Solid oxide cell system

Abstract

In a solid oxide cell system (1) having a solid oxide cell module (100) to which a plurality of solid oxide cell stacks (10) are connected and capable of switching between an SOFC mode and an SOEC mode, during any period during an operating period, at least one solid oxide cell stack (10) is controlled to operate in the SOFC mode or the SOEC mode, and input / output to at least one other solid oxide cell stack (10) is stopped and the solid oxide cell system is controlled to an idle state in which it does not operate in either the SOFC mode or the SOEC mode.

Description

[Technical field]

[0001] The present disclosure relates to solid oxide cell systems. [Background technology]

[0002] A solid oxide fuel cell (SOFC) can output electricity and heat using hydrogen, hydrocarbon, or carbon monoxide as raw materials. It can also operate as a solid oxide electrolysis cell (SOEC) that electrolyzes water vapor or carbon dioxide into hydrogen, carbon monoxide, or oxygen, which is the reverse reaction. A power storage and supply system using a reversible SOC (Solid Oxide Cell) that has the functions of power generation and electrolysis has been proposed (see, for example, Patent Document 1). [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Patent No. 6881007 Summary of the Invention [Problem to be solved by the invention]

[0004] Typically, power storage and supply systems have a stack structure in which multiple SOCs are stacked. In conventional systems using reversible SOCs, the operating temperature differs for each operating mode, so a downtime is required to adjust the operating temperature of the SOC stack when switching between operating modes. If the temperature is suddenly changed during this downtime, there is a risk that the SOC will be physically damaged by heat and its durability will be reduced. On the other hand, there is an issue that the downtime causes a delay in responding to requested input and output.

[0005] The present disclosure discloses technology for solving the problems described above, and aims to provide a solid oxide cell system that can suppress a decrease in SOC durability without delaying output when switching operation modes. [Means for solving the problem]

[0006] The solid oxide cell system of the present disclosure comprises: a solid oxide cell module including a solid oxide cell stack that can switch between a SOFC mode in which a first gas is used to generate electricity and output the electricity and a SOEC mode in which electricity is input and a second gas is electrolyzed, the solid oxide cell stack being connected in plurality; a control device for controlling the operation of the plurality of solid oxide cell stacks; The control device includes: During any period during which the operation of the solid oxide cell stack is controlled while switching between the SOFC mode and the SOEC mode, at least one of the solid oxide cell stacks is controlled to operate in the SOFC mode or the SOEC mode, and input / output of power to at least another solid oxide cell stack is stopped, and the solid oxide cell stack is controlled to a dormant state in which it does not operate in either the SOFC mode or the SOEC mode. death, maintain a temperature of the solid oxide cell stack controlled to a dormant state when a mode after the dormant state of the solid oxide cell stack controlled to a dormant state is the same as a mode before the dormant state, and control a temperature of the solid oxide cell stack controlled to a dormant state to an operating temperature of the mode after the dormant state when a mode after the dormant state of the solid oxide cell stack controlled to a dormant state is different from the mode before the dormant state; It is structured as follows. Effect of the Invention

[0007] According to the present disclosure, it is possible to improve responsiveness when switching between operation modes and suppress deterioration in the durability of the SOC stack. [Brief description of the drawings]

[0008] [Figure 1] FIG. 1 is a diagram showing a configuration of a solid oxide cell system according to a first embodiment. [Diagram 2]FIG. 2 is a diagram showing a configuration of a SOC stack according to the first embodiment. [Diagram 3] FIG. 2 is a diagram for explaining the operation in a SOFC mode in the solid oxide cell system according to the first embodiment. [Figure 4] FIG. 2 is a diagram for explaining operation in an SOEC mode in the solid oxide cell system according to the first embodiment. [Diagram 5] 5A and 5B are diagrams showing input / output control patterns and temperature control patterns of the SOC stack provided in the solid oxide cell system according to the first embodiment in comparison with those of a comparative example. Fig. 5A shows an input / output control pattern of the SOC stack when switching the operation mode of the solid oxide cell system in the comparative example, Fig. 5B shows a temperature control pattern of the SOC stack when switching the operation mode of the solid oxide cell system in the comparative example, Fig. 5C shows an input / output control pattern of each SOC stack when switching the operation mode of the solid oxide cell system according to the first embodiment, and Fig. 5D shows a temperature control pattern of each SOC stack when switching the operation mode of the solid oxide cell system according to the first embodiment. [Figure 6] 4 is a flowchart for explaining the control state of the SOC stack when switching between operation modes of the solid oxide cell system according to the first embodiment. [Figure 7] 7A and 7B are diagrams showing input / output control patterns and temperature control patterns of the SOC stack provided in the solid oxide cell system according to the second embodiment in comparison with those of the comparative example. Fig. 7A shows the input / output control pattern of the SOC stack when the operation mode of the solid oxide cell system in the comparative example is switched, Fig. 7B shows the temperature control pattern of the SOC stack when the operation mode of the solid oxide cell system in the comparative example is switched, Fig. 7C shows the input / output control pattern of each SOC stack when the operation mode of the solid oxide cell system according to the second embodiment is switched, and Fig. 7D shows the temperature control pattern of each SOC stack when the operation mode of the solid oxide cell system according to the second embodiment is switched. [Figure 8]10 is a flowchart for explaining the control state of the SOC stack when switching between operation modes of the solid oxide cell system according to the second embodiment. [Figure 9A] 10 is a flowchart for explaining a method of controlling the temperature of the SOC stack provided in the solid oxide cell system according to the third embodiment. [Figure 9B] 10 is a flowchart for explaining a method of controlling the temperature of the SOC stack provided in the solid oxide cell system according to the third embodiment. [Figure 10] FIG. 2 is a diagram showing an example of a hardware configuration of a control device of a solid oxide cell system according to the first to third embodiments. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0009] Hereinafter, an embodiment of a solid oxide cell system according to the present disclosure will be described with reference to the drawings. This disclosure is directed to a solid oxide cell system using a reversible SOC having both SOFC and SOEC functions. In addition, the same reference numerals in each drawing indicate the same or corresponding parts. Therefore, detailed descriptions thereof may be omitted to avoid duplication. In the following, the solid oxide cell will be referred to as the SOC, the solid oxide cell stack as the SOC stack, and the solid oxide cell module as the SOC module, and the operating mode in which the SOC stack operates as a SOFC will be referred to as the SOFC mode, and the operating mode in which it operates as an SOEC will be referred to as the SOEC mode.

[0010] Embodiment 1 The solid oxide cell system according to the first embodiment will be described below with reference to the drawings. <Solid oxide cell system configuration> FIG. 1 is a diagram showing the configuration of a solid oxide type cell system according to Embodiment 1, and FIG. 2 is a diagram showing the configuration of an SOC stack. In FIG. 1, a solid oxide type cell system 1 includes a gas supply unit 21 that supplies raw material gas required during the SOFC mode, a steam supply unit 22 that supplies steam (H2O) during the SOEC mode, a temperature adjustment device 20 that adjusts the temperature of the supplied gas and steam, an SOC module 100 to which the gas adjusted to a preset temperature by the temperature adjustment device 20 is supplied, and a control device 200 that controls the operation mode switching of the temperature adjustment device 20 and the SOC module 100 and the opening and closing of valves V1 - V6 provided in the gas piping. These are the main components 1A of the solid oxide type cell system 1 shown in the dotted area of FIG. 1. An external device 300 is connected to the SOC module 100. The external device 300 is a load to which the power generated by the SOC module 100 during the SOFC mode is supplied or a current source that supplies power to the SOC module 100 during the SOEC mode.

[0011] The SOC module 100 is an assembly in which a plurality of SOC stacks 10_1 - 10_n (n is a natural number of 2 or more) are connected. Each SOC stack 10 is provided with a temperature adjuster 18 for the SOC stack. The temperature adjuster 18 is, for example, a heater such as a heater. When collectively referring to the SOC stacks, they are referred to as SOC stack 10.

[0012] <Configuration of SOC Stack> Here, with reference to FIG. 2, the structure of the plurality of SOC stacks 10 that constitute the SOC module 100 will be described. The SOC module 100 is an assembly in which a plurality of SOC stacks 10_1 - 10_n (n is a natural number of 2 or more) are connected. Each SOC stack 10 is configured by stacking a plurality of SOCs 11_1 - 11_m (m is a natural number of 2 or more).

[0013] Taking the k-th (1 < k ≤ m; k is a natural number) SOC11_k as an example, SOC11 has a structure in which an air electrode 12 and a fuel electrode 14 sandwich an electrolyte 13, and is connected to an adjacent SOC11 by an interconnector 15. A diffusion prevention layer may be inserted between the air electrode 12 and the electrolyte 13 to suppress material deterioration. When referring to SOCs in general, they are called SOC11s.

[0014] The control device 200 includes a system control unit 201 and a temperature control unit 202. The system control unit 201 performs operations such as switching the operation mode of the SOC module 100 and controlling the opening and closing of valves V1 - V6 provided in the gas pipeline. The temperature control unit 202 controls the temperature adjustment device 20 so that the supplied gas and water vapor reach a preset temperature, and controls the temperature adjuster 18 for the SOC stack so that each SOC stack 10 reaches a preset temperature.

[0015] The external device 300 is a load or a current source as described above. Examples of the load to which the energy generated by the SOC module 100 in the SOFC mode is supplied include, for example, a power converter or a motor connected via a power converter. Examples of the current source supplied to the SOC module 100 in the SOEC mode include current sources such as a power converter or the grid.

[0016] The gas supply unit 21 supplies hydrogen (H2) etc. as the raw material gas on the fuel electrode side required in the SOFC mode, and supplies hydrogen, carbon dioxide (CO2) etc. in the SOEC mode. It may be in a form that has gas cylinders externally and supplies them to the gas supply unit 21. Also, the gas supplied to the air electrode in the SOFC mode is, for example, oxygen (O2), air (Air), etc. These are also used in the SOEC mode, and since the gas species are theoretically the same before (upstream) and after (downstream) the supply, the gas may be circulated and used.

[0017] The temperature adjustment device 20 adjusts the piping temperature of the (upstream) gas and water vapor supplied to the SOC module 100, and is, for example, a heater or a heating device provided around the piping. In addition, the downstream gas generated from the SOC module 100 may be used as a heat source to heat the upstream gas.

[0018] The solid oxide cell system 1 may include optional components such as a reformer 30, a steam generator 31, a water storage section 32, a condenser 33, a gas storage section 34, and a storage gas adjustment section 35. The reformer 30 is used in the SOFC mode when city gas (gas mainly composed of methane) is used. The downstream gas generated from the SOC module 100 may be supplied as fuel to a burner, which is a heat source during reforming.

[0019] The water vapor generator 31 heats water supplied from the water storage unit 32 to generate water vapor, and supplies the water vapor to the SOC module 100 via the water vapor supply unit 22. Water vapor may be supplied directly from the outside without using the water vapor generator 31.

[0020] The water storage unit 32 stores water to be supplied to the steam generator 31. The steam in the downstream gas on the fuel electrode side discharged from the SOC module 100 may be collected and reused as the supply gas or fuel for the reformer 30.

[0021] The condenser 33 dehydrates the fuel electrode side downstream gas discharged from the SOC module 100. For example, in the SOFC mode, the condenser 33 separates the water vapor generated in the SOC module 100 from unreacted hydrogen, etc. by dehydration, and in the SOEC mode, the condenser 33 separates the hydrogen, etc. generated in the SOC module 100 from unreacted water vapor by dehydration.

[0022] The gas storage unit 34 collects the downstream gas (hydrogen, etc.) on the fuel electrode side discharged from the SOC module 100 in the SOEC mode and stores it as the upstream gas on the fuel electrode side required in the SOFC mode. The gas discharged from the SOC module 100 may be directly supplied to the outside of the system.

[0023] The gas storage adjuster 35 appropriately processes and adjusts the gas in order to store each gas in the gas storage unit 34. For example, the gas is compressed by a compressor, the fuel electrode side downstream gas discharged from the SOC module 100 in the SOEC mode, for example, a mixed gas such as hydrogen and carbon monoxide (CO) is separated by a separator, or the form of the gas is adjusted by synthesizing methane by a methanation reactor using, for example, hydrogen and carbon monoxide (CO). The gas adjusted by the gas storage adjuster 35 is stored in the gas storage unit 34.

[0024] In addition, in the drawings showing the configuration of the solid oxide cell system in FIG. 1 and subsequent figures, each line shall indicate the following content. Solid line: Gas flow path before reaction (upstream) Dash-dotted line: Gas flow path after reaction (downstream) Dashed line: Gas flow path used other than for fuel cells and steam electrolysis reactions Black arrow: Gas (hydrogen, nitrogen, carbon monoxide, hydrocarbon, steam, carbon dioxide, etc.) supplied to or discharged from the fuel electrode White arrow: Gas (oxygen, air, etc.) supplied to or discharged from the air electrode

[0025] <Operation in SOFC mode> Next, the operation of the solid oxide cell system 1 in the SOFC mode will be described. FIG. 3 shows the gas flow in FIG. 1 in thick lines during the SOFC mode. In the SOFC mode, the gases described below are supplied to the fuel electrode 14 and the air electrode 12 respectively, and the generated electric power is output.

[0026] (1) Supply of gas to the SOC module 100 (upstream) A gas mainly composed of hydrogen is supplied to the fuel electrode 14 side. The gas mainly composed of hydrogen is supplied from the gas supply unit 21 to the SOC module 100 via the temperature adjuster 20. A gas mainly composed of hydrogen may be supplied from the gas storage unit 34. A gas mainly composed of methane may be supplied to the fuel electrode 14 side. The gas mainly composed of methane is supplied to the SOC module 100 from the gas storage unit 34 via the temperature adjustment device 20. Alternatively, the gas may be supplied from the outside via the reformer 30. Also, the gas may be supplied from the gas storage unit 34 via the reformer 30. In the reformer 30, steam reforming is carried out by the following reaction using steam supplied from the water storage unit 32, and the reformed gas is supplied to the fuel electrode 14 side. CH4+H2O → CO+3H2 As will be explained below, when the SOC stack 10 in the SOC module 100 is not operating in SOFC mode and is undergoing temperature adjustment or is idle, a purge gas or reducing gas mainly composed of hydrogen and nitrogen is supplied from the gas supply unit 21 or the gas storage unit 34 to the fuel electrode 14 side.

[0027] Oxygen or air is supplied to the air electrode 12 side from a gas supply unit 21. Oxygen or air is also supplied to the air electrode 12 side of the SOC stack 10 in the SOC module 100 that is not operating in the SOFC mode and is undergoing temperature adjustment or is at rest. In gas supply to the SOC module 100, the opening and closing direction of valve V1 determines the supply source of gas to the fuel electrode 14 side. When the gas supplied to the fuel electrode 14 side is gas mainly composed of methane, the opening and closing direction operation of valve V2 supplies the gas mainly composed of methane from the gas storage unit 34 to the reformer 30. The opening and closing direction of valve V3 is determined by whether or not gas is supplied from the reformer 30. These valves V1-V3 are three-way valves, and their opening and closing direction operations are controlled by the system control unit 201.

[0028] (2) Gas discharge from SOC module 100 (downstream) On the fuel electrode 14 side, when a gas mainly composed of hydrogen is supplied, steam and unreacted hydrogen are discharged. When a gas mainly composed of methane is supplied, steam and carbon dioxide are discharged. The discharged gas may be directly discharged to the outside. However, in Fig. 3, the steam and other gases are separated by the condenser 33, and then hydrogen and carbon dioxide may be separated by the gas adjustment unit 35 for storage. The steam may be stored in the water storage unit 32. On the air electrode 12 side, unreacted oxygen or air is discharged. The discharged gas may be returned to the gas supply unit 21 to circulate in the system.

[0029] In the discharge of gas from the SOC module 100, when the reformer 30 operates by opening and closing the valve V5, water can be supplied from the water storage unit 32. Also, a part of the discharged gas can be supplied as fuel for the heat supply burner of the reformer 30 according to the opening and closing direction of the valve V4. The valve V4 is a three-way valve, and the valve V5 is an on-off valve. The opening and closing directions and operations are controlled by the system control unit 201.

[0030] Note that the temperature adjustment device 20 can be configured to have a heat exchange function and heat the supply gas by heat exchange with the discharged gas. Also, the temperature of the temperature adjustment device 20 during operation, the temperature of the temperature adjuster 18 for the SOC stack, and the temperature of the reformer 30 are controlled to the set temperatures by the temperature control unit 202, respectively.

[0031] <Operation in SOEC mode> Next, the operation of the solid oxide fuel cell system 1 in the SOEC mode will be described. Fig. 4 shows the gas flow in the SOEC mode in Fig. 1 with thick lines. In the SOEC mode, the gases described below are supplied to the fuel electrode 14 and the air electrode 12 respectively, and an electrolysis reaction occurs due to the input power.

[0032] (1) Gas supply to the SOC module 100 (upstream) A gas mainly composed of water vapor is supplied to the fuel electrode 14 side from a water vapor supply unit 22. Water vapor may be introduced directly from the outside, or water supplied from a water storage unit 32 may be heated in a water vapor generator 31 to generate water vapor, as shown in Fig. 4. Hydrogen may also be supplied from a gas storage unit 34 or a gas supply unit 21, mixed with water vapor in a temperature adjustment device 20, and supplied to the fuel electrode 14 side. Also, a gas containing carbon dioxide as a main component may be supplied to the fuel electrode 14 side from the gas supply unit 21. At this time, a mixed gas of water vapor and carbon dioxide may be supplied to the fuel electrode 14 side. As will be explained below, when the SOC stack 10 in the SOC module 100 is not operating in SOEC mode and is undergoing temperature adjustment or is idle, a purge gas or reducing gas mainly composed of hydrogen and nitrogen is supplied from the gas supply unit 21 or the gas storage unit 34 to the fuel electrode 14 side.

[0033] Oxygen or air is supplied to the air electrode 12 side from a gas supply unit 21. Oxygen or air is also supplied to the air electrode 12 side of the SOC stack 10 in the SOC module 100 that is not operating in the SOEC mode and is undergoing temperature adjustment or is at rest. In supplying gas to the SOC module 100, the supply source of gas to the fuel electrode 14 side is determined by the opening / closing direction of the valve V1 and the opening / closing of the valve V6. The valve V1 is a three-way valve, and the valve V6 is an on-off valve. The opening / closing direction and the opening / closing operation are controlled by the system control unit 201.

[0034] (2) Gas discharge from SOC module 100 (downstream) From the fuel electrode 14 side, when a gas mainly composed of water vapor is supplied, hydrogen and unreacted water vapor are discharged, and when a gas mainly composed of carbon dioxide is supplied, carbon monoxide and unreacted carbon dioxide are discharged. The discharged gas may be directly discharged to the outside of the system. However, in FIG. 4, water vapor and other gases are separated by the condenser 33, and then hydrogen and carbon monoxide are separated by the gas conditioning unit 35 for storage, or a mixed gas containing hydrogen and carbon monoxide may be directly introduced into the methanation reactor to produce methane. Gases such as hydrogen, carbon monoxide, and methane processed by the gas conditioning unit 35 for storage are stored in the gas storage unit 34. The unreacted water vapor may be stored in the water storage unit 32 and supplied to the fuel electrode 14 again. From the air electrode 12 side, the generated oxygen or air in a state of high oxygen concentration is discharged. The discharged gas may be returned to the gas supply unit 21 to circulate the system.

[0035] Note that the temperature adjustment device 20 can be configured to have a heat exchange function to heat the supply gas by heat exchange with the discharged gas. Also, the water vapor generator 31 can be configured to have a heat exchange function to generate water vapor by heat exchange with the discharged gas. Also, similar to the SOFC mode, the temperature of the temperature adjustment device 20 during operation and the temperature of the temperature regulator 18 for the SOC stack are controlled by the temperature control unit 202 to the set temperatures respectively.

[0036] Next, the operation of the SOC module 100 according to the first embodiment will be described. However, the plurality of SOC stacks 10 included in the SOC module 100 are provided with pipes and valves (not shown) so that gas supply and discharge can be performed independently, and the power input / output is controlled so that each operation mode can be controlled independently, and temperature control is possible independently.

[0037] <Example of the operation of the SOC module 100> Next, the operation of the SOC module 100 according to the first embodiment will be described with reference to FIGS. 5 and 6. FIG. 5 is a diagram showing the operation control pattern and temperature control pattern of the SOC stack when switching the operation mode of the solid oxide cell system according to the first embodiment in comparison with a comparative example. FIGS. 5A and 5B are comparative examples, and FIGS. 5C and 5D are solid oxide cell system according to the first embodiment. In FIGS. 5A-5D, the horizontal axis is time, and for convenience of explanation, time blocks t1-t9 each having a time width are used for explanation. In FIGS. 5A and 5C, the vertical axis shows the power input / output in arbitrary units from -3 to +3. The positive direction is the SOFC mode in which power is generated and output to the outside, and the negative direction is the SOEC mode in which electrolysis is performed by input from the outside. Input / output requests to the system are shown by hatching with dots, and the SOC stack is controlled so that the input / output is in accordance with the request. In FIGS. 5B and 5D, the vertical axis shows the operating temperature of the SOC stack, and shows the temperature control pattern corresponding to the operation of the SOC stack in FIGS. 5A and 5C, respectively.

[0038] The SOC module 100 according to the first embodiment described below includes three SOC stacks 10, each of which is designated as stack A, B, and C. The stacks A, B, and C have the same functions. The SOC module of the comparative example also includes three equivalent stacks, i.e., it is equivalent to having three stacks A. In the comparative example, the three SOC stacks operate in the same way, while the SOC stacks A, B, and C according to the first embodiment operate independently. Each stack allows ±3 power input / output control. Furthermore, each SOC stack requires a rest period of at least one hour block when switching between operation modes. During the rest period, the stack input / output is zero. Each SOC stack is also required to maintain the SOEC operating temperature T EC The temperature was raised to 100°C and the device was operated in the SOEC mode at the SOFC operating temperature T FC The temperature is lowered to 0.5 to operate in SOFC mode.

[0039] In Figures 5A and 5C, an input request of "3" is made at time blocks t1 and t2, an output request of "3" is made at time blocks t3 and t4, an input request of "3" is made at time blocks t5 and t6, an output request of "3" is made at time blocks t7 and t8, and an input request of "3" is made at time block t9.

[0040] In the comparative example shown in FIG. 5A and FIG. 5B, in time blocks t1 and t2, each SOC stack is controlled in response to an input of "1" and operates in SOEC mode. That is, three SOC stacks corresponding to an input of "1" correspond to a total of "3" inputs. At this time, each SOC stack is in SOEC mode, so each SOC stack operates at an SOEC operating temperature T EC is controlled by.

[0041] Even if an output request of "3" is received in time block t3, all SOC stacks cannot respond because they require a rest period, and the output becomes 0. At this time, the operating temperature is set to the SOEC operating temperature T EC to SOFC operating temperature T FC After one time block has elapsed, at time block t4, each SOC stack enters the SOFC mode and is controlled at output "1", making it possible to respond to a total output request of "3". At this time, since the SOC stacks are in the SOFC mode, each SOC stack is at the SOFC operating temperature T FC is controlled by.

[0042] In addition, even if an input request for “3” is received in time block t5, all SOC stacks cannot respond because they require a rest period, and the operating temperature is set to the SOFC operating temperature T FC SOEC operating temperature T EC At time block t6 after one time block has elapsed, each SOC stack becomes in SOEC mode and is able to respond to the input request of "3". At this time, since the OC stack is in SOEC mode, each SOC stack is heated to the SOEC operating temperature T EC After that, the input / output control and operating temperature control of the SOC stack are repeated in the same manner.

[0043] In the input / output control patterns and operating temperature control patterns of stacks A, B, and C of the present embodiment 1 shown in Fig. 5C and Fig. 5D, in time block t1, stack C of the SOC stack 10 responds to the input request "3" and operates in the SOEC mode. At this time, the other stacks A and B are in a quiescent period, but stack A is operating at the SOFC operating temperature T FC Stack B is maintained at the SOEC operating temperature T EC The temperature is currently rising. In time block t2, stack A is maintained at the idle period and the SOFC operating temperature T FC Stack B operates in SOEC mode in response to the input request of “3”, stack C enters a pause period, and the SOFC operating temperature T FC The temperature is lowered to

[0044] In time block t3, the output request is switched to "3", and the SOFC operating temperature T FC Stack A, which had been maintained at 1000 sq. m, operates in SOFC mode and outputs “3.” Stack B is in a quiescent period, but the SOEC operating temperature T EC The stack C is maintained at the SOFC operating temperature T FC The temperature continues to fall to .

[0045] In time block t4, stack A is in a rest period, and the SOEC operating temperature T EC Stack B is heated to the SOEC operating temperature T EC and stack C operates in SOFC mode, outputting “3”.

[0046] At time block t5, the input request is switched to “3”, the stack A is kept in the idle period, and the SOEC operating temperature T EC The temperature continues to rise to the SOEC operating temperature T EC Stack B, which had been maintained at 300°C, operates in SOEC mode in response to the input request of "3," and stack C enters a pause period and the SOFC operating temperature T FC is maintained.

[0047] In time block t6, stack A responds to the input request of "3" and operates in the SOEC mode, stack B enters the pause period, and the SOFC operating temperature T FC is cooled down, and stack C maintains the pause period while the SOFC operating temperature T FC is maintained.

[0048] <Control Pattern of SOC Stack> FIG. 6 is a diagram showing the control pattern of the SOC stack according to Embodiment 1. Hereinafter, stack C shown in FIGS. 5C and 5D will be described as an example. First, stack C is controlled to operate in the SOEC mode in time block t1 (step S101), and is controlled to cool down to the SOFC operating temperature T FC in time blocks t2 and t3 (step S102).

[0049] It is controlled to operate in the SOFC mode in time block t4 (step S103), and is controlled to maintain the SOFC operating temperature T FC in time blocks t5 - t6 (step S104). It is controlled to operate in the SOFC mode in time block t7 (step S105), and is controlled to increase the SOEC operating temperature T EC in time blocks t8 - t9 (step S106). Here, the control in time block t9 corresponds to the control of stack B in time block t1. Therefore, although the control of stack C after time block t10 is not shown, it will be described with reference to the control of stack B after time block t2.

[0050] Stack C is controlled to operate in the SOEC mode in time block t10 (step S107), and the SOEC operating temperature T EC is maintained in time blocks t11 and t12 (step S107). Time block t13 returns to time block t1 again and is controlled to operate in the SOEC mode (step S101).

[0051] Stack A shown in FIGS. 5C and 5D is an example in which stacks start from step S104 in FIG. 6, and stack B starts from step S106 in FIG. 6 and circulates.

[0052] As described above, in the first embodiment, the SOC module 100 includes a plurality of SOC stacks 10, and each of the plurality of SOC stacks 10 is independently controlled in terms of input / output and temperature. In addition, during the operation period of the SOC module 100, all of the SOC stacks 10 are controlled so as not to operate in the same operation mode. As a result, it is possible to suppress deterioration of the SOC stacks 10 more effectively than in the comparative example, in which all of the SOC stacks 10 operate in the same operation mode during the operation period. Furthermore, if each SOC stack 10 continues to operate in the same mode, degradation is likely to progress. In the first embodiment, the operation mode of each SOC stack 10 is switched within a certain period of time, so that degradation of each SOC stack 10 can be suppressed.

[0053] In addition, because all the SOC stacks 10 are controlled not to operate in the same operation mode, the idle periods of all the SOC stacks 10 do not overlap, and all the SOC stacks 10 are not idle, i.e., at least one SOC stack 10 is operating in any operation mode while at least one other SOC stack 10 is idle, so there is no period during which an input / output request cannot be responded to, there is no delay in the input / output request, and response is improved. Note that there may be periods during which none of the SOC stacks 10 is stopped.

[0054] Furthermore, since control is performed so that all SOC stacks 10 do not operate in the same operation mode, one SOC stack 10 has a larger input / output than in the comparative example, but while operating in one operation mode, it is possible to adjust the temperature of another SOC stack 10 during a pause period. This makes it possible to perform control that can suppress deterioration of the SOC stack 10 in response to input / output requests. For example, by operating one SOC stack 10 in the same operation mode multiple times, it is possible to suppress the number of temperature changes, and by setting a longer temperature adjustment period than in the comparative example, it is possible to slow down the temperature adjustment speed and reduce the load on the SOC stack 10.

[0055] As described above, according to the first embodiment, a solid oxide cell system includes a solid oxide cell module having a solid oxide cell stack that can switch between a SOFC mode in which a first gas is used to generate electricity and output electric power, and a SOEC mode in which electric power is input and a second gas is electrolyzed, the solid oxide cell system including a control device that controls the operation of the plurality of solid oxide cell stacks, and the control device controls at least one of the plurality of solid oxide cell stacks to operate in the SOFC mode or the SOEC mode rather than in a dormant state during any period during which the control device controls the operation of the solid oxide cell stack while switching between the SOFC mode and the SOEC mode, and controls at least one other solid oxide cell stack to a dormant state in which the input and output of electric power is stopped and the solid oxide cell stack does not operate in either the SOFC mode or the SOEC mode. Therefore, there is no period during which all the solid oxide cell stacks are stopped, that is, there is no period during which input and output requests cannot be responded to, and therefore there is no delay in input and output requests, and response ability is improved. The first gas is, for example, a gas whose main component is hydrogen or a gas whose main component is methane supplied to the fuel electrode side, and oxygen or air supplied to the air electrode side, and the second gas is, for example, a gas whose main component is water vapor or a gas whose main component is carbon dioxide supplied to the fuel electrode side, and oxygen or air supplied to the air electrode side.

[0056] Moreover, by suppressing the number of temperature changes and providing a longer temperature adjustment period, the temperature adjustment speed can be reduced, thereby reducing the load on the SOC stack 10 and suppressing a decrease in the durability of the SOC stack.

[0057] Embodiment 2. The solid oxide cell system according to Embodiment 2 will be described below with reference to the drawings. In Embodiment 2, the operation of the SOC module 100 in response to input / output requirements different from those in Embodiment 1 will be described. Note that the configuration of the solid oxide cell system 1 according to Embodiment 2 is the same as that in Embodiment 1, and the operations in the SOEC mode and the SOFC mode are also the same, so the description thereof will be omitted.

[0058] <Operation of SOC Module 100> The operation of the SOC module 100 according to Embodiment 2 will be described with reference to FIGS. 7 and 8. FIG. 7 is a diagram showing a comparison of the operation control pattern and temperature control pattern of the SOC stack when switching the operation mode of the solid oxide cell system according to Embodiment 2 with a comparative example. FIGS. 7A and 7B are for the comparative example, and FIGS. 7C and 7D are for the solid oxide cell system according to Embodiment 2. The horizontal axis, vertical axis, and legend in the figure are the same as those in FIGS. 5A-5D.

[0059] In FIGS. 7A and 7C, an input requirement of "3" is made in time block t1, an output requirement of "3" is made in time blocks t2 and t3, an input requirement of "3" is made in time block t4, an output requirement of "3" is made in time blocks t5 and t6, an input requirement of "3" is made in time block t7, and an output requirement of "3" is made in time blocks t8 and t9. That is, it is an example in which an input requirement for 1 time block and an output requirement for 2 time blocks are repeated.

[0060] In the comparative example shown in FIG. 7A and FIG. 7B, in time block t1, each SOC stack is controlled in response to an input of "1" and operates in SOEC mode. That is, the three SOC stacks corresponding to the input of "1" correspond to a total of "3" inputs. At this time, each SOC stack is in SOEC mode, so that each SOC stack is controlled to the SOEC operating temperature T EC is controlled by.

[0061] Even if an output request of "3" is received in time block t2, all SOC stacks cannot respond because they require a rest period, and the output becomes 0. At this time, the operating temperature is set to the SOEC operating temperature T EC to SOFC operating temperature T FC After one time block has elapsed, at time block t3, each SOC stack enters the SOFC mode and is controlled at output "1", making it possible to respond to a total output request of "3". At this time, since the SOC stacks are in the SOFC mode, each SOC stack is at the SOFC operating temperature T FC is controlled by.

[0062] Even if an input request of "3" is received in the next time block t4, all SOC stacks cannot respond because they require a rest period. Furthermore, since an output request of "3" is received in time block t5, the operating temperature of each SOC stack in time block t4 is set to the SOFC operating temperature T FC is maintained. In time block t5, in response to the output request of “3”, each SOC stack operates at SOFC operating temperature T FC Since the value of "1" is maintained, each of them is controlled in the SOFC mode to output "1".

[0063] In the time block t6, the output request of “3” is maintained, but in the next time block t7, an input request of “3” is received, so in the time block t6, each SOC stack is in a quiescent period, and the operating temperature is increased to the SOFC operating temperature T FC from SOEC operating temperature T EC In other words, the output request for time block t6 cannot be met. When an input request "3" is received at time block t7, each SOC stack is controlled in SOEC mode and responds to an input request "1", making it possible to respond to a total of "3" input requests.

[0064] On the other hand, unlike FIG. 7A, if each SOC stack is controlled in SOFC mode while remaining in time block t5 in response to an output request of “3” in time block t6, a pause period is required in time block t7, and therefore the input request of “3” cannot be accommodated.

[0065] In this way, a period during which temperature adjustment is suspended is required when switching the operation mode, and therefore, in the comparative example, a dead time occurs during which input / output requests cannot be responded to.

[0066] In the input / output control patterns and operating temperature control patterns of stacks A, B, and C of the second embodiment shown in FIG. 7C and FIG. 7D, in time block t1, stack C of the SOC stack 10 operates in the SOEC mode in response to the input request "3." At this time, the other stacks A and B are in a quiescent period, but both stacks A and B are in a quiescent period. FC is maintained.

[0067] In time block t2, when the output request is switched to "3", both stacks A and B are controlled in SOFC mode, stack A outputs "2", stack B outputs "1", and the total output is controlled to be "3". Stack C enters a rest period, and the SOFC operating temperature T FC The temperature is lowered to

[0068] In the time block t3, the output request of “3” continues, the output of stack A is controlled from “2” to “1”, the output of stack C is controlled to be “2”, stack B is in a rest period, and the SOEC operating temperature T EC The temperature is raised to .

[0069] In the next time block t4, in response to the input request of "3", stack B responds and operates in the SOEC mode. Although the other stacks A and C are in the rest period, both stacks A and C maintain the SOFC operating temperature T FC therein.

[0070] In the next time block t5, when switching to the output request of "3", both stacks A and C are controlled in the SOFC mode. Stack A outputs "1", stack C outputs "2", and they are controlled to output a total of "3". Stack B enters the rest period and the SOFC operating temperature T FC is cooled down.

[0071] In time block t6, the output request of "3" continues. Stack C is controlled such that its output changes from "2" to "1", stack B is controlled to output "2", and stack A enters the rest period. The SOEC operating temperature T EC is heated up. Thereafter, each SOC stack is controlled with a similar input / output control pattern and operating temperature control pattern to respond to the input / output requests. In each of time blocks t2, t3, t5, t6, t8, and t9, among the two SOC stacks controlled in the SOFC mode, one stack is an example of the first SOC stack and the other SOC stack is an example of the second SOC stack.

[0072] <Control Pattern of SOC Stack> FIG. 8 is a diagram showing the control pattern of the SOC stack according to Embodiment 1. Hereinafter, stack C shown in each control pattern of FIGS. 7C and 7D will be described as an example. First, stack C operates in the SOEC mode in time block t1 and is controlled to respond to the input of "3" (step S201). Time block t2 is a rest period and is controlled to cool down to the SOFC operating temperature T FC therein (step S202).

[0073] In the time block t3, the SOFC mode is selected and “2” is output (step S203). The time block t4 is a quiescent period, but the SOFC operating temperature T FC is maintained (step S204). In time block t5, the control is made to be in the SOFC mode and to output "2" (step S205), and in time block t6, the control is made to be in the SOFC mode and to output "1" (step S206).

[0074] The time block t7 is a quiescent period, but the SOFC operating temperature T FC is maintained (step S207). In time block t8, the control is performed so that the mode is the SOFC mode and "1" is output (step S208).

[0075] The time block t9 is a rest period, during which the SOEC operating temperature T EC The temperature is controlled to rise to (step S209). After that, the process returns to step S201 and the control is repeated. Stack A shown in FIGS. 7C and 7D is an example in which the stacks start from step S204 in FIG. 8, and stack B starts from step S207 in FIG. 8 and circulates.

[0076] In this way, even for requests different from the input / output requests shown in the first embodiment, the SOC module 100 is provided with multiple SOC stacks 10, and the multiple SOC stacks 10 are each independently controlled for input / output and temperature, and are controlled so that all the SOC stacks 10 do not operate in the same operation mode during the operation period of the SOC module 100. Therefore, as in the first embodiment, there is no period during which an input / output request cannot be responded to, so there is no delay in the input / output request, and response performance is improved.

[0077] As described above, according to the second embodiment, the same effects as those of the first embodiment are achieved. In addition, in embodiment 2, the control device controls the first SOC stack and the second SOC stack to operate in SOFC mode during any period of the operating period, and controls the output power of the first SOC stack and the output power of the second SOC stack to be different from each other, thereby improving the freedom to adjust the output power of the solid oxide cell system.

[0078] Embodiment 3 The solid oxide cell system according to the third embodiment will be described below with reference to the drawings. In the first and second embodiments, it has been described that the SOC module 100 includes a plurality of SOC stacks 10, and the input / output control and temperature control are performed independently for each of the plurality of SOC stacks 10. In the third embodiment, a specific method of temperature control during a rest period of each SOC stack 10 will be described.

[0079] During the rest period of the SOC stack 10, (1) When switching from SOEC mode to SOFC mode, the SOC stack 10 is heated to the SOEC operating temperature T EC to SOFC operating temperature T FC (cooling the SOC stack), (2) When switching from SOFC mode to SOEC mode, the SOC stack 10 is heated to the SOFC operating temperature T FC SOEC operating temperature T EC (heating the SOC stack), (3) The temperature of the SOC stack 10 is set to the SOEC operating temperature T EC or SOFC operating temperature T FC maintain Either: Below, the temperature control methods for the above cases (1) and (2) will be explained.

[0080] 9A and 9B are flow charts showing a procedure for temperature control, which will be described with reference to the gas flow shown in FIG.

[0081] (1) Cooling of SOC stack When the temperature of the SOC stack 10 is to be lowered (No in step S301), the power input / output and heat supply to the target SOC stack 10 are interrupted (step S302). The interruption of the heat supply is achieved by turning off the heater of the SOC stack temperature regulator 18. When gas is not to be supplied to the target SOC stack 10 (No in step S303), the valve (not shown) of the gas pipe to the target stack 10 of the SOC module 100 is closed, thereby allowing heat to dissipate naturally.

[0082] When gas is supplied to the target SOC stack 10 (Yes in step S303), the method of controlling the temperature differs depending on the type of gas supplied (step S305). When hydrogen is supplied from the gas storage unit 34 to the fuel electrode 14 side of the target SOC stack 10, and hydrogen or nitrogen or a mixed gas thereof, purge gas, and reducing gas are supplied from the gas supply unit 21 to the air electrode 12 side of the target SOC stack 10, and oxygen or air is supplied from the gas supply unit 21 to the air electrode 12 side, high-temperature residual gas remaining in the target SOC stack 10 is scavenged to cool the target SOC stack 10 (step S307). Here, by adjusting the temperature of the gas supplied to the target SOC stack 10 in the temperature adjustment device 20, it becomes possible to efficiently cool the target SOC stack 10. In other words, it becomes possible to adjust the temperature drop rate of the target SOC stack 10. In the temperature adjustment device 20, for example, the temperature may be set lower than when operating in the SOEC mode or the SOFC mode. Furthermore, the purge gas and reducing gas supplied to the fuel electrode 14 side may be supplied from outside the system.

[0083] When methane is supplied from the gas storage unit 34 to the fuel electrode 14 side of the target SOC stack 10 and steam is supplied from the steam supply unit 22, steam reforming occurs on the electrode. CH4+H2O → CO+3H2 This reaction is called internal reforming, and since it is an endothermic reaction, it is possible to cool the target stack while discharging hydrogen (step S306). As described above, the discharged hydrogen is separated in the storage gas adjustment unit 35 and stored in the gas storage unit 34 or discharged to the outside. At this time, oxygen or air is supplied from the gas supply unit 21 to the air electrode 12 side. The methane and water vapor supplied to the fuel electrode 14 side may be supplied from outside the system, and the water vapor may be generated in a water vapor generator 31 from water supplied from a water reservoir 32 . When internal reforming is used, the temperature drop rate can be adjusted by adjusting the gas flow rate.

[0084] SOEC operating temperature T EC to SOFC operating temperature T FC When cooling to , the target temperature is the SOFC operating temperature T FC If the target temperature is reached, the process ends (Yes in step S303). If the target temperature is not reached, any of the above-mentioned methods may be repeated, or a different method may be used. The temperature drop rate may be adjusted using these methods so that the target temperature is reached within a preset time. At this time, the temperature of the SOC stack 10 may be dropped by selecting or combining an appropriate method according to the situation.

[0085] (2) Heating the SOC stack When the temperature of the SOC stack 10 is to be increased (Yes in step S301), the power input / output to the target SOC stack 10 is interrupted (step S311). When heat is not supplied to the target SOC stack 10 (No in step S312), the target SOC stack 10 is heated by radiant heat (step S313). The temperature is increased by utilizing radiant heat from other SOC stacks operating in the SOFC mode or from SOC stacks with a higher temperature than the target SOC stack 10. At this time, a valve (not shown) of the gas piping of the target SOC stack 10 is closed to prevent gas from being supplied. Alternatively, a purge gas or a reducing gas is supplied to the fuel electrode 14 side from the gas supply unit 21 or from outside the system, and oxygen or air is supplied to the air electrode 12 side from the gas supply unit 21. Here, the temperature of the gas supplied to the target SOC stack 10 is adjusted by the temperature adjustment device 20, so that the target SOC stack 10 can be efficiently heated. That is, the temperature increase rate of the target SOC stack 10 can be adjusted.

[0086] When heat is supplied to the target SOC stack 10 (Yes in step S312), the temperature can be controlled using a heater or the like of the SOC stack temperature regulator 18 (step S314). In this case, too, a purge gas or a reducing gas can be supplied to the fuel electrode 14 side from the gas supply unit 21 or from outside the system, and oxygen or air can be supplied to the air electrode 12 side from the gas supply unit 21. By adjusting the temperature of the gas supplied to the target SOC stack 10 in the temperature regulator 20 together with the SOC stack temperature regulator 18, it becomes possible to efficiently increase the temperature of the target SOC stack 10. In other words, it becomes possible to adjust the rate at which the temperature of the target SOC stack 10 is increased.

[0087] SOFC operating temperature T FC SOEC operating temperature T EC When heating to , the target temperature is the SOEC operating temperature T EC If the target temperature is reached, the process ends (Yes in step S315). If the target temperature is not reached, any of the above-mentioned methods may be repeated, or a different method may be used. The heating rate may be adjusted from these methods so that the target temperature is reached within a preset time. At this time, the SOC stack 10 may be heated by selecting or combining an appropriate method according to the situation.

[0088] As described above, according to the third embodiment, the temperature of the SOC stack during the pause period is controlled so that the temperature reaches the target temperature within a preset time, so that the SOC stack during the pause period can be controlled to the target temperature without inducing a sudden change in temperature, and deterioration of the SOC stack due to heat can be suppressed. In addition, since the temperature is controlled to reach the target temperature during the pause period, there is no delay in input / output requests, which contributes to improved responsiveness.

[0089] 10 is a diagram showing an example of a hardware configuration of a control device 200 included in the solid oxide cell systems according to embodiments 1 to 3. The control device 200 includes a processor 1000 and a storage device 2000. The processor 1000 is configured, for example, with a CPU (Central Processing Unit), an ASIC (Application Specific Integrated Circuit), a DSP (Digital Signal Processor), an FPGA (Field Programmable Gate Array), or the like.

[0090] The main storage device of the storage device 2000 is composed of a volatile storage device such as a random access memory, and the auxiliary storage device is a non-volatile storage device such as a flash memory or a hard disk. A specific program executed by the processor 1000 is stored in the auxiliary storage device, and the processor 1000 reads and executes this program as appropriate to perform various arithmetic processing. At this time, the specific program is temporarily saved from the auxiliary storage device to the volatile storage device, and the processor 1000 reads the program from the volatile storage device. The processor 1000 may output data such as the results of the arithmetic processing to the volatile storage device of the storage device 2000, or may save the data in the auxiliary storage device via the volatile storage device.

[0091] In order to enable remote control, a transmitting device and a receiving device (neither shown) may be provided as a communication module for communicating with the outside.

[0092] <Other embodiments> In the first and second embodiments, the SOC module 100 has been described as including three stacks A, B, and C that can be controlled independently, but the number of stacks is not limited to three. Also, an assembly of multiple stacks controlled in the same manner as stacks A, B, and C may be provided, and each group may be controlled independently as stack groups A, B, and C. If control is performed so that all groups are not in the same operation mode during the operation period of the solid oxide cell system 1, or are not in a pause period at the same time, the same effects as those of the first and second embodiments can be achieved.

[0093] Although the present disclosure describes various exemplary embodiments and examples, the various features, aspects, and functions described in one or more embodiments are not limited to application to a particular embodiment, but may be applied to the embodiments alone or in various combinations. Therefore, countless modifications not exemplified are assumed within the scope of the technology disclosed in this specification, including, for example, modifying, adding, or omitting at least one component, and further, extracting at least one component and combining it with a component of another embodiment. [Explanation of symbols]

[0094] 1: solid oxide cell system, 10: SOC stack, 11: SOC, 12: air electrode, 13: electrolyte, 14: fuel electrode, 15: interconnector, 18: temperature regulator for SOC stack, 20: temperature regulator, 21: gas supply section, 22: steam supply section, 30: reformer, 31: steam generator, 32: water storage section, 33: condenser, 34: gas storage section, 35: storage gas regulator, 100: SOC module, 200: control device, 201: system control section, 202: temperature control section, 1000: processor, 2000: storage device.

Claims

1. A solid oxide cell module having a solid oxide cell stack capable of switching between an SOFC mode in which power is generated using a first gas and power is output, and an SOEC mode in which power is input and a second gas is electrolyzed, and a plurality of the solid oxide cell stacks are connected; A control device for controlling the operation of a plurality of the solid oxide cell stacks; and The control device is configured to: During any period within an operation period of controlling the operation of the solid oxide cell stack while switching between the SOFC mode and the SOEC mode, at least one of the plurality of solid oxide cell stacks is controlled to operate in the SOFC mode or the SOEC mode, power input and output to at least one other solid oxide cell stack is stopped, and it is controlled to be in a standby state where it does not operate in either the SOFC mode or the SOEC mode; When the mode after the standby state of the solid oxide cell stack controlled to be in the standby state is the same as the mode before the standby state, the temperature of the solid oxide cell stack controlled to be in the standby state is maintained, and when the mode after the standby state of the solid oxide cell stack controlled to be in the standby state is different from the mode before the standby state, the temperature of the solid oxide cell stack controlled to be in the standby state is controlled to the operating temperature of the mode after the standby state. A solid oxide cell system.

2. The control device is configured to, during any period of the operation period, control at least one of the plurality of solid oxide cell stacks to operate in the SOFC mode or the SOEC mode, stop power input and output to at least one other solid oxide cell stack, and control it to be in a standby state where it does not operate in either the SOFC mode or the SOEC mode. The solid oxide cell system according to claim 1.

3. The plurality of solid oxide cell stacks include a first solid oxide cell stack and a second solid oxide cell stack. The control device controls such that, in any period of the operation period, the first solid oxide fuel cell stack and the second solid oxide fuel cell stack operate in the SOFC mode, and in that period, the output power of the first solid oxide fuel cell stack and the output power of the second solid oxide fuel cell stack are different from each other. The solid oxide fuel cell system according to claim 1.

4. The plurality of the solid oxide fuel cell stacks include a first solid oxide fuel cell stack and a second solid oxide fuel cell stack. The control device controls such that, in any period of the operation period, the first solid oxide fuel cell stack and the second solid oxide fuel cell stack operate in the SOFC mode, and in that period, the output power of the first solid oxide fuel cell stack and the output power of the second solid oxide fuel cell stack are different from each other. The solid oxide fuel cell system according to claim 2.

5. The control device controls the power and temperature input and output for each of the plurality of the solid oxide fuel cell stacks. The solid oxide fuel cell system according to any one of claims 1 to 4.

6. is provided with a stack temperature adjuster for adjusting the temperature of each of the solid oxide fuel cell stacks. The control device when cooling the solid oxide fuel cell stack in a resting state within a preset time, natural heat dissipation of the solid oxide fuel cell stack, stopping heat supply by the stack temperature adjuster, scavenging the gas remaining in the solid oxide fuel cell stack to the outside, performs temperature control using at least one of causing an endothermic reaction to occur in the solid oxide fuel cell stack. The solid oxide fuel cell system according to claim 5.

7. a stack temperature adjuster for adjusting the temperature of each of the solid oxide fuel cell stacks, and a temperature adjusting device for adjusting the temperature of the first gas and the second gas. The control device when heating the solid oxide fuel cell stack in a resting state within a preset time, performs temperature control using at least one of heat supply by the stack temperature adjuster and supply of the gas heated by the temperature adjusting device. The solid oxide fuel cell system according to claim 5.

8. The control device ​ When raising the temperature of the solid oxide fuel cell stack in a rest state within a preset time, The solid oxide fuel cell system according to claim 5, wherein temperature control is performed using radiant heat from another solid oxide fuel cell stack operating in the SOFC mode or the SOEC mode.

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