Hydrogen production system and hydrogen production method

Abstract

To achieve both suppression of degradation in a water electrolysis stack and hydrogen production efficiency in a hydrogen production system for producing hydrogen using a plurality of water electrolysis stacks.SOLUTION: The hydrogen production system according to the present invention sets an upper current limit value that can suppress degradation of a water electrolysis stack in accordance with the degradation characteristics of the water electrolysis stack, and controls power distribution to the water electrolysis stack based on the upper current limit value and a prediction result of hydrogen production efficiency.SELECTED DRAWING: Figure 14

Description

[Technical Field]

[0001] The present invention relates to a hydrogen production system that produces hydrogen using a plurality of water electrolysis stacks. [Background technology]

[0002] In order to popularize hydrogen energy, there is a need to reduce the price of hydrogen. In order to reduce the price of hydrogen, it is necessary to reduce the cost required to produce hydrogen. Hydrogen can be produced, for example, by methods such as the electrolysis of water (hereafter referred to as water electrolysis). The cost of producing hydrogen can be broadly divided into capital expenses (CAPEX) and operating expenses (OPEX). OPEX consists of the cost of procuring the electricity used in water electrolysis and the cost of maintaining the system. To reduce CAPEX, the following efforts are required.

[0003] - Reduction of equipment costs -Improvement of facility utilization rate (increase in hydrogen production volume) Extending the useful life of equipment (reducing equipment depreciation costs)

[0004] In recent years, hydrogen production using renewable energy has been attracting attention, but because the amount of electricity generated by renewable energy fluctuates due to wind power and weather, improving the operating rate of hydrogen production facilities is a challenge. One possible solution is to use storage batteries to level out power consumption before producing hydrogen, but the introduction of storage batteries increases the cost of the equipment, making it difficult to reduce CAPEX. Therefore, technology that can reduce CAPEX without using storage batteries is needed. Therefore, among the above efforts, improving the useful life of the equipment is an important issue.

[0005] To extend the service life of a hydrogen production system, it is necessary to suppress the deterioration of the water electrolysis cells, which are its components. At the same time, it is also important to improve the electrolysis efficiency of the water electrolysis stack.

[0006] Patent Document 1 below describes a technology for improving the electrolysis efficiency of a water electrolysis system. The document aims to "enable the achievement of the best electrolysis efficiency according to the amount of power supplied from a variable voltage power supply," and describes the following technology: "A water electrolysis system 10 includes a water electrolysis device 14 and a power supply device 18 including a solar cell 16. The water electrolysis device 14 includes a plurality of water electrolysis stacks 40a-40d and power adjustment units 42a-42d connected to each of the water electrolysis stacks 40a-40d, which individually adjust the power supplied from the solar cell 16 to enable the water electrolysis stacks 40a-40d to operate at the best efficiency" (see abstract).

[0007] Non-Patent Document 1 below describes a water electrolysis system operation method in which the number of water electrolysis stacks operated in parallel is gradually increased as the power input to the water electrolysis system increases.

[0008] Japanese Patent Application No. 2021-023663 is a prior patent application (hereinafter referred to as the "prior application") filed by the inventor of the present application. This application describes a method for suppressing deterioration of a water electrolysis stack by controlling the power distribution between the stacks. [Prior art documents] [Patent documents]

[0009] [Patent Document 1] Japanese Patent Application Laid-Open No. 2007-031813 [Non-patent literature]

[0010] [Non-Patent Document 1] B. Flamm et al., Applied Energy 281, 116031 (2021). Summary of the Invention [Problem to be solved by the invention]

[0011] As will be described later, the technologies described in Patent Document 1 and Non-Patent Document 1 each have high hydrogen production efficiency, but are thought to have room for improvement in terms of suppressing deterioration of the water electrolysis stack. On the other hand, the prior application is suitable for suppressing deterioration of the water electrolysis stack, but is thought to have room for improvement in terms of hydrogen production efficiency.

[0012] The present invention has been made in view of the above-described problems, and an object of the present invention is to achieve both suppression of deterioration of water electrolysis stacks and high hydrogen production efficiency in a hydrogen production system that produces hydrogen using multiple water electrolysis stacks. [Means for solving the problem]

[0013] The hydrogen production system according to the present invention sets an upper current limit that can suppress deterioration of the water electrolysis stack in accordance with the deterioration characteristics of the water electrolysis stack, and controls power distribution to the water electrolysis stack based on the upper current limit and the predicted hydrogen production efficiency. [Effects of the Invention]

[0014] The hydrogen production system according to the present invention can suppress deterioration of the water electrolysis stack while improving hydrogen production efficiency. Other objects, configurations, advantages, etc. of the present invention will become clear from the description of the following embodiments. [Brief explanation of the drawings]

[0015] [Figure 1] 1 shows an example of the configuration of a hydrogen production system used in a case study of the prior art. [Figure 2] 2 shows the time-dependent fluctuation of the power input to the hydrogen production system of FIG. 1. [Figure 3] The results of trial calculations of the hydrogen production efficiency of the hydrogen production system shown in Figure 1 are shown below. [Figure 4] The results of a trial calculation of the change over time in the operating state of the first stack in subsystem 1 are shown below. [Figure 5] The time-dependent changes in Figure 4 are shown in frequency distribution. [Figure 6] The results of similar calculations of the changes over time in the operating state of each stack are shown below. [Figure 7] The results of a trial calculation of the change over time in the operating state of the first stack in subsystem 1 are shown below. [Figure 8] The time-dependent changes in Figure 7 are shown in frequency distribution. [Figure 9] The results of similar calculations of the changes over time in the operating state of each stack are shown below. [Figure 10] The results of a trial calculation of the change over time in the operating state of the second stack (stack 1-2) in subsystem 1 are shown below. [Figure 11] The time-dependent changes in Figure 10 are shown in frequency distribution. [Figure 12] The results of similar calculations of the changes over time in the operating state of each stack are shown below. [Figure 13] The results of trial calculations of the degradation suppression effect and hydrogen production efficiency of Patent Document 1, Non-Patent Document 1, and the prior application are shown below. [Figure 14] 1 is a configuration diagram of a hydrogen production system 1 according to a first embodiment. [Figure 15] The results of a trial calculation of the change over time in the operating state of the first stack (stack 3-1) of subsystem 3 are shown below. [Figure 16] The change over time in FIG. 15 is shown as a frequency distribution. [Figure 17] The following shows the results of similar calculations of the change over time in the operating state of each stack when an operating priority stack and a stop priority stack are assigned. [Figure 18] The results of calculations of the degradation suppression effect and hydrogen production efficiency are shown below. [Figure 19] FIG. 1 is a configuration diagram of a hydrogen production system 1 according to a second embodiment. [Figure 20] FIG. 1 is a configuration diagram of a hydrogen production system 1 according to a third embodiment. [Figure 21] FIG. 1 is a configuration diagram of a hydrogen production system 1 according to a fourth embodiment. DETAILED DESCRIPTION OF THE INVENTION

[0016] <Issues with the conventional technology> Before describing the embodiments of the present invention, the problems of the prior art will be described in the form of a case study, followed by the description of the configuration and operation procedure of a hydrogen production system according to the embodiments of the present invention.

[0017] Figure 1 shows an example of the configuration of a hydrogen production system used in a case study of the prior art. A hydrogen production system with six water electrolysis stacks is constructed by connecting three subsystems in parallel, each of which has two water electrolysis stacks connected in parallel. Each subsystem is equipped with auxiliary equipment 15 in addition to the water electrolysis stack.

[0018] Figure 2 shows the time variation of the power input to the hydrogen production system shown in Figure 1. This data example shows power generated from renewable energy sources filtered to an upper limit of 900 kW.

[0019] Figure 3 shows the results of trial calculations of the hydrogen production efficiency of the hydrogen production system shown in Figure 1. Here, the rated capacity of one water electrolysis stack is assumed to be 150kW, and one subsystem is configured for each 150 x 2 = 300kW. Each subsystem (stack + auxiliary equipment) is assumed to have the efficiency characteristics shown in Figure 3. Generally, the lower the power consumption, the higher the efficiency of the water electrolysis stack, and the hydrogen production efficiency monotonically increases as the input power decreases. On the other hand, the efficiency of the auxiliary equipment decreases on the low power side, and once the input power exceeds a certain level, the efficiency curve becomes almost flat. Because the power input to the subsystem is supplied to both the water electrolysis stack and the auxiliary equipment, the system efficiency is a combination of these efficiencies, and therefore the curve shown in Figure 3 has a maximum value.

[0020] Below, the hydrogen production efficiency of the entire system was calculated from the average efficiency of the three subsystems in the configuration shown in Figures 1 to 3. As described in Patent Document 1, the system operation control method used was to use the operating point at which the hydrogen production efficiency of the subsystems peaks, and, in principle, to distribute power approximately equally among the stacks. As shown in Figure 3, the maximum efficiency point is the operating point at approximately 15% of the rated output, so this was used whenever possible. The number of water electrolysis stacks to be operated was determined as follows:

[0021] (1) When the power supplied to the system is ≦ 6 × (rated output) × 15% The number of stacks in operation is (power) / (rated output x 15%). Each stack is operated at its maximum efficiency point.

[0022] (2) When the power supplied to the system is greater than 6 × (rated output) × 15% All stacks are running and the power is distributed equally among them.

[0023] Figure 4 shows the results of a trial calculation of the change over time in the operating state of the first stack in subsystem 1. Figure 5 shows the change over time in Figure 4 as a frequency distribution. As shown in Figures 4 and 5, the operating state frequently alternates between medium output, which is the maximum efficiency point, and high output. As explained in the prior application, this is an operating pattern in which the water electrolysis stack undergoes significant degradation.

[0024] Figure 6 shows the results of a similar calculation of the changes over time in the operating state of each stack. The stack deterioration rate was divided into three categories: "high deterioration," "medium deterioration," and "low deterioration," and the category to which each stack fell was also shown. In this example, the average deterioration rate was high at 100 μV / h, indicating that there are issues with suppressing deterioration. On the other hand, when the hydrogen production efficiency was calculated by averaging the efficiency of each subsystem weighted by the power value, the average efficiency of the entire system was found to be 65.9%. Because the maximum efficiency point is used frequently, this can be said to be a highly efficient operating method.

[0025] Furthermore, we performed trial calculations on the operation of each stack when using the operation method described in Non-Patent Document 1. Non-Patent Document 1 describes an example of operating four stacks, but we expanded this to six stacks and specified the stacks to be operated as follows:

[0026] (1) Power 0 to 150 kW: Only stack 1-1 is operating (2) Power 150-300kW: Stacks 1-1 and 2-1 operating (equal distribution) (3) Power 300-450kW: Stacks 1-1, 2-1, and 3-1 in operation (equal distribution) (4) Power 450-600kW: Stacks 1-1, 2-1, 3-1, and 3-2 in operation (equal distribution) (5) Power 600-750kW: Stacks 1-1, 2-1, 2-2, 3-1, and 3-2 in operation (equal distribution) (6) Power of 750 kW or more: All stacks operating (equal distribution)

[0027] Figure 7 shows the results of a trial calculation of the change over time in the operating state of the first stack in subsystem 1. Figure 8 shows the change over time in Figure 7 as a frequency distribution. As shown in Figures 7 and 8, in some stacks, frequent oscillations between high output and medium output are observed. As described in the previous application, this is an operating pattern in which the water electrolysis stack undergoes significant degradation. The average degradation rate was 57.7 μV / h. Regarding hydrogen production efficiency, the average efficiency was 65.4%. Compared to Patent Document 1, there was some improvement in suppressing degradation, but the efficiency decreased.

[0028] Figure 9 shows the results of similar calculations of the changes over time in the operating state of each stack. As in Figure 6, the stack deterioration rate is categorized into three levels: "high deterioration," "medium deterioration," and "low deterioration," and the level to which each stack falls is also shown.

[0029] Furthermore, the operation of each stack was estimated using the operation method described in the prior application. In the prior application, deterioration of the water electrolysis stack is suppressed by controlling the input power to the stack and preferentially allocating an operation pattern with a low deterioration rate that is less likely to deteriorate the stack. As an example, the results of allocating the "operation priority stack" and "stop priority stack" described in the prior application are described below.

[0030] Figure 10 shows the results of a trial calculation of the change over time in the operating state of the second stack (Stack 1-2) in Subsystem 1. Figure 11 shows the change over time in Figure 10 as a frequency distribution. As shown in Figures 10 and 11, the frequency of occurrence of intermediate outputs is reduced compared to Patent Document 1 and Non-Patent Document 1, and frequent fluctuations between high output and zero output are observed. This is characteristic of a low deterioration rate pattern, and the average deterioration rate was a low value of 37.5 μV / h. On the other hand, as shown in Figure 3, frequent use of high output and zero output resulted in frequent use of the low-efficiency region in the efficiency characteristics, resulting in an average efficiency of 63.5%, which is lower than Patent Document 1 and Non-Patent Document 1. Therefore, as a point to note when applying the prior application, it was found that frequent use of high output and zero output from the perspective of deterioration suppression may result in lower hydrogen production efficiency than conventional technology.

[0031] Figure 12 shows the results of similar calculations of the changes over time in the operating state of each stack. As in Figure 6, the stack deterioration rate is categorized into three levels: "high deterioration," "medium deterioration," and "low deterioration," and the level to which each stack falls is also shown.

[0032] FIG. 13 shows the results of calculations of the degradation suppression effect and hydrogen production efficiency of Patent Document 1, Non-Patent Document 1, and the prior application. The horizontal axis represents the reciprocal of the voltage degradation rate, and the vertical axis represents the average value of the hydrogen production efficiency. As can be seen from the graph, these prior art technologies involve a trade-off between degradation suppression and hydrogen production efficiency. Therefore, the present invention aims to achieve both degradation suppression and hydrogen production efficiency in the water electrolysis stack. In particular, the present invention aims to find a power distribution method that is based on the degradation suppression control concept of the prior application and, among other things, can suppress a decline in hydrogen production efficiency.

[0033] <First Embodiment> FIG. 14 is a configuration diagram of a hydrogen production system 1 according to a first embodiment of the present invention. The hydrogen production system 1 is a system that produces hydrogen using renewable energy or AC (alternating current) power supplied from a power transmission and distribution system. The hydrogen production system 1 produces hydrogen by operating a water electrolysis stack 11 using the supplied power. The hydrogen production system 1 includes the water electrolysis stack 11, a DC / DC converter 12, an AC / DC rectifier 13, and a power distribution control unit 14.

[0034] The water electrolysis stack 11 produces hydrogen by electrolyzing water. In Fig. 14, two water electrolysis stacks 11 are connected in series (called a series section), and the two water electrolysis stacks 11 form a pair, which are then connected in parallel to form one subsystem. The hydrogen produced by the water electrolysis stack 11 is output to a transportation facility or a storage facility.

[0035] The AC / DC rectifier 13 converts the AC power supplied to the hydrogen production system 1 into DC (direct current) power and outputs it to the DC / DC converter 12. The DC / DC converter 12 supplies power to the water electrolysis stack 11, thereby controlling the operating state of the water electrolysis stack 11.

[0036] The power distribution control unit 14 outputs an operation command to the DC / DC converter 12, thereby controlling the operation state of the water electrolysis stack 11 via the DC / DC converter 12. The power distribution control unit 14 includes an operation plan formulation unit 141, a stack operation allocation unit 142, a power distribution command unit 143, a deterioration characteristic data management unit 144, a deterioration rate estimation unit 145, a hydrogen production efficiency data management unit 146, and a hydrogen production efficiency estimation unit 147.

[0037] The operation plan formulation unit 141 formulates an operation rotation plan for the water electrolysis stacks 11. The operation rotation here refers to the order in which each water electrolysis stack 11 is assigned either an operation-priority stack or a shutdown-priority stack, which will be described later, as its operating state. The stack operation allocation unit 142 determines the operating state of each water electrolysis stack 11 in accordance with the operation rotation plan formulated by the operation plan formulation unit 141. The power distribution command unit 143 provides a current command value to the DC / DC converter 12 so that the water electrolysis stack 11 operates in accordance with its operating state.

[0038] The deterioration characteristic data management unit 144 holds deterioration characteristic data describing the deterioration characteristics of the water electrolysis stack 11. The operation plan formulation unit 141 can formulate an operation rotation plan based on the deterioration characteristics. The deterioration rate estimation unit 145 estimates the deterioration rate of each water electrolysis stack 11 when it is assumed that the water electrolysis stack 11 is operated according to the plan.

[0039] The hydrogen production efficiency data management unit 146 holds hydrogen production efficiency data that describes the hydrogen production efficiency by the water electrolysis stack 11. The hydrogen production efficiency data describes the relationship between the power input to the water electrolysis stack 11 and the hydrogen production efficiency by the water electrolysis stack 11, as shown in Fig. 3, for example. The hydrogen production efficiency estimation unit 147 estimates the hydrogen production efficiency by the water electrolysis stack 11 based on the hydrogen production efficiency data.

[0040] The power distribution control unit 14 determines the power distribution to each water electrolysis stack 11 using both the estimated deterioration rate of the water electrolysis stack 11 and the estimated hydrogen production efficiency. In this embodiment, focusing on the existence of an output region within the output range of the water electrolysis stack 11 where the hydrogen production efficiency is high and the deterioration rate is low, the power distribution is controlled by actively utilizing this output region. The specific distribution procedure is described below. Some of the operating principles described in the prior application may be omitted.

[0041] The efficiency characteristics shown in FIG. 3 show that hydrogen production efficiency is at its maximum at 15% of the rated output, and is high in the low to medium output range. On the other hand, as described in the prior application, degradation is small when operating in an output range of 1 / 2 or less of the rated output. Therefore, it is considered that an output range of 1 / 2 or less of the rated output has high hydrogen production efficiency and a low degradation rate. In this embodiment, this output range is actively used to control power distribution. Specifically, it is considered that the power distribution control unit 14 distributes power as follows:

[0042] (1) Number of stacks to be operated = (power input to hydrogen production system 1) / (rated output of series section) × 2. If a fraction occurs, round up or down to the nearest integer. Within the output range of this number of stacks in operation, the input power is equally distributed to each series section. In principle, each water electrolysis stack that makes up one series section operates in the same way (however, there are slight differences depending on the level of health, which will be described later).

[0043] (2) When the input power is large and it is difficult to allocate power according to the above formula, an "operation priority stack" or "stop priority stack" is allocated as in the prior application, and power allocation is implemented with priority given to suppressing deterioration. An operation priority stack is a stack that allocates power preferentially compared to other water electrolysis stacks 11. A stop priority stack is a stack that prioritizes stopping the power supply compared to other water electrolysis stacks 11. A similar operating mode may be allocated to each series section. In this case, each series section is assigned either an "operation priority series section (high allocation series section)" or a "stop priority series section (low allocation series section)."

[0044] Each series section is typically connected to a DC bus, and the voltage on the DC bus is the same. Therefore, the same DC bus voltage is supplied to each series section, and the input power to the series section is controlled by the input current to the series section. In other words, to operate the series section within an output range of less than half the rated output of the series section, the input current to the series section should be equal to or less than the upper current limit calculated by dividing half the rated output of the series section by the DC bus voltage.

[0045] In light of the above, if the power input to the hydrogen production system 1 is equal to or less than (upper limit of input current to the series unit) x (operating voltage of the series unit at that time) x number of parallel-connected series units, then the number of stacks to operate = (power input to the hydrogen production system 1) / (upper limit of input current to the series unit x operating voltage of the series unit at that time), rounded up or down to an integer. If the input power is greater than this, then operation will prioritize degradation suppression as described in (2) above.

[0046] The order in which operation-priority stacks and shutdown-priority stacks are assigned may be changed for each series section. For example, the first series section of subsystem 1 operates as an operation-priority stack from 00:00 to 06:00, and as a shutdown-priority stack from 06:00 to 12:00. The second series section of subsystem 1 operates as a shutdown-priority stack from 00:00 to 06:00, and as an operation-priority stack from 06:00 to 12:00. This allows the hydrogen production efficiency and other factors to be balanced between the series sections.

[0047] FIG. 15 shows the results of a trial calculation of the change over time in the operating state of the first stack (stack 3-1) of subsystem 3 in this embodiment. FIG. 16 shows the change over time in FIG. 15 as a frequency distribution. By setting the number of operating stacks to "(input power) / (stack rating) × 2," the proportion of stacks operating within a range of less than half the rated power increased compared to the prior application. Furthermore, during high-power operation, distribution control assigning stacks with priority to operation and stacks with priority to shutdown resulted in operation with a low degradation rate pattern of "alternating between high and zero power," as in the prior application. As a result, the average degradation rate was a low value of 42 μV / h. Regarding hydrogen production efficiency, the frequency of use of the high-efficiency range of less than half the rated power increased, resulting in an average efficiency of 65.8%. This is a high value almost comparable to that of Patent Document 1. Therefore, it was demonstrated that the power distribution method according to this embodiment enables low-degradation, highly efficient operation.

[0048] Figure 17 shows the results of a similar calculation of the change over time in the operating state of each stack when an operation-priority stack and a stoppage-priority stack are assigned in this embodiment. As in Figure 6, the stack deterioration rate is categorized into three types: "high deterioration," "medium deterioration," and "low deterioration," and the category to which each stack falls is also shown.

[0049] Figure 18 shows the results of trial calculations of the degradation suppression effect and hydrogen production efficiency in this embodiment. In Patent Document 1, Non-Patent Document 1, and the prior application, it was difficult to achieve both degradation suppression and hydrogen production efficiency. As shown in Figure 18, this embodiment enables highly durable and highly efficient operation.

[0050] <First embodiment: Summary> The hydrogen production system 1 according to the first embodiment uses an upper current limit that can suppress deterioration of the water electrolysis stack 11, and also uses an output range that provides good production efficiency as estimated by the hydrogen production efficiency estimation unit 147. This makes it possible to achieve both suppression of deterioration of the water electrolysis stack and high hydrogen production efficiency.

[0051] The hydrogen production system 1 according to the first embodiment switches between (1) an operation mode that achieves both degradation suppression and hydrogen production efficiency, and (2) an operation mode that prioritizes degradation suppression, depending on the magnitude of the input power. This allows the system to efficiently achieve both degradation suppression of the water electrolysis stack and hydrogen production efficiency, even when using a power source whose power value fluctuates significantly over time, such as renewable energy.

[0052] <Embodiment 2> 19 is a configuration diagram of a hydrogen production system 1 according to a second embodiment of the present invention. In addition to the configuration described in the first embodiment, the second embodiment includes a power generation amount prediction unit 21. The power generation amount prediction unit 21 may be configured as a part of the hydrogen production system 1, or may be configured as a functional unit separate from the hydrogen production system 1.

[0053] The power generation amount prediction unit 21 predicts the amount of power generated by renewable energy according to a known method, such as (a) prediction using meteorological data 22 (data describing meteorological conditions such as weather and wind conditions), (b) obtaining data on the amount of power generated from renewable energy power generation facilities in real time, or (c) a combination of these.

[0054] The power distribution control unit 14 receives the predicted power generation amount from the power generation amount prediction unit 21 and allocates the operating state of each water electrolysis stack 11 accordingly. For example, when the power generation amount is high, the number of operation-priority stacks is increased. This is because if the power generation amount increases while maintaining the number of stacks, the power distributed to the shutdown-priority stacks increases, which may increase the number of transitions between high output and medium output and accelerate deterioration. When the power generation amount is low, power consumption is reduced by turning off the subsystems, including the auxiliary machinery 15. It is desirable to turn off each subsystem so that the power consumption of the hydrogen production system 1 is at least less than the power input to the hydrogen production system 1. However, it is not always realistic to turn off a subsystem every time there is a sudden drop in input power. For example, it is appropriate to operate the system by turning off a subsystem if the period during which the input power is below the reference value is equal to or exceeds a threshold value.

[0055] <Third Embodiment> 20 is a configuration diagram of a hydrogen production system 1 according to a third embodiment of the present invention. In addition to the configuration described in the first embodiment, the third embodiment includes a deterioration monitoring unit 3. The deterioration monitoring unit 3 may be configured as a part of the hydrogen production system 1, or may be configured as a functional unit separate from the hydrogen production system 1.

[0056] The deterioration monitoring unit 3 receives, for example, the output current and output voltage of the water electrolysis stack 11 from the power distribution control unit 14 and uses this to calculate the state of health (SOH) of the water electrolysis stack 11. The power distribution control unit 14 assigns an operating state to each water electrolysis stack 11 according to the SOH. The deterioration monitoring unit 3 also monitors the power consumption of the auxiliary equipment 15, the amount of hydrogen produced by the hydrogen production system 1, etc.

[0057] For example, the power distribution control unit 14 allocates operating states to the water electrolysis stack 11 with a reduced SOH so that the number of times that the stack performs an operation with a high deterioration rate (for example, frequent alternation between high output and medium output) is reduced compared to the other water electrolysis stacks 11. This makes it possible to avoid a situation in which only a specific stack deteriorates early and requires replacement, thereby reducing maintenance costs associated with replacement.

[0058] The hydrogen production efficiency estimation unit 147 may correct the estimated result of the hydrogen production efficiency according to the calculation result of the health level by the deterioration monitoring unit 3. For example, for a stack in which deterioration is progressing, the prediction result is revised downward (the production efficiency is estimated lower). Specifically, for a stack (or a series section) whose health level has fallen below the reference value, the efficiency characteristic of FIG. 3 may be reacquired, and the hydrogen production efficiency may be recalculated according to the reacquired efficiency characteristic. The efficiency characteristic of FIG. 3 may be prepared in advance for each health level value, for example, or may be reacquired by operating the subsystem in maintenance mode and actually measuring the efficiency characteristic.

[0059] The hydrogen production efficiency estimation unit 147 may also acquire changes over time in the power consumption of the auxiliary machinery 15 and correct the estimated result of the hydrogen production efficiency accordingly. For example, during times when the power consumption of the auxiliary machinery 15 is high, the power supplied to the water electrolysis stack 11 decreases, and the estimated result of the hydrogen production efficiency may be corrected accordingly. Specifically, among the efficiency characteristics of the subsystem shown in Figure 3, the component corresponding to the relationship between the auxiliary machinery 15 and its power consumption will change, so the efficiency characteristics of Figure 3 may be acquired again accordingly, and the hydrogen production efficiency may be recalculated according to the reacquired efficiency characteristics.

[0060] <Fourth Embodiment>

[0061] 21 is a configuration diagram of a hydrogen production system 1 according to a fourth embodiment of the present invention. In addition to the configuration described in the first embodiment, the fourth embodiment includes a management system 41 and a distributor 42. The management system 41 and the distributor 42 may be configured as part of the hydrogen production system 1, or may be configured as functional units separate from the hydrogen production system 1.

[0062] In this embodiment, the distributor 42 switches between supplying the electricity generated by the renewable energy power generation facility 43 to the water electrolysis stack 11 and selling the electricity to the consumer 44 (i.e., outputting the received electricity to the power transmission and distribution system) in accordance with an instruction from the management system 41. The management system 41 instructs the distributor 42, for example, on the distribution ratio between the two.

[0063] The management system 41 also collects demand data for various types of energy (electricity, heat, hydrogen, etc.) from consumers 44 and controls energy distribution based on this data. For example, it can predict electricity demand and the spot price of energy that reflects it, and implement control such as increasing the electricity sales ratio when electricity demand is high and producing hydrogen when electricity demand is low. Data on the supply amounts of these energies can also be collected in the same way, and the above control can be implemented based on the balance between supply and demand.

[0064] When the amount of power supplied to the hydrogen production system 1 is large, the number of stacks that can be allocated to the shutdown priority stacks decreases relatively. In such a case, the distributor 42 may increase the rate at which power is sold to the consumers 44 (in other words, if the amount of power generation decreases, the rate at which power is sold decreases accordingly). This reduces the power supplied to the water electrolysis stacks 11, and therefore increases the number of stacks that can be allocated to the shutdown priority stacks. As a result, deterioration of the water electrolysis stacks 11 can be suppressed. In this case, it is desirable that the power distribution control unit 14 creates an operation rotation plan by performing the power distribution described in the first embodiment so that each stack is operated within an output range that is highly efficient and has low deterioration.

[0065] <Modifications of the present invention> The present invention is not limited to the above-described embodiments and includes various modifications. For example, the above-described embodiments have been described in detail to clearly explain the present invention, and are not necessarily limited to those including all of the described configurations. Furthermore, it is possible to replace part of the configuration of one embodiment with the configuration of another embodiment, or to add the configuration of another embodiment to the configuration of one embodiment. Furthermore, it is possible to add, delete, or replace part of the configuration of each embodiment with other configurations.

[0066] In the above embodiment, the power distribution control unit 14 and each of its functional units can be configured by hardware such as a circuit device that implements these functions, or by software that implements these functions being executed by a processor or other computing device. The same applies to the power generation amount prediction unit 21, the degradation monitoring unit 3, and the management system 41. [Explanation of symbols]

[0067] 1: Hydrogen production system 11: Water electrolysis stack 12: DC / DC converter 13:AC / DC rectifier 14: Power distribution control unit 21: Power generation forecasting section 3: Deterioration monitoring section 41: Management System

Claims

1. A hydrogen production system that produces hydrogen using a plurality of water electrolysis stacks, a power converter that controls power supplied to the water electrolysis stack; a power distribution control unit that controls the power converter to control power distributed to the water electrolysis stack; and The power distribution control unit a deterioration rate estimation unit that has a deterioration characteristic indicating the susceptibility of the water electrolysis stack to deterioration; a hydrogen production efficiency estimation unit that estimates the hydrogen production efficiency of the water electrolysis stack; and The power distribution control unit controls power distribution to the water electrolysis stack based on a current upper limit value that suppresses deterioration of the water electrolysis stack, which is set according to the deterioration characteristics, and a prediction result from the hydrogen production efficiency estimation unit. A hydrogen production system characterized by:

2. the hydrogen production system includes one or more series sections, each of which is configured to include one or more water electrolysis stacks connected in series, and each series section is further connected in parallel, so that the number of series sections corresponds to the number of parallel connections; The power supplied to the hydrogen production system is (the upper limit of the current)×(the operating voltage of the series unit at the upper limit of the current)×(the number of the series units connected in parallel) If: The power distribution control unit is configured to: (power supplied to the hydrogen production system) ÷ ((current upper limit value) × (operating voltage of the series section at the current upper limit value)) The number of parallel connections is rounded up to the nearest integer value.

2. The hydrogen production system according to claim 1.

3. the hydrogen production system includes one or more series sections, each of which is configured to include one or more water electrolysis stacks connected in series, and each series section is further connected in parallel, so that the number of series sections corresponds to the number of parallel connections; the power distribution control unit includes an operation plan formulation unit that formulates an operation rotation plan for the water electrolysis stack; the power distribution control unit includes a stack operation allocation unit that allocates an operation state of the water electrolysis stack in the operation rotation plan, The power supplied to the hydrogen production system is (the upper limit of the current)×(the operating voltage of the series unit at the upper limit of the current)×(the number of the series units connected in parallel) If it exceeds The stack operation allocation unit sets the operation state of the serial unit as a multi-distribution series section that receives a larger power distribution than the other series sections over a predetermined period of time; a small-allocation series section that receives less power allocation than the other series sections over a predetermined period of time; Assign one of the 2. The hydrogen production system according to claim 1.

4. the stack operation allocation unit sequentially allocates the high-allocation series section and the low-allocation series section in a first order as an operation state of a first series section among the plurality of series sections in the operation rotation plan; The stack operation allocation unit sequentially allocates the high-allocation series section and the low-allocation series section in a second order different from the first order as an operation state of a second series section different from the first series section among the plurality of series sections in the operation rotation plan.

4. The hydrogen production system according to claim 3.

5. the water electrolysis stack receives power from a variable power source whose power value fluctuates over time; the power distribution control unit receives a result of predicting the amount of power generated by the variable power source, The power distribution control unit controls power distribution to the water electrolysis stack in accordance with the predicted power generation amount.

2. The hydrogen production system according to claim 1.

6. the hydrogen production system includes one or more series sections, each of which is configured to include one or more water electrolysis stacks connected in series, and each series section is further connected in parallel, so that the number of series sections corresponds to the number of parallel connections; the hydrogen production system includes one or more subsystems configured by one or more of the series sections and auxiliary equipment required to operate the series sections; If the predicted power generation amount is equal to or less than a predetermined reference power generation amount for a predetermined period of time, The power distribution control unit stops the power supply for each of the subsystems so that the power consumption of the hydrogen production system is equal to or less than the predicted power generation amount.

6. The hydrogen production system according to claim 5.

7. the power distribution control unit acquires a deterioration state of the water electrolysis stack; The power distribution control unit assigns an operating state of the water electrolysis stack according to the acquired deterioration state.

2. The hydrogen production system according to claim 1.

8. the hydrogen production efficiency estimation unit, when the acquired degradation state is less than a reference value, reacquires data describing the relationship between the hydrogen production efficiency of the water electrolysis stack and the input power to the water electrolysis stack; The hydrogen production efficiency estimation unit re-estimates the hydrogen production efficiency of the water electrolysis stack in accordance with the re-acquired data. The hydrogen production system according to claim 7 .

9. the power distribution control unit acquires a change over time in power consumption of auxiliary machinery of the water electrolysis stack; The hydrogen production efficiency estimation unit corrects the predicted result of the hydrogen production efficiency according to the acquired change over time in the power consumption. The hydrogen production system according to claim 8 .

10. the hydrogen production system further includes a distributor that switches between supplying the power supplied from the variable power source to the water electrolysis stack or outputting the power to a power transmission and distribution system; The hydrogen production system further includes a management system that controls the ratio at which the distributor distributes the supplied power between the water electrolysis stack and the power grid in accordance with power demand.

6. The hydrogen production system according to claim 5.

11. the power distribution control unit receives a result of predicting the amount of power generated by the variable power source, the management system controls the distributor to output a first proportion of the supply power to the power transmission and distribution system when the predicted amount of power generation is a first amount of power generation; When the predicted amount of power generation is a second amount of power generation that is smaller than the first amount of power generation, the management system controls the distributor to output a portion of the supply power at a second rate that is smaller than the first rate to the power transmission and distribution system. The hydrogen production system according to claim 10.

12. the management system controls the distributor to output a portion of the supply power at a first rate to the power transmission and distribution system when the power demand is a first amount of power; When the power demand is a second amount of power that is smaller than the first amount of power, the management system controls the distributor to output a portion of the supply power at a second rate that is smaller than the first rate to the power transmission and distribution system. The hydrogen production system according to claim 10.

13. The management system controls the ratio according to the heat demand, the amount of heat supplied to the heat demand, the hydrogen demand, and the amount of hydrogen supplied by the hydrogen production system. The hydrogen production system according to claim 10.

14. The hydrogen production system supplies power supplied from renewable energy to the water electrolysis stack.

2. The hydrogen production system according to claim 1.

15. A hydrogen production method for producing hydrogen using a plurality of water electrolysis stacks, comprising: a step of controlling a power converter that controls power supplied to the water electrolysis stacks, thereby controlling power distributed to each of the water electrolysis stacks; In the step of controlling the power converter, The power to be distributed to each of the water electrolysis stacks is controlled based on a deterioration prediction of the water electrolysis stack calculated based on deterioration characteristics indicating the susceptibility of the water electrolysis stack to deterioration, a current upper limit value for suppressing deterioration of the water electrolysis stack set based on the deterioration characteristics, and a prediction of hydrogen production efficiency of the water electrolysis stack. A method for producing hydrogen.

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