Water electrolysis system

Abstract

To provide a water electrolysis system, in which a degraded water electrolysis stack can be determined without suddenly changing a load, or stopping the water electrolysis stack, during operation.SOLUTION: A water electrolysis system comprises: multiple water electrolysis stacks 21; a direct-current power supply 22 for driving the water electrolysis stack 21 to which a direct-current power is supplied; a current monitoring device 24 for measuring a current flowing in the water electrolysis stack 21; a voltage monitoring device 23 for measuring a voltage applied to the water electrolysis stack 21; a calculation unit 13 for estimating an electric resistance of the water electrolysis stack 21 changing according to a degradation state from the current value measured by the current monitoring device 24 and the voltage value measured by the voltage monitoring device 23, determining the degradation state of the water electrolysis stack 21 based on the estimated result of the electric resistance, and outputting the determination result; and a display control unit 11 for outputting the degradation state of the water electrolysis stack 21 to a display device after receiving the determination result from the calculation unit.SELECTED DRAWING: Figure 1

Description

[Technical field]

[0001] The present invention relates to a technique for diagnosing deterioration of a water electrolysis stack included in a water electrolysis system. [Background technology]

[0002] In recent years, with the increase in emissions of greenhouse gases such as carbon dioxide, environmental issues such as global warming and energy issues such as the depletion of petroleum resources have been attracting attention. From this perspective, hydrogen energy has been attracting attention as a clean alternative energy source. However, in order to replace existing fossil fuels with hydrogen energy, a large amount of hydrogen is required.

[0003] Water electrolysis equipment is one method of producing hydrogen. Demonstration projects for large-scale water electrolysis equipment are underway to curb global warming. In particular, a demonstration project for a hydrogen production equipment of several tens of megawatts (MW) that uses electricity generated by offshore wind power is underway in Europe, and it is expected that water electrolysis equipment will continue to become larger in the future. In the production of MW-class hydrogen using water electrolysis equipment, the water electrolysis stack (water electrolyzer) is characterized by its low voltage and high current characteristics of several hundred V and several thousand A.

[0004] Because the equipment costs of water electrolysis stacks are high, it is necessary to extend the operating time in order to reduce the cost of the entire water electrolysis system. To extend the operating time, it is necessary to detect degraded water electrolysis stacks early and suppress the deterioration through operational control. However, much is unknown about the electrochemical reactions in water electrolysis stacks. For this reason, it is important to develop a water electrolysis system equipped with a deterioration diagnosis function.

[0005] When a water electrolysis system is scaled up to the MW level, the means to estimate the system status becomes an issue. A method for diagnosing deterioration is required that at least (1) does not shut down all water electrolysis systems, and (2) does not cause abrupt changes in the system load.

[0006] Patent Document 1 describes a method for diagnosing battery degradation from changes over time in the current and voltage values ​​of a water electrolysis stack by varying the battery load. According to the method described in Patent Document 1, the impedance can be obtained by suddenly changing the current and performing a Fourier transform on the current and voltage data. The battery state is then estimated from the impedance measurement data.

[0007] Furthermore, Patent Document 2 describes a method of obtaining the electrical resistance of a water electrolysis stack from changes in current and voltage when a water electrolysis device is stopped, and using this as a guideline to diagnose battery degradation. [Prior art documents] [Patent documents]

[0008] [Patent Document 1] JP 2019-117180 A [Patent Document 2] Special Publication No. 2023-509550 Summary of the Invention [Problem to be solved by the invention]

[0009] However, in the case of a large-scale hydrogen production device, it is difficult to apply the method described in Patent Document 1 because the load cannot be changed suddenly. Furthermore, the temperature of the water electrolysis device changes with the load change. For example, in a calculation with four cells and a water flow rate of 0.6 cc / min / cm 2 , and electrolytic area 44 cm 2 2A / cm for water electrolysis equipment 2 When a current of 1200 kcal / L is applied, the water temperature rises by 12°C in 40 seconds, making it impossible to obtain impedance for a long period of time at a constant temperature. For these reasons, it is considered difficult to apply the method described in Patent Document 1.

[0010] It is also known that when the water electrolysis device is stopped, the catalyst applied to the oxygen generating electrode is oxidized and reduced, which accelerates the deterioration of the electrode. Furthermore, in the case of a water electrolysis system with a multiple series-parallel configuration, the oxide in a highly oxidized state on the electrode may discharge, causing a large reverse current to flow in the water electrolysis stack, which further accelerates the deterioration. For this reason, it is considered difficult to apply the method described in Patent Document 2.

[0011] In view of the above circumstances, there has been a demand for a method for determining whether a water electrolysis stack is deteriorated during operation of a water electrolysis system, without suddenly changing the load or stopping the water electrolysis stack. [Means for solving the problem]

[0012] In order to solve the above problems, a water electrolysis system of one embodiment of the present invention includes a plurality of water electrolysis stacks, a DC power supply that supplies DC power to the water electrolysis stacks to drive the water electrolysis stacks, a current monitoring device that measures and monitors a current flowing through the water electrolysis stacks, a voltage monitoring device that measures and monitors a voltage applied to the water electrolysis stacks, a calculation unit, and a display control unit. The calculation unit receives the current measurement values ​​from the current monitoring device and the voltage measurement values ​​from the voltage monitoring device, estimates the electrical resistance of the water electrolysis stack that changes depending on the degradation state from the time-series current measurement values ​​and voltage measurement values, determines the degradation state of the water electrolysis stack based on the estimated electrical resistance, and outputs the determination result.The display control unit receives the determination result from the calculation unit and outputs the degradation state of the water electrolysis stack to the display device. Effect of the Invention

[0013] According to at least one aspect of the present invention, during operation of a water electrolysis system, it is possible to quantitatively estimate the electrical resistance of the water electrolysis stack and determine the degradation state of the water electrolysis stack based on the estimated electrical resistance without suddenly varying the load or stopping the water electrolysis stack, thereby making it possible to identify a degraded water electrolysis stack from among a plurality of water electrolysis stacks. Problems, configurations and effects other than those described above will become apparent from the following description of the embodiments. [Brief description of the drawings]

[0014] [Figure 1] 1 is a diagram showing a schematic configuration of a water electrolysis system according to a first embodiment of the present invention. [Diagram 2] 1 is a diagram showing an example of the hardware configuration of each device constituting a water electrolysis system according to a first embodiment of the present invention. FIG. [Diagram 3] FIG. 1 is a diagram showing an equivalent circuit of a water electrolysis stack in a first embodiment of the present invention. [Figure 4] 5 is a flowchart showing an example of a procedure for a degradation diagnosis process performed by the water electrolysis system according to the first embodiment of the present invention. [Diagram 5] FIG. 3 is a diagram showing an example of voltage measurement results and current measurement results (current density) of the water electrolysis system according to the first embodiment of the present invention. [Figure 6] FIG. 4 is a diagram showing an example of extracted results of voltage measurement and current measurement in a designated period of the water electrolysis stack in the first embodiment of the present invention. [Figure 7] FIG. 4 is a diagram showing an example of an electric resistance estimated from the measurement results of current and voltage during load fluctuation in the water electrolysis system according to the first embodiment of the present invention, and an example of a deterioration determination threshold value for the electric resistance. [Figure 8] FIG. 11 is a diagram showing an example of voltage measurement results (changes in voltage over time) of the water electrolysis stack in the second embodiment of the present invention. [Figure 9] 10 is a flowchart showing an example of a procedure for a degradation diagnosis process performed by a water electrolysis system according to a second embodiment of the present invention. [Figure 10] FIG. 11 is a graph showing an example of changes over time in current density and voltage in a water electrolysis system according to a second embodiment of the present invention. [Figure 11] FIG. 11 is a diagram showing a schematic configuration of a water electrolysis system according to a third embodiment of the present invention. [Figure 12] 13 is a flowchart showing an example of a procedure for a degradation diagnosis process performed by a water electrolysis system according to a third embodiment of the present invention. [Figure 13]FIG. 13 is a diagram showing an example of the change over time in current density of a water electrolysis stack when the resistance value of a slip resistor is adjusted in the third embodiment of the present invention. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0015] DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, examples of modes for carrying out the present invention (hereinafter, referred to as "embodiments") will be described with reference to the accompanying drawings.

[0016] In this specification and the accompanying drawings, identical or similar components are given the same reference numerals, and duplicate explanations may be omitted, or only differences may be explained. In addition, when there are multiple identical or similar components, they may be explained with different subscripts added to the same reference numerals. In addition, when it is not necessary to distinguish between these multiple components, the subscripts may be omitted. The number of each component may be singular or plural, unless otherwise specified.

[0017] <First embodiment> First, a water electrolysis system according to a first embodiment of the present invention will be described with reference to Figures 1 to 7. The water electrolysis system according to this embodiment is a multi-connection water electrolysis system configured by connecting a plurality of water electrolysis stacks.

[0018] [Outline of water electrolysis system] FIG. 1 is a diagram showing a schematic configuration of a water electrolysis system according to a first embodiment of the present invention. The water electrolysis system 1 includes a control device 10 and a water electrolysis device 20. The control device 10 controls the water electrolysis device 20, and is mainly composed of a display control device 11, a display device 12, and a computing device 13. The water electrolysis device 20 includes multiple water electrolysis stacks 21, a DC power supply 22, multiple voltage monitoring devices 23, and multiple current monitoring devices 24.

[0019] The water electrolysis device 20 is provided with a plurality of water electrolysis stacks 21 that electrolyze water. As an example, the water electrolysis stack 21 has a structure in which a plurality of thin components (water electrolysis cells) that electrolyze water to produce hydrogen and oxygen are stacked. The DC power source 22 and each water electrolysis stack 21 are electrically connected in series and parallel by a power cable. The DC power source 22 is configured to supply DC power to each water electrolysis stack 21.

[0020] 1 shows a configuration in which all the water electrolysis stacks 21 are connected in series and parallel to the DC power supply 22, the water electrolysis stacks 21 may be connected in parallel, in series, or independently. The independently connected configuration refers to a form in which the two-dimensionally arranged water electrolysis stacks 21 are replaced with a single stack.

[0021] The display control device 11 (an example of a display control unit) will be described. The display control device 11 has a function of issuing a current change command to cause the DC power source 22 to vary the current output, and a function of issuing a start command to cause the voltage monitoring device 23 and the current monitoring device 24 to start measurement. The display control device 11 also has a notification function (output processing function) of receiving a calculation result from the calculation device 13 and notifying the driver of the calculation result, and an input processing function of generating an input signal in response to the driver's operation of the input device 35 (see FIG. 2 described later). The display control device 11 may be configured integrally with the display device 12, like a notebook PC or a tablet terminal.

[0022] The current change command may be either a control to increase or decrease the output current of the DC power supply 22. The control to increase or decrease the output current of the water electrolysis device 20 and the amount of current change may be considered to be predetermined. However, although it depends on the capacity of the water electrolysis stack 21, when the current density of the current passing through each water electrolysis stack 21 is 0.5 A / cm 2 ~2A / cm 2 It is preferable that the range does not exceed this.

[0023] In an experiment using the water electrolysis stack 21 according to this embodiment,2 If the current density is less than 2 A / cm, the water electrolysis stack 21 will deteriorate. 2 At the above current densities, the water electrolysis stack 21 deteriorated quickly and the water electrolysis efficiency was low. However, this numerical range of the current density is only an example. The above notification is performed by displaying a warning or the like on the display screen of the display device 12 and ending the deterioration determination, but may also be further notified by an alarm sound or the like.

[0024] The display control device 11 and the arithmetic device 13 can be configured using, for example, a microcontroller or a PC (Personal Computer).

[0025] Next, the water electrolysis stack 21 will be described. The water electrolysis stack 21 is, for example, a device made by stacking water electrolysis cells (not shown) including a proton permeable membrane, and produces hydrogen and oxygen using water as a raw material. A preferred example of the water electrolysis stack 21 is a solid polymer electrolyte membrane (PEM: Polymer Electrolyte Membrane) type water electrolysis stack.

[0026] Next, the DC power supply 22 will be described. The DC power supply 22 is a device capable of supplying DC current to each of the multiple water electrolysis stacks 21. In this embodiment, the average current density is calculated as an index of the DC current. The average current density is the average value of the current density of the DC current output by each water electrolysis stack 21 in the water electrolysis system 1. The DC power supply 22 has a function of changing the output current in response to a current change command from the display control device 11. There may be multiple DC power supplies.

[0027] Next, the voltage monitoring device 23 and the current monitoring device 24 will be described. The voltage monitoring device 23 is a device that measures the voltage applied to each water electrolysis stack 21. The current monitoring device 24 is a device that measures the current passing through each water electrolysis stack 21. The voltage monitoring device 23 and the current monitoring device 24 have a function of measuring the voltage value and the current value at a predetermined time interval Δt (see FIG. 6 described later). The predetermined time interval Δt is preferably 4 ms or less. However, this value is based on the experimental results of a relatively small water electrolysis system, and may be changed depending on the time constant of the water electrolysis stack.

[0028] The voltage monitoring device 23 and the current monitoring device 24 have a function of receiving a measurement command to start measurement from the display control device 11 and starting measurement of the voltage applied to and the current passing through each water electrolysis stack 21 at the above-mentioned predetermined time interval. In addition, the voltage monitoring device 23 and the current monitoring device 24 have a transfer function of ending the measurement a predetermined time after the start of the measurement and transferring all the voltage and current measurement results from the start to the end of the measurement to the calculation device 13.

[0029] Next, the calculation device 13 (an example of a calculation unit) will be described. The calculation device 13 has a calculation function of receiving the measurement results of the voltage and current from the voltage monitoring device 23 and the current monitoring device 24 in chronological order, and calculating the reaction electric resistance R0 and the reaction capacitance C1 of the water electrolysis stack 21 described below. The calculation device 13 also has a function of determining the deterioration state of the water electrolysis stack 21 based on the reaction electric resistance R0 and / or the reaction capacitance C1 described below. Furthermore, the calculation device 13 searches for a change point of the voltage and current from the measurement results of the voltage and current. The change point is the time when the output of the DC power supply 22 changes. This time is set to 0 s. The reaction electric resistance R0 and the reaction capacitance C1 will be described in detail below.

[0030] [Hardware configuration of each device in the water electrolysis system] Next, the hardware configuration of each device constituting the water electrolysis system 1 will be described with reference to Fig. 2. Here, an example of the hardware configuration of the display control device 11 and the computer included in the arithmetic device 13 will be described.

[0031] FIG. 2 is a diagram showing an example of the hardware configuration of the computers included in the display control device 11 and the arithmetic device 13. As shown in FIG. 2, each block may be selected according to the function and purpose of each device. The calculator 30 may be, for example, a personal computer or a microcontroller.

[0032] The computer 30 includes a CPU (Central Processing Unit) 31, a ROM (Read Only Memory) 32, a RAM (Random Access Memory) 33, a display device 12, an input device 35, a non-volatile storage 36, and a communication interface 37. The components within the computer 30 are connected to each other via a system bus so as to be able to transmit and receive data to each other.

[0033] The CPU 31, the ROM 32, the RAM 33, and the non-volatile storage 36 constitute a control unit. This control unit is used as an example of a computer that controls the operation of the display control device 11 or the arithmetic device 13. The CPU 31 reads out software programs that realize the functions of each device from the ROM 32, and loads the programs into the RAM 33 for execution.

[0034] The ROM 32 is used as an example of a non-volatile memory (recording medium). The ROM 32 records an OS (Operating System), various parameters, programs for operating each device, and the like. The RAM 33 is used as an example of a volatile memory. Variables, parameters, and the like generated in the process of the arithmetic processing of the CPU 31 are temporarily written into the RAM 33. Instead of the CPU 31, other processors such as an MPU (Micro Processing Unit) may be used as the arithmetic processing device.

[0035] The display device 12 is a monitor such as a liquid crystal display, and displays a GUI screen, results of processing performed by the CPU 31, etc. The input device 35 generates an input signal according to an operation by the driver or the like, and outputs it to the CPU 31. For example, a mouse, a keyboard, etc. are used as the input device 35, and the driver or the like can input information and instructions by operating the input device 35. The display device 12 and the input device 35 may be integrated into a touch panel. Note that the display device 12 and the input device 35 may be omitted from the arithmetic device 13.

[0036] The nonvolatile storage 36 is an example of a recording medium, and is capable of storing data used by a program, data obtained by executing a program, and the like. For example, information related to the operation and measurement of the water electrolysis system 1 is stored in the nonvolatile storage 36. The nonvolatile storage 36 may also store an OS or a program executed by the CPU 31. As the nonvolatile storage 36, a hard disk drive (HDD), a solid state drive (SSD), a disk medium using light or magnetism, a semiconductor memory card, or the like is used. The program may be provided to each device via a wired or wireless transmission medium such as a local area network (LAN), the Internet, or digital satellite broadcasting.

[0037] The communication interface 37 may be, for example, a network interface card (NIC). The communication interface 37 is configured to be capable of transmitting and receiving various data to and from an external device via a communication network such as a LAN or the Internet to which a terminal is connected, or a dedicated line. The communication means may be either wireless communication such as Wi-Fi (registered trademark) or LTE (Long Term Evolution) (registered trademark), or wired communication.

[0038] [Equivalent circuit of water electrolysis stack] Next, an equivalent circuit of the water electrolysis stack 21 will be described with reference to FIG. FIG. 3 is a diagram showing an example of an equivalent circuit of the water electrolysis stack 21. It is generally known that an equivalent circuit of the water electrolysis stack 21 alone can be expressed as a series-parallel circuit of three parameters: electric resistance R0, reaction electric resistance (hereinafter also referred to as "reaction resistance") R1, and reaction capacitance C1.

[0039] For example, a PEM-type water electrolysis stack is mainly composed of an electrolyte membrane, electrodes arranged to sandwich the electrolyte membrane, and a catalyst layer interposed between the electrolyte membrane and the electrodes. The electrodes include an electrode that generates oxygen and hydrogen ions from water, and an electrode that generates hydrogen from the hydrogen ions.

[0040] The electric resistance R0 is the total resistance loss of the water electrolysis stack 21 based on the structure of the water electrolysis stack 21 (resistance of the electrolyte membrane, support material, electrodes, contact resistance, etc.). The reaction electric resistance R1 is the resistance loss at the interfaces between the electrolyte membrane and the two electrodes. The reaction capacitance C1 is the double layer capacitance at the interfaces between the electrolyte membrane and the two electrodes. The reaction electric resistance R1 and the reaction capacitance C1 are indexes that reflect the state of the water electrolysis stack 21, and change depending on the deterioration state of the water electrolysis stack 21.

[0041] In this embodiment, a PEM water electrolysis stack is taken as an example, but the present invention is not limited to this example. The electric resistance R0 of the entire water electrolysis stack, the reaction electric resistance R1 that changes depending on the deterioration state, and the reaction capacitance C1 can be applied to water electrolysis stacks of other types by applying them to the water electrolysis stacks of other types.

[0042] Changes in the parameters of the equivalent circuit cause changes in the current and / or voltage during load fluctuations. Conversely, it is possible to estimate the parameters of the equivalent circuit by measuring the changes over time in the current and voltage during load fluctuations. In other words, the deterioration of the water electrolysis stack 21 can be estimated from the changes in the parameters of the equivalent circuit. According to the equivalent circuit in FIG. 3, the change dE in the voltage applied to the water electrolysis stack 21 is the sum of the change in voltage applied to the electrical resistance R0 and the change in voltage applied to the reaction capacitance C1 (Equation (1)).

[0043]

number

[0044] In this case, the amounts of change dE, dI, and dq of the voltage, current, and charge can be expressed by equations (2), (3), and (4), respectively, where τ is time.

[0045]

number

number

number

[0046] As shown in the following equation (5), in the short time after the current is changed from the steady state, the current I passing through the reaction resistor R1 is R1 It is assumed that the value of is almost the same as in the steady state. R1 The value of is the current I passing through the reactive capacitance C1. C1 The change is small compared to the value of . Conversely, the reaction capacitance C1 causes a small change in voltage compared to the current.

number

[0047] The current I passing through the reactive capacitance C1 C1 is expressed by the following equation (6).

number

[0048] The integral over Δt is approximated to a trapezoid, and the charge dq stored in the reaction capacitance C1 is expressed by the following equation (7).

number

[0049] Therefore, dE, dI, and dq can be calculated from the current and voltage measurement results. Based on the current and voltage measurement results from time (t-Δt) to time t, the estimation error μ(t-Δt, t) of the electrical resistance R0 and reaction capacitance C1 can be expressed by the following equation (8). Equation (8) shows the estimation error of the electrical resistance R0 and reaction capacitance C1 during Δt.

number

[0050] The estimation error μ(0,t) of the electrical resistance R0 and reaction capacitance C1 from the current measurement results and voltage measurement results from 0[s] to t[s] is expressed by the following equation (9). In other words, the estimation error μ(0,t) is the root mean square error between multiple Δt between 0[s] and t[s]. In the equation, i is a natural number (i=1,2,…,n).

number

[0051] Equation (9) is a function of electrical resistance R0 and reaction capacitance C1. Electrical resistance R0 and reaction capacitance C1 can be calculated by finding the minimum value of the estimation error μ(0,t) in equation (9). The electrical resistance R0 and reaction capacitance C1 when the estimation error μ(0,t) is at its minimum are expressed by equations (10) and (11). By partially differentiating equation (9) with respect to R0 and C1, the equations dμ / dR0=0 and dμ / dC1=0 are obtained. By solving R0 and C1 from these two equations, we obtain equations (10) and (11).

[0052]

number

number

[0053] [Deterioration diagnosis process] Next, the deterioration diagnosis process performed by the water electrolysis system 1 will be described with reference to FIG. FIG. 4 is a flowchart showing an example of a procedure for the degradation diagnosis process performed by the water electrolysis system 1.

[0054] First, the operation screen (display control device 11) of the display device 12 receives a start command from the operator and issues measurement commands to the voltage monitoring devices 23 and current monitoring devices 24 of each water electrolysis stack 21 (step S1).

[0055] After issuing the measurement command, the display control device 11 issues a current change command to the DC power supply 22 to change the output (e.g., current density) of the DC power supply 22 (step S2). After a predetermined time, the voltage monitoring device 23 and the current monitoring device 24 stop measurement and transfer the voltage and current measurement results to the calculation device 13. The display control device 11 generates a display screen including information such as the output of the DC power supply 22, the voltage measurement results and current measurement results for each water electrolysis stack 21, and displays it on the display device 12.

[0056] [How to find the change point] 5 is a diagram showing an example of voltage measurement results and current measurement results (current density) of the water electrolysis system 1. In FIG. 5, the vertical axis on the left side represents current density (A / cm 2 ), the vertical axis on the right indicates voltage (V) and the horizontal axis indicates time (s).

[0057] In step S2, the arithmetic unit 13 determines a change point from the measurement results of the voltage and current, as shown in Fig. 5. There is a difference between the time when the command is issued from the display control unit 11 and the time when the DC power supply 22 receives the command and changes the output of the DC power supply 22, and it is necessary to determine the time when the output changes.

[0058] A typical method for determining the change point is to determine the upper and lower limits of the current and voltage from the measurement results for a certain time before the change point, taking noise into consideration, and to determine the latest time at which these upper and lower limits are not exceeded as 0s (the change point). This is because the current and voltage outputs (measurement results) of the voltage monitoring device 23 and the current monitoring device 24 contain noise, and the current and voltage fluctuate within a certain range even in steady state. In the example shown in Fig. 5, the voltage measurement result 51 and the current measurement result 52 start to change in the voltage and current values ​​at the change point. However, the method for determining the change point is not limited to the above method.

[0059] Next, the arithmetic unit 13 extracts the measurement results of the voltage and current from the change point (t=0) to the specified time. In the present embodiment, the specified time is 10 seconds as an example, but the length of the specified time is not limited to this.

[0060] [Voltage and current measurement results] 6 is a diagram showing an example of extracted results of voltage measurement and current measurement (current density) for a specified period of time of the water electrolysis stack 21. In FIG. 6, the vertical axis on the left side represents current density (A / cm 2 6, the vertical axis on the right side indicates voltage (V) and the horizontal axis indicates time (s). In the example shown in FIG 6, a voltage measurement result 61 and a current measurement result 62 are shown.

[0061] After the processing of step S2, the calculation device 13 estimates the electrical resistance R0 and reaction capacitance C1 of each water electrolysis stack 21 by calculating the extracted results of the voltage and current of each water electrolysis stack 21 using the above-mentioned equations (10) and (11) (step S3).

[0062] Next, the computing device 13 determines whether the estimated result of the electric resistance R0 of each water electrolysis stack 21 exceeds a preset threshold value for deterioration determination (one example of a reference value of the electric resistance) (step S4). Fig. 7 shows an example of the electric resistance R0 estimated from the measurement results of the current and voltage during load fluctuation of the water electrolysis system 1 and the threshold value used for deterioration determination of the electric resistance R0.

[0063] In the determination process of step S4, when the estimated result of the electric resistance R0 exceeds the threshold value (YES determination in step S4), the calculation device 13 diagnoses that the water electrolysis stack 21 is degraded, and sends the diagnosis result to the display control device 11. In this way, by comparing the estimated result of the electric resistance R0 with the threshold value, it is possible to easily diagnose whether the water electrolysis stack 21 is degraded or not.

[0064] Next, the display control device 11 receives the diagnosis result from the arithmetic device 13 and issues a report (step S5). Specifically, the display control device 11 displays the diagnosis result on the display device 12 and notifies the driver. The driver may be notified by sound in addition to the display.

[0065] In the determination process of step S4, if the calculation device 13 determines that the estimated result of the electric resistance R0 does not exceed the threshold value (NO determination in step S4) or after the process of step S5, the deterioration diagnosis process ends. Note that the calculation device 13 may display on the display device 12 that the estimated result of the electric resistance R0 does not exceed the threshold value, that is, that the water electrolysis stack 21 has not reached a deteriorated state.

[0066] In the water electrolysis system 1 according to the embodiment described above, the calculation device 13 estimates the electrical resistance R0 (an element of an equivalent circuit) of the water electrolysis stack 21, which changes depending on the degradation state, from the time-series voltage measurement values ​​and current measurement values ​​received from the voltage monitoring device 23 and the current monitoring device 24. The calculation device 13 then determines the degradation state of the water electrolysis stack 21 based on the estimated electrical resistance R0, and outputs the determination result.

[0067] By adopting the above-described configuration, it is possible to quantitatively estimate the electrical resistance of the water electrolysis stack and determine the deterioration state of the water electrolysis stack based on the estimated electrical resistance without suddenly varying the load or stopping the water electrolysis stack during operation of the water electrolysis system 1 (large-scale hydrogen production device). Then, it is possible to formulate an operation method for the water electrolysis device based on the deterioration state of the water electrolysis stack.

[0068] Furthermore, in the water electrolysis system 1 according to the present embodiment described above, the arithmetic device 13 acquires current measurement values ​​and voltage measurement values ​​measured at a predetermined time interval Δt after the DC power of the DC power supply 22 changes from a steady state, and performs a process of estimating the electric resistance R0 of the water electrolysis stack 21 at an arbitrary time t using the difference between the current measurement values ​​and the difference between the voltage measurement values ​​during the predetermined time interval Δt.

[0069] As described above, according to this embodiment, the electrical resistance R0 (and the reaction capacitance C1) is calculated taking into account the predetermined time interval Δt, so it is possible to determine the degradation state of the water electrolysis stack 21 even if there are small fluctuations in the current and voltage of the water electrolysis stack 21. When determining the degradation state of the water electrolysis stack 21, the fluctuation range of the output current of the DC power supply 22 can be small. Furthermore, since the current measurement value measured at the predetermined time interval Δt is used, it is possible to deal with changes in the current over time that occur in various curved shapes, and the degradation state of the water electrolysis stack 21 can be determined.

[0070] [Determination of deterioration state using reaction capacitance] In the above-described first embodiment, the degradation state of the water electrolysis stack 21 is determined using the electric resistance R0 of the water electrolysis stack 21, but the degradation state of the water electrolysis stack 21 may be determined using the reaction capacitance C1. For example, the computing device 13 estimates the reaction capacitance C1 of the water electrolysis stack 21 from the current measurement value (measurement result) of the current monitoring device 24 and the voltage measurement value (measurement result) of the voltage monitoring device 23, compares the reaction capacitance C1 with a preset degradation determination threshold value (an example of a reference value for reaction capacitance), determines the degradation state of the water electrolysis stack 21, and outputs the determination result.

[0071] Reaction capacitance C1 (electrical double layer) is a parameter related to the surface area of ​​the catalyst or the contact between the catalyst and an electrode (e.g., carbon paper). Catalyst degradation reduces the surface area of ​​the catalyst, resulting in a low capacitance value. Alternatively, poor contact between the catalyst and the electrode can result in a high capacitance value. These phenomena cannot be expressed in electrical resistance, and therefore cannot be determined from the electrical resistance. Using reaction capacitance C1 to determine the deterioration state of the water electrolysis stack 21 makes it possible to determine the location and cause of catalyst deterioration.

[0072] In this manner, by using the reaction capacitance C1, it is possible to determine the deterioration of the water electrolysis stack 21 due to a change in the state of the catalyst. For example, the computing device 13 may first determine the deterioration state of the water electrolysis stack 21 using the electrical resistance R0, and if it is determined that the water electrolysis stack 21 is deteriorated, determine the deterioration of the catalyst using the reaction capacitance C1. This makes it possible to detect the deterioration of the catalyst of the water electrolysis stack 21. Note that the deterioration state may be determined initially using only the reaction capacitance C1.

[0073] (Modification 1 of Deterioration State Judgment) In the above-described embodiment, the estimation result of the parameters of the equivalent circuit is directly compared with the threshold value, but this is not limited to the example. For example, the computing device 13 may calculate a difference between an average electrical resistance, which is an average value of the electrical resistances R0 of the multiple water electrolysis stacks 21, and the electrical resistance R0 of the water electrolysis stack 21, and compare the difference with a preset reference value of the deviation of the electrical resistances to determine the degradation state of the water electrolysis stack 21. The reference value of the deviation of the electrical resistances is, for example, a reference value of the standard deviation of the electrical resistances of each water electrolysis stack 21.

[0074] By adopting such a configuration, it is possible to realize a more robust determination of the deterioration state even when the measurement result includes a transient abnormal value. Note that, even in the determination method based on the average electrical resistance, it is possible to use reaction capacitance instead of electrical resistance.

[0075] (Modification 2 of Deterioration State Judgment) Furthermore, for example, the computing device 13 may calculate information representing a change from a previously estimated electrical resistance R0 of the water electrolysis stack 21 to a currently estimated electrical resistance R0, and compare the information representing the change in electrical resistance with a preset reference value for the change in electrical resistance to determine the degradation state of the water electrolysis stack 21.

[0076] For example, suppose that the estimated result for the electrical resistance R0 of a particular water electrolysis stack 21 in the February inspection was 0.020 Ω, the estimated result for the March inspection was 0.021 Ω, the estimated result for the April inspection was 0.022 Ω, and the estimated result for the May inspection was 0.025 Ω. Since the rate of increase in the electrical resistance in the May inspection was clearly faster than the estimated results for the most recent few months, the computing device 13 issues a warning of deterioration of the water electrolysis stack 21.

[0077] However, because the rate of change in the electrical resistance over the past month is high, it is possible that there is another problem other than the deterioration of the water electrolysis stack 21, such as poor recent water quality management. For example, an abnormality in the system state of the water electrolysis system 1 is assumed as another problem. One example of an abnormality in the system state is inappropriate operating conditions. Therefore, the content of the alert may be "system abnormality" or "abnormal operating conditions." Note that the determination method based on the change in electrical resistance between the previous time and the current time can also be performed using reaction capacitance instead of electrical resistance.

[0078] <Second embodiment> A water electrolysis system according to a second embodiment of the present invention will be described with reference to Figures 8 to 10. In this embodiment, parts that are the same as or similar to those in the first embodiment are given the same reference numerals and detailed description will be omitted.

[0079] The difference between this embodiment and the first embodiment is that the equations (22) and (23) described later are incorporated into the calculation of the calculation device 13. This calculation method makes it possible to extract not only the electric resistance R0 and the reaction capacitance C1, but also the reaction resistance R1. The principle is described below.

[0080] According to the equivalent circuit of the water electrolysis stack 21 (FIG. 3), the change dE1 in the voltage E1 applied to the reaction resistor R1 is expressed as the current I C1 It depends on, which is expressed by the following equation (12).

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[0081] Equation (12) is rewritten as equation (13), where dI R1 is the current I passing through the reactive resistor R1 within the time dt R1 is the amount of change.

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[0082] The reaction resistance R1 and the time constant τ of the equivalent circuit are defined as in equations (14) and (15).

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[0083] Here, equation (13) can be rewritten as equation (16).

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[0084] As shown in equation (17), the current I passing through the reactive resistor R1 in the equivalent circuit R1 and the current I passing through the reactive capacitance C1 C1 The sum of these is the total current I (electrolysis current).

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[0085] Substituting equation (17) into equation (16) gives equation (18).

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[0086] Equation (18) is a first-order linear differential equation, and its solution is expressed by equation (19).

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[0087] Integrating equation (12) with respect to time t gives equation (20). The voltage E1 applied to the reactive resistor R1 is determined by equation (20).

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[0088] Substituting equation (19) into equation (20) gives equation (21).

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[0089] The voltage E applied to the water electrolysis stack 21 from time 0 to time t is expressed by equation (22).

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[0090] The current change rate dI / dt of the DC power supply 22 can be calculated from the current value measured by the current monitoring device 24. When the current change rate dI / dt of the sweep is a constant v, equation (22) can be rewritten as equation (23). E(0) is the voltage immediately before the current is changed.

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[0091] From the change in current over time, the current change rate v when the current is swept is extracted, and the change in voltage over time is fitted with equation (23), thereby making it possible to estimate the electrical resistance R0, the reaction resistance R1, and the reaction capacitance C1. That is, in this embodiment, as can be seen from equation (23), even if there is no change in the voltage applied to the water electrolysis stack 21, if there is a change in the current, the parameters of the equivalent circuit can be identified. Furthermore, in this embodiment, the current change rate dI / dt is a constant, but even if the current change rate dI / dt is not a constant, the electrical resistance R0, the reaction resistance R1, and the reaction capacitance C1 can be estimated.

[0092] [Changes in voltage over time] Here, the fitting process in equation (23) will be described with reference to FIG. 8 is a diagram showing an example of the voltage measurement results (change in voltage over time) of the water electrolysis stack 21 in the second embodiment of the present invention. In Fig. 8, the vertical axis represents voltage (V) and the horizontal axis represents time (s).

[0093] The above-mentioned equation (23) is rewritten into the form of the following equation (24), where P1, P2, and τ are fitting parameters. For the experimental voltage values ​​shown as plot points in Figure 8, P1, P2, and τ shown in equation (24) are selected so as to be closest to the experimental values, and the fitting result shown by the solid line is obtained.

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[0094] Then, by comparing equations (23) and (24), the electrical resistance R0 and the reaction resistance R1 are obtained as shown in equations (25) and (26). In addition, the reaction capacitance C1 is derived from the time constant τ and the reaction resistance R1 as shown in equation (27).

[0095]

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[0096] [Deterioration diagnosis process] Next, the deterioration diagnosis process performed by the water electrolysis system 1 according to this embodiment will be described with reference to FIG. FIG. 9 is a flowchart showing an example of a procedure for the degradation diagnosis process of the water electrolysis system 1 according to this embodiment.

[0097] First, the operation screen (display control device 11) of the display device 12 receives a start command from the operator and issues measurement commands to the voltage monitoring devices 23 and current monitoring devices 24 of each water electrolysis stack 21 (step S11).

[0098] After issuing the measurement command, the display control device 11 issues a current change command to the DC power supply 22, and linearly changes the output (e.g., current density) of the DC power supply 22 (step S12). After a predetermined time, the voltage monitoring device 23 and the current monitoring device 24 stop measurement and transfer the measurement results of the voltage and current to the calculation device 13. The processing of steps S11 and S12 is basically the same as steps S1 and S2 in FIG.

[0099] The reason why "linearly" is described in step S12 is because it is assumed that dI / dt is a constant. In this embodiment, for convenience of explanation, the current I changes linearly, but the current I does not have to actually change linearly. In that case, the above-mentioned formula (22) holds, but since it is a nonlinear regression, formula (23) changes depending on the fitting formula.

[0100] In step S12, the calculation device 13 extracts the measurement results of the voltage and current from the change point (t=0) to a specified time (e.g., 10 s) in the same manner as in the first embodiment. Fig. 10 shows an example of the change over time in current density and voltage in the water electrolysis system 1 according to this embodiment. In Fig. 10, the vertical axis on the left side represents the current density (A / cm 2 10, the vertical axis on the right side indicates voltage (V) and the horizontal axis indicates time (s). In FIG 10, an example of a nearly linear voltage change over time 101 and a nearly linear current change over time 102 are shown.

[0101] The calculation device 13 estimates the electrical resistance R0, reaction resistance R1, and reaction capacitance C1 of the water electrolysis stack 21 by calculating the extracted results of the voltage and current of each water electrolysis stack 21 using the above-mentioned equation (23) (step S13). In step S13, the calculation device 13 estimates the constant v (sweep rate) of the current change rate dI / dt from the above-mentioned linear regression of the current change over time, and then estimates the electrical resistance R0, reaction resistance R1, and reaction capacitance C1 from the voltage change over time using equation (23).

[0102] 4, the calculation device 13 determines whether the estimated result of the electric resistance R0 of each water electrolysis stack 21 exceeds a preset threshold value for determining deterioration (step S14). If the estimated result of the electric resistance R0 exceeds the threshold value (YES determination in step S14), the calculation device 13 sends a diagnosis result to the display control device 11. The display control device 11 receives the diagnosis result from the calculation device 13 and notifies the driver.

[0103] When it is determined that the estimation result of the electric resistance R0 does not exceed the threshold value (NO determination in step S14), or after the processing of step S15, the arithmetic device 13 ends the deterioration diagnosis processing.

[0104] In the water electrolysis system 1 according to the present embodiment described above, the calculation device 13 acquires current measurement values ​​and voltage measurement values ​​from when the DC power of the DC power supply 22 changes from the steady state to an arbitrary time t, and performs a process of estimating the electric resistance R0 of the water electrolysis stack 21 at the arbitrary time t using the current measurement values ​​and voltage measurement values ​​from the time when the DC power changes from the steady state (t=0) to the arbitrary time t.

[0105] In this manner, the water electrolysis system 1 according to the present embodiment estimates (by nonlinear regression) the electrical resistance R0, the reaction resistance R1, and the reaction capacitance C1 using the measured values ​​of the current and voltage between times 0 and t, and taking into consideration the voltage E applied to the entire water electrolysis stack 21. Therefore, in addition to the effects of the first embodiment, the present embodiment enables determination of the deterioration state that is more resistant to noise than the first embodiment.

[0106] Note that the deterioration state determination using the reaction capacitance and the first and second modifications of the deterioration state determination described in the first embodiment can also be applied to the water electrolysis system 1 according to this embodiment.

[0107] <Third embodiment> A water electrolysis system according to a third embodiment of the present invention will be described with reference to Figures 11 to 13. This embodiment is a modification of the first and second embodiments, and the same components as or similar components to those of the first and second embodiments are denoted by the same reference numerals and detailed description thereof will be omitted.

[0108] [Outline of water electrolysis system] FIG. 11 is a diagram showing a schematic configuration of a water electrolysis system according to a third embodiment of the present invention. The water electrolysis system 1A shown in Fig. 11 includes a control device 10 and a water electrolysis device 20A. The water electrolysis system 1A according to this embodiment differs from the water electrolysis system 1 according to the first embodiment in three major points.

[0109] The first difference is that one slip resistor 25 is connected to the series line of the series-parallel water electrolysis stacks 21 that constitute the water electrolysis apparatus 20A. The second difference is that the resistance value of the slip resistor 25 can be adjusted from the operation screen (display control device 11) of the display device 12. In other words, the display control device 11 has a function of issuing a command to change the resistance of the slip resistor 25. The display control device 11 and each slip resistor 25 are connected. The third difference is that the current monitoring devices 24 can transmit current measurement results to the display control device 11. The display control device 11 and each current monitoring device 24 are connected to each other.

[0110] The current density of some of the water electrolysis stacks 21 may deviate from the predetermined current density range due to variations in the degree of deterioration of the multiple water electrolysis stacks 21. According to the configuration of the water electrolysis system 1A of the present embodiment, the current density of each water electrolysis stack 21 can be made uniform by adjusting the resistance value of the slip resistor 25 before performing the deterioration diagnosis process shown in Fig. 4 or 9.

[0111] [Deterioration diagnosis process] Next, the deterioration diagnosis process performed by the water electrolysis system 1A will be described with reference to FIG. Fig. 12 is a flowchart showing an example of a procedure for degradation diagnosis processing by the water electrolysis system 1A. The processing in the flowchart of Fig. 12 is characterized in that it adjusts the value of current density, and is positioned as a pre-processing of the degradation diagnosis processing shown in Figs. 4 and 9.

[0112] First, the operation screen (display control device 11) of the display device 12 receives a start command from the operator and issues a measurement command to the current monitoring devices 24 of the individual water electrolysis stacks 21 (step S21).

[0113] After that, the display control device 11 issues a resistance change command to the slip resistance device 25 (step S22).

[0114] Next, the current monitoring device 24 transmits the measured current density value to the display control device 11 (step S23). In this figure, the current monitoring device 24 transmits the current density value, but the display control device 11 may be configured to calculate the current density from the current measurement result from the current monitoring device 24.

[0115] Next, the display control device 11 determines whether the measured current density satisfies a preset criterion (step S24). A typical method for setting the current density criterion is whether the current density of each water electrolysis stack 21 reaches a current density range in which a deterioration diagnosis process can be performed. Alternatively, another method for setting the current density criterion is whether the deviation (e.g., standard deviation) of the current density of each water electrolysis stack 21 is smaller than a preset threshold value for the deviation of the current density.

[0116] If the current density does not satisfy the criterion (NO in step S24), the display control device 11 proceeds to step S22. Then, based on the current density and the criterion, the display control device 11 determines the resistance value of the slip resistor 25 connected to the series line to which the corresponding water electrolysis stack 21 is connected, and again outputs a resistance change command to the slip resistor 25 (step S22). Next, the current monitoring device 24 and the display control device 11 execute the processes of steps S23 and S24, respectively.

[0117] In the above description, it is assumed that the measurement command output to the current monitoring device 24 in step S21 is continued until the current density satisfies the standard, but this is not limiting. A process of outputting a measurement command to the current monitoring device 24 (step S21) may be executed every time a resistance change command is issued to the slip resistor 25.

[0118] If the current density of each water electrolysis stack 21 satisfies the criterion (NO in step S25), the display control device 11 ends this process. Thereafter, the display control device 11 performs a degradation diagnosis process shown in Fig. 4 or Fig. 9, and receives from the computing device 13 a diagnosis result for each water electrolysis stack 21 based on the measurement results of the voltage and current of each water electrolysis stack 21.

[0119] Fig. 13 is a diagram showing an example of the change over time in the current density of the water electrolysis stack 21 when the resistance value of the slip resistor 25 is adjusted. In Fig. 13, the vertical axis represents the current density (A / cm 2 ), and the horizontal axis indicates time (s).

[0120] The current density of the current passing through the water electrolysis stack 21 varies depending on the degree of deterioration of the water electrolysis stack 21. A water electrolysis stack 21 that is only slightly deteriorated has a high current density, and the current density decreases as the deterioration of the water electrolysis stack 21 increases. Here, when the resistance value of the slip resistor 25 is adjusted to be larger, in the water electrolysis stack 21 connected in series with the slip resistor 25, the current density decreases significantly if the deterioration of the water electrolysis stack 21 is small. Similarly, when the resistance value of the slip resistor 25 is adjusted to be larger, the current density decreases slightly if the deterioration of the water electrolysis stack 21 is moderate, and the current density increases if the deterioration of the water electrolysis stack 21 is significant.

[0121] Due to deterioration or characteristic variations of the water electrolysis stacks 21, the current density of some water electrolysis stacks 21 may be higher than that of other water electrolysis stacks. By increasing the resistance value of the slip resistor 25 connected in series to the water electrolysis stack 21 with a high current density, the current densities of the water electrolysis stacks 21 connected in the same series line can be made closer to a uniform state.

[0122] Increasing the resistance value of the slip resistor 25 decreases the current density of the water electrolysis stacks 21 in the same series line as the slip resistor 25. As a result, the variation (deviation) in the current density of the water electrolysis stacks 21 in the target series line is reduced. Ultimately, the variation in the current density of each water electrolysis stack 21 in the three series lines of the water electrolysis apparatus 20A shown in Fig. 11 is also adjusted to improve the variation.

[0123] In the water electrolysis system 1A, the operator does not need to consider adjusting the resistance value of the slip resistor 25, as the display control device 11 automatically adjusts it. In addition, there is no need to calculate the amount of resistance adjustment, and the current densities of all parallel circuits can be made the same by slowly increasing the resistance value of the slip resistor 25 in the series line having the highest current density.

[0124] Such a control mechanism can be incorporated in either the operation screen (display control device 11) or the arithmetic device 13. When the control mechanism is incorporated in the operation screen (display control device 11), the current monitoring device 24 communicates with the display control device 11. When the control mechanism is incorporated in the arithmetic device 13, the current monitoring device 24 communicates with the display control device 11 via the arithmetic device 13.

[0125] Although the slip resistor 25 is used in this embodiment, any device capable of controlling the current density of the water electrolysis stack 21, that is, a variable resistor, may be used. Such a device may be a rotary volume or a thermistor.

[0126] As described above, the water electrolysis system 1A according to this embodiment includes a variable resistor connected in series to one or more water electrolysis stacks 21. When the current (current density in this example) flowing through the water electrolysis stack 21 does not satisfy the condition for determining the degradation state of the water electrolysis stack 21, the display control device 11 controls the resistance value of the variable resistor connected in series to the corresponding water electrolysis stack 21 to increase.

[0127] By adopting such a configuration, even if there is variation in the state of the water electrolysis stack 21, it becomes possible to determine which water electrolysis stack has deteriorated without suddenly changing the load during operation of a large-scale hydrogen production device.

[0128] In the above-described embodiment, a resistance change command is output to the slip resistor 25 in step S22, but the process of step S22 may be omitted. For example, the resistance value of the slip resistor 25 may not be changed initially, and only when the current density does not satisfy the standard in step S24 may the process of step S22 be executed to adjust the resistance value of the slip resistor 25.

[0129] As described above, the present invention is not limited to the above-described embodiment, and various other modified examples and application examples are possible without departing from the gist of the invention described in the claims. For example, the above-described embodiment has been described in detail and specifically in order to explain the present invention in an easy-to-understand manner, and is not necessarily limited to having all of the components described. In addition, it is possible to replace a part of the configuration of one embodiment with a component of another embodiment. It is also possible to add a component of another embodiment to the configuration of one embodiment. It is also possible to add, replace, or delete other components to or from part of the configuration of each embodiment.

[0130] In addition, the above-mentioned configurations, functions, processing units, etc. may be realized in part or in whole by hardware, for example, by designing them as integrated circuits. As the hardware, a broad processor device such as an FPGA (Field Programmable Gate Array) or an ASIC (Application Specific Integrated Circuit) may be used. [Explanation of symbols]

[0131] 1,1A...water electrolysis system, 10...control device, 11...display control device (display control unit), 12...display device, 13...arithmetic unit (arithmetic unit), 20,20A...water electrolysis device, 21...water electrolysis stack, 22...DC power supply, 23...voltage monitoring device, 24...current monitoring device, 25...slip resistor, C1...reaction capacitance, R0...electrical resistance, R1...reaction electric resistance (reaction resistor)

Claims

1. A plurality of water electrolysis stacks; a DC power source that supplies DC power to the water electrolysis stack to drive the water electrolysis stack; a current monitoring device that measures and monitors a current flowing through the water electrolysis stack; a voltage monitoring device that measures and monitors a voltage applied to the water electrolysis stack; a calculation unit that receives current measurement values ​​from the current monitoring device and voltage measurement values ​​from the voltage monitoring device, estimates an electrical resistance of the water electrolysis stack that changes depending on a degradation state of the water electrolysis stack from the time-series current measurement values ​​and voltage measurement values, determines a degradation state of the water electrolysis stack based on the estimated electrical resistance, and outputs the determination result; a display control unit that receives a determination result from the calculation unit and outputs a deterioration state of the water electrolysis stack to a display device. Water electrolysis system.

2. The DC power source changes DC power from a steady state, The calculation unit acquires the current measurement value and the voltage measurement value measured at a predetermined time interval after the DC power of the DC power supply changes from a steady state, and estimates the electrical resistance of the water electrolysis stack at an arbitrary time by using a difference between the current measurement value and the voltage measurement value at the predetermined time interval. The water electrolysis system according to claim 1 .

3. The DC power source changes DC power from a steady state, The calculation unit acquires the current measurement value and the voltage measurement value from a time when the DC power of the DC power supply changes from a steady state to an arbitrary time, and estimates the electrical resistance of the water electrolysis stack at the arbitrary time by using the current measurement value and the voltage measurement value from a time when the DC power changes from the steady state to the arbitrary time. The water electrolysis system according to claim 1 .

4. The calculation unit compares the estimated result of the electric resistance with a preset reference value of the electric resistance to determine a deterioration state of the water electrolysis stack. The water electrolysis system according to claim 1 .

5. The calculation unit calculates a difference between an average electrical resistance, which is an average value of electrical resistances of the plurality of water electrolysis stacks, and the electrical resistance of the water electrolysis stack, and compares the difference with a preset reference value of deviation of the electrical resistance to determine a deterioration state of the water electrolysis stack. The water electrolysis system according to claim 1 .

6. The calculation unit calculates information representing a change from a previously estimated electric resistance of the water electrolysis stack to a currently estimated electric resistance, and compares the information representing the change in electric resistance with a preset reference value for the change in electric resistance to determine a deterioration state of the water electrolysis stack. The water electrolysis system according to claim 1 .

7. The calculation unit estimates a reaction capacitance of the water electrolysis stack at the arbitrary time, which changes depending on a deterioration state of the water electrolysis stack, in addition to the electrical resistance of the water electrolysis stack at the arbitrary time, determines a deterioration state of the water electrolysis stack based on the estimated reaction capacitance, and outputs the determination result to the display control unit. The water electrolysis system according to claim 2 or 3.

8. The calculation unit compares the estimated reaction capacitance with a preset reference value of the reaction capacitance to determine a deterioration state of the water electrolysis stack. The water electrolysis system according to claim 7.

9. The calculation unit calculates a difference between an average reaction capacitance, which is an average value of reaction capacitances of the plurality of water electrolysis stacks, and the reaction capacitance of the water electrolysis stack, and compares the difference with a reference value of the deviation of the reaction capacitance to determine a deterioration state of the water electrolysis stack. The water electrolysis system according to claim 7.

10. The calculation unit calculates information representing a change from a previously estimated reaction capacitance of the water electrolysis stack to a currently estimated reaction capacitance, and compares the information representing the change in reaction capacitance with a preset reference value for change in reaction capacitance to determine a deterioration state of the water electrolysis stack. The water electrolysis system according to claim 7.

11. A variable resistor is connected in series with one or more of the water electrolysis stacks, When the current flowing through the water electrolysis stack does not satisfy a condition for determining a deterioration state of the water electrolysis stack, the display control unit controls the resistance value of the variable resistor connected in series with the corresponding water electrolysis stack in a direction to increase. The water electrolysis system according to claim 1 .

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