JP2013209735A - Sunlight utilization system - Google Patents

Abstract

PROBLEM TO BE SOLVED: To improve durability of a photoelectrode in a sunlight utilization system in which water-electrolysis is performed using a photoelectrode having an optical semiconductor catalyst.SOLUTION: A sunlight utilization system includes a water-electrolysis part provided with a pair of electrodes with one side supporting an optical semiconductor catalyst and decomposing an electrolyte solution utilizing sunlight energy applied to the optical semiconductor catalyst, an oxygen storage part for storing oxygen generated by the water-electrolysis part, an electrolyte solution storage part for storing an electrolyte solution, a fluid passage for connecting the oxygen storage part, the water-electrolysis part and the electrolyte solution storage part, and a recovery condition determination part for determining whether or not a predetermined recovering condition has been met for recovering the electrolyte solution to the electrolyte solution storage part from the water-electrolysis part. When it is determined by the recovery condition determination part that the recovery condition has been met, the electrolyte solution is pushed out from the water-electrolysis part by the pressure of the oxygen stored in the oxygen storage part, the electrolyte solution is recovered to the electrolyte solution storage part through the fluid passage.

Description

  The present invention relates to a novel sunlight utilization system. More specifically, the solar light utilization system of the present invention relates to improvement of a system that decomposes water using a photo-semiconductor catalyst activated by sunlight and uses the obtained hydrogen and oxygen for a fuel cell reaction or the like.

An optical semiconductor catalyst that decomposes water by using the energy of sunlight is known (see Patent Document 1). If this photo-semiconductor catalyst is used, water can be decomposed with small electric power, and as a result of decomposing water, hydrogen and oxygen with high purity can be obtained.
Patent Documents 2 and 3 disclose a system that supplies hydrogen obtained by decomposing water using sunlight to a fuel cell.

JP 2006-299368 A JP 2000-144464 A Japanese Unexamined Patent Publication No. 2000-333481

  Examples of the solar light utilization system include titanium dioxide (TiO2), iron oxide (Fe2O3), niobium oxide (Nb2O5), strontium titanate (SrTiO3), barium titanate (BaTiO3), tungsten oxide (WO3), and bismuth vanadium. There is a technique using an electrode having a semiconductor such as an oxide (BiVO4) (hereinafter also referred to as a photoelectrode) and using a technique for decomposing water (for example, see Patent Document 2 and Patent Document 3). These photoelectrodes have a very strong affinity for water. Therefore, under conditions where the photoelectrode is immersed in the electrolyte for a long time, the photoelectrode material laminated on the base electrode peels off, the structure collapses, and as a result, the amount of sunlight converted into current is small. There is a risk of significant reduction.

  In the system as described above, an impurity removal filter may be installed in the electrolyte circulation line in order to remove impurities in the electrolyte. Even in such a case, the impurities in the electrolyte solution that cannot be completely removed by the impurity removal filter are deposited and adhered on the photoelectrode by the immersion of the photoelectrode in the electrolyte solution for a long time. There is a possibility that the original performance cannot be exhibited.

  Therefore, an object of the present invention is to improve the durability of a photoelectrode in a solar light utilization system in which water decomposition is performed using a photoelectrode having a photosemiconductor catalyst.

The solar light utilization system according to the first aspect of the present invention includes:
A water-splitting part having a pair of electrodes carrying a photo-semiconductor catalyst on one side and decomposing an electrolyte solution using solar energy irradiated to the photo-semiconductor catalyst;
An oxygen storage unit for storing oxygen generated in the water splitting unit;
An electrolytic solution storage unit for storing the electrolytic solution;
A fluid passage connecting the oxygen storage unit, the water decomposition unit, and the electrolyte storage unit;
A recovery condition determination unit that determines whether or not a predetermined recovery condition for recovering the electrolytic solution from the water splitting unit to the electrolytic solution storage unit is satisfied,
When the recovery condition determination unit determines that the recovery condition is satisfied, the electrolytic solution is pushed out from the water decomposition unit by the pressure of oxygen stored in the oxygen storage unit, and the electrolytic solution is passed through the fluid passage. It is a solar power utilization system that is collected in a storage unit.

  With the above configuration, when it is determined that a predetermined recovery condition is established, the electrolytic solution is recovered from the water splitting unit to the electrolytic solution storage unit, so that the electrode (photoelectrode) on which the photo semiconductor catalyst is supported However, it is possible to avoid a situation in which the liquid remains immersed in the electrolytic solution for a long time. Therefore, it can contribute to the life extension of the photoelectrode. Furthermore, since the electrolytic solution is recovered by using the pressure of oxygen stored in the oxygen storage unit during operation of the solar light utilization system (more specifically, during the decomposition of water), energy is saved.

According to the second aspect of the present invention, the solar light utilization system includes:
A pressure detection unit for detecting the pressure in the oxygen storage unit;
A fluid pump provided in the fluid passage,
When the recovery condition determination unit determines that the recovery condition is satisfied and the pressure in the oxygen storage unit detected by the pressure detection unit is equal to or lower than a predetermined pressure, the fluid pump is operated to The electrolytic solution is recovered from the decomposition unit into the electrolytic solution storage unit.
According to such a configuration, when the pressure in the oxygen storage unit becomes equal to or lower than a predetermined pressure and the pressure for recovering the electrolyte is insufficient, the fluid pump is operated to continuously execute the recovery of the electrolyte. can do.

According to a third aspect of the present invention, the solar light utilization system is
After the recovery of the electrolytic solution is completed, the fluid pump is operated to bring the inside of the fluid passage to a negative pressure.
According to such a configuration, when the solar system is restarted after collecting the electrolyte, the electrolyte is transferred from the electrolyte storage unit to the inside of the fluid path using the negative pressure formed inside the fluid path. It can be supplied to the suction water decomposition unit. As a result, the system can be restarted quickly.

According to a fourth aspect of the present invention, the solar light utilization system is
A daily illuminance detector for detecting the daily illuminance for the electrode,
The said collection condition judgment part judges that the said collection conditions were satisfied, when the said day illumination intensity becomes below predetermined illumination intensity. Thereby, when the daily illuminance is equal to or lower than the predetermined illuminance and water decomposition by using sunlight becomes difficult or impossible, it is possible to avoid a situation in which the photoelectrode is unnecessarily immersed in the electrolytic solution.

According to a fifth aspect of the present invention, in the solar light utilization system,
The collection condition determination unit determines that the collection condition is satisfied when a predetermined time comes.
The predetermined time may be set arbitrarily. For example, the predetermined time may be a fixed time. Alternatively, the daily sunset time may be set as the predetermined time based on the daily sunset time data. By doing so, the electrolytic solution can be recovered when water splitting by using sunlight becomes difficult or impossible due to sunset. Thereby, the situation where a photoelectrode continues being immersed in electrolyte solution unnecessarily can be avoided.

According to a sixth aspect of the present invention, the solar light utilization system includes:
A recovery instruction input unit for inputting an instruction to recover the electrolyte solution,
The recovery condition determination unit determines that the recovery condition is satisfied when an instruction to recover the electrolyte is input to the recovery instruction input unit.
According to such a configuration, for example, the user manually inputs an instruction to collect the electrolytic solution to the collection instruction input unit, whereby the electrolytic solution can be collected. Thereby, it is possible to avoid a situation where the photoelectrode is continuously immersed in the electrolytic solution unnecessarily by collecting the electrolytic solution during a period in which water splitting by the solar system is not performed.

According to a seventh aspect of the present invention, the solar light utilization system is
A weather information input unit for receiving weather information,
The collection condition determination unit determines that the collection condition is satisfied when the weather information input unit receives predetermined weather information.
According to such a configuration, when the sunlight is reduced due to cloudy or rainy weather and water decomposition by using sunlight cannot be sufficiently performed, or when such a situation is expected, the electrolytic solution is recovered and the photoelectrode is recovered. It is possible to avoid a situation in which the film is unnecessarily immersed in the electrolytic solution. Alternatively, when the electrolytic solution is expected to freeze due to snowfall or a decrease in temperature, it is possible to collect the electrolytic solution and prevent malfunction of the device due to the freezing of the electrolytic solution.

According to an eighth aspect of the present invention, the solar light utilization system is
A temperature detector for detecting the temperature of the electrolyte solution,
The recovery condition determination unit determines that the recovery condition is satisfied when the temperature of the electrolytic solution detected by the temperature detection unit is equal to or lower than a predetermined temperature.
According to this, by collecting the electrolytic solution when the temperature of the electrolytic solution is lowered, it becomes possible to prevent a failure of the device due to the freezing of the electrolytic solution.

The control method according to the ninth aspect of the present invention is:
A control method for a solar light utilization system having a pair of electrodes carrying a light semiconductor catalyst on one side and decomposing an electrolyte using solar energy irradiated to the light semiconductor catalyst,
Storing oxygen generated in the water splitting unit in an oxygen storage unit;
A determination step of determining whether or not a predetermined recovery condition for recovering the electrolytic solution from the water splitting unit to the electrolytic solution storage unit is satisfied;
When it is determined that the recovery condition is satisfied, the step of pushing out the electrolytic solution from the water splitting unit by the pressure of oxygen stored in the oxygen storage unit and recovering the electrolytic solution to the electrolytic solution storage unit through a fluid passage; And a control method.
By this method, the same effect as that of the first aspect can be obtained.

FIG. 1 is a block diagram showing a configuration of a sunlight utilization system according to an embodiment of the present invention. FIG. 2 is a flowchart showing the amount of water control. FIG. 3 is a flowchart showing the electrolytic solution recovery control. FIG. 4 is a flowchart showing control for restarting the solar light utilization system.

  In the above, the photo-semiconductor catalyst refers to a catalyst capable of decomposing water into hydrogen and oxygen by using solar energy and adding a small electric power assist thereto. Examples of such semiconductor materials include TiO2 (titanium dioxide), Fe2O3 (iron oxide), Nb2O5 (niobium oxide), SrTiO3 (strontium titanate), BaTiO3 (barium titanate), ZrO (zinc oxide), SnO2 (tin dioxide), Examples thereof include cadmium sulfide (CdS), WO3 (tungsten oxide), BiVO4 (bismuth vanadium oxide), and the like. When such a catalyst is attached to one of a pair of electrodes, immersed in an electrolytic solution, a predetermined voltage is applied to the electrodes and sunlight is irradiated, moisture in the electrolytic solution is electrolyzed on the surface of the catalyst. The externally applied voltage is appropriately set depending on the catalyst. This voltage can be supplied from the fuel cell. Of course, an external power source such as a battery, a solar cell, or a system power source can also be used. The electrolyte and the concentration of the electrolyte can be arbitrarily selected according to the type of semiconductor, the system application, and the like.

  A known type of fuel cell such as a solid polymer electrolyte type or a solid oxide type can be used for the fuel cell portion. Hydrogen obtained in the water splitting section is supplied to the hydrogen electrode of the fuel cell. The hydrogen obtained in the water splitting part is temporarily stored in a hydrogen storage part made of a hydrogen storage alloy or the like, and the pressure is adjusted and supplied to the hydrogen electrode. Oxygen obtained in the water splitting unit can also be temporarily stored in the oxygen storage unit and mixed with the air supplied to the air electrode of the fuel cell. By controlling the amount of oxygen in the air sent to the air electrode, the output characteristics of the fuel cell can be controlled.

  The produced water produced by the fuel cell reaction is collected in the fuel cell part and appropriately added to the electrolyte in the water splitting part. An electrolytic solution circulation path is provided between the water splitting section and the fuel cell section, and the electrolytic solution is circulated in this circulation path, and fuel cell water is added continuously or intermittently to this circulation path. In addition, it is possible to supplement the decrease in water content of the electrolytic solution accompanying water splitting.

Examples of the present invention will be described below. FIG. 1 is a block diagram illustrating a configuration of a solar light utilization system 1 according to the embodiment. The sunlight utilization system 1 includes a water splitting module 3, a fuel cell 20, a heat exchanger 21, and a control circuit 80.
The water splitting module 3 is formed by connecting a plurality of unit cells of the water splitting device. The unit cell of the water splitting apparatus includes an electrode carrying the above-described oxide semiconductor catalyst made of an oxide and an electrolytic cell that is airtight and can transmit sunlight, and the electrode is immersed in the electrolytic cell. The electrolyte is an alkaline (eg, sodium hydroxide), acid (eg, dilute sulfuric acid) or neutral (eg, carbonate) electrolyte. The electrode is connected to a power source and a voltage of 1.23 V or less is applied. The

  In this example, each unit cell is provided with a daily illuminometer 60, and the flow rate of the electrolyte can be controlled in units of cells according to the illuminance. Adjustment of the flow rate of the electrolytic solution is performed by the control device 80 controlling the opening degree of the flow rate control valves V10, V12, and V14. A water level gauge 50 is attached to the water splitting module 3.

A hydrogen line 4, an oxygen line 6, and a circulation line 40 are drawn from the water splitting module 3. Hydrogen gas and oxygen gas obtained by water decomposition in the water splitting module 3 are separated and sent to the hydrogen line 4 and the oxygen line 6, respectively.
The hydrogen fed to the hydrogen line 4 is dehumidified by the dehumidifying film 5 and then accumulated in the hydrogen pressure vessel 31. A pressure gauge 35 is attached to the hydrogen pressure vessel 31. A hydrogen container 32 detachable in parallel with the hydrogen pressure container 31 is provided. For example, when the hydrogen pressure vessel 31 is full, the valve V16 is opened and the hydrogen gas in the hydrogen gas line 4 is stored in the vessel 32. The detachable hydrogen container 32 can be used as a hydrogen gas source for, for example, a fuel cell vehicle, a motorcycle, or a portable generator.

  A city gas reforming line 35 as an external hydrogen source is connected to the hydrogen pressure vessel 31. When the hydrogen derived from the water splitting module 3 is insufficient, hydrogen is supplied from the city gas reforming line 35 as an external hydrogen source to the gas utilization device 70 such as the fuel cell 20, household electric appliances, and gas appliances. The city gas reforming line 35 is provided with a valve V18.

  The hydrogen line 4 on the outlet side of the hydrogen pressure vessel 31 branches into two and is connected to the fuel cell 20 and the gas utilization device 70, respectively. Thereby, the hydrogen in the hydrogen pressure vessel 31 is supplied to the fuel cell 20 and the gas utilization device 70. A valve V <b> 20 is provided in a portion of the hydrogen line 4 from the outlet of the hydrogen pressure vessel 31 to the branch point of the hydrogen line 4. The supply of hydrogen from the hydrogen pressure vessel 31 to the fuel cell 20 and the gas utilization device 70 can be controlled by the valve V20. A valve V22 is provided in the hydrogen line 4 from the branch point to the gas utilization device 70. The supply of hydrogen from the hydrogen pressure vessel 31 to the gas utilization device 70 can be controlled by the valve V22.

  The oxygen line 6 is provided with a dehumidifying film 7. The oxygen line 6 is connected to the oxygen pressure vessel 33, and oxygen in the oxygen line 6 is stored in the oxygen pressure vessel 33. A pressure gauge 36 is attached to the oxygen pressure vessel 33. The oxygen line 6 on the outlet side of the oxygen pressure vessel 33 branches into two and is connected to the fuel cell 20 and the gas utilization device 70, respectively. In the oxygen line 6, a valve V <b> 24 is provided at a portion from the outlet of the oxygen pressure vessel 33 to the branch point of the oxygen line 6. A valve V26 is provided in the oxygen line 6 from the branch point to the fuel cell 20, and a valve V28 is provided in the oxygen line 6 from the branch point to the gas utilization device 70.

The oxygen line 6 on the outlet side of the oxygen pressure vessel 33 is also connected to the electrolyte circulation line 40 via the valve V24. The valve V24 communicates the oxygen pressure vessel 33 with the fuel cell 20 and / or the gas utilization device 70 (hereinafter referred to as a normal operation state), and communicates the oxygen pressure vessel 33 with the circulation line 40 (hereinafter referred to as a normal operation state). , Referred to as a purge state).
By setting the valve V24 to a normal operation state and opening the valve V26, oxygen in the oxygen pressure vessel 33 can be mixed into the supply air to the fuel cell 20 and the output characteristics thereof can be adjusted. The oxygen can be supplied to the gas utilization device 70 by setting the valve V24 to the normal operation state and opening the valve V28.

  In this system 1, the electrolytic solution is circulated between the heat exchanger 21 and the water splitting module 3 via the circulation line 40. The circulating electrolyte can be supplied independently to each unit cell. Further, the circulation line 40 collects the generated water generated in the fuel cell 20 and supplies it to the water splitting module 3 by mixing it with the electrolyte. Thereby, in the water decomposition module 3, the water fall of the electrolyte solution accompanying the electrolysis of water can be supplemented.

  In the middle of the circulation line 40, a circulation pump 41, valves V30 and V32, a filter 45, a liquid temperature sensor 46, and a pressure sensor 47 are installed. Furthermore, an electrolytic solution concentration sensor (pH sensor) 42, an electrolytic solution reserve tank 43, and a water supply unit 44 as an external water source are connected to the circulation line 40. The circulation pump 41 is installed downstream of the water splitting module 3 and upstream of the electrolyte reserve tank 43 in the flow direction of the electrolyte in the circulation line 40 in the normal operation state of the system 1. The valve V <b> 32 is an air release valve and is installed on the downstream side of the circulation pump 41 and the upstream side of the electrolyte reserve tank 43. The liquid temperature sensor 46 is used to measure the temperature of the electrolytic solution in the circulation line 40. The pressure sensor 47 is used to measure the pressure in the circulation line 40 immediately upstream of the circulation pump 41.

  The circulation line 40 and the electrolyte reserve tank 43 are connected via a valve V30. The valve V30 includes a port on the upstream side of the circulation line 40 (hereinafter referred to as an upstream port), a port on the downstream side of the circulation line 40 (hereinafter referred to as a downstream port), and a port on the electrolyte reserve tank 43 side (hereinafter referred to as a port). A tank side port). Among these three ports, the upstream port and the downstream port communicate with each other and the tank side port is closed (hereinafter referred to as a normal operation state), and the upstream port and the downstream port communicate with the tank side port, A state where the upstream port and the downstream port are closed (hereinafter referred to as a purge / restart state), a state where the upstream port and the tank side port are communicated and the downstream port is communicated with the outside air (hereinafter, pump purge state) And a state in which the upstream port and the tank port are in communication with each other and the downstream port is closed (hereinafter referred to as a negative pressure application state). The electrolyte reserve tank 43 is provided with a water level gauge 48 for measuring the electrolyte water level. The water supply unit 44 is connected to the circulation line 40 via the valve V34.

  The fuel cell 20 may be a solid polymer type or a solid oxide type. The air supply line 30 of the fuel cell 20 is provided with a fan 15 and thermometers 17 and 18. The output power of the fuel cell 20 is sold through the DC / AC converter 23 and supplied to the gas utilization device 70. It is also possible to supply power from the fuel cell 20 to the water splitting module 3. When there is no need to store as hydrogen heat or hydrogen, it is possible to provide an energy system that can supply electricity through a switching device directly from a solar cell power source joined in tandem to the back of the water splitting module 3. The fuel cell 20 has a discharge line 78 from the hydrogen electrode side.

  The generated water accumulated in the generated water drain 25 of the fuel cell 20 is supplied to the circulation line 40 via the water supply line 26. Reference sign V36 is a check valve. In this example, the generated water is sucked into the flow of the electrolytic solution in the circulation line 40, but the generated water may be sent into the circulation line 40 by a pump.

  The heat exchanger 21 has a structure that can take in the exhaust heat of the water splitting module 3 and the fuel cell 20. A circulation line 75 for circulating a heat medium such as water is provided between the fuel cell 20 and the heat exchanger 21, and the circulation of the heat medium is controlled by a pump 76 and a valve V38. On the other hand, as described above, the heat exchanger 21 and the water splitting module 3 are connected by the circulation line 40 for the electrolyte. By passing the electrolytic solution through the heat exchanger 21, the temperature of the electrolytic solution can be controlled. By heat exchange, the heat exchanger 21 cools the fuel cell 20 and takes out heat accompanying the fuel cell reaction as hot water to the outside. The amount of exhaust heat from the fuel cell 20 depends on the external output voltage. The amount of heat exhausted from the water splitting module 3 depends on the amount of energy absorbed by infrared light. When heat exchange is not established, the circulation line 40 may be separated from the heat exchanger 21.

  The control circuit 80 calculates the amount of water consumed in the electrolytic solution and the amount of generated water that can be supplied to control the amount of water supplied from the water supply unit 44. The control device 80 controls the valves V <b> 22 and V <b> 28 according to the load of the gas utilization device 70 and also controls the amount of power supplied to the gas utilization device 70 via the DC / AC converter 23.

Control of the amount of water added from the water supply unit 44 will be described based on the flowchart of FIG.
The water decomposition amount A in the water decomposition module 3 can be obtained from, for example, the pressure change in the hydrogen pressure vessel 31 and / or the oxygen pressure vessel 33 (that is, the generation amount of hydrogen and / or oxygen) (FIG. 2, step 101). (Refer to (S101)).
On the other hand, the amount of water accumulated in the drain 25 of the fuel cell 20 can be calculated as follows.
First, the amount Wfc of water generated by the fuel cell reaction is
Wfc = 9.34 × 10 ⁻⁸ × Pe / Vc [kg / sec].
Here, Pe: Output [W] Vc: Cell voltage.

On the other hand, in the fuel cell 20, moisture is taken away with the air exhaust. The carry-away amount Wa can be calculated based on the temperature / humidity of the air sent to the fuel cell 20, the temperature / humidity of the exhausted air, and the amount of air supplied.
Therefore, the amount of water accumulated in the drain 25 of the fuel cell 20 (that is, the amount of generated water that can be supplied) B is B = Wfc−Wa (step 103).
The fuel cell 20 may dry up depending on the operating conditions, and the amount of generated water accumulated in the drain 25 may be less than the amount of water consumed by the water splitting module 3.
Therefore, the control circuit 80 calculates the difference (C) between the amount A of water consumed in the water splitting module 3 and the amount B of generated water that can be supplied (step 105). The valve V34 is controlled (step 107) to supply water to the electrolyte from an external water source.

The operation of the control circuit 80 theoretically keeps the amount of the electrolyte constant.
In this embodiment, a water level meter 50 is provided in the water splitting module 3 to measure the water level in the electrolyte bath (step 109). The control circuit 80 compares the electrolyte level in the electrolyte bath with a predetermined threshold value (step 111), and when the electrolyte level falls outside the predetermined threshold range (step 111: NO), An alarm is activated as an abnormal situation such as water leakage has occurred (step 113).
It is also possible to control the valve V34 so that this water level becomes constant by feedback control based on the water level of the electrolytic cell. However, such control makes it difficult to grasp that an abnormal situation such as water leakage occurs in the system.
The circulation line 40 may be separated from the heat exchanger 21.

  Next, electrolyte solution recovery control according to the present invention will be described with reference to FIG. The electrolytic solution recovery control according to the present invention makes the photoelectrode unnecessary for the electrolytic solution for a long time when sufficient solar energy cannot be secured due to sunset or cloudy weather or when the system is intentionally shut down. This control is performed in order to avoid remaining immersed or to avoid freezing of the electrolyte in the circulation system, and is executed by the control circuit 80.

The control device 80 starts executing the control flow of FIG. 3 by timer control or at predetermined intervals. First, in step 201, the daily illuminance is measured using the daily illuminometer 60. Next, in step 203, it is determined whether or not the electrolyte temperature in the circulation line 40 measured by the liquid temperature sensor 46 is 0 ° C. or less. When the electrolytic solution temperature is 0 ° C. or lower, the electrolytic solution may freeze, and thus the process proceeds to step S207 and the electrolytic solution is recovered. When the electrolyte temperature is higher than 0 ° C., the process proceeds to step S205, and it is determined whether or not the measured daily illuminance is equal to or less than a predetermined illuminance lx. If the measured daily illuminance is greater than the predetermined illuminance lx, it is determined that there is no need to recover the electrolyte, and the process returns to step 201. If the measured daily illuminance is less than or equal to the predetermined illuminance lx, the process proceeds to step 207.
In step 207, power supply from the external power source to the water splitting module 3 is stopped, the operation of the circulation pump 41 is stopped, and the valve V24 on the outlet side of the oxygen pressure vessel 33 is switched from the normal operation state to the purge state. As a result, the oxygen line 6 on the outlet side of the oxygen pressure vessel 33 communicates with the circulation line 40, and the oxygen line 6 does not communicate with the fuel cell 20 and the gas utilization device 70.

  Next, in step 209, the valve V30 connecting the electrolyte reserve tank 43 and the circulation line 40 is switched from the normal operation state to the purge / restart state. As a result, the high-pressure oxygen accumulated in the oxygen pressure vessel pushes out the electrolytic solution in the circulation line 40 and the water splitting module 3 into the electrolytic solution reserve tank 43.

  Next, at step 211, based on the measurement by the water level gauge 48 installed in the electrolyte reserve tank 43, it is determined whether or not the amount of electrolyte in the electrolyte reserve tank 43 has become a predetermined amount or more. This predetermined amount is set in advance as an amount when the electrolytic solution is completely recovered from the circulation path. If it is determined in step 211 that the amount of the electrolyte in the electrolyte reserve tank 43 is equal to or greater than the predetermined amount, it is determined that the recovery of the electrolyte from the circulation path is completed, and the process proceeds to step 213 where the valve V30 is turned on. Switching to the negative pressure application state, the circulation pump 41 is operated. Thereafter, the process proceeds to step 223.

If it is determined in step 211 that the amount of the electrolyte in the electrolyte reserve tank 43 is less than the predetermined amount, the process proceeds to step 215, and it is determined whether or not the pressure in the oxygen pressure vessel 33 is equal to or lower than atmospheric pressure. If it is determined that the pressure in the oxygen pressure vessel 33 is higher than the atmospheric pressure, the control returns to step 211 and continues to push out the electrolyte solution by the oxygen pressure.
If it is determined in step 215 that the pressure in the oxygen pressure vessel 33 is equal to or lower than the atmospheric pressure, the electrolyte cannot be pushed out by the pressure in the oxygen pressure vessel 33. Therefore, the process proceeds to step 217, and the valve V30 is pumped. Switching to the purge state, the circulation pump 41 is operated, and thereby the electrolytic solution is recovered. At this time, a check valve may be provided between the oxygen line 6 and the circulation line 40 so that the electrolyte does not flow backward from the circulation line 40 to the oxygen line 6.

In the next step 219, as in step 211, it is determined whether or not the amount of the electrolyte in the electrolyte reserve tank 43 has become a predetermined amount or more. Step 219 is repeated until the amount of electrolyte in the electrolyte reserve tank 43 reaches a predetermined amount or more.
If it is determined in step 219 that the amount of the electrolyte in the electrolyte reserve tank 43 has reached a predetermined amount or more, it is determined that the recovery of the electrolyte from the circulation path has been completed, and the process proceeds to step 221 where negative pressure is applied to the valve V30. Switch to state. Next, the process proceeds to step 223.
In step 223, the valve V32 is opened. In this state, when the circulation pump 41 continues to operate, the inside of the electrolyte circulation path including the circulation line 40 becomes negative pressure.

Next, in step 225, it is determined based on the measurement by the pressure sensor 47 whether or not the pressure P1 inside the circulation line 40 has become lower than the predetermined pressure α within the predetermined time T. If it is determined that the pressure P1 inside the circulation line 40 has become smaller than the predetermined pressure α within the predetermined time T, the process proceeds to step 229, the circulation pump 41 is stopped, and the valve V32 is closed in step 231. Thus, the control of FIG. 3 is finished.
If the pressure P1 in the circulation line 40 does not become lower than α even after the predetermined time T has elapsed in step 225, it is determined that an abnormality such as leakage in the circulation system or performance deterioration of the circulation pump 41 has occurred. Proceeding to 227, all the valves are operated to the safe side, and all the power sources of the system 1 are stopped, and an abnormality notification (alarm) is performed.

  Next, the control when the system 1 is restarted after the electrolytic solution is collected in the electrolytic solution reserve tank 43 by the control of FIG. 3 will be described with reference to FIG. The control flow of FIG. 4 is executed by the control circuit 80 based on timer settings and / or at predetermined intervals. First, in step 301, the daily illuminance is measured using the daily illuminometer 60. In the next step 303, it is determined whether or not the measured daily illuminance is greater than or equal to a predetermined illuminance lx. When the measured daily illuminance is lower than the predetermined illuminance lx, the process returns to step 301 and the daily illuminance is measured again. If it is determined in step 303 that the daily illuminance is greater than or equal to the predetermined illuminance lx, the process proceeds to step 305, where it is determined whether or not the outside air temperature measured by the outside air temperature sensor (not shown) is higher than 0 ° C. When the measured outside air temperature is 0 ° C. or lower, there is a possibility of destruction of the equipment due to freezing of the electrolytic solution. Therefore, the process does not proceed to restart of the system 1 but returns to step 301 again to measure the daily illuminance. If it is determined that the outside air temperature is higher than 0 ° C., the process proceeds to step 307, the valve V24 is switched to the normal operation state, the valve V30 is switched to the purge / restart state, and the circulation pump 41 is operated.

  Since the inside of the circulation line 40 after the electrolytic solution recovery is negative pressure by the control of FIG. 3, the electrolytic solution is supplied from the inside of the electrolytic solution reserve tank 43 to the circulation line 40 by switching the valve 30 to the purge / restart state. The circulation line 40 can be quickly filled with the electrolyte solution, and thus the system 1 can be restarted quickly. In the next step 309, based on the measurement by the water level meter 50, it is determined whether or not the water level of the electrolyte in the water splitting module 3 has become equal to or higher than a predetermined water level β set during normal operation. Step 309 is repeated until the water level of the electrolyte in the water splitting module 3 becomes equal to or higher than the predetermined water level β. When the water level becomes equal to or higher than the predetermined water level β, the process proceeds to the next step 311. In step 311, power supply to the water splitting module 3 is started, and the valve V30 is switched to a normal operation state. Thus, the normal operation including water splitting is started, thereby completing the control in FIG.

In the control of FIG. 3 of the above embodiment, the illuminance measured by the sunshine clock 60 and the electrolyte temperature measured by the liquid temperature sensor 46 are used as execution conditions for the control for recovering the electrolyte after step 207. However, the present invention is not limited to this.
For example, instead of this, it may be determined that the execution condition of the electrolyte solution recovery control is satisfied when a predetermined time comes. The predetermined time may be a fixed time, or may be configured such that the sunset time (or a time in the vicinity thereof) based on daily calendar data provided by an organization such as the National Astronomical Observatory is updated daily as the predetermined time. By doing so, the electrolytic solution can be collected when water splitting by using sunlight becomes difficult or impossible due to sunset.

  Further, instead of or in addition to the above execution conditions, weather information provided from a meteorological observatory or a weather information providing service company may be used as an execution condition for electrolyte recovery control. According to such a configuration, when the sunshine is reduced due to cloudy or rainy weather and water decomposition by using sunlight is not sufficiently performed, or when such a situation is expected, the electrolytic solution is recovered and the photoelectrode It is possible to avoid a situation in which the film is unnecessarily immersed in the electrolytic solution. Alternatively, when the electrolytic solution is expected to be frozen due to snowfall or a decrease in temperature, the electrolytic solution can be collected to prevent a malfunction of the device due to the freezing of the electrolytic solution.

  Furthermore, execution of the electrolytic solution recovery control in and after S207 may be started by an instruction input from the user. Thereby, it is possible to avoid a situation where the photoelectrode is continuously immersed in the electrolytic solution unnecessarily by collecting the electrolytic solution during a period in which water splitting by the solar system is not performed. The instruction input may be performed on the control circuit 80, or a device for input may be provided separately.

Note that the control for recirculating the electrolyte and starting normal operation after S307 in FIG. 4 is also started at a predetermined time (a fixed time, a sunrise time based on calendar data, or a time in the vicinity thereof). Or execution may be started by a user instruction input, or weather information may be used as an execution condition.
In the above embodiment, the case where a power source for applying a voltage between electrodes is connected has been described. However, if a photo semiconductor catalyst capable of decomposing water into hydrogen and oxygen with only solar energy is used, it is not necessary to connect a power source.
In the above embodiment, when the electrolyte reserve tank 43 may be included in the electrolyte circulation path during normal operation of the system 1, the purge / restart state is used instead of the normal operation state of the valve V30. Also good.
Further, means for blocking communication between the water splitting module 3 and the hydrogen line 4 may be provided during a period other than during normal operation of the system 1.

  The present invention is not limited to the description of the embodiment and examples of the invention. Various modifications are also included in the present invention as long as those skilled in the art can easily conceive without departing from the scope of the claims.

DESCRIPTION OF SYMBOLS 1 Solar power utilization system 3 Water splitting module 20 Fuel cell 21 Heat exchanger 31 Hydrogen pressure vessel 33 Oxygen pressure vessel 35, 36 Pressure gauge V24, V30, V32 Valve 40 Circulation line 41 Circulation pump 43 Electrolyte reserve tank 46 Liquid temperature sensor 47 Pressure sensor 48, 50 Water level meter 60 Day light meter 80 Control circuit

Claims (16)

A water-splitting part having a pair of electrodes carrying a photo-semiconductor catalyst on one side and decomposing an electrolyte solution using solar energy irradiated to the photo-semiconductor catalyst;
An oxygen storage unit for storing oxygen generated in the water splitting unit;
An electrolytic solution storage unit for storing the electrolytic solution;
A fluid passage connecting the oxygen storage unit, the water decomposition unit, and the electrolyte storage unit;
A recovery condition determination unit that determines whether or not a predetermined recovery condition for recovering the electrolytic solution from the water splitting unit to the electrolytic solution storage unit is satisfied,
When the recovery condition determination unit determines that the recovery condition is satisfied, the electrolytic solution is pushed out from the water decomposition unit by the pressure of oxygen stored in the oxygen storage unit, and the electrolytic solution is passed through the fluid passage. A solar light utilization system characterized by being collected in a storage unit. A pressure detection unit for detecting the pressure in the oxygen storage unit;
A fluid pump provided in the fluid passage,
When the recovery condition determination unit determines that the recovery condition is satisfied and the pressure in the oxygen storage unit detected by the pressure detection unit is equal to or lower than a predetermined pressure, the fluid pump is operated to The solar light utilization system according to claim 1, wherein the electrolytic solution is recovered from the decomposition unit into the electrolytic solution storage unit.   The solar light utilization system according to claim 2, wherein after the recovery of the electrolytic solution is completed, the fluid pump is operated to make the inside of the fluid passage have a negative pressure. A daily illuminance detector for detecting the daily illuminance for the electrode,
The solar light utilization system according to any one of claims 1 to 3, wherein the collection condition determination unit determines that the collection condition is satisfied when the daily illuminance is equal to or less than a predetermined illuminance. .   The solar light utilization system according to any one of claims 1 to 3, wherein the recovery condition determination unit determines that the recovery condition is satisfied when a predetermined time comes. A recovery instruction input unit for inputting an instruction to recover the electrolyte solution,
The recovery condition determination unit determines that the recovery condition is satisfied when an instruction to recover the electrolyte is input to the recovery instruction input unit. The solar light utilization system in any one of -3. A weather information input unit for receiving weather information,
The sun according to any one of claims 1 to 3, wherein the recovery condition determination unit determines that the recovery condition is satisfied when the weather information input unit receives predetermined weather information. Light utilization system. A temperature detector for detecting the temperature of the electrolyte solution,
The said collection condition judgment part judges that the said collection condition was satisfied when the temperature of the said electrolyte solution detected by the said temperature detection part is below predetermined temperature, The any one of Claims 1-3 characterized by the above-mentioned. The solar power utilization system described in Crab. A control method for a solar light utilization system having a pair of electrodes carrying a light semiconductor catalyst on one side and decomposing an electrolyte using solar energy irradiated to the light semiconductor catalyst,
Storing oxygen generated in the water splitting unit in an oxygen storage unit;
A determination step of determining whether or not a predetermined recovery condition for recovering the electrolytic solution from the water splitting unit to the electrolytic solution storage unit is satisfied;
When it is determined that the recovery condition is satisfied, the step of pushing out the electrolytic solution from the water splitting unit by the pressure of oxygen stored in the oxygen storage unit and recovering the electrolytic solution to the electrolytic solution storage unit through a fluid passage; And a control method. Detecting the pressure in the oxygen reservoir;
When the determination step determines that the recovery condition is satisfied, and the pressure in the oxygen storage unit detected by the pressure detection unit is equal to or lower than a predetermined pressure, a fluid pump provided in the fluid passage is provided. The control method according to claim 9, further comprising a step of recovering the electrolyte solution from the water splitting unit to the electrolyte storage unit by being operated.   The control method according to claim 10, further comprising the step of setting the inside of the fluid passage to a negative pressure by operating the fluid pump after the recovery of the electrolytic solution is completed. Detecting a daily illuminance for the electrode,
The control method according to claim 9, wherein the determining step determines that the collection condition is satisfied when the daily illuminance is equal to or less than a predetermined illuminance.   The control method according to claim 9, wherein the determination step determines that the collection condition is satisfied when a predetermined time comes. Inputting an instruction to collect the electrolyte solution,
The determination step determines that the recovery condition is satisfied when an instruction to recover the electrolytic solution is input to the recovery instruction input unit. The control method in any one of. A weather information receiving step for receiving weather information,
The control method according to claim 9, wherein the determination step determines that the recovery condition is satisfied when predetermined weather information is received in the weather information reception step. A temperature detection step of detecting the temperature of the electrolyte solution,
The determination step determines that the recovery condition is satisfied when the temperature of the electrolytic solution detected in the temperature detection step is equal to or lower than a predetermined temperature. The control method described.

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