JP2022142852A - Control device, water electrolysis system, operation method of water electrolysis device, and program - Google Patents

Abstract

To provide other techniques for improving efficiency of a water electrolysis device.SOLUTION: A control device is configured to allow hydrogen produced in a water electrolysis device to be stored in a hydrogen storage part connected to the water electrolysis device. The control device calculates a scheduled operating time of the water electrolysis device from an inputted hydrogen demand. When the scheduled operating time is less than a predetermined operating time threshold, the water electrolysis device is in a cold start state, and an operation stop condition is satisfied that the amount obtained by subtracting a hydrogen demand from the amount of hydrogen stored in the hydrogen storage part is greater than a predetermined storage threshold, the control device does not cause the water electrolysis device to operate while when the operation stop condition is not satisfied, the control device causes the water electrolysis device to operate for at least the scheduled operating time. The operating time threshold is a value near a minimum time at which a basic unit of hydrogen production becomes substantially constant in a relation between an operating time from the cold start of the water electrolysis device and the basic unit of hydrogen production.SELECTED DRAWING: Figure 3

Description

The present invention relates to a water electrolysis device.

2. Description of the Related Art Conventionally, there has been proposed a technique for improving the efficiency of a water electrolyzer that generates hydrogen and oxygen by electrolyzing water (see, for example, Patent Document 1). In Patent Document 1, the temperature of circulating water supplied to a high-pressure water electrolysis device is detected, and when the temperature of the circulating water rises, the device is operated at a low current density lower than the current density during rated operation, A technology is disclosed in which when the temperature of the circulating water is maintained within a certain temperature range, the operation shifts to the rated operation, and during the rated operation, the operation is performed at a preset current density based on the temperature of the circulating water.

JP 2012-153965 A

In the case of the technique described in Patent Document 1, it is necessary to provide a temperature sensor for detecting the temperature of the circulating water, and it is necessary to perform complicated control according to the detected circulating water temperature. Therefore, a technique for improving the efficiency of the water electrolysis device through simpler control is desired.

The present invention has been made to solve the above-described problems, and an object of the present invention is to provide another technique for improving the efficiency of a water electrolysis device.

The present invention has been made to solve at least part of the above problems, and can be implemented as the following modes.

(1) According to one aspect of the present invention, there is provided a control device that controls a water electrolysis device that produces hydrogen by electrolyzing water. The control device is configured to be able to store hydrogen produced in the water electrolysis device in a hydrogen storage unit connected to the water electrolysis device, and the control device determines the calculating a scheduled operating time of the water electrolysis device, wherein the scheduled operating time is less than a predetermined operating time threshold, the water electrolysis device is in a cold start state, and the hydrogen demand is calculated from the hydrogen storage amount in the hydrogen storage unit; If a shutdown condition that the reduced amount is greater than a predetermined storage threshold is satisfied, the water electrolysis device is not operated; The operation time threshold is set in the vicinity of the minimum time at which the hydrogen production unit consumption becomes substantially constant in the relationship between the operation time from the cold start of the water electrolysis device and the hydrogen production unit consumption. value.

Here, the cold start state is a state in which the efficiency of the water electrolysis device is not good, such as when a period of time has passed since the operation of the water electrolysis device was stopped.
According to this configuration, the water electrolysis device is not always operated when a hydrogen demand is received, and the scheduled operation time of the water electrolysis device calculated from the hydrogen demand is within a range in which the water electrolysis device is not efficient. When the amount of stored hydrogen is sufficiently larger than the required amount of hydrogen, the water electrolyzer is not operated. Then, the water electrolysis device can be operated when the water electrolysis device is not in a cold start state or when the planned operation time is within a range in which the efficiency of the water electrolysis device is improved. Therefore, when a request for hydrogen is received, the efficiency of the water electrolysis device can be improved compared to the case where the water electrolysis device is always operated regardless of the state of the water electrolysis device. Moreover, according to this configuration, when the efficiency of the water electrolysis device becomes low, the efficiency of the water electrolysis device is improved by not operating the water electrolysis device, so that the control can be simplified.

(2) In the control device of the above aspect, even if it is determined that the water electrolysis device is in a cold start state when the operation stoppage duration of the water electrolysis device is greater than a predetermined operation stoppage duration time threshold. good. With this configuration, a sensor or the like for determining the cold start state is not required, which contributes to cost reduction.

(3) According to another aspect of the present invention, there is provided a water electrolysis system including a water electrolysis device that produces hydrogen by electrolyzing water, and a control device that controls the water electrolysis device. In this water electrolysis system, the water electrolysis device is configured so that hydrogen produced in the water electrolysis device can be stored in a hydrogen storage unit connected to the water electrolysis device, and the control device has the above configuration. is a control device.

According to this configuration, the water electrolysis device is not always operated when a hydrogen demand is received, and the scheduled operation time of the water electrolysis device calculated from the hydrogen demand is within a range in which the water electrolysis device is not efficient. When the amount of stored hydrogen is sufficiently larger than the required amount of hydrogen, the water electrolyzer is not operated. Then, the water electrolysis device can be operated when the water electrolysis device is not in a cold start state or when the planned operation time is within a range in which the efficiency of the water electrolysis device is improved. Therefore, when a request for hydrogen is received, the efficiency of the water electrolysis device can be improved compared to the case where the water electrolysis device is always operated regardless of the state of the water electrolysis device. Moreover, according to this configuration, when the efficiency of the water electrolysis device becomes low, the efficiency of the water electrolysis device is improved by not operating the water electrolysis device, so that the control can be simplified.

(4) In the water electrolysis system of the above aspect, the water electrolysis device includes n solid polymer type water electrolysis stacks (an integer of n≧1), and each of the n water electrolysis stacks has On the other hand, a power supply unit capable of individually distributing input power input from a power source is provided, and when the water electrolysis device is operated, the control device controls m ( an integer of 1 ≤ m ≤ n) of the water electrolysis stacks are selected, and the power supply unit is controlled to supply each of the m water electrolysis stacks with power of a current equal to or higher than the lower limit current value; The lower limit current value is the current value at which the current efficiency of the water electrolysis stack is 98% or more and the total power efficiency, which is the product of the power efficiency of the power supply and the power efficiency of the water electrolysis stack, is maximized. and m may be determined according to the input power, and may be the maximum number of power that can be supplied to each of the m water electrolysis stacks at the lower limit current value.

According to this configuration, the number of water electrolysis stacks to be operated can be determined according to the input power. Then, electric power with a current equal to or higher than the lower limit current value can be supplied to each of the water electrolysis stacks to be operated. The lower limit current value is set to maximize the total power efficiency within the current range that can reduce the amount of so-called cross leakage, so the durability of the water electrolysis stack is improved and the efficiency of the water electrolysis stack is increased. can be made appropriate. Therefore, the efficiency of the water electrolysis device can be further improved.

(5) According to another aspect of the present invention, there is provided a method of operating a water electrolysis device configured to store hydrogen produced by electrolysis of water in a hydrogen storage unit connected thereto. This method of operating a water electrolysis device includes calculating a scheduled operating time of the water electrolysis device from an input hydrogen demand amount, calculating the scheduled operating time of the water electrolysis device from a predetermined operating time threshold value, and performing a cold start of the water electrolysis device. and when the operation stop condition is satisfied that the amount obtained by subtracting the hydrogen demand amount from the hydrogen storage amount in the hydrogen storage unit is larger than a predetermined storage threshold, the water electrolysis device is not operated and the operation If the stop condition is not satisfied, the water electrolysis device is operated for at least the scheduled operation time, and the operation time threshold is the relationship between the operation time from the cold start of the water electrolysis device and the hydrogen production unit consumption. in the vicinity of the minimum time at which the hydrogen production unit consumption becomes substantially constant.

According to this method of operating a water electrolyzer, the water electrolyzer is not always operated when a hydrogen demand is received. When the amount of stored hydrogen is sufficiently larger than the required amount of hydrogen, the water electrolyzer is not operated. Then, the water electrolysis device can be operated when the water electrolysis device is not in a cold start state or when the planned operation time is within a range in which the efficiency of the water electrolysis device is improved. Therefore, when a request for hydrogen is received, the efficiency of the water electrolysis device can be improved compared to the case where the water electrolysis device is always operated regardless of the state of the water electrolysis device.

(6) According to another aspect of the present invention, there is provided a program for controlling a water electrolysis device configured to store hydrogen produced by electrolysis in a hydrogen storage unit connected thereto. This program has a function of calculating a scheduled operation time of the water electrolysis device from the hydrogen demand input to the computer, and a function of calculating the scheduled operation time of the water electrolysis device from the hydrogen demand input to the computer, and when the operation stop condition is satisfied that the amount obtained by subtracting the hydrogen demand amount from the hydrogen storage amount in the hydrogen storage unit is larger than a predetermined storage threshold, the water electrolysis device is not operated and the operation and a function of operating the water electrolysis device for at least the scheduled operation time when a stop condition is not satisfied, wherein the operation time threshold is set to a cold start of the water electrolysis device. It is a value in the vicinity of the minimum time at which the hydrogen production unit consumption becomes substantially constant in the relationship between the operation time from the start and the hydrogen production unit unit.

If the computer that controls the water electrolyzer functions according to this program, the water electrolyzer will not necessarily be operated when a hydrogen demand is received. is in a range in which the efficiency of the water electrolyzer is not good, and when the amount of stored hydrogen is sufficiently larger than the required amount of hydrogen, the water electrolyzer is not operated. Then, the water electrolysis device can be operated when the water electrolysis device is not in a cold start state or when the planned operation time is within a range in which the efficiency of the water electrolysis device is improved. Therefore, when a request for hydrogen is received, the efficiency of the water electrolysis device can be improved compared to the case where the water electrolysis device is always operated regardless of the state of the water electrolysis device. Also, the program for improving the efficiency of the water electrolysis device can be simplified.

The present invention can be implemented in various aspects, for example, a methane production system comprising a water electrolysis system, a carbon dioxide recovery system comprising a water electrolysis system, a hydrogen station comprising a water electrolysis system, and a computer program. It can be implemented in the form of a server device for distribution, a non-temporary storage medium storing a computer program, or the like.

BRIEF DESCRIPTION OF THE DRAWINGS It is a schematic diagram which shows notionally the structure of the water electrolysis system of embodiment. 1 is an explanatory diagram conceptually showing a schematic configuration of a water electrolysis cell; FIG. It is a flow chart which shows operation existence decision processing in a control device. FIG. 2 is a diagram conceptually showing the relationship between operation time and hydrogen production unit consumption; FIG. 4 is an explanatory diagram of power supply control in a control device; FIG. 4 is an explanatory diagram of the lower limit current value of the embodiment;

<Embodiment>
FIG. 1 is a schematic diagram conceptually showing the configuration of a water electrolysis system 100 according to one embodiment of the present invention. A hydrogen reservoir 300 is connected to the water electrolysis system 100 of the present embodiment, and hydrogen produced in the water electrolysis system 100 is supplied to the hydrogen consuming device 400 via the hydrogen reservoir 300 . The remaining hydrogen is stored in hydrogen storage unit 300 . The water electrolysis system 100 of this embodiment is installed, for example, in a factory, and supplies hydrogen to a fuel cell forklift as the hydrogen consuming device 400 .

A water electrolysis system 100 of this embodiment includes a water electrolysis device 50 and a control device 30 . The water electrolysis device 50 includes four water electrolysis stacks 10 , a power supply unit 20 that distributes power to the four water electrolysis stacks 10 , and a water supply unit that can supply water to the four water electrolysis stacks 10 . a portion 40; The water electrolysis system 100 electrolyzes water in each water electrolysis stack 10 to generate oxygen and hydrogen.

When distinguishing the four water electrolysis stacks 10, they are called a first water electrolysis stack 11, a second water electrolysis stack 12, a third water electrolysis stack 13, and a fourth water electrolysis stack 14, respectively. Note that the number of water electrolysis stacks 10 is not limited to that of the present embodiment, and can be arbitrarily set according to the purpose.

The water electrolysis stack 10 is formed by stacking a plurality of water electrolysis cells using a polymer electrolyte membrane as a diaphragm.
FIG. 2 is an explanatory diagram conceptually showing the schematic configuration of the water electrolysis cell 10C. The water electrolysis cell 10</b>C is a PEM (Polymer Electrolyte Membrane) type water electrolysis cell and has a membrane electrode assembly (hereinafter referred to as “MEA”) 1 . The MEA 1 has an oxygen electrode 1b that decomposes water to generate oxygen and protons (hydrogen ions) and a hydrogen electrode that generates hydrogen from hydrogen ions on both sides of an electrolyte membrane 1a that can pass protons (H ⁺ ) and water. and the pole 1c are joined together. A power supply 5 made of a metal mesh or the like is arranged on the surface of the oxygen electrode 1b, and a separator 4 is arranged via a gasket 2 on the MEA 1 on the side of the oxygen electrode 1b. Similarly, a power supply 6 made of a metal mesh or the like is arranged on the surface of the hydrogen electrode 1c, and a separator 4 is arranged on the side of the hydrogen electrode 1c of the MEA 1 with a gasket 3 interposed therebetween. The separator 4 is a so-called bipolar plate.

The structure of the water electrolysis cell 10C is not particularly limited as long as water electrolysis is possible. For example, the water electrolysis cell 10C is
(a) a bipolar circulation system in which water is circulated on both the oxygen electrode side and the hydrogen electrode side;
(b) Any one-side circulation system in which water is circulated only on the oxygen electrode side may be used.

In the water electrolysis cell 10C, when water is supplied from the water supply unit 40 to the oxygen electrode side, when electric power is supplied, water is electrolyzed at the oxygen electrode 1b to generate oxygen and hydrogen ions. The oxygen produced is discharged along with some of the water that has not been electrolyzed. The hydrogen ions generated at the oxygen electrode 1b move to the hydrogen electrode side together with water (accompanied water) and combine with electrons at the hydrogen electrode 1c to become hydrogen. The hydrogen produced at the hydrogen electrode 1c is discharged together with permeated water that has permeated the electrolyte membrane and associated water.

As shown in FIG. 2, hydrogen generated at the hydrogen electrode 1c permeates the electrolyte membrane 1a due to the pressure difference between the hydrogen electrode and the oxygen electrode (the pressure on the hydrogen electrode side is high) and the hydrogen concentration difference. It may move to the oxygen electrode side. Similarly, oxygen generated at the oxygen electrode 1b may move to the hydrogen electrode side due to the oxygen concentration difference between the hydrogen electrode side and the oxygen electrode side. This is also called "cross leak". Cross leak tends to occur in the low current range.

The power supply unit 20 ( FIG. 1 ) is connected to the power source 200 and each of the four water electrolysis stacks 10 . The power supply unit 20 has a so-called power regulator, and distributes the input power input from the power source 200 to each of the four water electrolysis stacks 10 individually.

The control device 30 controls the operation of the water electrolysis system 100 as a whole. Specifically, when a request for hydrogen supply is input to the water electrolysis system 100 , the control device 30 performs operation/non-operation determination processing for determining whether or not the water electrolysis device 50 is to be operated. In addition, the control device 30 performs power supply control by controlling the power supply unit 20 to supply power to the water electrolysis stack 10 . In power supply control, the number of water electrolysis stacks 10 to be operated by supplying power from the power source 200 is determined, and the input power from the power source 200 is distributed to the determined number of water electrolysis stacks 10 . Furthermore, it controls the supply of hydrogen from the hydrogen reservoir 300 to the hydrogen consuming device 400 . Each control in the control device 30 will be detailed later.

A program that implements the above-described operation/non-operation determination process, power supply control, and the like may be stored in advance in the control device 30 . Alternatively, the program may be provided by a program provider via a communication network. Also, the program may be stored in a commercially available and distributed portable storage medium. In this case, the portable storage medium may be set in an external or built-in reading device, and the program may be read and executed by the control device 30 . Various types of storage media such as CD-ROMs, DVD-ROMs, flexible disks, optical disks, magneto-optical disks, IC cards, and USB memory devices can be used as portable storage media. A program stored in such a storage medium is read by a reader.

The water supply unit 40 is configured to supply water to the oxygen electrode 1b of the water electrolysis stack 10 . Water supplied to the oxygen electrode 1b serves as a raw material for electrolysis. The structure of the water supply unit 40 is not particularly limited as long as it can supply a required amount of water to the operating water electrolysis stack 10 (hereinafter also referred to as "operating water electrolysis stack"). Even if water is supplied to the oxygen electrode 1b of the water electrolysis stack 10, electrolysis is not performed unless power is supplied. Therefore, the water supply device may supply water to all the water electrolysis stacks 10 at the same time, or may selectively supply water to the water electrolysis stacks 10 that are in operation.

The water electrolysis system 100 may further include a second water supply unit for supplying water to the hydrogen electrode 1c of the water electrolysis stack 10. FIG. When water is supplied to the hydrogen electrode 1c during electrolysis, desorption of hydrogen gas adsorbed on the surface of the hydrogen electrode 1c can be promoted.

A power supply 200 supplies power to the water electrolysis stack 10 . In this embodiment, power source 200 is a renewable energy source. That is, the input power inputted to the power supply unit 20 fluctuates relatively greatly. The type of power supply 200 is not particularly limited, and may be a commercial power supply.

Hydrogen reservoir 300 is connected to water electrolysis system 100 and to hydrogen consuming device 400 . Specifically, the hydrogen storage unit 300 includes a hydrogen tank (not shown), is connected downstream of the flow path through which hydrogen generated in the water electrolysis stack 10 of the water electrolysis system 100 flows, and can store hydrogen inside the hydrogen tank. is. In addition, according to instructions from the control device 30, the hydrogen in the hydrogen tank is supplied to the hydrogen consumption device 400 at a predetermined flow rate. Further, the hydrogen storage unit 300 is provided with a hydrogen remaining amount sensor 302 that detects the amount of hydrogen in the hydrogen tank.

The hydrogen consuming device 400 is a device that uses hydrogen as an energy source, and various devices that use hydrogen as an energy source, such as a fuel cell forklift, a fuel cell automobile, a hydrogen airplane, and a fuel cell plant, can be applied. Hydrogen consuming device 400 is connected to water electrolysis system 100 via hydrogen reservoir 300 and is supplied with hydrogen produced in water electrolysis system 100 . Hydrogen consuming device 400 outputs the required hydrogen amount (hydrogen demand amount) to control device 30 .

FIG. 3 is a flow chart showing operation presence/absence determination processing in the control device 30 .
Control device 30 receives hydrogen demand a [Nm3] from hydrogen consuming device 400 (step S102), and calculates scheduled operation time t1 (step S104). The scheduled operating time t1 is the time required for the water electrolysis device 50 to generate the hydrogen demand amount a [Nm3]. The control device 30 calculates the scheduled operation time t1 using a pre-stored map showing the relationship between the operation time of the water electrolysis device 50 and the hydrogen production amount, a calculation formula, and the like. Although the hydrogen demand a is input from the hydrogen consuming device 400 in this embodiment, it may be input from an input device different from the hydrogen consuming device 400 in other embodiments. For example, a person may input using an operation panel provided in the water electrolysis system 100, a keyboard connected to the water electrolysis system 100, or the like.

In step S106, the control device 30 determines whether or not the scheduled operating time t1 is smaller than the operating time threshold T1. The operating time threshold value T1 is set to the minimum time at which the hydrogen production unit consumption becomes approximately constant in the relationship between the operation time from the cold start of the water electrolysis device 50 and the hydrogen production unit consumption. The basic unit of hydrogen production is the amount of electric power required to produce a unit amount of hydrogen in the water electrolysis device 50 . In the present embodiment, cold start refers to starting the operation of the water electrolysis device 50 after a predetermined period of time or more has elapsed since the operation of the water electrolysis device 50 was stopped. Although the predetermined time can be set arbitrarily, it is preferable to set the time to the extent that the water electrolysis device 50 is sufficiently cooled. In this embodiment, the predetermined time is set to 10 hours at night, for example, assuming driving from 7:00 to 21:00. This predetermined time is hereinafter referred to as "operation stop duration time threshold value T2".

FIG. 4 is a diagram conceptually showing the relationship between operation time and hydrogen production unit consumption. The horizontal axis of FIG. 4 is the operating time from the cold start of the water electrolysis device 50 . As shown in the figure, the hydrogen production unit consumption decreases with the length of the operating time from the cold start up to the operating time threshold T1, and is substantially constant after the operating time threshold T1. The inventors investigated the relationship between the operation time from the cold start and the hydrogen production unit consumption for a plurality of months in which the temperature of the water supplied to the water electrolysis stack 10 (hereinafter also referred to as electrolyzed water) was different. . This is because it is considered that the water temperature has a great influence on the hydrogen production unit consumption. As a result, the relationship between the operation time from the cold start and the hydrogen production unit consumption was substantially the same for a plurality of months, and the relationship shown in FIG. 4 was obtained. The reason is considered as follows. The higher the temperature of the water to be electrolyzed, the less electrical energy is required for electrolysis. Therefore, when the temperature of the water to be electrolyzed is low, the power consumption in electrolysis is large until the water temperature rises, and the chiller power for controlling the temperature of the water electrolysis stack 10 is small. On the other hand, when the temperature of the water to be electrolyzed is high, the water temperature rises quickly, so the power consumption in electrolysis is small and the chiller power is large. This balance is thought to have resulted in similar trends in multiple months with different water temperatures. Here, the electric energy used for calculating the hydrogen production unit consumption is the electric energy consumed by the water electrolysis system 100 as a whole. Further, FIG. 4 shows the discrete data obtained by the above survey as an approximated curve whose values converge. Power approximation was used as the approximation curve.

As shown in FIG. 4, when the operating time is equal to or greater than the operating time threshold T1, the hydrogen production unit consumption is lower than when the operating time is shorter than the operating time threshold T1, and is substantially constant. Therefore, the efficiency of the water electrolysis device 50 can be improved by operating the water electrolysis device 50 for a time equal to or greater than the operating time threshold value T1.

As shown in FIG. 3, when the scheduled operating time t1 is equal to or greater than the operating time threshold T1 (NO in step S106), the control device 30 determines to operate the water electrolysis device 50 (step S112), and determines whether or not to operate. After finishing the process, the operation of the water electrolysis device 50 is started. A method of operating the water electrolysis device 50 will be described later. As described above, when the operating time is longer than the operating time threshold value T1, the efficiency of the water electrolysis device 50 can be improved.

On the other hand, when the scheduled operating time t1 is smaller than the operating time threshold T1 (YES in step S106), the control device 30 proceeds to step S108.

In step S108, the control device 30 determines whether or not the shutdown duration time t2 is greater than the shutdown duration time threshold value T2. In the present embodiment, the operation stop duration time t2 is the time from when the operation of the water electrolysis device 50 is stopped until the input of the hydrogen demand amount a is received. The operation of the water electrolysis device 50 is stopped when the power supply or water supply to all the water electrolysis stacks 10 is stopped. In step S108, the control device 30 determines whether or not the water electrolysis device 50 is in a cold start state when the water electrolysis device 50 produces hydrogen of the received hydrogen demand amount a.

When the shutdown duration time t2 is equal to or less than the shutdown duration threshold value T2 (NO in step S108), the control device 30 determines to operate the water electrolysis device 50 (step S112), and terminates the operation presence/absence determination process. , the operation of the water electrolysis device 50 is started. At this time, the water electrolysis device 50 is not in a cold start state, and the efficiency of the water electrolysis device 50 can be improved.

On the other hand, if the shutdown duration t2 is greater than the shutdown duration threshold T2 (YES in step S106), the control device 30 proceeds to step S110.

In step S110, control device 30 determines whether or not the amount obtained by subtracting hydrogen demand amount a [Nm3] from hydrogen storage amount b [Nm3] in hydrogen storage unit 300 is greater than a predetermined storage threshold value c [Nm3]. . The retention threshold c is a value as a margin and can be arbitrarily set. In this embodiment, for example, it is set to the daily average usage amount. As the hydrogen storage amount, the measurement result input from the hydrogen remaining amount sensor 302 provided in the hydrogen storage unit 300 is used.

If the calculation result in step S110 shows that the amount obtained by subtracting the hydrogen demand amount a from the hydrogen storage amount b in the hydrogen storage unit 300 is equal to or less than the predetermined storage threshold value c (NO in step S110), the control device 30 performs water electrolysis. It is determined to operate the device 50 (step S112), the operation presence/absence determination process is terminated, and the operation of the water electrolysis device 50 is started. That is, when the hydrogen demand amount a from the hydrogen stored in the hydrogen storage unit 300 is supplied to the hydrogen consumption device 400, the amount of hydrogen remaining in the hydrogen storage unit 300 becomes equal to or less than the storage threshold value c. , the water electrolysis device 50 is operated. In this way, the amount of hydrogen larger than the storage threshold value c can be stored in the hydrogen storage unit 300 .

On the other hand, when the amount obtained by subtracting the hydrogen demand amount a from the hydrogen storage amount b in the hydrogen storage unit 300 is greater than the predetermined storage threshold value c (YES in step S110), the control device 30 does not operate the water electrolysis device 50. is determined (step S114), and the operation presence/absence determination process is terminated. Then, the control device 30 controls the hydrogen storage unit 300 to supply the hydrogen demand amount a from the hydrogen stored in the hydrogen storage unit 300 to the hydrogen consumption device 400 . That is, the control device 30 causes the hydrogen consuming device 400 to supply the hydrogen stored in the hydrogen storage unit 300 without operating the water electrolysis device 50 .

The condition that the control device 30 satisfies all of the three conditions for determining whether or not to be satisfied in steps S106, S108, and S110 is also referred to as a "shutdown condition."

As described above, when the control device 30 determines to operate the water electrolysis device 50 in the operation presence/absence determination process (step S112), the operation of the water electrolysis device 50 is started. After starting the operation of the water electrolysis device 50, the control device 30 controls the water supply unit 40 (FIG. 1) to supply water to all the water electrolysis stacks 10, and performs supply power control described below.

FIG. 5 is an explanatory diagram of power supply control in the control device 30. As shown in FIG. The left side of FIG. 5 shows changes over time in the input power input to the power supply unit 20 . The right side of FIG. 5 shows the power distribution corresponding to variations in input power. "I _LOW " shown in the figure is the lower limit current value (described later).

As described above, the power source 200 is a renewable energy source and the amount of power generation fluctuates, so the input power input to the power supply unit 20 fluctuates as illustrated. The control device 30 of the present embodiment determines the number of working water electrolysis stacks so that the current supplied to one water electrolysis stack 10 is equal to or higher than the lower limit current value _ILOW . Specifically, from the input power, the maximum number of water electrolysis stacks 10 to which power can be supplied at the lower limit current value I _LOW is determined as the number of water electrolysis stacks 10 to be operated, and the determined number of water electrolysis stacks 10 , to evenly distribute the input power. That is, in the water electrolysis system 100 of this embodiment, the water electrolysis system 100 is always operated with power equal to or higher than the lower limit current value I _LOW .

In the example shown in FIG. 5, when power is supplied to one water electrolysis stack 10 at the lower limit current value I _LOW at time <1>, the remaining input power is smaller than the lower limit current value I _LOW . determines that the number of water electrolysis stacks 10 (working water electrolysis stacks) to which power is supplied is one, and supplies all of the input power only to the first water electrolysis stack 11 (FIG. 1).

At time <2>, when power is supplied to the two water electrolysis stacks 10 at the lower limit current value _ILOW , the remaining input power is 0, so the controller 30 sets the number of working water electrolysis stacks to two. The input power is evenly distributed to the first water electrolysis stack 11 and the second water electrolysis stack 12 at the lower limit current value _ILOW .

At time <3>, when power is supplied to the two water electrolysis stacks 10 at the lower limit current value I _LOW , the rest of the input power is smaller than the lower limit current value I _LOW . The number is determined to be two. Then, the rest of the input power is evenly distributed to the first water electrolysis stack 11 and the second water electrolysis stack 12, and combined with the lower limit current value _ILOW , the current density higher than the lower limit current value _ILOW is applied to the first water electrolysis stack. 11 and the second water electrolysis stack 12 .

At the time <4>, even if power is supplied to the four water electrolysis stacks 10 at the lower limit current value _ILOW , the input power remains. ). Then, the rest of the input power is evenly distributed to the four water electrolysis stacks 10, and combined with the lower limit current value I _LOW , the current density is greater than the lower limit current value I _LOW . distribute to

As described above, in the water electrolysis system 100 of the present embodiment, when selecting the water electrolysis stack 10 according to the number of working water electrolysis stacks, in ascending order from the first water electrolysis stack 11 (from the smallest number to the largest number). )select.

FIG. 6 is an explanatory diagram of the lower limit current value I _LOW in this embodiment. FIG. 6 shows the relationship between the current density and the overall power efficiency in the water electrolysis stack 10 for four types of water electrolysis cells (10 μm, 25 μm, 50 μm, 175 μm) having different thicknesses of the electrolyte membrane 1a. Here, the total current efficiency is the product of the power efficiency of the water electrolysis stack 10 and the power efficiency of the power supply 200 (described later). In the present embodiment, a current lower than the lower limit current value I _LOW is not supplied to the water electrolysis stack 10, so in FIG _. . As shown, the lower limit current value varies depending on the thickness of the electrolyte membrane 1a. As shown in the case of using the electrolyte membrane 1a with a film thickness of 25 μm, the lower limit current value I _LOW in this embodiment is higher than the current value _IM at which the total power efficiency is maximized. Similarly, when the film thickness is 10 μm, the lower limit current value I _LOW is higher than the current value that maximizes the total power efficiency. When the electrolyte membrane 1a with a film thickness of 50 μm is used, the lower limit current value I _LOW substantially coincides with the current value I at which the total power efficiency is maximized. When the electrolyte membrane 1a with a film thickness of 175 μm is used, the lower limit current value I _LOW is almost 0, and the entire current range can be used. In the present embodiment, for each film thickness, the current efficiency per working water electrolysis stack is 98% or more, and the power efficiency of the power supply 200 and the power efficiency per working water electrolysis stack are The current that maximizes the total power efficiency, which is the product, is the lower limit current value I _LOW . The lower limit current value I _LOW can be determined, for example, by the method described in Japanese Patent Application No. 2020-88153.

When the controller 30 operates the water electrolysis device 50 in this manner, the number of water electrolysis stacks 10 to be operated can be determined according to the input power input from the power source 200 . Then, electric power with a current equal to or higher than the lower limit current value I _LOW can be supplied to each of the water electrolysis stacks 10 to be operated. Therefore, it is possible to suppress a decrease in the current of the electric power supplied to the water electrolysis stack 10, and it is possible to suppress deterioration of the electrolyte membrane due to a low current. In addition, the current efficiency per working water electrolysis stack is 98% or more, and the total power efficiency, which is the product of the power efficiency of the power supply 200 and the power efficiency per working water electrolysis stack, is maximum. is set to the lower limit current value I _LOW , the power efficiency of the water electrolysis stack 10 can be made appropriate.

As described above, according to the water electrolysis system 100 of the present embodiment, when the control device 30 receives the hydrogen demand amount a, the water electrolysis device 50 is not always operated, but the operation stop condition is satisfied. If the operation stop condition is satisfied, the water electrolysis device 50 is not operated, and if the operation stop condition is not satisfied, the water electrolysis device 50 is operated. The operation stop condition is set to a condition in which the efficiency of the water electrolysis device 50 is deteriorated, and when the operation stop condition is satisfied, the water electrolysis device 50 is not operated. is reduced. As a result, the efficiency of the water electrolysis device 50 can be improved.

The operation stop condition consists of three conditions, and if even one condition is not met, the operation stop condition is not satisfied, so the water electrolysis device 50 is operated. Therefore, if the scheduled operating time t1 is equal to or greater than the operating time threshold T1, the water electrolysis device 50 is operated. As described above, if the operation time is equal to or greater than the operation time threshold value T1, the efficiency of the water electrolysis device 50 can be improved even if the cold start is performed. Further, even if the scheduled operating time t1 is shorter than the operating time threshold T1, the water electrolysis device 50 is operated unless the cold start is performed. If it is not a cold start, the efficiency of the water electrolysis device 50 is high, so the efficiency of the water electrolysis device 50 can be improved.

In addition, even if the scheduled operating time t1 is shorter than the operating time threshold T1 and the start is cold, and the requested hydrogen amount a can be supplied by the hydrogen in the hydrogen storage unit 300, the remainder of the requested hydrogen amount a is supplied. is less than or equal to the storage threshold value c, the water electrolysis device 50 is operated. Therefore, the amount of hydrogen stored in the hydrogen storage unit 300 can be maintained at or above the storage threshold value c.

In addition, according to the control device 30 of the present embodiment, when the efficiency of the water electrolysis device 50 is low, the water electrolysis device 50 is not operated, thereby improving the efficiency of the water electrolysis device, thereby simplifying the control. can do. Therefore, computational resources can be reduced. Moreover, compared with the technique described in Patent Document 1, since no temperature sensor is required, an increase in the number of parts of the water electrolysis system can be suppressed. Therefore, it is possible to contribute to suppression of system complication, downsizing, and cost reduction.

Moreover, according to the water electrolysis system 100 of the present embodiment, the number of water electrolysis stacks 10 to be operated can be determined according to the input power input from the power supply 200 . Then, power with a current equal to or higher than the lower limit current value I _LOW can be supplied to each of the water electrolysis stacks to be operated. When the input power fluctuates and the input power is small, it is possible to prevent the supplied power from becoming low compared to the case where the power is evenly distributed to all four water electrolysis stacks. Under low current conditions, hydrogen and oxygen permeate the electrolyte membrane (generally referred to as "cross-leak"), causing oxygen and water to react on the catalyst to generate hydrogen peroxide, which decomposes the electrolyte membrane. This may cause deterioration of the water electrolysis stack. According to the water electrolysis system 100 of the present embodiment, it is possible to suppress the deterioration of the electrolyte membrane because it is possible to suppress the supply power from being lowered.

<Modification of this embodiment>
The present invention is not limited to the above-described embodiments, and can be implemented in various aspects without departing from the scope of the invention. For example, the following modifications are possible.

- The operation presence/absence determination process in the above embodiment may be applied to the water electrolysis system described in Japanese Patent Application No. 2020-88153 and Japanese Patent Application Laid-Open No. 2020-84259. When applied to the water electrolysis system, the hydrogen storage unit 300 is connected downstream of the flow path through which hydrogen generated in the water electrolysis system flows, and the hydrogen consumption device 400 is connected to the hydrogen storage unit 300, as in the present embodiment. , and the hydrogen generated in the water electrolysis system is preferably supplied to the hydrogen consuming device 400 via the hydrogen reservoir 300 .

- The water electrolysis device 50 is not limited to the above embodiment, and can be applied to any water electrolysis device. For example, one water electrolysis stack 10 may be provided. In addition, it is possible to use various water electrolysis devices such as alkaline type water electrolysis devices and SOEC (Solid Oxide Electrolysis Cells) in addition to PEM (Polymer Electrolyte Membrane) type water electrolysis devices. can be done.

- In addition, in the operation presence/absence determination process, the operation method of the water electrolysis device after it is determined to operate is not limited to the above-described embodiment, and any operation method can be adopted. For example, power supplied from the power supply 200 may be evenly distributed to the four water electrolysis stacks 10 .

- In the above-described embodiment, an example is shown in which the water electrolysis device 50 is in a cold start state by judging that the operation stoppage duration time t2 is equal to or greater than the operation stoppage duration time threshold value T2. The cold start state may be determined according to another condition. For example, the determination may be made based on the temperature of the water electrolysis stack 10 when the control device 30 receives the hydrogen demand a. As the temperature of the water electrolysis stack 10, for example, the temperature inside the water supply port to the water electrolysis stack 10, the temperature of the heat medium for adjusting the temperature of the water electrolysis stack 10, or the like can be used. A cold start can be determined when these temperatures are low (arbitrary values with poor efficiency are set).

- In the above-described embodiment, an example in which hydrogen generated in the water electrolysis system 100 is supplied to the hydrogen consuming device 400 via the hydrogen reservoir 300 is shown, but the present invention is not limited to this. For example, the configuration may further include a flow path for supplying hydrogen from the water electrolysis system 100 to the hydrogen consuming device 400 without passing through the hydrogen reservoir 300 .

- In the above-described embodiment, the operating time threshold T1 is set to the minimum time at which the hydrogen production unit consumption is substantially constant in the relationship between the operation time from the cold start of the water electrolysis device 50 and the hydrogen production unit consumption. However, it is not limited to this, and can be set near the minimum time. Here, when the neighborhood range is ±α of the minimum time when the hydrogen production unit consumption becomes substantially constant, α can be defined as follows. Hydrogen production intensity when operating time is (minimum time at which hydrogen production intensity becomes approximately constant - α) and hydrogen production intensity when operating time is the minimum time at which hydrogen production intensity becomes approximately constant is 10% of the difference between the maximum value of the hydrogen production unit consumption in the relationship between the operation time and the hydrogen production unit consumption shown in FIG. Also in this way, the efficiency of the water electrolysis device 50 can be improved.

Although the present invention has been described above based on the embodiments and modifications, the above-described embodiments are intended to facilitate understanding of the present invention, and do not limit the present invention. This invention may be modified and modified without departing from its spirit and scope of the claims, and this invention includes equivalents thereof. Also, if the technical features are not described as essential in this specification, they can be deleted as appropriate.

1...MEA
DESCRIPTION OF SYMBOLS 1a... Electrolyte membrane 1b... Oxygen electrode 1c... Hydrogen electrode 2, 3... Gasket 4... Separator 5, 6... Feeder 10... Water electrolysis system 10, 11, 12, 13, 14... Water electrolysis stack 10C... Water electrolysis cell 20 Power supply unit 30 Control unit 40 Water supply unit 50 Water electrolysis device 100 Water electrolysis system 200 Power supply 300 Hydrogen reservoir 302 Remaining hydrogen sensor 400 Hydrogen consumption device

Claims (6)

A control device for controlling a water electrolysis device that produces hydrogen by electrolysis of water,
The water electrolysis device is configured to store hydrogen produced in the water electrolysis device in a hydrogen storage unit connected to the water electrolysis device,
The control device is
calculating the scheduled operating time of the water electrolysis device from the input hydrogen demand;
The scheduled operation time is less than a predetermined operation time threshold, the water electrolysis device is in a cold start state, and the amount obtained by subtracting the hydrogen demand amount from the hydrogen storage amount in the hydrogen storage unit is less than the predetermined storage threshold. If the operation stop condition of being large is satisfied, the water electrolysis device is not operated, and if the operation stop condition is not satisfied, the water electrolysis device is operated for at least the scheduled operation time,
The driving time threshold is
In the relationship between the operating time from the cold start of the water electrolysis device and the hydrogen production unit consumption, it is a value near the minimum time at which the hydrogen production unit consumption becomes substantially constant.
Control device. The control device according to claim 1,
determining that the water electrolysis device is in a cold start state when the shutdown duration of the water electrolysis device is greater than a predetermined shutdown duration time threshold;
Control device. A water electrolysis system comprising: a water electrolysis device that produces hydrogen by electrolysis of water; and a control device that controls the water electrolysis device,
The water electrolysis device is configured to store hydrogen produced in the water electrolysis device in a hydrogen storage unit connected to the water electrolysis device,
The control device is
A control device according to claim 1 or claim 2,
water electrolysis system. The water electrolysis system according to claim 3,
The water electrolysis device is
n solid polymer type water electrolysis stacks (an integer of n≧1);
a power supply unit capable of individually distributing input power input from a power supply to each of the n water electrolysis stacks;
The control device is
When operating the water electrolysis device,
m (integer of 1 ≤ m ≤ n) water electrolysis stacks are selected from the n water electrolysis stacks, and the power supply unit is controlled to each of the m water electrolysis stacks, supply power with current equal to or higher than the lower limit current value,
The lower limit current value is
A current value at which the current efficiency of the water electrolysis stack is 98% or more and the total power efficiency, which is the product of the power supply efficiency of the power supply and the power efficiency of the water electrolysis stack, is maximized,
Said m is
is determined according to the input power, and is the maximum number of power that can be supplied to each of the m water electrolysis stacks at the lower limit current value;
water electrolysis system. A method of operating a water electrolysis device configured to be able to store hydrogen produced by electrolysis of water in a hydrogen storage unit connected thereto, comprising:
calculating the scheduled operating time of the water electrolysis device from the input hydrogen demand;
The scheduled operation time is less than a predetermined operation time threshold, the water electrolysis device is in a cold start state, and the amount obtained by subtracting the hydrogen demand amount from the hydrogen storage amount in the hydrogen storage unit is less than the predetermined storage threshold. If the operation stop condition of being large is satisfied, the water electrolysis device is not operated, and if the operation stop condition is not satisfied, the water electrolysis device is operated for at least the scheduled operation time,
The driving time threshold is
In the relationship between the operating time from the cold start of the water electrolysis device and the hydrogen production unit consumption, it is a value near the minimum time at which the hydrogen production unit consumption becomes substantially constant.
A method of operating a water electrolysis device. A program for controlling a water electrolysis device configured to store hydrogen produced by electrolysis of water in a hydrogen storage unit connected thereto, the program comprising:
a function of calculating a scheduled operating time of the water electrolysis device from the input hydrogen demand;
The scheduled operation time is less than a predetermined operation time threshold, the water electrolysis device is in a cold start state, and the amount obtained by subtracting the hydrogen demand amount from the hydrogen storage amount in the hydrogen storage unit is less than the predetermined storage threshold. and a function of not operating the water electrolysis device when the operation stop condition of being large is satisfied, and operating the water electrolysis device for at least the scheduled operation time when the operation stop condition is not satisfied. A program for
The driving time threshold is
In the relationship between the operating time from the cold start of the water electrolysis device and the hydrogen production unit consumption, it is a value near the minimum time at which the hydrogen production unit consumption becomes substantially constant.
program.

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