficiently stored by water electrolysis in the water electrolysis mode, but utilization of the power generated by the reversible fuel cell system 100 in the power generation mode is limited. On the other hand, if the ratio of the operation time in the water electrolysis mode to the operation time in the power generation mode is small, power generated by the reversible fuel cell system 100 in the power generation mode can be fully utilized, but hydrogen storage by water electrolysis in the water electrolysis mode is limited, which may result in excessive consumption of hydrogen. The ratio of the operation time in the water electrolysis mode to the operation time in the power generation mode can be, for example, 1:0.1 or more and 1:10 or less, or 1:0.5 or more and 8 or less. The ratio of the operation time in the power generation mode to the operation time in the water electrolysis mode may be set as appropriate based on measurements or variables related to the amount of hydrogen consumed in the power generation mode and / or the amount of hydrogen stored in the water electrolysis mode.

[0072] As shown in FIG. 5 , when the power generation mode is started (S300), the water electrolysis mode operation time is set as a variable for operation control (determination condition) (S310). The water electrolysis mode operation time is the time during which the water electrolysis mode was operated immediately before the started power generation mode. Measurement of the power generation mode operation time then begins (S320), and the power generation mode is continued until a predetermined time has elapsed (S330). This predetermined time continues until the operation time of the power generation mode falls within a predetermined ratio range between the operation times of the power generation mode and the water electrolysis mode (i.e., if the ratio between the operation time of the power generation mode and the operation time of the water electrolysis mode is, for example, 1:0.1 or greater and 1:10 or less, the predetermined time continues for one-tenth of the water electrolysis mode operation time set in S310). Next, if the ratio of the operation time of the power generation mode to the operation time of the water electrolysis mode is within a predetermined ratio, the power generation mode is continued, but if the ratio deviates from the predetermined ratio, the power generation mode is stopped (S340, S350). (That is, if the ratio of the operation time of the power generation mode to the operation time of the water electrolysis mode is, for example, 1:0.1 or more and 1:10 or less, the power generation mode is continued while the operation time of the power generation mode is 1 / 10 or more and 10 times or less the operation time of the water electrolysis mode, and the power generation mode is stopped when the operation time of the power generation mode becomes 10 times or more the operation time of the water electrolysis mode.)

[0073] So far, we have explained the first to third aspects of the method for operating a reversible fuel cell, but the method for operating a reversible fuel cell of the present invention may be implemented by implementing the first to third aspects individually, or by combining the first to third aspects in any desired manner.

[0074] [2-4. Simulation] Using the reversible fuel cell system according to the present invention, a simulation was carried out to examine the effect on the system when the operating time in water electrolysis (SOEC) mode was changed. The simulation was carried out using commercial simulation software, Aspen Plus version 12.1. In SOEC mode, the efficiency was calculated assuming hydrogen production using 1kW of power and that "the hydrogen stored in SOEC mode is used up in SOFC mode within a certain period of continuous operation (24 hours in this case)." For SOEC mode, the calculation was performed assuming a temperature of 800°C and a thermoneutral potential (1.286V).

[0075] The simulation was performed under the following operating patterns A and B, with the setting that a heat shortage of 68.9 W occurs when raising the temperature to 800°C. Operation pattern A: Supplement the insufficient heat by supplying heat from an external source Operation pattern B: Reaction occurs at a potential higher than the thermoneutral potential, and Joule heating compensates for the lack of heat.

[0076] Figure 6 shows the simulation results for the relationship between operation time in water electrolysis (SOEC) mode and system efficiency, and Figure 7 shows the simulation results for the relationship between operation time in water electrolysis (SOEC) mode and output ratio (power output / power supply).

[0077] The system efficiency of the reversible fuel cell system of the present invention is calculated by the following formula.

[0078]

number

[0079] As shown in Figure 6, there is a difference in system efficiency between operation patterns A and B, and it was found that this difference in efficiency changes depending on the SOEC operation time. Also, as shown in Figure 7, in terms of output ratio (power output / power supply), it was found that operation pattern A was able to extract more of the supplied power as electrical energy.

[0080] <3. Other embodiments of the reversible fuel cell system> The reversible fuel cell system and its operating method according to the embodiment of the present invention have been described above. Hereinafter, a reversible fuel cell system according to another embodiment of the present invention will be described with reference to the drawings.

[0081] FIG. 8 is a schematic diagram showing a reversible fuel cell system according to a second embodiment of the present invention, and FIG. 9 is a schematic diagram showing a reversible fuel cell system according to a third embodiment of the present invention. In addition, explanations that overlap with the above content may be omitted as appropriate.

[0082] [3-1. Second embodiment of reversible fuel cell system] 8, a reversible fuel cell system 200 according to the second embodiment of the present invention includes a reversible fuel cell 110, a fuel supply unit 120, an oxygen supply unit 130, and a control unit 140. The reversible fuel cell 110, the fuel supply unit 120, the oxygen supply unit 130, and the control unit 140 are basically as described above, and detailed description thereof will be omitted.

[0083] A hydrogen storage alloy is stored in the fuel storage device 121 provided in the fuel supply unit 120. By providing the fuel storage device 121 with a hydrogen storage alloy, the fuel storage device 121 can store a large amount of hydrogen in a small volume.

[0084] The reversible fuel cell system 200 further includes a waste heat supply unit 170 that can supply waste heat Q of the reversible fuel cell 110 to the fuel storage device 121 in the power generation mode. In the power generation mode, the reversible fuel cell system 200 can generate power by extracting hydrogen from the fuel storage device 121 using the waste heat Q of the reversible fuel cell 110, which is supplied by the waste heat supply unit 170. By extracting hydrogen from the fuel storage device 121 using the waste heat Q, the waste heat Q can be effectively utilized, and the power generation efficiency (and round trip (charge / discharge efficiency)) of the reversible fuel cell system 200 can be improved.

[0085] Any device can be used as the exhaust heat supply unit 170 as long as it can supply the exhaust heat Q of the reversible fuel cell 110 in the power generation mode to the fuel storage device 121 and extract hydrogen from the fuel storage device 121. A typical example of the exhaust heat supply unit 170 is a heat exchanger.

[0086] The reversible fuel cell system 200 can perform water electrolysis and power generation by repeating the water electrolysis mode and power generation mode described above using the reversible fuel cell 110. The reversible fuel cell system 200 may also have the hydrogen measurement unit described above and operate using the first power generation stop hydrogen amount described above. The reversible fuel cell system 200 may also have the hydrogen storage amount measurement device described above and operate using the second power generation stop hydrogen amount described above.

[0087] [3-2. Third embodiment of reversible fuel cell system] 9, a reversible fuel cell system 300 according to the third embodiment of the present invention includes a reversible fuel cell 110, a fuel supply unit 120, an oxygen supply unit 130, and a control unit 140. The reversible fuel cell 110, the fuel supply unit 120, the oxygen supply unit 130, and the control unit 140 are basically as described above, and detailed description thereof will be omitted.

[0088] The fuel storage device 121 included in the fuel supply unit 120 includes a pressurized tank (not shown). By including the pressurized tank in the fuel storage device 121, the fuel storage device 121 can store a large amount of hydrogen in a small volume.

[0089] The pressure tank may be kept warm by a heat insulator to prevent condensation of water inside the pressure tank. Since water does not condense inside the pressure tank but can be supplied to the anode 112 as water vapor, the water electrolysis efficiency and power generation efficiency (as well as round-trip efficiency (charge / discharge efficiency)) can be improved.

[0090] Furthermore, the fuel storage device 121 further stores carbon dioxide, the fuel supply unit 120 has a methanation catalyst device 125 that produces methane from hydrogen and carbon dioxide, and the fuel supply unit 120 stores a high energy density gas containing methane produced in the methanation catalyst device 125 in the fuel storage device 121. The reversible fuel cell system 300 can store a high energy density gas in the fuel storage device 121, and can store the gas in a small volume.

[0091] The methanation catalyst device 125 is provided with a methanation catalyst, in which the reaction shown in the following formula (5) proceeds. CO2+ 4H2→ CH4+ 2H2O...Formula (5) Any methanation catalyst can be used as long as it can produce methane using carbon dioxide.

[0092] Furthermore, the methanation catalyst device 125 is installed inside the fuel storage device 121 and upstream of the fuel storage device 121. By providing a plurality of methanation catalyst devices 125, it is possible to efficiently generate methane and store a gas with high energy density in the fuel storage device 121. The methanation catalyst device 125 may be installed either inside the fuel storage device 121 or upstream of the fuel storage device 121.

[0093] The reversible fuel cell system 300 can perform water electrolysis and power generation by repeating the water electrolysis mode and power generation mode described above using the reversible fuel cell 110. The reversible fuel cell system 300 may also have the hydrogen measurement unit described above and operate using the first power generation stop hydrogen amount described above. The reversible fuel cell system 300 may also have the hydrogen storage amount measurement device described above and operate using the second power generation stop hydrogen amount described above. [Industrial Applicability]

[0094] The reversible fuel cell system of the present invention has a simplified system configuration, and can operate stably while preventing excessive consumption (and depletion) of hydrogen even when switching between water electrolysis and power generation, making it an industrially promising energy system. [Explanation of symbols]

[0095] 100,200,300 Reversible Fuel Cell System 110 Reversible fuel cell 112 Fuel electrode 114 Air electrode 116 Solid electrolyte 120 Fuel supply section 121 Fuel storage device 122 1st fuel pipe 123 2nd fuel pipe 124 Hydrogen storage amount measuring device 125 Methanation catalyst device 130 Oxygen supply unit 140 Control Unit 150 Hydrogen measurement unit 160 Charge / discharge section 170 Exhaust heat supply section

Claims

1. 1. A reversible fuel cell system, comprising: a reversible solid oxide fuel cell having an anode, an cathode, and a solid electrolyte disposed between the anode and the cathode, and capable of reversibly performing water electrolysis and power generation; a fuel supply unit that supplies a fuel gas containing hydrogen and / or water vapor to the fuel electrode; an oxygen supply unit that supplies an oxygen-containing gas to the air electrode; a control unit that switches between a water electrolysis mode in which power is received from an external source and water is electrolyzed by the reversible fuel cell, and a power generation mode in which hydrogen and oxygen are used to generate power by the reversible fuel cell; and the fuel supply unit includes a fuel storage device that stores the fuel gas, a hydrogen storage amount measuring device that measures the amount of hydrogen stored in the fuel storage device, a first fuel pipe that connects the fuel storage device to the fuel electrode and distributes the fuel gas from the fuel storage device to the fuel electrode, and a second fuel pipe that connects the fuel storage device to the fuel electrode and distributes the fuel gas from the fuel electrode to the fuel storage device, A reversible fuel cell system, wherein the flow direction of the fuel gas in the first fuel pipe and the second fuel pipe is the same in both the water electrolysis mode and the power generation mode.

2. 2. The reversible fuel cell system according to claim 1, further comprising a bypass pipe connecting the first fuel pipe and the second fuel pipe.

3. 10. The reversible fuel cell system of claim 1, wherein the fuel storage device comprises a hydrogen storage alloy.

4. 10. The reversible fuel cell system of claim 1, wherein the fuel storage device comprises a pressurized tank.

5. A method for operating a reversible fuel cell system according to any one of claims 2 to 4, comprising: in the water electrolysis mode, a fuel gas containing water vapor is supplied to the anode via a first pipe to perform water electrolysis, and the fuel gas with an increased hydrogen content is discharged to a second pipe, and a portion of the fuel gas with an increased hydrogen content is recycled to the first pipe via the bypass pipe; In the power generation mode, fuel gas containing hydrogen is supplied to the anode via a first pipe to generate power, and the fuel gas with an increased amount of water vapor is discharged to a second pipe, and a portion of the fuel gas with an increased amount of water vapor is recycled to the first pipe via the bypass pipe. A method for operating a reversible fuel cell system.

6. determining a recycling amount of the hydrogen-rich fuel gas that has passed through the anode based on the amount of hydrogen produced in the water electrolysis mode; 6. The method for operating a reversible fuel cell system according to claim 5, wherein the amount of fuel gas with a high water vapor content that has passed through the fuel electrode and is recycled is determined based on the amount of hydrogen consumed in the power generation mode.

7. 6. The method for operating a reversible fuel cell system according to claim 5, wherein the hydrogen stored in the water electrolysis mode is used up in the power generation mode within a predetermined period.

8. The method for operating a reversible fuel cell system according to claim 7, wherein the predetermined period is 0.5 days or more and 7 days or less.

9. 6. The method for operating a reversible fuel cell system according to claim 5, wherein the operation times of the water electrolysis mode and the power generation mode are set so that the system efficiency of the reversible fuel cell system is 50% or more.

10. A method for operating a reversible fuel cell system according to any one of claims 1 to 4, comprising: a step (P1) of setting a first power generation stop hydrogen amount; a step (P2) of measuring the amount of hydrogen consumed in the power generation mode after the step (P1), and stopping the power generation mode when the amount of hydrogen consumed exceeds the first power generation stop hydrogen amount; A method for operating a reversible fuel cell system comprising:

11. 11. The method for operating a reversible fuel cell system according to claim 10, further comprising the step (Q1) of measuring the amount of hydrogen stored in the power generation mode and stopping the power generation mode when the amount of hydrogen stored falls below a second power generation stop hydrogen amount.

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