Fuel cell system

Abstract

To provide a technology for suppressing an increase in power consumption at startup in a fuel cell system including a plurality of stacks.SOLUTION: The fuel cell system includes: a first fuel cell stack; a second fuel cell stack; a first cooling system configured to circulate a coolant through the first fuel cell stack; a second cooling system configured to circulate the coolant through the second fuel cell stack; and a heat transfer system configured to enable circulation or cutoff of the coolant between the first cooling system and the second cooling system.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] This specification discloses a fuel cell system. [Background technology]

[0002] A fuel cell system may include multiple fuel cell stacks connected to a battery. For example, when starting the fuel cell system, one stack may be started with power from the battery, and after this one stack has started, the other stacks may be started (Patent Document 1). [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Application Publication No. 2022-117829 Summary of the Invention [Problem to be solved by the invention]

[0004] When multiple stacks are installed, even if the stacks are started sequentially, the power consumption for starting the multiple stacks tends to increase. This tendency is particularly noticeable when starting at low temperatures. The increased power consumption during startup can sometimes lead to a decrease in fuel economy.

[0005] The present specification provides a technique for suppressing an increase in power consumption during startup in a fuel cell system equipped with multiple stacks. [Means for solving the problem]

[0006] The technology disclosed in this specification is embodied in a fuel cell system including a first fuel cell stack, a second fuel cell stack, a first cooling system that circulates a coolant through the first fuel cell stack, a second cooling system that circulates the coolant through the second fuel cell stack, and a heat transfer system that can allow and block the flow of the coolant between the first cooling system and the second cooling system.

[0007] According to the above fuel cell system, when starting up the fuel cell system, when one of the first and second fuel cell stacks, for example, the first fuel cell stack generates power and the second fuel cell stack does not, the first fuel cell stack is heated as the first fuel cell stack generates power, and the temperature of the coolant circulating through the first cooling system is also raised. By circulating the coolant from the first cooling system to the second cooling system in the heat transfer system, the coolant is circulated through the second fuel cell stack, and the second fuel cell stack is heated. In other words, the heat generated in the first fuel cell stack is used by the second fuel cell stack via the heat transfer system. This reduces or avoids the use of power from the battery or the first fuel cell stack. As a result, the power consumption required to start power generation in the multiple fuel cell stacks is reduced. [Brief explanation of the drawings]

[0008] [Figure 1] 1 is a diagram showing an overview of a fuel cell system disclosed in this specification. [Figure 2] FIG. 1 is a flowchart illustrating an example of a process executed when starting up a plurality of fuel cell stacks in a fuel cell system. [Figure 3] FIG. 10 is a flowchart showing another example of a process executed when starting operation of a plurality of fuel cell stacks in a fuel cell system. DETAILED DESCRIPTION OF THE INVENTION

[0009] One aspect of the fuel cell system disclosed in this specification can include a first fuel cell stack, a second fuel cell stack, a first cooling system that circulates a refrigerant through the first fuel cell stack, a second cooling system that circulates the refrigerant through the second fuel cell stack, and a heat transfer system that can allow and block the flow of the refrigerant between the first cooling system and the second cooling system.

[0010] Another aspect of the fuel cell system may further include a control device that controls the power generation of the first fuel cell stack and the second fuel cell stack, and the control device may include executing a first start-up process that performs a start-up operation to initiate power generation by the first fuel cell stack and the second fuel cell stack, a determination process that determines, after the first start-up process, which of the first fuel cell stack and the second fuel cell stack is capable of generating power, a first power generation process that generates power using one of the first fuel cell stack and the second fuel cell stack that is determined to be capable of generating power in the determination process, and does not generate power using the other fuel cell stack, and a heating process that supplies the refrigerant circulating through the one fuel cell stack to the other fuel cell stack via the heat transfer system to raise the temperature of the other fuel cell stack.

[0011] The first startup process and determination process determine which fuel cell stack is capable of generating electricity, and one of the fuel cell stacks capable of generating electricity generates electricity, while the other fuel cell stack that is not capable of operating is placed on standby. The coolant in the one fuel cell stack that is generating electricity is heated, and the heated coolant heats up the other fuel cell stack. Therefore, for example, when starting fuel cell stacks below freezing, it is possible to select a fuel cell stack that is capable of generating electricity and generate electricity, and then heat and thaw the other fuel cell stack that was unable to generate electricity due to freezing or other reasons. This reduces power consumption and allows the other fuel cell stacks to be started up efficiently.

[0012] In the above aspect, the first cooling system may include a first radiator, the second cooling system may include a second radiator, the first power generation process may be a process of generating power in one of the fuel cell stacks without the refrigerant flowing through one of the radiators of the one fuel cell stack, and the temperature increase process may be a process of increasing the temperature of the other of the fuel cell stacks without the refrigerant flowing through the other radiator of the other fuel cell stack. This prevents heat from being lost in the refrigerant by the first and second radiators, thereby efficiently increasing the temperatures of the first and second fuel cell stacks.

[0013] In one aspect of the present invention, after the temperature increase process, a second start-up process is performed to start up the other fuel cell stack to start power generation, thereby reducing power consumption and reliably starting power generation in the other fuel cell stack.

[0014] Another aspect of the fuel cell system may further include a control device that controls the power generation of the first fuel cell stack and the second fuel cell stack, and the control device may execute a first startup process that performs a startup operation to initiate power generation of one of the first fuel cell stack and the second fuel cell stack, and a temperature increase process that supplies the coolant circulating through the one fuel cell stack to the other of the first fuel cell stack and the second fuel cell stack to increase the temperature of the other fuel cell stack. This can reduce the power consumption required to increase the temperature and start multiple fuel cell stacks, even when the possibility of gas flow paths freezing is low.

[0015] In another aspect of the present invention, the control device may execute a second startup process after the temperature rise process to start power generation in the other fuel cell stack. Also, in another aspect of the present invention, the temperature rise process may be executed by restricting the use of power supplied to the other fuel cell stack from a battery included in the fuel cell system.

[0016] The fuel cell system (hereinafter simply referred to as the system) 2 disclosed in this specification will be described in detail below with reference to the accompanying drawings. Fig. 1 shows an overview of the system 2, and Fig. 2 shows a flowchart of the start-up process executed by a control device 100 included in the system 2.

[0017] System 2 is not particularly limited, but can be applied as, for example, a power source for driving a moving body such as a vehicle or as a stationary power generation facility. The type of fuel cell in System 2 is not particularly limited, but application to a polymer electrolyte fuel cell (PEFC) may be meaningful in terms of its operating temperature.

[0018] (Fuel cell stack) 1, the system 2 includes fuel cell stacks (hereinafter simply referred to as stacks) 10, 20, cooling systems 30, 40, a battery 50, a heat transfer system 60, and a control device 100. The number of stacks included in the system 2 is not limited to two, but is not particularly limited as long as there is more than one, and may be changed as needed.

[0019] The various sensors, valves, switches, etc. in the stacks 10, 20, fuel gas systems 12, 22, oxidant gas systems 14, 24, and cooling systems 30, 40 are appropriately connected to the control device 100 so that signals can be input and output to and from the control device 100. The control device 100 is configured as a so-called computer. The control device 100 includes, for example, a processor and memory, and is capable of executing applications required for controlling power generation, including the start-up of the fuel cell stacks 10, 20 of the system 2.

[0020] The stacks 10, 20 are formed by stacking known cells having a configuration according to the type of fuel cell. The stacks 10, 20 are electrically connected to a battery 50, and are configured to be able to use power supplied from the battery 50 and to supply power generated by the stacks 10, 20 to the battery 50. The stacks 10, 20 are examples of the first fuel cell stack and the second fuel cell stack, respectively, disclosed in this specification.

[0021] (Fuel gas system and oxidizer gas system) The stacks 10 and 20 each include a fuel gas system 12 or 22 for circulating a fuel gas such as hydrogen, and an oxidant gas system 14 or 24 for circulating an oxidant gas such as air. The fuel gas systems 12 and 22 may be connected to the same fuel gas supply source. Alternatively, the oxidant gas systems 14 and 24 may be connected to the same oxidant gas supply source.

[0022] (cooling system) 1, the stacks 10 and 20 are equipped with cooling systems 30 and 40, respectively. The cooling systems 30 and 40 are equipped with pipes 32 and 42 through which a predetermined refrigerant for cooling the stacks 10 and 20 flows, pumps 34 and 44 for circulating the refrigerant, and radiators 36 and 46. The pumps 34 and 44 and the radiators 36 and 46 may have any known configuration.

[0023] The cooling system 30 can form a circulation flow path 32a that circulates the refrigerant through the stack 10 by a pump 34 without passing through a radiator 36. The circulation flow path 32a is composed of a flow path 33a, a flow path 10a for the refrigerant within the stack 10, a flow path 33b, and a flow path 33c. The pump 34 is provided on the flow path 33a on the upstream side of the stack 10 so as to flow the refrigerant toward the stack 10.

[0024] The cooling system 30 also forms a circulation flow path 32b that circulates the refrigerant through the stack 10 via the radiator 36. The circulation flow path 32b is made up of flow paths 33a, 10a, flow paths 33b, 33d, and flow paths 36a and 33e for the refrigerant in the radiator 36. Flow paths 33d and 33e branch off from the circulation flow path 32a. A valve 38 is provided at the point where flow path 33d branches off from the circulation flow path 32a so that the circulation flow paths 32a and 32b can be formed, respectively. The valve 38 is formed so that it opens in two directions so that a portion of the circulation flow path 32a can be formed, and so that it opens in two directions so that a portion of the circulation flow path 32b can be formed.

[0025] Furthermore, the flow path 33b through which the refrigerant is discharged from the stack 10 is provided with valves 66 and 68. These valves 66 and 68 will be described later.

[0026] The cooling system 40 can form a circulation flow path 42a that circulates the refrigerant through the stack 20 by a pump 44 without passing through a radiator 46. The circulation flow path 42a is composed of a flow path 43a, a flow path 20a for the refrigerant in the stack 20, a flow path 43b, and a flow path 43c. The pump 44 is provided on the flow path 43a on the upstream side of the stack 20 so as to flow the refrigerant toward the stack 20.

[0027] The cooling system 40 can also form a circulation flow path 42b that circulates the refrigerant through the stack 20 via the radiator 46. The circulation flow path 42b is made up of flow paths 43a, 20a, flow path 43b, and flow path 46a and flow path 43e for the refrigerant in the radiator 36. Flow paths 43d and 43e branch off from the circulation flow path 42a. A valve 48 is provided at the portion where flow path 43d branches off from the circulation flow path 42a so that the circulation flow path 42a and the circulation flow path 42b can be formed, respectively. The valve 48 is formed so that it opens in two directions so that a portion of the circulation flow path 42a can be formed, and so that it opens in two directions so that a portion of the circulation flow path 42b can be formed.

[0028] Furthermore, the flow path 43b of the circulation flow path 42a through which the refrigerant is discharged from the stack 20 is provided with a communication flow path 64 that branches off toward the cooling system 30. A shut valve 70 is provided downstream of the communication flow path 64. The communication flow path 64 and the shut valve 70 will be described later.

[0029] (Heat transfer system) The heat transfer system 60 is configured to form a circulation flow path 60a as needed between the stacks 10 and 20, in other words, between the cooling system 30 and the cooling system 40. The circulation flow path 60a allows a refrigerant to flow and blocks the flow of the refrigerant. The heat transfer system 60 also includes communication flow paths 62 and 64 that communicate between the cooling systems 30 and 40, as well as flow paths 43a, 20a, and 43b in the cooling system 40, valves 66 and 68, and a shutoff valve 70.

[0030] The communication flow path 62 is connected to a valve 66 in the cooling system 30, and is connected to a circulation flow path 42a in the cooling system 40 downstream of the pump 44 and upstream of the stack 20. The refrigerant flowing from the valve 66 through the communication flow path 62 merges with a flow path 43a of the cooling system 40.

[0031] Communication flow path 64 is connected to a valve 68 on flow path 33b in cooling system 30, and is connected to flow path 43b in cooling system 40. Communication flow path 64 is connected to circulation flow path 32a via valve 66, without passing through pump 44, for refrigerant from cooling system 40. The refrigerant flowing through communication flow path 64 is merged with circulation flow path 32a of cooling system 30 via valve 68.

[0032] Valve 66 is disposed on flow path 33b and is formed to be open in two directions, that is, to the cooling system 30 and valve 68, so as to form a part of circulation flow path 32a. Valve 66 is also formed to be open in two directions, that is, to the stack 10 and communication flow path 62, so that the refrigerant discharged from stack 10 flows into communication flow path 62.

[0033] Valve 68 is formed on flow path 33c downstream of valve 66. Valve 68 is formed to be open in two directions, toward valve 66 and valve 38, so as to form part of circulation flow path 32a. Valve 68 is also formed to be open in two directions, toward communication flow path 64 and valve 66, so as to merge refrigerant supplied from communication flow path 64 into circulation flow path 42a.

[0034] The shutoff valve 70 is disposed on the flow path 43b downstream of the branching portion to the communication flow path 64. The shutoff valve 70 is formed to be open in two directions, to the flow path 43b and to the valve 48, so that the circulation flow path 42a can be formed. The shutoff valve 70 is also formed to block the refrigerant from the stack 20 from flowing into the valve 48 and to allow the refrigerant to flow into the communication flow path 64.

[0035] According to the heat transfer system 60, the flow of refrigerant between the cooling systems 30 and 40 can be blocked by opening and closing the valves 66, 68 and the shut valve 70. Furthermore, according to the heat transfer system 60, a circulation flow path 60a through which the refrigerant flows between the cooling systems 30 and 40 can be newly formed by opening and closing the valves 66, 68, and 80 in a different manner. In the circulation flow path 60a, the refrigerant flowing through the circulation flow path 32a by the pump 34 flows into the flow path 20a of the stack 20 via the valve 66, the communication flow path 62, and the flow path 43a. Furthermore, the refrigerant discharged from the flow path 20a flows into the flow path 43b and the communication flow path 64, reaches the valve 68, and merges with the circulation flow path 32a.

[0036] Next, a startup process executed by the control device 100 when starting power generation at the start of the system 2 will be described. Note that the following process is mainly executed when the system 2 is in a low-temperature environment. During startup in a low-temperature environment, in the cooling systems 30 and 40 of the stacks 10 and 20, the valves 38 and 48 are controlled so that the refrigerant circulates through the circulation paths 32a and 42a without passing through the radiators 36 and 46, respectively. This is to promote the temperature rise of the stacks 10 and 20 by preventing the radiators 36 and 46 from cooling the refrigerant. In addition, the valves 66 and 68 and the shutoff valve 70 are controlled so that the refrigerant does not flow through the circulation path 60a of the heat transfer system 60.

[0037] The control device 100 performs a start-up operation to start power generation by supplying hydrogen and oxygen to both stacks 10 and 20 using power supplied from the battery 50 (step S10). Step S10 for performing this start-up operation is an example of the first start-up process in this specification.

[0038] Next, a determination is made based on the status of the stacks 10, 20 as to whether startup of the stacks 10, 20 is permitted (step S20). This determination can be made, for example, from the hydrogen flow rate and power generation voltage when supply of oxygen and hydrogen to the stacks 10, 20 is started and power generation is attempted. For example, in a low-temperature environment below freezing, the hydrogen pipes may freeze, preventing hydrogen from flowing and causing voltage inversion. By detecting such phenomena, the control device 100 can determine which stacks cannot be started. When the outside air temperature is below freezing, it is difficult to determine which of the stacks 10, 20 cannot be started due to freezing, so these startup and determination processes are effective. Step S20 for making this determination is an example of the determination process disclosed in this specification.

[0039] In step S20, if both stacks 10 and 20 can be started, power generation is started immediately (step S30), and this process is ended.

[0040] On the other hand, in step S20, for example, when stack 10 can be started but stack 20 cannot be started, power generation is started for stack 10, and the start-up operation of stack 20 is stopped and the start-up operation is put on standby for power generation (step S40). When the start-up operation of stack 20 is stopped, control device 100 stops pump 44 and also closes shut valve 70 to stop the inflow of refrigerant into circulation flow path 42a. This step S40 of power generation is an example of the first power generation process disclosed in this specification.

[0041] When the stack 10 starts generating power, the temperature of the stack 10 rises. As the temperature of the stack 10 rises, the temperature of the refrigerant flowing through the stack 10 and the cooling system 30 also rises. Note that the temperature rise may be promoted by heating the stack 10 using power supplied from the battery 50.

[0042] Next, the control device 100 determines whether the temperature of the stack 10 has risen sufficiently (for example, whether the warm-up operation has ended) (step S50). This determination can be made, for example, based on the temperature of the stack 10 detected by the control device 100 or the temperature of the refrigerant circulating through the cooling system 30. Alternatively, for example, the control device 100 can determine that the warm-up operation has ended when the temperature of the stack 10 or the like reaches or exceeds a preset threshold temperature. When the warm-up operation of the stack 10 has ended, the temperature of the refrigerant circulating through the circulation flow path 32a of the cooling system 30 in the stack 10 also usually exceeds 0°C. While the warm-up operation of the stack 10 has not ended, the power generation (warm-up operation) of the stack 10 continues. Note that step S50 may be replaced by continuing to operate the stack 10 for a preset time.

[0043] When the control device 100 determines that the warm-up operation of the stack 10 has been completed, the control device 100 heats up the stack 20, for which the start-up operation has been stopped (step S60). The refrigerant circulating through the circulation flow path 32a of the cooling system 30 of the stack 10 is supplied to the cooling system 40 via the heat transfer system 60, thereby raising the temperature of the stack 20. That is, the heat generated in the stack 10 is transferred and utilized to raise the temperature of the stack 20. Note that in the temperature raising process of the stack 20, fuel gas and oxidant gas are not supplied. Step S60, in which the temperature is raised, is an example of the temperature raising process in this specification.

[0044] The control device 100 opens the valves 66 and 68 toward the stack 20, thereby forming a circulation flow path 60a of the heat transfer system 60. As the refrigerant passes through the flow path 20a of the stack 20, the frozen portion of the stack 20 is heated and thawed, allowing gas to flow.

[0045] Next, the control device 100 detects, for example, the temperature of the stack 20 and the temperature of the refrigerant circulating through the stack 20, and determines whether the temperature of the stack 20 has risen sufficiently (step S70). The criterion for determining whether the temperature has risen is, for example, the temperature at which the frozen portion of the stack 20 is estimated to have thawed and be in a state where it is capable of generating electricity. The control device 100 determines that the frozen portion of the stack 20 has thawed when the temperature of the stack 10 exceeds a preset threshold temperature, for example, 0°C. The refrigerant circulating through the stack 10 is supplied to the stack 20 by the heat transfer system 60 until thawing of the stack 20 is completed. Note that step S70 may be replaced by continuously flowing the refrigerant through the circulation flow path 60a for a predetermined time.

[0046] When the control device 100 determines that the thawing of the stack 20 has been completed, the control device 100 performs a start-up operation again (step S80) to start supplying hydrogen and oxygen to the stack 20 to generate power in the stack 20, and then ends this process. In conjunction with the execution of this start-up operation, the control device 100 appropriately stops the flow of refrigerant through the heat transfer system 60. To stop the heat transfer system 60, the control device 100 operates the valves 66 and 68 so that the refrigerant circulates independently through the circulation paths 32a and 42a. Step S80 of performing this start-up operation again is another example of the second start-up process disclosed in this specification.

[0047] By the above process, for example, when the stack 10 can be started but the stack 20 is frozen and cannot be started, the use of power to thaw the frozen portion of the stack 20 is suppressed or avoided. This suppresses power consumption when starting the system 2. As a result, even at temperatures below freezing, the use of battery power is suppressed and multiple stacks 10, 20 can be started.

[0048] In the above embodiment, in step S60, the temperature is increased until the frozen portion of the stack 20 is thawed, but this is not limiting. The temperature may be increased until the normal warm-up operation of the stack 20 is completed.

[0049] In the above embodiment, a heat transfer system 60 is described that supplies the refrigerant circulating through stack 10 to stack 20, but a circulation flow path of a heat transfer system that supplies the refrigerant circulating through stack 20 to stack 10 can also be constructed.

[0050] In the embodiment already described, the control device 100 performs a process to determine which stack 20 cannot be started, but this is not limiting. For example, when the outside air temperature of the system 2 is at a temperature at which the stacks 10, 20 are not expected to freeze, only one of the stacks 10, 20 may be started, and then the other stacks may be heated and started. An example of such a start-up process for the stacks 10, 20 is shown in FIG. 3.

[0051] 3, the control device 100 first performs a startup operation to start power generation in the stack 10 (step S110). Step S110, in which the startup operation is performed for the stack 10, is another example of the first startup process disclosed in this specification. The control device 100 performs power generation in the stack 10 without performing power generation for the stack 20 (step S120). Step S120, in which power generation is performed only in the stack 10, is another example of the first power generation process disclosed in this specification.

[0052] Thereafter, the control device 100 determines whether or not the warm-up of the stack 10 has been completed (step S130). This step S130 may be replaced by continuing the operation of the stack 10 for a predetermined time.

[0053] When the control device 100 determines that the warm-up operation of the stack 10 is completed, the control device 100 increases the temperature of the stack 20 (step S140). The control device 100 operates the valves 66, 68 and the shutoff valve 70 to form the circulation flow path 60a, and supplies the refrigerant of the cooling system 30 to the cooling system 40, thereby increasing the temperature of the stack 20. Step S130, in which the temperature of the stack 20 is increased, is another example of the temperature increase process disclosed in this specification.

[0054] The control device 100 determines whether the temperature of the stack 20 has risen sufficiently (step S150). The determination criterion here is, for example, whether the stack 20 has reached a warm-up completion temperature obtained by a normal warm-up operation. This step S150 may be replaced by continuously flowing the refrigerant through the circulation flow path 60a for a predetermined time.

[0055] When the control device 100 determines that the temperature of the stack 20 has reached the warm-up completion temperature, it performs a start-up operation to start power generation in the stack 20 (step S160), and ends this process. Step S150 of performing the start-up operation of the stack 20 is another example of the second start-up process in this specification.

[0056] In this way, warm-up operation is performed only for stack 10, and then by utilizing the heat from stack 10, warm-up of stack 20 can be completed without generating (operating) power from stack 20. Even if the outside air temperature of system 2 is at a temperature at which stacks 10 and 20 will not freeze, simultaneous warm-up operation of multiple stacks 10 and 20 can be avoided, power consumption can be reduced, and improved power efficiency can be expected.

[0057] In the process shown in Fig. 3, the warm-up operation of the stack 10 may also use power supplied from the battery 50. This allows the warm-up operation of the stack 10 to be completed quickly. When the temperature of the stack 20 is raised, the use of power supplied from the battery 50 may be limited (reduced or not used). This further reduces power consumption.

[0058] Specific examples of the technology disclosed in this specification have been described in detail above, but these are merely examples and do not limit the scope of the claims. The technology described in the claims includes various modifications and variations of the specific examples exemplified above, such as a fuel cell control method. The technical elements described in this specification or in the drawings exhibit technical utility either alone or in various combinations, and are not limited to the combinations described in the claims at the time of filing. The technology exemplified in this specification or in the drawings can achieve multiple objectives simultaneously, and achieving one of these objectives itself has technical utility. [Explanation of symbols]

[0059] 2 fuel cell system, 10, 20 fuel cell stack, 12, 22 fuel gas system, 14, 24 oxidizer gas system, 30, 40 cooling system, 32a, 32b, 42a, 42b circulation flow path, 34, 44 pump, 50 battery, 60 heat transfer system, 60a circulation flow path, 62, 64 communication flow path, 38, 48, 66, 68 valve, 70 shutoff valve, 100 control device

Claims

1. a first fuel cell stack; a second fuel cell stack; a first cooling system for circulating a coolant through the first fuel cell stack; a second cooling system that circulates the coolant through the second fuel cell stack; a heat transfer system capable of circulating and blocking the refrigerant between the first cooling system and the second cooling system; A fuel cell system comprising:

2. a control device for controlling power generation by the first fuel cell stack and the second fuel cell stack; the control device performs a first startup process to start power generation by the first fuel cell stack and the second fuel cell stack; a determination process for determining which of the first fuel cell stack and the second fuel cell stack is capable of generating electricity after the start-up process; a first power generation process in which one of the first fuel cell stack and the second fuel cell stack determined to be capable of generating power in the determination process generates power, and the other fuel cell stack does not generate power; a temperature raising process in which the coolant flowing through the one fuel cell stack is supplied to the other fuel cell stack via the heat transfer system to raise the temperature of the other fuel cell stack; The fuel cell system according to claim 1 , wherein the fuel cell system executes the above.

3. the first cooling system includes a first radiator; the second cooling system includes a second radiator; the first power generation process is a process of generating power in one of the fuel cell stacks in a state where the refrigerant does not flow through one of the radiators included in the one of the fuel cell stacks, 3. The fuel cell system according to claim 2, wherein the temperature increase process is a process of increasing the temperature of the other fuel cell stack in a state where the coolant does not flow through the other radiator provided in the other fuel cell stack.

4. 4. The fuel cell system according to claim 2, wherein the control device executes a second start-up process to start a start-up operation for starting power generation in the other fuel cell stack after the temperature increase process.

5. a control device for controlling power generation by the first fuel cell stack and the second fuel cell stack; the control device performs a first startup process to start an operation of one of the first fuel cell stack and the second fuel cell stack; a first power generation process in which one of the fuel cell stacks generates power and the other fuel cell stack does not generate power; a temperature raising process in which the coolant flowing through the one fuel cell stack is supplied to the other fuel cell stack of the first fuel cell stack and the second fuel cell stack to raise the temperature of the other fuel cell stack; The fuel cell system according to claim 1 , wherein the fuel cell system executes the above.

6. 6. The fuel cell system according to claim 5, wherein the control device executes a second start-up process to start a start-up operation for starting power generation in the other fuel cell stack after the temperature increase process.

7. 7. The fuel cell system according to claim 5, wherein the temperature increase process is performed by restricting the other fuel cell stack from using power supplied from a battery provided in the fuel cell system.

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