Fuel cell system and control method for fuel cell system

Abstract

To effectively use surplus power generated by a fuel cell, while maintaining the power generation efficiency of the fuel cell.SOLUTION: A fuel cell system 100 is provided which comprises: a fuel cell 10 that causes fuel gas supplied to a fuel electrode 12 and oxidizing gas supplied to an air electrode 11 to react with each other to generate power; an electrolysis cell 20 that electrolyzes water vapor supplied to a hydrogen electrode 22 to generate hydrogen; a converter 40 that converts DC power generated by the fuel cell 10 into AC power and outputs the AC power to a power system PS; and a control unit 90 that performs control to increase a current consumption value of the electrolysis cell 20 when the AC power obtained by converting the DC power generated by the fuel cell 10 is larger than a power demand requested from the power system PS.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present disclosure relates to a fuel cell system and a method for controlling a fuel cell system. [Background technology]

[0002] Fuel cells, which generate electricity by chemically reacting a fuel gas with an oxidizing gas, have excellent characteristics such as excellent power generation efficiency and environmental friendliness. Among these, solid oxide fuel cells (hereinafter referred to as "SOFC") use ceramics such as yttria-stabilized zirconia ceramics as an electrolyte, and generate electricity by reacting hydrogen, city gas, natural gas, petroleum, methanol, gasification gas produced by gasification equipment from carbon-containing raw materials, biomass gas made from biomass, and other gases as fuel gas in a power generation chamber with a high-temperature atmosphere of approximately 700°C to 1000°C (see, for example, Patent Document 1).

[0003] Patent Document 1 discloses an SOFC system that combines an SOFC with a turbocharger. In Patent Document 1, exhaust fuel gas discharged from the SOFC is combusted in a combustor, and the combustion gas is supplied to a turbine to rotate the turbine. A compressor connected to the turbine compresses oxidizing gas and supplies it to the air electrode. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Patent No. 6922016 Summary of the Invention [Problem to be solved by the invention]

[0005] In the fuel cell disclosed in Patent Document 1 and the like, when the generated electricity is supplied to a power grid to which other power sources (for example, power sources generated by renewable energy such as solar or wind power) are connected, the power that the fuel cell must output to meet the power demand of the power grid fluctuates according to changes in the power generated by the other power sources.

[0006] For example, if the power output of the fuel cell decreases, the power output by the fuel cell needs to be reduced, but if the temperature in the generating chamber drops as a result of reducing the fuel cell output, the power generation efficiency will decrease. Furthermore, if the fuel cell is operated to maintain the temperature in the generating chamber, surplus power will be generated compared to the power that the fuel cell should output.

[0007] The present disclosure has been made in consideration of these circumstances, and aims to provide a fuel cell system and a control method for a fuel cell system that can effectively utilize surplus electricity generated by a fuel cell while maintaining the power generation efficiency of the fuel cell. [Means for solving the problem]

[0008] In order to solve the above problems, the present disclosure employs the following means. The fuel cell system according to the present disclosure comprises a fuel cell having an air electrode and a fuel electrode, which generates electricity by reacting a fuel gas supplied to the fuel electrode with an oxidizing gas supplied to the air electrode; an electrolysis cell having an oxygen electrode and a hydrogen electrode, which generates hydrogen by steam electrolysis of water vapor supplied to the hydrogen electrode; a first conversion unit which converts DC power generated by the fuel cell into AC power and outputs the AC power to a power grid; and a control unit which controls the electrolysis cell to increase its current consumption value when the AC power converted from the DC power generated by the fuel cell is greater than the power demand required by the power grid.

[0009] In a control method for a fuel cell system according to the present disclosure, the fuel cell system includes a fuel cell having an air electrode and an anode, and generating electricity by reacting a fuel gas supplied to the anode with an oxidizing gas supplied to the air electrode; an electrolytic cell having an oxygen electrode and a hydrogen electrode, and generating hydrogen by steam electrolysis of water vapor supplied to the hydrogen electrode; and a first conversion unit that converts DC power generated by the fuel cell into AC power and outputs the AC power to a power grid, and includes a first control step of controlling the electrolytic cell to increase its current consumption when the AC power converted from the DC power generated by the fuel cell is greater than the power demand required by the power grid. [Effects of the Invention]

[0010] According to the present disclosure, it is possible to provide a fuel cell system and a control method for a fuel cell system that can effectively utilize surplus power generated by a fuel cell while maintaining the power generation efficiency of the fuel cell. [Brief explanation of the drawings]

[0011] [Figure 1] 1 is a configuration diagram showing a power system of a fuel cell system according to an embodiment of the present disclosure. [Figure 2] 1 is a configuration diagram showing a gas system of a fuel cell system according to an embodiment of the present disclosure. [Figure 3] FIG. 1 is a cross-sectional view illustrating an example of a solid oxide electrochemical cell according to an embodiment of the present disclosure. [Figure 4] FIG. 1 is a perspective view illustrating one embodiment of a solid oxide electrochemical cell module according to an embodiment of the present disclosure. [Figure 5] FIG. 1 is a cross-sectional view of a solid oxide electrochemical cell cartridge according to an embodiment of the present disclosure. [Figure 6] FIG. 2 is a cross-sectional view showing an example of the arrangement of fuel cells and electrolysis cells in an electrochemical cell cartridge. [Figure 7] 4 is a flowchart illustrating a control method for a fuel cell system according to an embodiment of the present disclosure. [Figure 8]8 is a flowchart showing the hydrogen demand following mode of FIG. 7. [Figure 9] 8 is a flowchart showing the high-efficiency load following operation mode of FIG. 7. [Figure 10] 8 is a flowchart showing the steam electrolysis operation mode of FIG. 7. [Figure 11] 10 is a graph showing the relationship between the change in load current and the power of the fuel cell in a high-efficiency load following operation mode. [Figure 12] 10 is a graph showing the relationship between the change in load current of the fuel cell and the temperature of the generating chamber in the high-efficiency load following operation mode. [Figure 13] 10 is a graph showing the relationship between the change in load current and the power of the fuel cell in the steam electrolysis operation mode and the hydrogen demand following mode. [Figure 14] 10 is a graph showing the relationship between the change in load current of the fuel cell and the temperature of the power generating chamber in the steam electrolysis operation mode and the hydrogen demand following mode. [Figure 15] 10 is a graph showing time series changes in power and generator room temperature in a high-efficiency load following operation mode. [Figure 16] 1 is a graph showing time series changes in power and power-generating room temperature in a steam electrolysis operation mode. [Figure 17] 10 is a graph showing time series changes in power and generator room temperature in hydrogen demand following mode. DETAILED DESCRIPTION OF THE INVENTION

[0012] In the following, for the sake of convenience, the positional relationship of each component described using the expressions "upper" and "lower" with respect to the plane of the paper indicates the vertically upper side and the vertically lower side, respectively. Furthermore, in this embodiment, for components that can obtain similar effects in the vertical direction and the horizontal direction, the vertical direction on the plane of the paper is not necessarily limited to the vertically upper and lower directions, but may correspond to, for example, a horizontal direction perpendicular to the vertical direction.

[0013] A fuel cell system 100 according to an embodiment of the present disclosure will now be described with reference to the drawings. Fig. 1 is a configuration diagram showing the power system of the fuel cell system 100 according to this embodiment.

[0014] As shown in FIG. 1, the fuel cell system 100 of this embodiment includes a fuel cell 10, an electrolytic cell 20, an auxiliary device 30, a converter (first conversion unit) 40, a converter (second conversion unit) 45, a switching unit (first switching unit) S1, a switching unit (second switching unit) S2, a switching unit S3, and a control unit 90.

[0015] The fuel cell 10 has an air electrode 11 and a fuel electrode 12, and is a device that generates electricity by causing a reaction between a fuel gas FG supplied to the fuel electrode 12 and air (oxidizing gas) supplied to the air electrode 11. The electrolysis cell 20 has an oxygen electrode 21 and a hydrogen electrode 22, and is a device that electrolyzes water vapor supplied to the hydrogen electrode 22 to generate hydrogen. The auxiliary equipment 30 is a general term for various devices (compressors, blowers, valves, heat exchangers, etc.) that assist the operation of the fuel cell system 100, and operates using a portion of the electricity generated by the fuel cell 10 or AC power supplied from the power system PS.

[0016] The converter 40 is a device that converts the DC power generated by the fuel cell 10 into AC power and outputs it to the power system PS. The converter 45 is a device that converts AC power supplied from the power system PS or the fuel cell 10 into DC power and outputs it to the electrolytic cell 20 .

[0017] The switching unit S1 is a device (switch) that switches between a supply state (first supply state) in which the DC power generated by the fuel cell 10 is supplied to the electrolysis cell 20, and a cut-off state (first cut-off state) in which the DC power generated by the fuel cell 10 is not supplied to the electrolysis cell 20. The switching unit S2 is a device (switch) that switches between a supply state (second supply state) in which the DC power generated by the DC power generation unit 200 is supplied to the electrolytic cell 20, and a cut-off state (second cut-off state) in which the DC power generated by the DC power generation unit 200 is not supplied to the electrolytic cell 20.

[0018] The DC power generation unit 200 is a device that converts renewable energy such as solar power or wind power into DC power. The DC power generated by the DC power generation unit 200 is converted into AC power by a converter 210 and output to the power grid PS. When the energy source of the DC power generation unit 200 is natural energy such as solar power or wind power, the DC power generated by the DC power generation unit 200 varies greatly depending on the state of the natural energy, such as the weather and the time of day.

[0019] The switching unit S3 is a device (switch) that switches between a supply state in which DC power is supplied from the converter 45 to the electrolytic cell 20 and a cut-off state in which DC power is not supplied from the converter 45 to the electrolytic cell 20.

[0020] The control unit 90 is a device that controls each part of the fuel cell system 100, including the fuel cell 10, the electrolytic cell 20, the auxiliary equipment 30, the converter 40, the converter 45, the switching unit S1, the switching unit S2, and the switching unit S3.

[0021] Next, a gas system of a fuel cell system 100 according to an embodiment of the present disclosure will be described with reference to the drawings. Fig. 2 is a configuration diagram showing the gas system of a fuel cell system 100 according to an embodiment of the present disclosure. Note that, since the DC power generation unit 200 is connected only to the electrical system, the DC power generation unit 200 is not shown in Fig. 2, which shows the gas system.

[0022] As shown in FIG. 2, the fuel cell system 100 according to this embodiment includes a fuel cell 10, an electrolytic cell 20, a regenerative heat exchanger 50, a cooler 60, a hydrogen concentration meter 70, blowers 81, 82, and 83, on-off valves 91 and 92, and control valves 93, 94, 95, and 96.

[0023] The regenerative heat exchanger 50 is a device that exchanges heat between air supplied by a blower 81 and flowing through an air line L1, and air discharged from the air electrode 11 and oxygen electrode 21 and flowing through an air line L2. The amount of air supplied from the air line L1 to the regenerative heat exchanger 50 and the amount of air supplied from the air line L1 to a bypass line L3 without being supplied to the regenerative heat exchanger 50 are adjusted by the apertures of control valves 94, 95, and the air flows join downstream of the regenerative heat exchanger 50. The air heated to a predetermined temperature by this flow rate distribution adjustment is supplied to the air electrode 11 and oxygen electrode 21.

[0024] The control unit 90 adjusts the opening of the control valve 93 to control the amount of fuel gas FG supplied from the fuel gas line L4 to the fuel electrode 12 of the fuel cell 10. Exhaust fuel gas containing unreacted fuel components such as hydrogen is discharged from the fuel electrode 12 to the fuel gas line L5. Hydrogen produced at the hydrogen electrode 22 of the electrolysis cell 20 is also discharged to the fuel gas line L5.

[0025] A portion of the mixed gas of exhaust fuel gas and hydrogen pressurized by the blower 82 in the fuel gas line L5 is recirculated from the recirculation line L6 to the fuel gas line L4. The recirculation amount of the mixed gas of exhaust fuel gas and hydrogen introduced into the recirculation line L6 is adjusted by the aperture of the control valve 96.

[0026] A portion of the mixed gas of exhaust fuel gas and hydrogen, pressurized by the blower 82 in the fuel gas line L5, is guided to the recirculation line L6, and the remainder is supplied to the cooler 60. The cooler 60 cools the gas guided from the fuel gas line L5 with cooling water to condense the moisture contained in the gas, which is then discharged to the water line L7 and recovered as drain. The hydrogen-containing gas from which the moisture has been removed is guided to the fuel gas line L8. The concentration of hydrogen contained in the gas flowing through the fuel gas line L8 is detected by the hydrogen concentration meter 70 and transmitted to the control unit 90.

[0027] When the on-off valves 91 and 92 are closed, the entire amount of the hydrogen-containing gas introduced into the fuel gas line L8 is supplied to an external hydrogen storage device (not shown). When the on-off valves 91 and 92 are open, part of the hydrogen-containing gas is introduced into the hydrogen storage device, and the other part is pressurized by the blower 83 and introduced from the fuel gas line L9 to the fuel gas line L4, and supplied to the fuel electrode 12 of the fuel cell 10.

[0028] The water line L7 supplies pure water that becomes steam that is electrolyzed at the hydrogen electrode 22 of the electrolytic cell 20. The pure water supplied to the water line L7 becomes steam in the recirculation line L6. The steam in the recirculation line L6 is led to the fuel gas line L4. The steam mixed with the fuel gas FG in the fuel gas line L4 is led to the hydrogen electrode 22 of the electrolytic cell 20 via the supply line L10.

[0029] Next, with reference to Figure 3, a solid oxide electrochemical cell will be described that is used as the air electrode 11 and fuel electrode 12 in a fuel cell 10, and as the oxygen electrode 21 and hydrogen electrode 22 in an electrolysis cell 20. Figure 3 is a cross-sectional view showing an example of a solid oxide electrochemical cell according to one embodiment of the present disclosure. In the following description, a first electrode 109 corresponds to the fuel electrode 12 of the fuel cell 10, and a second electrode 113 corresponds to the air electrode 11 of the fuel cell 10. Furthermore, the first electrode 109 corresponds to the hydrogen electrode 22 of the electrolysis cell 20, and the second electrode 113 corresponds to the oxygen electrode 21 of the electrolysis cell 20.

[0030] As an example of this embodiment, a cylindrical cell stack using a substrate tube will be described with reference to FIG. 3. When a substrate tube is not used, for example, an electrode may be formed thick and used as the substrate tube, and the use of a substrate tube is not limited. Furthermore, although the substrate tube in this embodiment is described as having a cylindrical shape, the substrate tube may be tubular and does not necessarily have to have a circular cross section, and may have an elliptical cross section, for example. A cell stack such as a flat tubular cylinder in which the peripheral side surface of a cylinder is crushed vertically may also be used.

[0031] The cell stack 101 includes, for example, a cylindrical base tube 103, a plurality of electrochemical unit cells 105 formed on the outer peripheral surface of the base tube 103, and an interconnector 107 formed between adjacent electrochemical unit cells 105. Each electrochemical unit cell 105 is formed by stacking a first electrode 109, a solid electrolyte membrane 111, and a second electrode 113. The cell stack 101 also includes a lead film 115 electrically connected via the interconnector 107 to the second electrode 113 of the electrochemical unit cell 105 formed at one end of the plurality of electrochemical unit cells 105 formed on the outer peripheral surface of the base tube 103 in the axial direction of the base tube 103, and a lead film 115 electrically connected to the first electrode 109 of the electrochemical unit cell 105 formed at the other end.

[0032] The substrate tube 103 is made of a porous material, and its main component is, for example, CaO-stabilized ZrO2 (CSZ), a mixture of CSZ and nickel oxide (NiO) (CSZ+NiO), Y2O3-stabilized ZrO2 (YSZ), or MgAl2O4. The substrate tube 103 supports the electrochemical unit cell 105, the interconnector 107, and the lead film 115, and also diffuses the fuel gas supplied to the inner peripheral surface of the substrate tube 103 through the pores of the substrate tube 103 to the first electrode 109 formed on the outer peripheral surface of the substrate tube 103.

[0033] The first electrode 109 is made of a composite oxide of Ni and a zirconia-based electrolyte material, and for example, Ni / YSZ is used. The thickness of the first electrode 109 is 50 μm to 250 μm, and the first electrode 109 may be formed by screen-printing a slurry. In this case, the Ni contained in the first electrode 109 has a catalytic effect on the fuel gas. This catalytic effect causes a reaction with the fuel gas supplied via the base tube 103, for example, a mixed gas of methane (CH4) and steam, and reforms it into hydrogen (H2) and carbon monoxide (CO).

[0034] The first electrode 109 reacts with the hydrogen (H) and carbon monoxide (CO) obtained by reforming and oxygen ions (O) supplied through the solid electrolyte membrane 111. 2-) near the interface with the solid electrolyte membrane 111 to produce water (H2O) and carbon dioxide (CO2). The electrochemical unit cell 105 generates electricity using electrons released from the oxygen ions. Fuel gases that can be supplied to the first electrode 109 of the solid oxide electrochemical cell include hydrocarbon gases such as hydrogen (H2), carbon monoxide (CO), and methane (CH4), city gas, and natural gas, as well as gasification gas produced by gasification equipment from carbon-containing materials such as petroleum, methanol, and coal, and biogas made from biomass.

[0035] The solid electrolyte membrane 111 is mainly made of YSZ, which has gas-tightness and high oxygen ion conductivity at high temperatures. The solid electrolyte membrane 111 is formed by converting oxygen ions (O 2 -) to the first electrode 109. The thickness of the solid electrolyte film 111 located on the surface of the first electrode 109 is 10 μm to 100 μm, and the solid electrolyte film 111 may be formed by screen printing a slurry.

[0036] The second electrode 113 is made of, for example, LaSrMnO3-based oxide or LaCoO3-based oxide, and the second electrode 113 is formed by screen printing or by applying a slurry to the second electrode 113 using a dispenser. The second electrode 113 dissociates oxygen in an oxidizing gas such as air supplied near the interface with the solid electrolyte membrane 111, and combines with electrons supplied from the outside to generate oxygen ions (O 2- ) is generated.

[0037] The second electrode 113 can also have a two-layer structure. In this case, the layer (intermediate layer) on the solid electrolyte membrane 111 side exhibits high ionic conductivity and is made of a material with excellent catalytic activity. The layer (conductive layer) on the intermediate layer may be made of a perovskite-type oxide represented by Sm-doped ceria or Sr- and Ca-doped LaMnO3. This can further improve power generation performance. An oxidizing gas is a gas containing approximately 15% to 30% oxygen. Typically, air is suitable, but other gases such as a mixture of combustion exhaust gas and air, or a mixture of oxygen and air can also be used.

[0038] The interconnector 107 is made of M such as SrTiO3. 1-x L x The interconnector 107 is made of a conductive perovskite oxide represented by TiO3 (M is an alkaline earth metal element, and L is a lanthanoid element), and the slurry is screen-printed. The interconnector 107 is a dense film that prevents the fuel gas and the oxidizing gas from mixing. The interconnector 107 also has stable durability and electrical conductivity in both oxidizing and reducing atmospheres. This interconnector 107 electrically connects the second electrode 113 of one electrochemical unit cell 105 to the first electrode 109 of the other electrochemical unit cell 105 in adjacent electrochemical unit cells 105, thereby connecting the adjacent electrochemical unit cells 105 in series.

[0039] The lead film 115 is required to have electronic conductivity and a thermal expansion coefficient close to that of the other materials constituting the cell stack 101. Therefore, a composite material of Ni and a zirconia-based electrolyte material, such as Ni / YSZ, or an M material such as an SrTiO3-based material is used. 1-x L x It is made of TiO3 (M is an alkaline earth metal element, and L is a lanthanoid element). This lead film 115 guides the DC power generated by the multiple electrochemical unit cells 105 connected in series by the interconnectors 107 to the vicinity of the end of the cell stack 101.

[0040] Next, an electrochemical cell cartridge and an electrochemical cell module according to this embodiment will be described with reference to Figures 4 and 5. Figure 4 is a perspective view showing one aspect of a solid oxide electrochemical cell module according to an embodiment of the present disclosure. Figure 5 is a cross-sectional view showing a solid oxide electrochemical cell cartridge according to an embodiment of the present disclosure.

[0041] As shown in Fig. 4, the electrochemical cell module 201 includes, for example, a plurality of electrochemical cell cartridges 203 and a module container 205 that houses the plurality of electrochemical cell cartridges 203. Although Fig. 4 illustrates a cylindrical cell stack 101, it may also be, for example, a flat cell stack. The electrochemical cell module 201 also includes a fuel gas supply pipe 207, a plurality of fuel gas supply branch pipes 207a, a fuel gas discharge pipe 209, and a plurality of fuel gas discharge branch pipes 209a. The electrochemical cell module 201 also includes an oxidizing gas supply pipe (not shown), an oxidizing gas supply branch pipe (not shown), an oxidizing gas discharge pipe (not shown), and a plurality of oxidizing gas discharge branch pipes (not shown).

[0042] The fuel gas supply pipe 207 is provided inside the module container 205 and is connected to a fuel gas supply unit that supplies fuel gas with a predetermined gas composition and a predetermined flow rate corresponding to the power generation amount of the electrochemical cell module 201, and is also connected to multiple fuel gas supply branch pipes 207a. This fuel gas supply pipe 207 branches and guides the fuel gas supplied from the fuel gas supply unit at a predetermined flow rate to the multiple fuel gas supply branch pipes 207a. Furthermore, the fuel gas supply branch pipe 207a is connected to the fuel gas supply pipe 207 and is also connected to the multiple electrochemical cell cartridges 203. This fuel gas supply branch pipe 207a guides the fuel gas supplied from the fuel gas supply pipe 207 to the multiple electrochemical cell cartridges 203 at a substantially uniform flow rate, thereby substantially uniforming the power generation performance of the multiple electrochemical cell cartridges 203.

[0043] The fuel gas discharge header 219 is an area surrounded by the lower casing 229b and lower tube plate 225b of the electrochemical cell cartridge 203, and is connected to a fuel gas discharge branch pipe 209a (not shown) via a fuel gas discharge hole 231b provided in the lower casing 229b. The multiple cell stacks 101 are joined to the lower tube plate 225b with a seal member 237b, and the fuel gas discharge header 219 collects exhaust fuel gas that passes through the insides of the base tubes 103 of the multiple cell stacks 101 and is supplied to the fuel gas discharge header 219, and guides it to the fuel gas discharge branch pipe 209a via the fuel gas discharge hole 231b.

[0044] An oxidizing gas with a predetermined gas composition and flow rate corresponding to the power generation amount of the electrochemical cell module 201 is branched into an oxidizing gas supply branch pipe and supplied to the plurality of electrochemical cell cartridges 203. The oxidizing gas supply header 221 is an area surrounded by the lower casing 229b, lower tube plate 225b, and lower insulator 227b of the electrochemical cell cartridge 203, and is connected to an oxidizing gas supply branch pipe (not shown) through an oxidizing gas supply hole 233a provided on the side surface of the lower casing 229b. The oxidizing gas supply header 221 guides the oxidizing gas at a predetermined flow rate, supplied from the oxidizing gas supply branch pipe (not shown) through the oxidizing gas supply hole 233a, to the power generation chamber 215 via an oxidizing gas supply gap 235a (described later).

[0045] The oxidizing gas discharge header 223 is an area surrounded by the upper casing 229a, upper tube plate 225a, and upper heat insulator 227a of the electrochemical cell cartridge 203, and is connected to an oxidizing gas discharge branch pipe (not shown) through oxidizing gas discharge holes 233b provided on the side surface of the upper casing 229a. The oxidizing gas discharge header 223 guides the exhaust oxidizing gas supplied to the oxidizing gas discharge header 223 from the power generating chamber 215 through an oxidizing gas discharge gap 235b (described later) to the oxidizing gas discharge branch pipe (not shown) through the oxidizing gas discharge holes 233b.

[0046] The upper tube plate 225a is fixed to the side plate of the upper casing 229a between the top plate of the upper casing 229a and the upper insulator 227a so that the upper tube plate 225a, the top plate of the upper casing 229a, and the upper insulator 227a are approximately parallel to each other. The upper tube plate 225a has a number of holes corresponding to the number of cell stacks 101 provided in the electrochemical cell cartridge 203, and the cell stacks 101 are inserted into the holes. The upper tube plate 225a airtightly supports one end of the multiple cell stacks 101 via either or both of a sealing member 237a and an adhesive member, and also isolates the fuel gas supply header 217 from the oxidizing gas discharge header 223.

[0047] The upper heat insulator 227a is disposed at the lower end of the upper casing 229a so that the upper heat insulator 227a, the top plate of the upper casing 229a, and the upper tube plate 225a are substantially parallel to each other, and is fixed to the side plate of the upper casing 229a. The upper heat insulator 227a has a plurality of holes formed therein corresponding to the number of cell stacks 101 provided in the electrochemical cell cartridge 203. The diameters of the holes are set larger than the outer diameters of the cell stacks 101. The upper heat insulator 227a has oxidizing gas discharge gaps 235b formed between the inner surfaces of the holes and the outer surfaces of the cell stacks 101 inserted through the upper heat insulator 227a.

[0048] The upper heat insulator 227a separates the power generating chamber 215 from the oxidizing gas discharge header 223, and prevents the atmosphere around the upper tube sheet 225a from becoming hot, thereby reducing its strength and increasing corrosion caused by the oxidizing agent contained in the oxidizing gas. Furthermore, a metal material with high temperature resistance, such as a Ni-based alloy, may be used to prevent the upper tube sheet 225a and other components from being thermally deformed due to the temperature difference caused by exposure to the high temperature inside the power generating chamber 215. The upper heat insulator 227a also guides the exhaust oxidizing gas, which has passed through the power generating chamber 215 and been exposed to high temperatures, through the oxidizing gas discharge gap 235b and into the oxidizing gas discharge header 223.

[0049] According to this embodiment, the structure of the electrochemical cell cartridge 203 described above allows the fuel gas and the exhaust oxidizing gas to flow in opposite directions inside and outside the cell stack 101. As a result, the exhaust oxidizing gas exchanges heat with the fuel gas that passes through the inside of the base tube 103 and is supplied to the power generation chamber 215, and is cooled to a temperature at which the upper tube plate 225a, made of a metal material, and other components will not undergo deformation, such as buckling, before being supplied to the oxidizing gas discharge header 223. The fuel gas is also heated by heat exchange with the exhaust oxidizing gas discharged from the power generation chamber 215, and is supplied to the power generation chamber 215. As a result, fuel gas that has been preheated to a temperature suitable for power generation can be supplied to the power generation chamber 215 without using a heater or the like.

[0050] The lower tube plate 225b is fixed to the side plate of the lower casing 229b between the bottom plate of the lower casing 229b and the lower insulator 227b so that the lower tube plate 225b, the bottom plate of the lower casing 229b, and the lower insulator 227b are approximately parallel to each other. The lower tube plate 225b has a plurality of holes corresponding to the number of cell stacks 101 provided in the electrochemical cell cartridge 203, and the cell stacks 101 are inserted into the holes. The lower tube plate 225b airtightly supports the other ends of the plurality of cell stacks 101 via either or both of a sealing member 237b and an adhesive member, and also separates the fuel gas discharge header 219 from the oxidizing gas supply header 221.

[0051] The lower heat insulator 227b is disposed at the upper end of the lower casing 229b so that the lower heat insulator 227b, the bottom plate of the lower casing 229b, and the lower tube plate 225b are substantially parallel to each other, and is fixed to the side plate of the lower casing 229b. The lower heat insulator 227b has a plurality of holes formed therein corresponding to the number of cell stacks 101 provided in the electrochemical cell cartridge 203. The diameters of the holes are set larger than the outer diameters of the cell stacks 101. The lower heat insulator 227b has an oxidizing gas supply gap 235a formed between the inner surface of the hole and the outer surface of the cell stack 101 inserted through the lower heat insulator 227b.

[0052] The lower insulator 227b separates the power generating chamber 215 from the oxidizing gas supply header 221, and prevents the atmosphere around the lower tube sheet 225b from becoming too hot, resulting in a decrease in strength and increased corrosion due to the oxidizing agent contained in the oxidizing gas. The lower tube sheet 225b and other components are made of a metal material that is resistant to high temperatures, such as Inconel, and this prevents the lower tube sheet 225b and other components from being thermally deformed due to increased temperature differences within the lower tube sheet 225b when exposed to high temperatures. The lower insulator 227b also guides the oxidizing gas supplied to the oxidizing gas supply header 221 to the power generating chamber 215 by passing it through the oxidizing gas supply gap 235a.

[0053] According to this embodiment, the structure of the electrochemical cell cartridge 203 described above allows the exhaust fuel gas and the oxidizing gas to flow in opposite directions inside and outside the cell stack 101. As a result, the exhaust fuel gas that passes through the inside of the base tube 103 and the power generation chamber 215 exchanges heat with the oxidizing gas supplied to the power generation chamber 215, and is cooled to a temperature that does not cause deformation such as buckling of the lower tube plate 225b made of a metal material, and is supplied to the fuel gas discharge header 219. The oxidizing gas is also heated by heat exchange with the exhaust fuel gas, and is supplied to the power generation chamber 215. As a result, the oxidizing gas heated to a temperature required for power generation can be supplied to the power generation chamber 215 without using a heater or the like.

[0054] The DC power generated in the power generation chamber 215 is conducted to the vicinity of the end of the cell stack 101 by lead films 115 made of Ni / YSZ or the like provided on the plurality of electrochemical single cells 105, and then collected by a current collecting member (not shown) of the electrochemical cell cartridge 203 via a current collecting plate (not shown) and taken out to the outside of each electrochemical cell cartridge 203. The DC power conducted out to the outside of the electrochemical cell cartridge 203 by the current collecting member is connected to each other so that the generated power of each electrochemical cell cartridge 203 is connected in a predetermined number of series and parallel, and is conducted out to the outside of the electrochemical cell module 201, where it is converted into predetermined AC power by a power conversion device (such as an inverter) such as a power conditioner (not shown), and is then supplied to a power supply destination (for example, a load facility or a power system).

[0055] Next, an example of the arrangement of the fuel cells 10 and electrolysis cells 20 in the electrochemical cell cartridge 203 will be described with reference to the drawings. Fig. 6 is a cross-sectional view showing an example of the arrangement of the fuel cells 10 and electrolysis cells 20 in the electrochemical cell cartridge 203. The electrochemical cell cartridge 203 shown in Fig. 6 has 36 cell stacks 101 arranged in 6 columns and 6 rows in a power generation chamber 215, which is the internal space of the module container 205.

[0056] 6, a first group 10A of 20 cell stacks 101 on the outer periphery and a second group 10B of four cell stacks 101 on the inner periphery are used as the air electrode 11 and fuel electrode 12 of the fuel cell 10. On the other hand, 12 cell stacks 101 sandwiched between the cell stacks 101 on the outer periphery and the inner periphery are used as the oxygen electrode 21 and hydrogen electrode 22 of the electrolysis cell 20.

[0057] As shown in Fig. 6, the fuel cell 10 includes a power generation chamber 215 in which the air electrode 11 and the fuel electrode 12 are disposed. The oxygen electrode 21 and the hydrogen electrode 22 of the electrolysis cell 20 are disposed in the power generation chamber 215. Because the fuel cell 10 and the electrolysis cell 20 share the power generation chamber 215, the heat generated when the fuel cell 10 generates electricity can be used to heat the oxygen electrode 21 and the hydrogen electrode 22 of the electrolysis cell 20 to an operable temperature. This increases the thermal efficiency of the fuel cell system 100.

[0058] Next, a control method for the fuel cell system 100 according to an embodiment of the present disclosure will be described. Fig. 7 is a flowchart showing the control method for the fuel cell system 100 according to an embodiment of the present disclosure. Each process shown in Fig. 7 is executed by a control program stored in the control unit 90.

[0059] In step S101, the control unit 90 acquires the power demand P of the power system PS (the amount of power required by the fuel cell system 100 taking into account the output of the DC power generation unit 200). In step S102, the control unit 90 acquires the power E generated by the DC power generation unit 200. In step S103, the control unit 90 acquires the hydrogen demand H required by the supply destination of the fuel gas line L8.

[0060] In step S104, the control unit 90 determines whether the value obtained by subtracting the power E from the power demand P is below a predetermined power threshold, and if YES, proceeds to step S105, and if NO, proceeds to step S108. If the power E is insufficient for the power demand P by more than the power threshold, the determination is NO, and the system transitions to the high-efficiency load-following operation mode in step S108. In other words, if the power E is insufficient for the power demand P by more than the power threshold, the high-efficiency load-following operation mode is prioritized over the hydrogen demand-following mode.

[0061] In step S105, the control unit 90 determines whether the hydrogen demand H acquired in step S103 exceeds a predetermined hydrogen threshold value, and if YES, proceeds to step S106, and if NO, proceeds to step S107.

[0062] In step S106, the control unit 90 executes the hydrogen demand following mode. The hydrogen demand following mode is a mode in which the processes shown in Fig. 8 are executed. The control and termination conditions of the hydrogen demand following mode will be described later.

[0063] In step S107, the control unit 90 determines whether the power demand P of the power system PS is greater than the power E generated by the DC power generation unit 200, and if YES, proceeds to step S108, and if NO, proceeds to step S109.

[0064] In step S108, the control unit 90 executes the high-efficiency load following operation mode. The high-efficiency load following operation mode is a mode in which the processes shown in FIG. In step S109, the control unit 90 executes the steam electrolysis operation mode. The steam electrolysis operation mode is a mode in which the processes shown in Fig. 10 are executed. After the steam electrolysis operation mode is executed, the process proceeds to step S108. When transitioning between the high-efficiency load following operation mode, the steam electrolysis operation mode, and the hydrogen demand following operation mode, it is preferable that the switching units S1, S2, and S3 are in an off state.

[0065] Next, the hydrogen demand following mode executed in step S106 of Fig. 7 will be described with reference to Fig. 8. Fig. 8 is a flowchart showing the hydrogen demand following mode of Fig. 7. In the hydrogen demand following mode, switching unit S3 is in a supply-enabled state, and switching units S1 and S2 are in a cut-off state. Power can be supplied from fuel cell 10 to power grid PS via converter (first conversion unit) 40, and power can be supplied from power grid PS to electrolytic cell 20 via converter (second conversion unit) 45. DC power generation unit 200 and electrolytic cell 20 are disconnected, and power can be supplied from DC power generation unit 200 to power grid PS.

[0066] In step S201, the control unit 90 determines a target load current for the fuel cell 10 within a range that does not exceed the power demand P. The control unit 90 controls the fuel cell 10 so that power according to the determined target load current is output. In step S202, the control unit 90 subtracts the hydrogen supply amount estimated from the hydrogen concentration meter 70 from the hydrogen demand H to calculate a deviation value ΔH. In step S203, the control unit 90 determines whether the deviation value ΔH is greater than 0. If the determination is YES, the control unit 90 sets the switching unit S3 to the supply state in step S204 and proceeds to step S205. If the determination in step S203 is NO, the control unit 90 proceeds to step S207.

[0067] In step S205, the control unit 90 increases the current consumption value of the electrolytic cell 20 so as to increase the amount of hydrogen supplied by the electrolytic cell 20, since the hydrogen demand H is greater than the hydrogen supply amount. In step S206, the control unit 90 increases the amount of pure water supplied to the water line L7 in order to supply water vapor to the electrolytic cell 20 in proportion to the increase in the current consumption value of the electrolytic cell 20. Thereafter, the process proceeds to step S210.

[0068] In step S207, the control unit 90 determines whether the power consumption of the electrolytic cell 20 is greater than 0. If YES, the control unit 90 sets the switching unit S3 to the supply state and proceeds to step S208, and if NO, proceeds to step S210. In step S208, because the hydrogen demand H is equal to or less than the hydrogen supply amount, and the power consumption of the electrolytic cell 20 is greater than 0 and hydrogen is being generated, the control unit 90 reduces the current consumption value of the electrolytic cell 20 so as to reduce the amount of hydrogen supplied by the electrolytic cell 20.

[0069] In step S209, the control unit 90 reduces the amount of pure water supplied to the water line L7 in order to supply water vapor to the electrolytic cell 20 in proportion to the decrease in the current consumption value of the electrolytic cell 20. Thereafter, the process proceeds to step S210. In step S210, the control unit 90 acquires the hydrogen demand H required by the supply destination of the fuel gas line L8.

[0070] In step S211, the control unit 90 determines whether the hydrogen demand H acquired in step S209 is below a predetermined hydrogen threshold (the same value as the predetermined hydrogen threshold in step S105), and if YES, in step S212, S3 is shut off and the processing of this flowchart is terminated, and if NO, step S201 is executed again. After the hydrogen demand following mode is terminated, the processing proceeds to step S107 in Figure 7.

[0071] Next, the high-efficiency load following operation mode executed in step S107 of Fig. 7 will be described with reference to Fig. 9. Fig. 9 is a flowchart showing the high-efficiency load following operation mode of Fig. 7. In the high-efficiency load following operation mode, switching unit S1 is in a state where power can be supplied, and switching units S2 and S3 are in a state where they are both shut off. Power can be supplied from fuel cell 10 to electrolytic cell 20 without going through converter (first conversion unit) 40 and converter (second conversion unit) 45, DC power generation unit 200 and electrolytic cell 20 are disconnected, and power can be supplied from DC power generation unit 200 to power grid PS.

[0072] In step S301, the control unit 90 operates the fuel cell 10 at a rated load and controls (load control) the temperature of the power generating chamber 215 to be constant. In step S302, the control unit 90 calculates a deviation value ΔP by subtracting the sending end output of the fuel cell system 100 (electric power output from the fuel cell system 100 to point T in FIG. 1) from the electric power demand P. In step S303, the control unit 90 controls the switching unit S1 to supply DC power generated by the fuel cell 10 to the electrolysis cell 20.

[0073] In step S304, the control unit 90 determines whether the deviation value ΔP is less than 0. If YES, the process proceeds to step S305, and if NO, the process proceeds to step S307. When the deviation value ΔP is less than 0, the sending end output of the fuel cell system 100 is greater than the power demand P of the power grid PS, which means that the power demand P is met and surplus power is being generated.

[0074] In step S305, since the deviation value ΔP is smaller than 0 and there is a surplus of power output at the sending end relative to the power demand P, the control unit 90 increases the current consumption value of the electrolytic cell 20 so as to consume the surplus power output at the sending end. In step S306, the control unit 90 increases the amount of pure water supplied to the water line L7 in order to supply water vapor to the electrolysis cell 20 in proportion to the increase in the current consumption value of the electrolysis cell 20.

[0075] In step S307, since the deviation value ΔP is equal to or greater than 0 and there is no surplus in the sending end output relative to the power demand P, the control unit 90 reduces the current consumption value of the electrolytic cell 20 so as to increase the sending end output. In step S308, the control unit 90 reduces the amount of pure water supplied to the water line L7 in order to supply water vapor to the electrolysis cell 20 in an amount commensurate with the reduction in the current consumption value of the electrolysis cell 20.

[0076] In step S309, the control unit 90 acquires the power demand P of the power system PS. In step S310, the control unit 90 acquires the power E generated by the DC power generation unit 200. In step S311, the control unit 90 determines whether the value obtained by subtracting the power E from the power demand P is below a predetermined power threshold, and if YES, proceeds to step S312, and if NO, proceeds to step S301. In step S312, the control unit 90 controls the switching unit S1 to be in a cut-off state in which the DC power generated by the fuel cell 10 is not supplied to the electrolysis cell 20, and ends the processing of this flowchart.

[0077] Next, the steam electrolysis operation mode executed in step S108 in Fig. 7 will be described with reference to Fig. 10. Fig. 10 is a flowchart showing the steam electrolysis operation mode in Fig. 7. In the steam electrolysis operation mode, the switching unit S2 is in a supply-enabled state, and the switching units S1 and S3 are in a cut-off state. As for the electrical system, the fuel cell 10 and the electrolytic cell 20, and the DC power generation unit 200 and the power system PS are disconnected.

[0078] In step S401, the control unit 90 determines a target load current for the fuel cell 10 within a range that does not exceed the power demand P. The control unit 90 controls the fuel cell 10 so that power according to the determined target load current is output. In step S402, the control unit 90 switches the switching unit S2 from the cut-off state to the supply state so that power is supplied from the DC power generation unit 200 to the electrolysis cell 20.

[0079] In step S403, the control unit 90 adjusts the amount of pure water supplied to the water line L7 in order to supply water vapor to the electrolysis cell 20 in an amount commensurate with the power supplied from the DC power generation unit 200 to the electrolysis cell 20. In step S404, the control unit 90 acquires the power demand P of the power system PS. In step S405 , the control unit 90 acquires the power E generated by the DC power generation unit 200 .

[0080] In step S406, the control unit 90 determines whether the power demand P of the power system PS is greater than the power E generated by the DC power generation unit 200. If YES, the control unit 90 sets S2 to a cutoff state in step S407 and ends the processing of this flowchart; if NO, the control unit 90 executes step S401 again.

[0081] Next, the relationship between the change in load current of the fuel cell 10 and the power and generating chamber temperature in each operation mode will be described. Fig. 11 is a graph showing the relationship between the load current value of the fuel cell 10 and the sending end output of the fuel cell system 100 in the high-efficiency load-following operation mode. Fig. 12 is a graph showing the relationship between the load current value of the fuel cell 10 and the generating chamber temperature in the high-efficiency load-following operation mode.

[0082] 11, in the high-efficiency load-following operation mode, the sending end output gradually increases to P2 until the load current of the fuel cell 10 reaches the rated current value Ir (the load current when the fuel cell 10 is operating at rated load). This is because in the high-efficiency load-following operation mode, the electrolytic cell 20 is not operated until the rated current value Ir is reached, and therefore no power is consumed by the electrolytic cell 20.

[0083] Furthermore, in the high-efficiency load-following operation mode, the sending end output gradually decreases from P2 to P1 until the load current of the fuel cell 10 reaches the upper limit current value Imax (the current at the maximum load at which the fuel cell 10 can operate) from the rated current value Ir. This is because, in the high-efficiency load-following operation mode, the power consumption of the electrolytic cell 20 gradually increases from the rated current value Ir to the upper limit current value Imax. In the high-efficiency load-following operation mode, the sending end output is controlled to meet the power demand P of the power grid.

[0084] 12, in the high-efficiency load-following operation mode, the temperature of the generating chamber gradually increases to the rated temperature Tr (the temperature of the generating chamber during rated load operation) until the load current of the fuel cell 10 reaches the rated current value Ir. This is because, in the high-efficiency load-following operation mode, the electrolytic cell 20 is not operated until the rated current value Ir is reached, and therefore no endothermic reaction occurs in the electrolytic cell 20.

[0085] Furthermore, in the high-efficiency load following operation mode, the generating chamber temperature remains constant at the rated temperature Tr until the load current of the fuel cell 10 reaches the upper limit current value Imax from the rated current value Ir. This is because the high-efficiency load following operation mode performs control to keep the generating chamber temperature constant.

[0086] Fig. 13 is a graph showing the relationship between the load current value of the fuel cell 10 and the sending end output of the fuel cell system 100 in the steam electrolysis operation mode and the hydrogen demand following mode. Fig. 14 is a graph showing the relationship between the load current value of the fuel cell 10 and the generating chamber temperature in the high-efficiency load following operation mode and the hydrogen demand following mode.

[0087] 13, in the steam electrolysis operation mode and the hydrogen demand following mode, the sending end output fluctuates within a range between the upper limit indicated by the solid line and the lower limit indicated by the dotted line until the load current of the fuel cell 10 reaches the rated current value Ir. This is because in the steam electrolysis operation mode and the hydrogen demand following mode, the temperature in the power generating chamber decreases due to the endothermic reaction in the electrolytic cell 20, causing a decrease in the output of the fuel cell 10 until the rated current value Ir is reached.

[0088] 14, in the steam electrolysis operation mode and the hydrogen demand tracking mode, the temperature of the power generating chamber fluctuates within a range between the upper limit indicated by the solid line and the lower limit indicated by the dotted line until the load current of the fuel cell 10 reaches the rated current value Ir. This is because, in the steam electrolysis operation mode and the hydrogen demand tracking mode, fluctuations in the power supplied to the electrolytic cell 20 occur, causing fluctuations in the temperature of the power generating chamber due to an endothermic reaction, until the load current of the fuel cell 10 reaches the rated current value Ir.

[0089] Next, we will explain the time series changes in power and room temperature in each operation mode. Fig. 15 is a graph showing the time series changes in power and room temperature in the high-efficiency load following operation mode. Fig. 16 is a graph showing the time series changes in power and room temperature in the steam electrolysis operation mode. Fig. 17 is a graph showing the time series changes in power and room temperature in the hydrogen demand following mode.

[0090] 15, in the high-efficiency load following operation mode, when the power demand of the power grid PS decreases from P4 to P3, the sending end output, which is the power output from the fuel cell system 100 to the power grid PS, also decreases from P4 to P3 in response. Similarly, when the power demand increases from P3 to P4, the sending end output also increases from P3 to P4 in response. When the power demand decreases from P4 to P3, surplus power from the fuel cell 10 is supplied to the electrolysis cell 20, and P6 of power is consumed in the fuel cell system 100.

[0091] To prevent a drop in the generating chamber temperature due to the endothermic reaction in the electrolytic cell 20, the output power of the fuel cell 10 is increased from P4 to P5. P6 - P5 + P4, which is the increase P6 in the amount of power consumed in the electrolytic cell 20 minus the increase P5 - P4 in the output power of the fuel cell 10, matches the decrease P4 - P3 in the sending end output. In this way, the generating chamber temperature is maintained constant so that it does not change over time.

[0092] Fig. 16 shows the time series changes in power and generator chamber temperature in the steam electrolysis operation mode when the power demand P of the power grid PS is constant. As shown in Fig. 16, in the steam electrolysis operation mode, the power consumption of the electrolytic cell 20 fluctuates with fluctuations in the DC power supplied to the electrolytic cell 20 from the DC power generation unit 200. Because the fuel cell 10 is controlled to maintain a constant load current, the output power, generating chamber temperature, and sending end output of the fuel cell 10 fluctuate depending on the state of the endothermic reaction of the electrolytic cell 20 as the power consumption of the electrolytic cell 20 fluctuates.

[0093] Figure 17 shows the time series changes in power and generating chamber temperature in hydrogen demand following mode when power demand P in the power grid PS is constant. As shown in Figure 17, in hydrogen demand following mode, the power consumption of the electrolytic cell 20 fluctuates as hydrogen demand H fluctuates. Because the fuel cell 10 is controlled to maintain a constant load current, the output power, generating chamber temperature, and sending end output of the fuel cell 10 fluctuate depending on the state of the endothermic reaction of the electrolytic cell 20 as the power consumption of the electrolytic cell 20 fluctuates.

[0094] The functions and effects of the fuel cell system 100 of this embodiment described above will be described. The fuel cell system 100 of this embodiment includes a fuel cell 10 that generates electricity by reacting fuel gas FG with an oxidizing gas, and an electrolysis cell 20 that produces hydrogen through steam electrolysis. DC power generated by the fuel cell 10 is converted to AC power by a converter 40 and output to the power grid PS. The DC power used for steam electrolysis in the electrolysis cell 20 is supplied from the fuel cell 10.

[0095] According to the fuel cell system 100 of this embodiment, when the AC power converted from the DC power generated by the fuel cell 10 is greater than the power demand P required from the power grid PS, the control unit 90 controls the switching unit S1 to supply the DC power generated by the fuel cell 10 to the electrolytic cell 20. This eliminates the need to reduce the power output by the fuel cell 10, allowing the fuel cell 10 to maintain high power generation efficiency. Furthermore, surplus power generated by the fuel cell 10 can be effectively utilized as power for steam electrolysis in the electrolytic cell 20. Furthermore, a portion of the power generated by the fuel cell 10 is converted into AC power by the converter (first conversion unit) 40 and the converter (second conversion unit) 45. Since the power is supplied to the electrolytic cell 20 via the switching unit S1 without passing through the AC / DC converter, there is no power loss due to DC / DC conversion and AC / DC conversion, and the system can be operated efficiently.

[0096] Furthermore, according to the fuel cell system 100 of this embodiment, the oxygen electrode 21 and the hydrogen electrode 22 of the electrolysis cell 20 are disposed in the power generation chamber 215 of the fuel cell 10, and therefore the heat generated during power generation in the fuel cell 10 can be used to heat the oxygen electrode 21 and the hydrogen electrode 22 of the electrolysis cell 20 to an operable temperature. This allows the thermal efficiency of the fuel cell system 100 to be improved.

[0097] Furthermore, according to the fuel cell system 100 of this embodiment, when the DC power generated by the DC power generation unit 200 is equal to or greater than the power demand P of the power grid PS, the control unit 90 controls the switching unit S2 to switch to a supply state in which the DC power generated by the DC power generation unit 200 is supplied to the electrolytic cell 20. In this way, the surplus power generated by the DC power generation unit 200 can be effectively used as power for steam electrolysis in the electrolytic cell 20.

[0098] According to the fuel cell system 100 of this embodiment, AC power supplied from the power grid PS is converted into DC power by the converter 45 and output to the electrolysis cell 20, so that the power supplied from the power grid PS can be used to promote hydrogen production in the electrolysis cell 20.

[0099] The fuel cell systems described in the above-described embodiments can be understood, for example, as follows. A fuel cell system (100) according to a first aspect of the present disclosure comprises a fuel cell (10) having an air electrode and a fuel electrode, and generating electricity by reacting a fuel gas supplied to the fuel electrode with an oxidizing gas supplied to the air electrode; an electrolysis cell (20) having an oxygen electrode and a hydrogen electrode, and generating hydrogen by steam electrolysis of water vapor supplied to the hydrogen electrode; a first conversion unit (40) converting DC power generated by the fuel cell into AC power and outputting it to a power grid (PS); and a control unit that controls the electrolysis cell to increase its current consumption value when the AC power converted from the DC power generated by the fuel cell is greater than the power demand required by the power grid.

[0100] A fuel cell system according to a first aspect of the present disclosure includes a fuel cell that generates electricity by reacting a fuel gas with an oxidizing gas, and an electrolytic cell that generates hydrogen through steam electrolysis. DC power generated by the fuel cell is converted to AC power by a first conversion unit and output to a power grid. DC power used for steam electrolysis in the electrolytic cell is supplied from the fuel cell.

[0101] In a fuel cell system according to a first aspect of the present disclosure, when the AC power converted from the DC power generated by the fuel cell is greater than the power demand from the power grid, the control unit controls the electrolytic cell to increase the current consumption value. This eliminates the need to reduce the power output by the fuel cell, thereby maintaining the power generation efficiency of the fuel cell. Furthermore, surplus power generated by the fuel cell can be effectively used for steam electrolysis in the electrolytic cell.

[0102] A fuel cell system according to a second aspect of the present disclosure is the first aspect, further comprising the following configuration: the fuel cell includes a power generation chamber (215) in which the air electrode and the fuel electrode are disposed, and the oxygen electrode and the hydrogen electrode of the electrolysis cell are disposed in the power generation chamber. In the fuel cell system according to the second aspect of the present disclosure, the oxygen electrode and hydrogen electrode of the electrolysis cell are disposed in the power generation chamber of the fuel cell, and the heat generated during power generation in the fuel cell can be used to heat the oxygen electrode and hydrogen electrode of the electrolysis cell to an operable temperature, thereby improving the thermal efficiency of the fuel cell system.

[0103] A fuel cell system according to a third aspect of the present disclosure is the first or second aspect, further comprising the following configuration: a first switching unit (S1) that switches between a first supply state in which DC power generated by the fuel cell is supplied to the electrolytic cell and a first cut-off state in which DC power generated by the fuel cell is not supplied to the electrolytic cell, and a second switching unit (S2) that switches between a second supply state in which DC power generated by a DC power generation unit is supplied to the electrolytic cell and a second cut-off state in which DC power generated by the DC power generation unit is not supplied to the electrolytic cell, wherein the control unit controls the first switching unit to switch to the first supply state when AC power converted from DC power generated by the fuel cell is greater than power demand requested by the power grid, and controls the second switching unit to switch to the second supply state when DC power generated by the DC power generation unit is equal to or greater than the power demand of the power grid.

[0104] In a fuel cell system according to a third aspect of the present disclosure, when the AC power converted from the DC power generated by the fuel cell is greater than the power demand from the power grid, the control unit controls the first switching unit to switch to a first supply state in which the DC power generated by the fuel cell is supplied to the electrolysis cell. This eliminates the need to reduce the power output by the fuel cell, thereby maintaining the power generation efficiency of the fuel cell. Furthermore, surplus power generated by the fuel cell can be effectively utilized for steam electrolysis in the electrolysis cell. Furthermore, when the DC power generated by the DC power generation unit is equal to or greater than the power demand of the power grid, the control unit controls the second switching unit to switch to a second supply state in which the DC power generated by the DC power generation unit is supplied to the electrolytic cell. In this way, the surplus power generated by the DC power generation unit can be effectively used as power for steam electrolysis in the electrolytic cell.

[0105] A fuel cell system according to a fourth aspect of the present disclosure is the first or second aspect, further comprising the following configuration: A second conversion unit (45) that converts AC power supplied from the power grid into DC power and outputs the DC power to the electrolysis cell. In the fuel cell system according to the fourth aspect of the present disclosure, AC power supplied from the power grid is converted to DC power by the second conversion unit and output to the electrolysis cell, and therefore, the power supplied from the power grid can be used to promote hydrogen production in the electrolysis cell.

[0106] In a control method for a fuel cell system according to a fifth aspect of the present disclosure, the fuel cell system includes a fuel cell having an air electrode and an anode, and generating electricity by reacting a fuel gas supplied to the anode with an oxidizing gas supplied to the air electrode; an electrolysis cell having an oxygen electrode and a hydrogen electrode, and generating hydrogen by steam electrolysis of water vapor supplied to the hydrogen electrode; and a first conversion unit that converts DC power generated by the fuel cell into AC power and outputs the AC power to a power grid, and includes a first control step of controlling the electrolysis cell to increase its current consumption value when the AC power converted from the DC power generated by the fuel cell is greater than the power demand required by the power grid.

[0107] According to a fifth aspect of the present disclosure, the fuel cell system includes a fuel cell that generates electricity by reacting a fuel gas with an oxidizing gas, and an electrolytic cell that generates hydrogen through steam electrolysis. The DC power generated by the fuel cell is converted to AC power by a first conversion unit and output to a power grid. The DC power used for steam electrolysis in the electrolytic cell is supplied from the fuel cell.

[0108] According to a control method for a fuel cell system according to a fifth aspect of the present disclosure, when the AC power converted from the DC power generated by the fuel cell is greater than the power demand required by the power grid, the first control step controls the electrolytic cell to increase its current consumption. This eliminates the need to reduce the power output by the fuel cell, thereby maintaining the power generation efficiency of the fuel cell. Furthermore, surplus power generated by the fuel cell can be effectively used for steam electrolysis in the electrolytic cell.

[0109] A control method for a fuel cell system according to a sixth aspect of the present disclosure is the fifth aspect, further comprising the following configuration: the fuel cell includes a power generation chamber (215) in which the air electrode and the fuel electrode are disposed, and the oxygen electrode and the hydrogen electrode of the electrolysis cell are disposed in the power generation chamber. According to the control method for a fuel cell system according to the sixth aspect of the present disclosure, the oxygen electrode and hydrogen electrode of the electrolysis cell are disposed in the power generation chamber of the fuel cell, and therefore the heat generated when the fuel cell generates electricity can be used to heat the oxygen electrode and hydrogen electrode of the electrolysis cell to an operable temperature, thereby improving the thermal efficiency of the fuel cell system.

[0110] A control method for a fuel cell system according to a seventh aspect of the present disclosure is the fifth or sixth aspect, further comprising the following configuration: The fuel cell system includes a first switching unit that switches between a first supply state in which DC power generated by the fuel cell is supplied to the electrolytic cell and a first cut-off state in which DC power generated by the fuel cell is not supplied to the electrolytic cell, and a second switching unit that switches between a second supply state in which DC power generated by a DC power generation unit is supplied to the electrolytic cell and a second cut-off state in which DC power generated by the DC power generation unit is not supplied to the electrolytic cell, and the first control step includes a second control step of controlling the first switching unit to switch to the first supply state when AC power converted from the DC power generated by the fuel cell is greater than power demand required by the power grid, and controlling the second switching unit to switch to the second supply state when the DC power generated by the DC power generation unit is equal to or less than the power demand of the power grid.

[0111] According to a seventh aspect of the present disclosure, in a control method for a fuel cell system, when the AC power converted from the DC power generated by the fuel cell is greater than the power demand from the power grid, the first control step controls the first switching unit to switch to a first supply state in which the DC power generated by the fuel cell is supplied to the electrolysis cell. This eliminates the need to reduce the power output by the fuel cell, thereby maintaining the power generation efficiency of the fuel cell. Furthermore, surplus power generated by the fuel cell can be effectively used for steam electrolysis in the electrolysis cell. Furthermore, when the DC power generated by the DC power generation unit is equal to or greater than the power demand of the power grid, the second control step controls the second switching unit to switch to a second supply state in which the DC power generated by the DC power generation unit is supplied to the electrolytic cell. In this way, surplus power generated by the DC power generation unit can be effectively used as power for steam electrolysis in the electrolytic cell.

[0112] A control method for a fuel cell system according to an eighth aspect of the present disclosure is the fifth or sixth aspect, further comprising the following configuration: the fuel cell system has a second conversion unit that converts AC power supplied from the power grid into DC power and outputs the DC power to the electrolysis cell. According to the control method for a fuel cell system according to the eighth aspect of the present disclosure, AC power supplied from the power grid is converted to DC power by the second conversion unit and output to the electrolysis cell, thereby enabling the use of power supplied from the power grid to promote hydrogen production in the electrolysis cell. [Explanation of symbols]

[0113] 10 fuel cell 11 Air electrode 12 Fuel electrode 20 electrolysis cells 21 Oxygen electrode 22 Hydrogen electrode 30 Auxiliary equipment 40 Converter (first conversion unit) 45 Converter (second conversion unit) 50 Regenerative heat exchanger 60 Cooler 70 Hydrogen concentration meter 81, 82, 83 Blower 90 Control Unit 91,92 On-off valve 93, 94, 95, 96 Control valves 100 Fuel Cell System 101 Cell Stack 103 Base tube 105 Electrochemical Single Cell 107 Interconnector 109 1st electrode 111 Solid electrolyte membrane 113 2nd electrode 115 Lead Film 200 DC power generation section 201 Electrochemical Cell Module 203 Electrochemical Cell Cartridge 215 Power Generation Room E-power FG Fuel Gas H Hydrogen demand Imax upper limit current value Ir Rated current value P electricity demand PS power system S1 Switching unit (first switching unit) S2 Switching unit (second switching unit) S3 Switching Unit Tr rated temperature ΔH deviation value ΔP deviation value

Claims

1. a fuel cell having an air electrode and an anode, which generates electricity by reacting a fuel gas supplied to the anode with an oxidizing gas supplied to the air electrode; an electrolysis cell having an oxygen electrode and a hydrogen electrode, which generates hydrogen by steam electrolysis of water vapor supplied to the hydrogen electrode; a first conversion unit that converts DC power generated by the fuel cell into AC power and outputs the AC power to a power grid; a second conversion unit that converts AC power supplied from the power grid into DC power and outputs the DC power to the electrolysis cell; a first switching unit that switches between a first supply state in which DC power generated by the fuel cell is supplied to the electrolysis cell and a first cut-off state in which DC power generated by the fuel cell is not supplied to the electrolysis cell; a second switching unit that switches between a second supply state in which DC power generated by a DC power generating unit is supplied to the electrolytic cell and a second cut-off state in which DC power generated by the DC power generating unit is not supplied to the electrolytic cell; a third switching unit that switches between a third supply state in which DC power is supplied from the second conversion unit to the electrolytic cell and a third cut-off state in which DC power is not supplied from the second conversion unit to the electrolytic cell; a control unit that controls the first switching unit, the second switching unit, and the third switching unit, The control unit When the AC power converted from the DC power generated by the fuel cell is greater than the power demand required by the power grid, the first switching unit is controlled to enter the first supply state, the second switching unit is controlled to enter the second cut-off state, and the third switching unit is controlled to enter the third cut-off state, thereby supplying DC power from the fuel cell to the electrolytic cell; when the DC power generated by the DC power generation unit is equal to or greater than the power demand of the power grid, controlling the first switching unit to switch to the first cut-off state, controlling the second switching unit to switch to the second supply state, and controlling the third switching unit to switch to the third cut-off state, thereby supplying DC power from the DC power generation unit to the electrolytic cell; a first switching unit configured to switch to the first shutoff state, a second switching unit configured to switch to the second shutoff state, and a third switching unit configured to switch to the third supply state when hydrogen demand exceeds a predetermined threshold, thereby supplying DC power from the second conversion unit to the electrolytic cell.

2. the fuel cell includes a power generation chamber in which the air electrode and the fuel electrode are disposed, 2. The fuel cell system according to claim 1, wherein the oxygen electrode and the hydrogen electrode of the electrolysis cell are disposed in the power generation chamber.

3. A method for controlling a fuel cell system, comprising: The fuel cell system includes: a fuel cell having an air electrode and an anode, which generates electricity by reacting a fuel gas supplied to the anode with an oxidizing gas supplied to the air electrode; an electrolysis cell having an oxygen electrode and a hydrogen electrode, which generates hydrogen by steam electrolysis of water vapor supplied to the hydrogen electrode; a first conversion unit that converts DC power generated by the fuel cell into AC power and outputs the AC power to a power grid; a second conversion unit that converts AC power supplied from the power grid into DC power and outputs the DC power to the electrolysis cell; a first switching unit that switches between a first supply state in which DC power generated by the fuel cell is supplied to the electrolysis cell and a first cut-off state in which DC power generated by the fuel cell is not supplied to the electrolysis cell; a second switching unit that switches between a second supply state in which DC power generated by a DC power generating unit is supplied to the electrolytic cell and a second cut-off state in which DC power generated by the DC power generating unit is not supplied to the electrolytic cell; a third switching unit that switches between a third supply state in which DC power is supplied from the second conversion unit to the electrolytic cell and a third cut-off state in which DC power is not supplied from the second conversion unit to the electrolytic cell, a first control step of supplying DC power from the fuel cell to the electrolytic cell by controlling the first switching unit to set the first supply state, controlling the second switching unit to set the second cut-off state, and controlling the third switching unit to set the third cut-off state when the AC power converted from the DC power generated by the fuel cell is greater than the power demand required by the power grid; a second control step of supplying DC power from the DC power generation unit to the electrolytic cell by controlling the first switching unit to set the first cutoff state, controlling the second switching unit to set the second supply state, and controlling the third switching unit to set the third cutoff state when the DC power generated by the DC power generation unit is equal to or greater than the power demand of the power grid; a third control step of supplying DC power from the second conversion unit to the electrolytic cell by controlling the first switching unit to the first shut-off state, controlling the second switching unit to the second shut-off state, and controlling the third switching unit to the third supply state when hydrogen demand exceeds a predetermined threshold.

4. the fuel cell includes a power generation chamber in which the air electrode and the fuel electrode are disposed, The method for controlling a fuel cell system according to claim 3 , wherein the oxygen electrode and the hydrogen electrode of the electrolytic cell are disposed in the power generation chamber.

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