Abstract:
A fuel cell configuration operable to provide a more uniform heat distribution within the fuel cell configuration is disclosed. A reactant gas, liquid or suspended solid (slurry) is circulated through the fuel cell configuration in such a manner that inherently hotter portions of the fuel cell are cooled. The more uniform heat distribution can enhance fuel cell life and operating characteristics.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
       [0001]    The present application is a continuation in part based on PCT application No. JP2008/055981, filed on Mar. 27, 2008, which claims priority to Japanese patent application no. 2007-195915, filed on Jul. 27, 2007, and Japanese patent application no. 2008-017241, filed on Jan. 29, 2008, the contents of which are incorporated by reference herein in their entirety. 
     
    
     FIELD OF THE INVENTION 
       [0002]    Embodiments of the present disclosure relate generally to fuel cell modules, and more particularly relate to fuel cell modules comprising a plurality of fuel cells. 
       BACKGROUND 
       [0003]    One of the next-generation candidates for electric power generation is a fuel cell. A fuel cell generates electric power by direct electrical power generation from a fuel and oxidizer in a manner similar to a battery. A fuel cell generally uses hydrogen and/or carbon based fuels, e.g., natural gas, hydrogen, methanol, coal (i.e., for a direct carbon fuel cell). The fuel is generally in a liquid (e.g., a direct methanol fuel cell) or gaseous form, although solid fuel (e.g., a slurred mixture of coal) has been used in some experimental fuel cells. 
         [0004]    Fuel cells are used in fuel cell modules and fuel cell apparatuses comprising fuel cell modules. One example of a fuel cell module comprises a fuel cell stack housed in a rectangular parallelepiped housing. A fuel cell stack generally comprises a plurality of fuel cells that are juxtaposed to each other, electrically coupled in series, and attached to a manifold. Some fuel cell modules comprise a plurality of fuel cell stacks in a housing. In such fuel cell modules, a heat insulator may be positioned between fuel cell stacks. 
         [0005]    When generating electricity with a fuel cell module or fuel cell apparatus, a fuel cell stack generates heat. Heat resulting from the generation of electricity is dissipated from between adjacent fuel cells. Although fuel cells positioned at the ends of a fuel cell stack in the direction in which the fuel cells are arrayed (array direction) can more easily dissipate heat, fuel cells positioned around the central portion cannot easily dissipate heat. 
         [0006]    Accordingly, there is a need for fuel cell modules in which a temperature distribution of a cell stack is closer to uniform. 
       SUMMARY 
       [0007]    A fuel cell configuration operable to provide a more uniform heat distribution within the fuel cell configuration is disclosed. A reactant gas, liquid or suspended solid (slurry) is circulated through the fuel cell configuration in such a manner that inherently hotter portions of the fuel cell are cooled. The more uniform heat distribution can enhance fuel cell life and operating characteristics. 
         [0008]    A first embodiment comprises a fuel cell module. The fuel cell module comprises a cell stack comprising a plurality of fuel cells arrayed adjacent to one another and having a cell stack length, a heat insulator, and a housing for housing the cell stack and the heat insulator. The heat insulator comprises a first portion and a second portion. The first portion faces an upper portion of a first side surface of the cell stack and has a length approximately equal to or longer than the cell stack length. The second portion is separated from the first portion and faces a lower portion of the side surface of the cell stack and has a length approximately equal to or longer than the cell stack length. 
         [0009]    A second embodiment comprises a fuel cell module. The fuel cell module comprises a cell stack comprising a plurality of fuel cells arrayed adjacent to one another, a heat insulator, and a housing for housing the cell stack and the heat insulator. The heat insulator is positioned to face a side surface of the cell stack and cover upper and lower portions of the side surface so as to provide a space for an inflow and circulation of a reactant gas from between the fuel cells. 
         [0010]    A third embodiment comprises a fuel cell apparatus. The fuel cell apparatus comprises fuel cell means operable to provide a uniform heat distribution within a fuel cell configuration, and a case for housing the fuel cell means. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0011]    Embodiments of the present disclosure are hereinafter described in conjunction with the following figures, wherein like numerals denote like elements. The figures are provided for illustration and depict exemplary embodiments of the present disclosure. The figures are provided to facilitate understanding of the present disclosure without limiting the breadth, scope, scale, or applicability of the present disclosure. The drawings are not necessarily made to scale. 
           [0012]      FIG. 1  is an illustration of a schematic perspective view of an exemplary fuel cell module according to an embodiment of the disclosure. 
           [0013]      FIG. 2  is an illustration of a cross-sectional view of an exemplary fuel cell module taken along a line A-A in  FIG. 1 . 
           [0014]      FIG. 3  is an illustration of a schematic perspective view of an exemplary cell stack assembly and heat insulators located on a side surface of the cell stack of the fuel cell module shown in  FIG. 2 . 
           [0015]      FIG. 4  is an illustration of a cross-sectional view of an exemplary fuel cell module according to an embodiment of the disclosure. 
           [0016]      FIG. 5A  is an illustration of a side view of an exemplary cell stack assembly and a heat insulator of the fuel cell module shown in  FIG. 4 , viewed from a first side of a reactant gas inlet. 
           [0017]      FIG. 5B  is an illustration of a side view of an exemplary cell stack assembly and a heat insulator of the fuel cell module shown in  FIG. 4 , viewed from a second side of a reactant gas inlet of  FIG. 5A . 
           [0018]      FIG. 6A  is an illustration of a side view of an exemplary cell stack assembly and a heat insulator of a fuel cell module viewed from a first side of a reactant gas inlet according to an embodiment of the disclosure. 
           [0019]      FIG. 6B  is an illustration of a side view of a cell stack assembly and a heat insulator of a fuel cell module viewed from a second side of a reactant gas inlet of  FIG. 6A  according to an embodiment of the disclosure. 
           [0020]      FIG. 7A  is an illustration of a schematic perspective view of a reactant gas inlet according to an embodiment of the disclosure. 
           [0021]      FIG. 7B  is an illustration of a schematic perspective view of an exemplary reactant gas inlet according to an embodiment of the disclosure. 
           [0022]      FIG. 8A  is an illustration of an exemplary state in which a heat insulator is coupled to a coupling member according to an embodiment of the disclosure. 
           [0023]      FIG. 8B  is an illustration of an exemplary state in which a heat insulator is coupled to a coupling member according to an embodiment of the disclosure. 
           [0024]      FIG. 9A  is an illustration of a schematic perspective view of an exemplary reactant gas inlet according to an embodiment according to an embodiment of the disclosure. 
           [0025]      FIG. 9B  is an illustration of an exemplary state in which heat insulators couple to the reactant gas inlet illustrated in  FIG. 9A  via a coupling member according to an embodiment of the disclosure. 
           [0026]      FIG. 10  is an illustration of a schematic perspective view of an exemplary fuel cell module according to an embodiment of the disclosure in which the housing and the like are not shown. 
           [0027]      FIG. 11  is an illustration of a cross-sectional view of an exemplary fuel cell module with the cell stack assembly in the housing shown in  FIG. 10  according to an embodiment of the disclosure. 
           [0028]      FIG. 12  is an illustration of an exploded perspective view of an exemplary fuel cell apparatus according to an embodiment of the disclosure. 
           [0029]      FIG. 13  is an illustration of a graph comprising exemplary results of an electricity generation test according to various embodiments of the disclosure. 
       
    
    
     DETAILED DESCRIPTION 
       [0030]    The following description is presented to enable a person of ordinary skill in the art to make and use the embodiments of the disclosure. The following detailed description is exemplary in nature and is not intended to limit the disclosure or the application and uses of the embodiments of the disclosure. Descriptions of specific devices, techniques, and applications are provided only as examples. Modifications to the examples described herein will be readily apparent to those of ordinary skill in the art, and the general principles defined herein may be applied to other examples and applications without departing from the spirit and scope of the disclosure. Furthermore, there is no intention to be bound by any expressed or implied theory presented in the preceding technical field, background, brief summary or the following detailed description. The present disclosure should be accorded scope consistent with the claims, and not limited to the examples described and shown herein. 
         [0031]    Embodiments of the disclosure are described herein in the context of one practical non-limiting application, namely, a hydrogen gas based fuel cell. Embodiments of the disclosure, however, are not limited to such hydrogen gas based fuel cell, and the techniques described herein may also be utilized in other applications. For example, embodiments may be applicable to liquid-fuel fuel cells, direct methanol fuel cells, direct ethanol fuel cells, direct carbon fuel cells, solid-fuel-in-suspended-liquid fuel cells, and the like. 
         [0032]    As would be apparent to one of ordinary skill in the art after reading this description, these are merely examples and the embodiments of the disclosure are not limited to operating in accordance with these examples. Other embodiments may be utilized and structural changes may be made without departing from the scope of the exemplary embodiments of the present disclosure. 
         [0033]      FIG. 1  is an illustration of a schematic perspective view of an exemplary fuel cell module  100  (module  100 ) according to an embodiment of the disclosure. The module  100  comprises a rectangular parallelepiped housing  2  and a cell stack assembly  8  housed in the housing  2 . The cell stack assembly  8  comprises a manifold  4 , two cell stacks  5  juxtaposed to each other, a reformer  6 , and a gas flow pipe  7 . 
         [0034]    The manifold  4  comprises a base  96  and a joint  95  disposed on the base  96 . The base  96  has a plate shape and the joint  95  has a frame shape. 
         [0035]    Each of the cell stacks  5  comprises a plurality of fuel cells  3  and a current collector (not shown). The each of the fuel cells  3  comprises a gas passage (not shown) through which a fuel gas flows. Each of the fuel cells  3  are arrayed adjacent to one another on the manifold  4 . The fuel cells  3  are arranged in an upright position and are electrically coupled in series via a current collector (not shown). The fuel cells  3  are each attached at their lower end  102  to the manifold  4  with an insulating binder (not shown), such as a glass sealant. Specifically, the fuel cells  3  are disposed on the base  96  so as to be surrounded by the joint  95  and the space between the fuel cells  3  and the joint  95  are filled with the insulating binder, thereby the fuel cells  3  are attached to the manifold  4 . 
         [0036]    The fuel cells  3  are hollow plates comprising a gas passage (not shown) through which a fuel gas flows. The fuel cells  3  may be, for example but without limitation, solid oxide fuel cells each comprising a fuel-side electrode, a solid electrolyte, an oxygen-side electrode on a supporting substrate, and the like. The fuel-side electrode, the solid electrolyte and the oxygen-side electrode each comprise an electricity generation portion. 
         [0037]    The reformer  6  is positioned above the cell stacks  5 . The reformer  6  reforms a fuel, such as natural gas or kerosene, to produce a hydrogen-containing gas (fuel gas) used in the fuel cells  3 . 
         [0038]    The fuel gas produced in the reformer  6  is supplied to the manifold  4  through the gas flow pipe  7 . The fuel gas in the manifold  4  is supplied to the gas passage (not shown) in the fuel cells  3 . 
         [0039]    In the embodiment shown in  FIG. 1 , a front face at a front side  108  and a back face at a back side  110  of the housing  2  are removed, and the cell stack assembly  8  is pulled out backward from the back of the housing  2 . In the module  100  illustrated in  FIG. 1 , the cell stack assembly  8  can be slid into the housing  2 . 
         [0040]      FIG. 2  is an illustration of a cross-sectional view of the module  100  taken along a line A-A in  FIG. 1 . The housing  2  comprises a double-layered structure comprising an inner wall  9  and an outer wall  10 . The outer wall  10  comprises an outer frame of the housing  2 , and the inner wall  9  substantially surrounds an electricity generation chamber  11 , which houses the fuel cells  3  comprising the cell stacks  5  of the cell stack assembly  8 . 
         [0041]    A space  93  between the inner wall  9  and the outer wall  10  in the module  100  comprises a flow passage  93  (space  93 ) through which a reactant gas is introduced into the fuel cells  3 . The reactant gas, such as air (an oxygen-containing gas), can be introduced into the fuel cells  3  through the flow passage. 
         [0042]    The module  100  comprises a reactant gas inlet  12  through which a reactant gas is introduced into the cell stacks  5 . Air can be introduced into the fuel cells  3  through the reactant gas inlet  12 . The reactant gas inlet  12  extends from a top surface  50  of the inner wall  9  to side faces  51 / 52  of the cell stacks  5  and is coupled to the flow passage  93  between the inner wall  9  and the outer wall  10 . A length of the reactant gas inlet  12  corresponds to a length of the cell stacks  5  in the array direction  104  of the fuel cells  3 . 
         [0043]    The reactant gas inlet  12  comprises an outlet  13  for introducing air into the fuel cells  3  at its lower end. The reactant gas inlet  12  comprises a pair of plates, which are juxtaposed to each other forming a passage for inlet gas. A bottom plate  94  may be attached to the lower ends of the pair of plates. The reactant gas inlet  12  is positioned between the two cell stacks  5  in the housing  2 . Depending on a number of the cell stacks  5 , for example in this embodiment, two reactant gas inlets  12  may be positioned to sandwich the cell stacks  5 . 
         [0044]    A temperature sensor  14  is inserted in the reactant gas inlet  12  from the top  54  of the housing  2  such that a temperature-measuring portion  15  of the temperature sensor  14  is located in the reactant gas inlet  12 . The temperature sensor  14  may be, for example but without limitation, a thermocouple, and the like. 
         [0045]    The fuel cells  3  may be operated at a predetermined temperature range. It is therefore necessary to measure the internal temperature of the electricity generation chamber  11 , preferably the temperature of the cell stacks  5  or the neighborhood thereof, and control the temperature. In the case that the fuel cells  3  are solid oxide fuel cells, since the operating temperature is significantly high, it is particularly necessary to measure and control the temperature. The temperature sensor  14  may therefore be placed such that the temperature-measuring portion  15  can measure the temperature of a central portion  56  ( FIG. 1 ) of the cell stacks  5 . The central portion  56  is located in the array direction  104  at about half the height  106  of the fuel cells  3  at which the cell stacks  5  have substantially the highest temperature. In this manner, temperature in the neighborhood of the cell stacks  5  can effectively be measured and controlled. The effective measurement and control of the temperature allows the generation of electricity less likely to decrease and make the fuel cells  3  of the cell stacks  5  less likely to damage due to degradation or thermal stress. The module  100  comprises heat insulators  16  in the electricity generation chamber  11  to maintain the internal temperature of the module  100  at high temperature. The heat insulators  16  can reduce excessive dissipation of internal heat of the module  100 , an excessive decrease in the temperature of the fuel cells  3  of the cell stacks  5 , and a decrease in the generation of the electricity. The heat insulators  16  may be a heat-insulating material having a high electrical resistance, and the like. 
         [0046]    The heat insulators  16  are positioned in a neighborhood of the cell stacks  5  to maintain the temperature of the fuel cells  3  of the cell stacks  5  at high temperature. In particular, as illustrated in  FIG. 2 , the heat insulators  16  are juxtaposed to the side surfaces  51 / 52  of the cell stacks  5  in the array direction  104 . In this manner, the heat insulators  16  can effectively reduce an excessive decrease in the temperature of the cell stacks  5 . 
         [0047]    In the embodiment shown in  FIG. 2 , the module  100  comprises four heat insulators  16 A,  16 B,  16 C, and  16 D each facing the side surfaces  51 / 52  of the cell stacks  5 . The heat insulators  16 A and  16 D are positioned between the side surfaces  52  of cell stacks  5  and the inner wall  9  of the housing  2 . The heat insulators  16 B and  16 C are positioned between the side surfaces  51  of the cell stacks  5  and the reactant gas inlet  12 . 
         [0048]    Heat insulators  16 A and  16 D may have a size approximately equal to or larger than the size of side surfaces  52  of the cell stacks  5  substantially surrounding the fuel cells  3 . The heat insulators  16  can make air (an oxygen-containing gas) from the reactant gas inlet  12  less likely to be discharged from the side surfaces  51 / 52  of the cell stacks  5 . This can facilitate the flow of air in the periphery of the fuel cells  3 . 
         [0049]    In this document, the phrase “a size approximately equal to or larger than the size of a side surfaces of each of the cell stacks  5 ”, as used herein, refers to a size having a length of about 90% or more of the length of each of the cell stacks  5  in the array direction  104  and a height of about 90% or more of the height  106  of each of the cell stacks  5 . 
         [0050]    The inner wall  9  comprises inner wall side surfaces  53  (internal sides) in the array direction  104 , the inner wall bottom  55  (internal bottom) substantially perpendicular to the inner wall side surfaces  53 , and inner wall top  57  (internal top) facing the inner wall bottom  55 . The module  100  further comprises an exhaust gas inner wall  59  of exhaust gas vent  17  juxtaposed to the inner wall bottom  55  and the inner wall side surfaces  53  of the inner wall  9  at a predetermined distance. The space  60  between the exhaust gas inner wall  59  of the exhaust gas vent  17  and the inner wall bottom  55  and the inner wall side surfaces  53  of the inner wall  9  forms an exhaust gas passage  60  (space  60 ). The exhaust gas passage  60  fluidically communicates with an exhaust port  18  at the bottom  48  of the housing  2 . 
         [0051]    In practice, an exhaust gas generated at startup of the module  100 , during the generation of electricity and at shutdown, flows through the exhaust gas passage  60  and is discharged from the exhaust port  18 . 
         [0052]    The exhaust port  18  may be formed by boring a hole or providing a pipe in the bottom  48  of the housing  2 . 
         [0053]      FIG. 3  is an illustration of a schematic perspective view of an exemplary cell stacks assembly and the heat insulators  16 A/ 16 D located on a side surfaces  52  of the cell stacks  5  of the module  100  shown in  FIG. 2 . In the embodiment shown in  FIGS. 2 and 3 , the heat insulators  16  are juxtaposed to the side surfaces  51 / 52  of the cell stacks  5  in the array direction  104 . Each of the heat insulators  16  is formed of a single plate material and comprises a depressed portion  34 . The depressed portion  34  approximately faces the central portion  56  of the side surfaces  52  of the cell stacks  5  in the array direction  104 . 
         [0054]    In an embodiment, each of the four heat insulators  16 A,  16 B,  16 C, and  16 D comprises the depressed portion  34 . In this manner, each of the heat insulators  16  such as the heat insulator  16 A/ 16 D shown in FIG.  3  and  16 B/ 16 C not shown in  FIG. 3  comprises a first portion  61 , a second portion  62 , a third portion  63 , a fourth portion  64 , and a fifth portion  65 . The first portion  61  faces an upper portion of each of the side surfaces  52  of the cell stacks  5 . The second portion  62  is separated from the first portion  61  and faces a lower portion of the each of the side surfaces  52  of the cell stacks  5 . The third portion  63  couples a first end  61   s  of the first portion  61  to a first end  62   s  of the second portion  62 . The fourth portion  64  couples a second end  61   t  of the first portion  61  to a second end  62   t  of the second portion  62 . The fifth portion  65  faces the cell stacks  5  with the first to fourth portions  61  to  64  interposed therebetween and covers an opening surrounded by the first to fourth portions  61  to  64 . A portion surrounded by the first to fifth portions  61  to  65  comprises the depressed portion  34 . 
         [0055]    Each of the heat insulators  16  comprise a depressed portion  34  facing the respective side surfaces  51 / 52  of the cell stacks  5 . Heat resulting from the generation of electricity in the cell stacks  5  can be dissipated via the depressed portions  34 . The depressed portions  34  can therefore decrease the temperature of the fuel cells  3  facing the depressed portions  34 . This can decrease the temperature difference between the ends  91 / 92  and the central portion  56  of the cell stacks  5 . In this manner, the temperature distribution of the cell stacks  5  can be closer to uniform. 
         [0056]    Since the depressed portion  34  approximately faces the central portion  56  of the side surfaces  51 / 52  of the cell stacks  5  in the array direction  104 , the depressed portion  34  can appropriately decrease the temperature of the fuel cells  3  around the central portion  56  of the cell stacks  5  in the array direction  104 . 
         [0057]    An oxygen-containing gas such as air supplied from the lower end  102  of the cell stacks  5  through the reactant gas inlet  12  flows through the fuel cells  3  to the upper end  101  of the cell stacks  5  and partly flows into the depressed portions  34 . Air in the depressed portion  34  circulates in the depressed portion  34  in response to the temperature distribution of the fuel cells  3  facing the depressed portion  34 . 
         [0058]    This can make the temperature distribution of the fuel cells  3  facing the depressed portion  34  closer to uniform. Consequently, the temperature distribution of the cell stacks  5  can be closer to uniform. 
         [0059]    As described above, the heat insulators  16 A and  16 D may have a size approximately equal to or larger than a size of side surfaces  51 / 52  of the cell stacks  5 . This allows air to be efficiently supplied to the fuel cells  3  and can reduce an excessive decrease in the temperature of the cell stacks  5 . 
         [0060]    A size of the depressed portion  34  can be appropriately determined on the basis of the shape of the fuel cells  3  in the cell stacks  5 , the length of the cell stacks  5  in the array direction  104 , and the temperature distribution of the cell stacks  5 . More specifically, a length of the depressed portion  34  in the array direction  104  may be about 60% or more or about 75% or more of the length of each of the cell stacks  5  in the array direction  104 . A height of the depressed portion  34  in the height  106  direction of the fuel cells  3  may be about 50% or more or about 70% or more of the height of the electricity generation portion (not shown) of the fuel cells  3 . For example, in the case of hollow plate type fuel cells  3  that comprise a fuel-side electrode, a solid electrolyte, and an oxygen-side electrode positioned on a supporting substrate in this order, the height of the electricity generation portion (not shown) corresponds to a height of the oxygen-side electrode (not shown). The depressed portion  34  may have a depth that allows air in the depressed portion  34  to circulate well in the depressed portion  34  and may be about 50% or more of a thickness of the heat insulators  16 . The depressed portion  34  may be symmetrical about the central portion  56  of the side surfaces  51 / 52  of the cell stacks  5  in the array direction  104 . 
         [0061]      FIG. 4  is an illustration of a cross-sectional view of an exemplary fuel cell module  400  (module  400 ) according to an embodiment of the disclosure.  FIGS. 5A and 5B  are side views of the cell stack assembly  8 , a heat insulator  20  and a heat insulator  21  placed on the side surfaces  51 / 52  of the cell stacks  5  of the cell stack assembly  8  shown in  FIG. 4 .  FIG. 5A  is viewed from a first side of the reactant gas inlet  12 , and  FIG. 5B  is viewed from a second side of the reactant gas inlet  12 . Module  400  may have functions, material, and structures that are similar to the module  100 . Therefore common features, functions, and elements may not be redundantly described here. The fuel cell module  400  is different from the module  100  in the structure of the heat insulators positioned on the side surfaces  51 / 52  of the cell stacks  5 . 
         [0062]    In  FIGS. 5A and 5B , the reformer  6  is not shown. The cell stacks  5  comprise, at each end  91 / 92 , a current collector  19  for receiving electric power generated by the cell stacks  5 . 
         [0063]    As illustrated in  FIGS. 5A and 5B , the module  400  comprises heat insulator  20  and heat insulator  21  juxtaposed to the side surfaces  51 / 52  of the cell stacks  5  in the array direction  104 . The heat insulator  20  comprises a plurality of heat-insulating plates  71 ,  72 ,  73 , and  74 . The heat insulator  21  comprises a plurality of heat-insulating plates  81 ,  82 ,  83 , and  84 . The heat-insulating plates  71  to  74  and the heat-insulating plates  81  to  84  correspond to the first to fourth portions  61  to  64  in the embodiment shown in  FIG. 3 . 
         [0064]    The module  400  further comprises an opening  22  comprising openings  22   x  and  22   y . The opening  22   x  is surrounded by heat-insulating plates  71 - 74  of the heat insulator  20  and the opening  22   y  is surrounded by plates  81 - 84  of the heat insulator  21 . The openings  22   x  and  22   y  each face approximately the central portion  56  of the side surfaces  51 / 52  of the cell stacks  5  in the array direction  104 . Unlike the module  100 , the side surfaces  51 / 52  of the cell stacks  5  facing the opening  22   x / 22   y  respectively are not covered with the heat insulator  20 / 21 . That is, the side surfaces  51 / 52  of the cell stacks  5  are partially exposed. 
         [0065]    Although the heat insulator  20  and the heat insulator  21  surrounding the opening  22   x / 22   y  comprise a plurality of plates, the heat insulator  20  and the heat insulator  21  may be a single plate, as in the heat insulator  16  in the embodiment shown in  FIG. 3 . More specifically, the heat insulator  20  and the heat insulator  21  may be a single heat-insulating plate having an opening. The opening  22  can easily be formed for both a heat insulator comprising a plurality of plates and a heat insulator comprising a single plate. 
         [0066]    As described above the heat insulators  20  and  21  comprising the opening  22  face the respective side surfaces  51 / 52  of the cell stacks  5 . In this manner, heat resulting from the generation of electricity in the cell stacks  5  can be dissipated via the opening  22 . The opening  22  can therefore decrease the temperature of the fuel cells  3  facing the opening  22 . This can decrease the temperature difference between the ends  91 / 92  ( FIG. 6A-6B ) and the central portion  56  of the cell stacks  5 . In this manner, the temperature distribution of the cell stacks  5  can be closer to uniform. 
         [0067]    The opening  22  approximately faces the central portion  56  of the side surfaces  51 / 52  of the cell stacks  5  in the array direction  104 . The opening  22  can therefore appropriately decrease the temperature of the fuel cells  3  around the central portion  56  of the cell stacks  5  in the array direction  104 . 
         [0068]    In the module  100  and the module  400 , air (an oxygen-containing gas) supplied from the lower end  102  of the cell stacks  5  through the reactant gas inlet  12  flows through the fuel cells  3  to the upper end  101  of the cell stacks  5  and partly flows into the opening  22 . Air in the opening  22   x / 22   y  circulates in the opening  22   x / 22   y  in response to the temperature distribution of the fuel cells  3  facing the respective opening  22   x / 22   y.    
         [0069]    In this manner, a temperature distribution of the fuel cells  3  facing the opening  22  can be closer to uniform. Consequently, the temperature distribution of the cell stacks  5  can be closer to uniform. In addition, this can make the generation of electricity in the cell stacks  5  less likely to decrease and make the fuel cells  3  in the cell stacks  5  less likely to damage. 
         [0070]    The heat insulators  20  and  21  may have a size approximately equal to or larger than the size of side surfaces  51 / 52  of the cell stacks  5 . This allows air to be efficiently supplied to the fuel cells  3  and can reduce an excessive decrease in the temperature of the cell stacks  5 . 
         [0071]    The size of the opening  22   x / 22   y  can be appropriately determined on the basis of the shape of the fuel cells  3  in the cell stacks  5 , the length of the cell stacks  5  in the array direction  104 , and the temperature distribution of the cell stacks  5 . More specifically, the length of the opening  22   x / 22   y  in the array direction  104  may be about 60% or more or about 75% or more of the length of each of the cell stacks  5  in the array direction  104 . The height of the opening  22   x / 22   y  in the height  106  direction may be about 50% or more or about 70% or more of the height of an electricity generation portion of the fuel cells  3 . For example, in the case of hollow plate type fuel cells  3 , the height of the electricity generation portion corresponds to the height of the oxygen-side electrode. 
         [0072]    The opening  22   x / 22   y  may be symmetrical about the central portion  56  of the side surfaces  51 / 52  of the cell stacks  5  in the array direction  104 . 
         [0073]    In the embodiment shown in  FIG. 4 , the module  400  comprises four heat insulators  20 A,  21 A,  20 B, and  21 B each facing the respective side surfaces  51 / 52  of the cell stacks  5 . The heat insulators  20 A and  20 B face the side surfaces  51  and are positioned on the side of the reactant gas inlet  12  and the heat insulators  21 A and  21 B face the side surfaces  52  and are positioned on the side of the inner wall  9  of the housing  2 . Each of the four heat insulators  20 A,  21 A,  20 B, and  21 B comprise the respective opening  22   x / 22   y . The heat insulators  20 A and  20 B each comprise the opening  22   x  and the heat insulators  21 A and  21 B each comprise the opening  22   y.    
         [0074]    As illustrated in  FIGS. 5A and 5B , the opening  22   x  is surrounded by the heat-insulating plates  71  to  74  of the heat insulator  20 , and the opening  22   y  is surrounded by the plates heat-insulating  81  to  84  of the heat insulator  21 . 
         [0075]    Distance L 1  between an upper end  78  of the opening  22   x  and the surface of the manifold  4  may be substantially the same as distance L 2  between an upper end  88  of the opening  22   y  and the surface of the manifold  4 . Distance L 3  between a lower end  79  of the opening  22   x  and the surface of the manifold  4  may be substantially the same as the distance L 4  between a lower end  89  of the opening  22   y  and the surface of the manifold  4 . The opening  22   x  may have substantially the same shape as the opening  22   y.    
         [0076]    In an embodiment, as illustrated in  FIG. 5A , the heat insulator  20  adjacent to the reactant gas inlet  12  further comprises an additional opening below the opening  22 . The additional opening is a reactant gas introducing portion  23  for introducing a reactant gas from the reactant gas inlet  12  into the fuel cells  3 . More specifically, a reactant gas from the reactant gas inlet  12  is introduced from the reactant gas introducing portion  23  into the periphery of the fuel cells  3  (between the fuel cells  3 ), flows upward in the height  106  direction, and is used for the generation of electricity in the fuel cells  3 . 
         [0077]    In the present embodiment, as described above, a reactant gas introduced from the reactant gas inlet  12  into the fuel cells  3  is air. 
         [0078]    An excess oxygen-containing gas such as air flowing upward between the fuel cells  3  in the height  106  direction, together with excess fuel gas flowing from the gas passage (not shown) within the fuel cells  3 , can be burned at the upper end  101  of the cell stacks  5 . This can efficiently increase the temperature of the reformer  6  positioned above the cell stacks  5  as shown in  FIG. 1 , promoting reforming in the reformer  6 . 
         [0079]    In the case that unused fuel gas and unused air in the generation of electricity in the fuel cells  3  are burned at the upper end  101  of the cell stacks  5 , the opening  22   x / 22   y  approximately faces the central portion  56  of the side surfaces  51 / 52  of the cell stacks  5  in the height  106  direction and may broaden toward the upper end  101 . In other words, the opening  22   x / 22   y  may be longer at the upper end  101  than at the lower end  102 . 
         [0080]    In this manner, the temperature of the upper end  101  of the cell stacks  5  is less likely to increase excessively because of a combustion reaction at the upper end  101  of the cell stacks  5 . This can also make the temperature of the lower end  102  of the fuel cells  3  less likely to decrease excessively because of excessive introduction of air from the reactant gas inlet  12  through the reactant gas introducing portion  23  at the lower end  102  of the fuel cells  3 . 
         [0081]    Thus, extending the opening  22   x / 22   y  toward an upper end of the opening  22  can decrease the temperature of the upper end  101  of the fuel cells  3  and result in the temperature of the lower end  102  of the fuel cells  3  less likely to decrease excessively. Consequently, the temperature distribution in the height  106  direction can be closer to uniform. 
         [0082]    As illustrated in  FIG. 5A , the heat insulator  20  comprises a plurality of plates, and the reactant gas introducing portion  23  is surrounded by the heat-insulating plates  71 ,  72 , and  74  of the heat insulator  20  and the manifold  4 . If the heat insulator  20  is a single plate, the reactant gas introducing portion  23  may be an indentation at the lower end of the heat insulator  20 . 
         [0083]    Each of the module  100  and the module  400  comprises a plurality of heat insulators adjacent to the side surfaces  51 / 52  of the cell stacks  5 . More specifically, each of the module  100  and the module  400  comprises four heat insulators facing the side surfaces  51 / 52  of the two cell stacks  5 . 
         [0084]    As explained above all the four heat insulators  16  facing respective side surfaces  51 / 52  of the cell stacks  5  comprise the depressed portion  34  in the module  100  and all the four heat insulators  20 / 21  facing respective side surfaces  51 / 52  of the cell stacks  5  comprise the opening  22   x / 22   y  in the module  400 . However, in one embodiment, at least one of the heat insulators facing each of the side surfaces  51 / 52  of the cell stacks  5  may comprise the depressed portion  34  in the module  100  or the opening  22   x / 22   y  in the module  400 . To facilitate the flow of air, the heat insulators adjacent to the reactant gas inlet  12  may comprises the depressed portion  34  or the opening  22 . 
         [0085]    The heat insulators  16 / 20 / 21  adjacent to the side surfaces  51 / 52  of the cell stacks  5  may be appropriately positioned based on the number of cell stacks  5  in the housing  2  and the number of reactant gas inlets  12 . For example, in a fuel cell module that comprises two cell stacks  5  juxtaposed to each other and the reactant gas inlets  12  at the outsides of the cell stacks  5 , heat insulators  16 / 20 / 21  may be positioned between the reactant gas inlets  12  and the cell stacks  5  and between the cell stacks  5 . 
         [0086]      FIGS. 6A and 6B  are illustrations of an exemplary cell stack assembly  24  to be housed in the housing  2  and heat insulators adjacent to the side surfaces  51 / 52  of the cell stacks  5  in a fuel cell module  600  according to an embodiment of disclosure.  FIG. 6A  is an illustration of a side view of the cell stack assembly  24  viewed from a first side of the reactant gas inlet  12 , and  FIG. 6B  is an illustration of a side view of the cell stack assembly  24  viewed from a second side of the reactant gas inlet  12 . In  FIGS. 6A and 6B , the reformer  6  is not shown, and the current collector  19  is positioned at each end  91 / 92  of the cell stacks  5 . 
         [0087]    In the cell stack assembly  24  illustrated in  FIGS. 6A and 6B , heat insulators  25 / 26 / 27 / 28  face the upper end  101  and the lower end  102  of side surfaces  51 / 52  of the cell stack  5 . In this manner, the heat insulators  25  and  27  are adjacent to the upper end  101  and the heat insulators  26  and  28  are adjacent to the lower end  102 . The heat insulators  25  and  26  are separated vertically from each other and the heat insulators  27  and  28  are separated vertically from each other. 
         [0088]    More specifically, in  FIG. 6A , a heat insulator  25  is adjacent to the upper end  101 , and a heat insulator  26  is adjacent to the lower end  102 . In  FIG. 6B , a heat insulator  27  is adjacent to the upper end  101 , and a heat insulator  28  is adjacent to the lower end  102 . 
         [0089]    The heat insulators  25 ,  26 ,  27 , and  28  may have a length approximately equal to or longer than the length of the cell stack  5  in the array direction  104 . The lengths L 25 , L 26 , L 27 , and L 28  of the heat insulators  25 ,  26 ,  27 , and  28  in the array direction  104  are larger than the length L 5  of each of the cell stacks  5  in the array direction  104 . A length approximately equal to or longer than the length of the cell stacks  5  refers to about 90% or more of the length of each of the cell stacks  5 . 
         [0090]    As mentioned above, in the cell stack assembly  24 , the heat insulators  25  and  27  are adjacent to the upper end  101  of the cell stacks  5  and are separated (vertically separated) in the height  106  direction from the heat insulators  26  and  28  adjacent to the lower end  102  of the cell stacks  5 . Thus, an opening  29  at which the side surfaces  51 / 52  of the cell stacks  5  is not covered with the heat insulators  25 ,  26 ,  27 , and  28  is positioned between the vertically separated heat insulators  25  and  26 , and  27  and  28  respectively. 
         [0091]    Heat resulting from the generation of electricity in the cell stacks  5  can be dissipated via the opening  29 . The opening  29  extends from one end  91  to the other end  92  of the side surfaces  51 / 52  of the cell stacks  5  in the array direction  104 . In other words, the opening  29  passes through the cell stack assembly  24  along the side surfaces  51 / 52  of the cell stacks  5  in the array direction  104 . 
         [0092]    The length of each of the cell stacks  5  in the array direction  104  may be the length L 5  between one end  91  and the other end  92  of the cell stacks  5  as shown in  FIG. 6A . 
         [0093]    The opening  29  can decrease the overall temperature of the fuel cells  3  in the cell stacks  5 . Furthermore, air in the opening  29  circulates between the central portion  56  in the array direction  104 , which has substantially the highest temperature in the cell stacks  5 , and the ends  91  and  92 , which have the substantially lowest temperature in the cell stacks  5 . The air circulation decreases the temperature of the central portion  56  and increases the temperatures of the ends  91  and  92 . Consequently, the temperature distribution of the cell stacks  5  can be closer to uniform. 
         [0094]    The heat insulator  26  is separated from the surface of the manifold  4  so that a reactant gas from the reactant gas inlet  12  can be introduced to the periphery of the fuel cells  3  (between the fuel cells  3 ). In other words, the heat insulator  26  is separated in the height  106  direction from the manifold  4 . Specifically, the heat insulator  26  is separated in the height  106  direction from the joint  95  (not shown in  FIG. 6A ) of the manifold  4 . 
         [0095]    When a heat insulator is placed to cover at least on a side surfaces  51 / 52  of the cell stacks  5  in the array direction  104  so as to make a space for the inflow and circulation of air from between the fuel cells  3 , part of air between the fuel cells  3  circulates in the space. This can make the temperature distribution of the cell stacks  5  closer to uniform. 
         [0096]    The heat insulators  16 B/ 16 C juxtaposed to the side surfaces  51  of the cell stacks  5  adjacent to the reactant gas inlet  12  and the heat insulators  16 A/ 16 D juxtaposed to the side surfaces  52  of the cell stacks  5  may be attached to the side surfaces  51 / 52  respectively and/or may form a continuous plate across the side surfaces  51 / 52  for each of the fuel cells  3 . This allows the heat insulators to maintain their shapes for an extended period of time. In particular, the heat insulators can maintain the shape of the depressed portion  34  or the opening  22  or  29  for an extended period of time. 
         [0097]      FIGS. 7A and 7B  illustrate schematic perspective views of exemplary reactant gas inlet  702  and  704  that can be used as the reactant gas inlet  12  of the module  100  respectively according to two embodiments of the disclosure. 
         [0098]    The reactant gas inlet  704  comprises a coupling member  30  for coupling a heat insulator adjacent to the reactant gas inlet  704 , whereas the reactant gas inlet  702  does not comprise the coupling member  30 . 
         [0099]    When the heat insulator  20  comprising the opening  22  ( FIG. 5A ) is placed on a side surfaces  51 / 52  of the cell stacks  5  adjacent to the reactant gas inlet  12 , the opening  22  may be securely coupled with the reactant gas inlet  12 . This allows the heat insulator  20  to maintain the shape of the opening  22  for a long period of time even when it may be hard for the heat insulator  20  alone to maintain the shape of the opening  22  for an extended period of time, depending on the type and the strength of the heat insulator  20 . 
         [0100]    If the heat insulator  20  comprising the opening  22  has a sufficient strength, for example, when the heat insulator  20  is a heat-insulating board, the reactant gas inlet  702  can be used to secure the heat insulator  20  having the opening  22  against the reactant gas inlet  702 . This allows the heat insulator  20  to maintain the shape of the opening  22  for a long period of time. 
         [0101]    If the heat insulator  20  comprising the opening  22  has a low strength, for example, when the heat insulator  20  is heat-insulating wool, the reactant gas inlet  704  can be used. The reactant gas inlet  704  comprises the coupling member  30  for coupling a heat insulator, specifically, an opening  22 . The heat insulator  20  comprising the opening  22  can be coupled with the coupling member  30  to attach the heat insulator  20  to the reactant gas inlet  704 . This allows the heat insulator  20  having the opening  22  to maintain shape of the opening  22  for an extended period of time even when the heat insulator  20  having the opening  22  has a low strength. 
         [0102]    In  FIG. 7B , the coupling member  30  comprises three columnar members  30 A,  30 B, and  30 C. The columnar members  30 A and  30 B are positioned in the height  106  direction. The columnar member  30 C is positioned in the longitudinal direction of the reactant gas inlet  704  that is in the array direction  104 , to couple the upper ends  706  of the columnar members  30 A and  30 B to each other. 
         [0103]    The opening  22  of the heat insulator  20  has a shape adapted to the shape of the coupling member  30  such that the opening  22  is coupled with the coupling member  30 . This allows the heat insulator  20  to maintain the shape of the opening  22  for an extended period of time. Thus, the opening  22  can be easily shaped by coupling the heat insulator  20  with the coupling member  30 . 
         [0104]    The coupling member  30  may have any shape adapted to the shape of the opening  22 , for example but without limitation, rectangular, circular, elliptical, or triangular, and the like. 
         [0105]    The reactant gas inlets  702  and  704  each comprise a plurality of outlets  13 . The outlets  13  comprise holes through which air is introduced to the cell stacks  5 . Distances d between adjacent holes are relatively small in a mid section  710  in the array direction  104  and relatively large at near ends  708  in the array direction  104 . This structure allows more air/gas to be supplied to the central portion  56  than to the ends  91 / 92  of the cell stacks  5  ( FIG. 1 ); dissipating heat more efficiently in the central portion  56  than at the ends  91 / 92  of the cell stacks  5 . Consequently, the temperature distribution of the cell stacks  5  can be closer to uniform. The outlets  13  may be positioned at constant intervals from each other. 
         [0106]      FIGS. 8A and 8B  are illustrations of exemplary states in which a heat insulator  20  is coupled to a coupling member  30  according to two embodiments of the disclosure. In the embodiments shown in  FIGS. 8A and 8B , a heat insulator  20  comprising an opening  22  is coupled with the reactant gas inlet  12  ( 704   FIG. 7B ) via the coupling member  30 . In the embodiment shown in  FIG. 8A , the heat insulator  20  comprises a single plate comprising an opening. In the embodiment shown in  FIG. 8B , the heat insulator  20  comprises a plurality of plates. In the embodiments shown in  FIGS. 8A and 8B , a reactant gas introducing portion  23  is not shown. 
         [0107]    The shape of the opening  22  of the heat insulator  20  is adapted to the shape of the coupling member  30  to couple the heat insulator  20  comprising the opening  22  with the coupling member  30 , thereby attach the heat insulator  20  to the reactant gas inlet  12 . In addition, the opening  22  can be easily shaped. 
         [0108]    Whether the heat insulator  20  comprising the opening  22  is a single plate having an opening illustrated in  FIG. 8A  or a heat insulator comprising a plurality of plates illustrated in  FIG. 8B , the heat insulator  20  can be appropriately formed in accordance with the shape of the housing  2  of the module  100 / 400 . 
         [0109]    For example, in the module  400  shown in  FIG. 4 , the heat insulator  20  comprising the opening  22  may comprise a plurality of plates shown in  FIG. 8B . This facilitates the fabrication of the fuel cell module  400 . 
         [0110]    More specifically, the heat-insulating plates  71  and  72  can be placed on the left and right sides of the coupling member  30  respectively and the heat-insulating plates  73  and  74  can be placed on the top and bottom of the coupling member  30  respectively. 
         [0111]    After the cell stack assembly  8  is slid into the housing  2 , the upper and lower heat-insulating plates  73  and  74  are inserted into spaces between the cell stacks  5  and the reactant gas inlet  12 . The upper heat-insulating plate  73  is inserted to be placed on the coupling member  30 . This allows the upper heat-insulating plate  73  to be positioned on the coupling member  30 . The lower heat-insulating plate  74  is placed on the manifold  4 . The left and right heat-insulating plates  71  and  72  are inserted from both sides of the housing  2  between the cell stacks  5  and the reactant gas inlet  12  to bring the left and right heat-insulating plates  71  and  72  into contact with the coupling member  30 . This allows the heat-insulating plates  71 ,  72 ,  73 , and  74  to be easily attached in the housing  2 . 
         [0112]    In this case, the upper heat-insulating plate  73  may have the same length as the coupling member  30  in the array direction  104 . The upper ends  806  of the left and right heat-insulating plates  71  and  72  may be at the same height as the upper end  808  of the heat-insulating plate  73 . The upper heat-insulating plate  73  and the lower heat-insulating plate  74  can be attached to the coupling member  30  by placing them between the left and right heat-insulating plates  71  and  72 . The heat-insulating plates  71 ,  72 ,  73 , and  74  may be attached to the coupling member  30  with an adhesive. 
         [0113]      FIG. 9A  is an illustration of a schematic perspective view of an exemplary reactant gas inlet  902  according to an embodiment of the disclosure.  FIG. 9B  is an illustration of an exemplary state in which heat insulators  25  and  26  couple to the reactant gas inlet  902  of  FIG. 9A  via coupling members  31  according to an embodiment of the disclosure. In the embodiments shown in  FIGS. 9A and 9B , the heat insulators  25  and  26  illustrated in  FIG. 6A  are coupled with the reactant gas inlet  902  in the module  600 . In the embodiment shown in  FIG. 9A  the reactant gas inlet  902  comprises coupling members  31 . In the embodiment shown in  FIG. 9B , the heat insulators  25  and  26  are positioned on the coupling members  31 . 
         [0114]    The heat insulators  25  and  26  may have a length approximately equal to or longer than the length of each of the cell stacks  5  in the array direction  104 . Thus, the coupling members  31  may extend from first end  906  to the second end  908  of the reactant gas inlet  902  in the array direction  104 . 
         [0115]    Thus, the opening  29  can be easily shaped by placing the heat insulators  25  and  26  on the coupling members  31 , facilitating the fabrication of the fuel cell module  600 . 
         [0116]    More specifically, as in fabrication of the module  400  described above, after the cell stack assembly  24  is slid into the housing  2 , the heat insulators  25  and  26  are inserted and placed on the coupling members  31 . 
         [0117]      FIG. 10  is an illustration of a schematic perspective view of an exemplary a fuel cell module  1100  (module  1100 ) according to an embodiment of the disclosure. The module  1100  comprises the housing  2 , the cell stack assembly  24 , the heat insulators  25 / 26 / 27 / 28  and an attaching member  32 . In  FIG. 10 , the housing  2  and the like are not shown. In  FIG. 10 , the heat insulators  27  and  28  are attached with the attaching member  32  which faces the reactant gas inlet  12  (not shown) with the cell stacks  5  interposed therebetween. The heat insulators  25  and  26  are also attached with the attaching member  32  in the same way as the heat insulators  27  and  28  (not shown).  FIG. 11  is an illustration of a cross-sectional view of the module  1100  shown in  FIG. 10  taken along a line B-B in  FIG. 10 . 
         [0118]    As illustrated in  FIG. 10 , a plate of the attaching member  32  faces the reactant gas inlet  12  with interposed therebetween the cell stacks  5 . The heat insulators  27  and  28  are positioned between the cell stacks  5  and the fixing member  32 . In other words, the attaching member  32  outside the cell stacks  5  is abutted against the heat insulators  27  and  28  to attach the heat insulators  27  and  28  to the cell stack assembly  24 . 
         [0119]    The attaching members  32  are coupled to attaching portions  33  of the reformer  6  and attaching portions  34  of the manifold  4 , for example, with screws and the like. Thus, the attaching members  32  can be attached to the reformer  6  and the manifold  4 , and substantially simultaneously the heat insulators  27  and  28  can be attached to the cell stack assembly  24 . The attaching member  32  may be formed of any heat-resistant material, for example but without limitation, a metal such as stainless steel, and the like. 
         [0120]    In the embodiments shown in  FIG. 10 , the attaching member  32  is attached to the reformer  6  and the manifold  4  through the attaching portions  33  and  34 . Alternatively, the attaching member  32  may be partially bent so that the attaching member  32  can be attached directly to the reformer  6  and the manifold  4 . The attaching member  32  may be attached to either the reformer  6  or the manifold  4 . 
         [0121]    Although the heat insulators  27  and  28  can be abutted against the attaching member  32  to be attached, the attaching member  32  may comprise a coupling member (not shown) for coupling the heat insulators  27  and  28 . This can facilitate the fabrication of the module  1100 . 
         [0122]    As described above, the fuel cells  3  in the modules  100 ,  400 , and  1100  may comprise solid oxide fuel cells that comprise a fuel-side electrode, a solid electrolyte, and an oxygen-side electrode positioned in this order on a supporting substrate. 
         [0123]    The fuel cells  3  may comprise a gas passage (not shown) within the supporting substrate. In the cell stack assembly  8  shown in  FIG. 1 , a fuel gas produced in the reformer  6  passes through the gas flow pipe  7  and the manifold  4  and then flows through a gas passage (not shown) within the supporting substrate from the lower end  102  to the upper end  101 . The fuel gas from the gas passage (not shown) reacts with air/gas from the reactant gas inlet  12 , thus generating electricity. 
         [0124]    The fuel cells  3  may have any shape, for example but without limitation, a plate, a cylinder, a hollow plate, and the like. To efficiently generate electricity with the fuel cells  3  in the cell stack  5 , the fuel cells  3  may have a hollow plate shape. 
         [0125]      FIG. 12  is an illustration of an exploded perspective view of an exemplary fuel cell apparatus  35  according to an embodiment of the disclosure. The fuel cell apparatus  35  comprises the module  100  illustrated in  FIG. 1 , auxiliaries for operating the module  100  (not shown), and a case  43 , comprising props  36  and an outer casing  37 , for housing the module  100 . For sake of simplicity, in the embodiment shown  FIG. 12  some components are not shown. 
         [0126]    The fuel cell apparatus  35  further comprises a module storage  39  and an auxiliary storage  40 , which are separated by a partition  38 , in the case  43 . The module storage  39  is positioned in the upper part of the case  43  and houses the module  1 . The auxiliary storage  40  is positioned in the lower part of the case  43  and houses auxiliaries for operating the module  100 . Examples of the auxiliaries housed in the auxiliary storage  40  (not shown in  FIG. 12 ) comprise a water supply unit for supplying the module  100  with water and other supply units for supplying the module  100  with a fuel gas and air. These auxiliaries are not shown in  FIG. 12 . 
         [0127]    The partition  38  comprises an air flow port  41  for sending air from the auxiliary storage  40  to the module storage  39 . The module storage  39  comprises an air outlet  42  for exhausting air from the module storage  39 . 
         [0128]    The fuel cell apparatus  35  comprises the module  100  having improved power generation performance as described above. The fuel cell apparatus  35  can therefore achieve high power generation efficiency. 
         [0129]    In the fuel cell apparatus  35 , when the fuel cells  3  are solid oxide fuel cells, auxiliaries for operating the fuel cells  3 , as well as the module  100 , can be miniaturized. This results in miniaturization of the fuel cell apparatus  35 . The fuel cell apparatus  35  comprising the solid oxide fuel cells  3  can operate under fluctuating load (load-following operation), which is required for household fuel cell apparatuses. The fuel cell apparatus  35  comprising the solid oxide fuel cells  3  can therefore be suitably used as a household fuel cell apparatus. 
         [0130]    In the module  100 , module  400  and the module  1100 , a fuel gas (hydrogen-containing gas) flows through the gas passage (not shown) within the fuel cells  3 , and air (an oxygen-containing gas) flows through the reactant gas inlet  12 . Alternatively, air/gas may flow through the gas passage (not shown) within the fuel cells  3 , and a fuel gas may flow through the reactant gas inlet  12 . In other words, a gas flowing through the reactant gas inlet  12  may be air or a fuel gas, which is a reactant gas used for the generation of electricity. 
         [0131]    In the module  400 , the heat insulator  20  juxtaposed to the side surfaces  51 / 52  of the cell stacks  5  adjacent to the reactant gas inlet  12  is a single heat-insulating plate illustrated in  FIG. 8A  or a heat insulator comprising four plates illustrated in  FIG. 8B . However, the heat insulator  20  may comprise two heat insulators: one comprises the reactant gas introducing portion  23  for introducing a reactant gas from the reactant gas inlet  12  into the cell stacks  5 , and the other comprises the opening  22  approximately facing the central portion  56  of side surfaces  51 / 52  of the cell stacks  5 . 
         [0132]    In this case, the one comprising the reactant gas introducing portion  23  may be formed of a heat-insulating board, and the other having the opening  22  may be formed of heat-insulating wool. 
       EXAMPLES 
       [0133]    A solid oxide fuel cell (hereinafter referred to as a fuel cell) was fabricated. The fuel cell comprised a supporting substrate, 10 gas passages within the supporting substrate, and a fuel-side electrode, a solid electrolyte, and an oxygen-side electrode positioned in this order on the supporting substrate. 
         [0134]    The supporting substrate was a hollow plate type supporting substrate composed of about 48% by volume NiO and about 52% by volume Y 2 O 3  and having a thickness of about 2 mm after firing-reduction. 
         [0135]    The fuel-side electrode was formed by applying a mixture of a NiO powder, a ZrO 2  powder in which Y 2 O 3  was dissolved as solid solution, an organic binder, and a solvent to the supporting substrate and drying the mixture. 
         [0136]    The solid electrolyte was formed by applying ZrO 2  in which about 8% by mole Y was dissolved as solid solution to the fuel-side electrode layer and drying the ZrO 2 . 
         [0137]    After the fuel-side electrode and the solid electrolyte formed on the supporting substrate were calcined, a mixed interconnector material comprising a LaCrO 3  oxide, an organic binder, and a solvent was applied to the supporting substrate and was fired. A La 0.6 Sr 0.4 Co 0.2 Fe 0.8 O 3  oxygen-side electrode was baked on the solid electrolyte, thus fabricating the fuel cell  3 . 
         [0138]    Seventy fuel cells  3  thus fabricated were aligned at about 2.5 mm intervals to fabricate the cell stacks  5 . The fuel cells  3  of the cell stacks  5  were attached at their lower end  102  to the manifold  4  with a glass sealant to fabricate a cell stack assembly  8 . 
         [0139]    After the cell stack assembly  8  was placed in the housing  2 , heat insulators were placed on the side surfaces  51 / 52  of the cell stacks  5  to fabricate a module  100 . The module  100  was subjected to a power generation test under conditions of AC of about 700 W, fuel utilization (Uf) of about 75%, and air utilization (Ua) of about 38%. 
         [0140]      FIG. 13  is a graph showing the results of an electricity generation test. In  FIG. 13 , “opening  22 ” in the legend means that the electricity generation test was performed with a module that comprised the cell stack assembly  8  illustrated in  FIGS. 5A and 5B , “opening  22 +attaching members  32 ” means that the electricity generation test was performed with a module that comprised the cell stack assembly  8  illustrated in  FIGS. 5A and 5B  and the attaching members  32  on both sides of the cell stack assembly  8 , and “opening  29 ” means that the electricity generation test was performed with a module that comprised a cell stack assembly  24  illustrated in  FIGS. 6A and 6B . “Conventional” means that the electricity generation test was performed with a module that comprised heat insulators having neither the opening  22  nor the opening  29 . 
         [0141]    The length of the opening  22  in the array direction  104  was about 75% of the length of each of the cell stacks  5 , and the height of the opening  22  was about 60% of the height of the oxygen-side electrode in the fuel cell  3 . The height of the opening  29  was about 60% of the height of the oxygen-side electrode in the fuel cell  3 . 
         [0142]    The temperatures of the cell stacks  5  were measured at about half the height of the fuel cells  3  in the array direction  104 . 
         [0143]      FIG. 13  shows that the conventional module that comprised heat insulators having neither the opening  22  nor the opening  29  on the side surfaces  51 / 52  of the cell stacks  5  had a temperature difference of approximately 160° C. between the ends  91 / 92  and the central portion  56  of the cell stacks  5 . In contrast, the module that comprised heat insulators  20  having the opening  22  had a temperature difference of approximately about 60° C. between the ends  91 / 92  and the central portion  56  of the cell stacks  5 . The installation of the heat insulators comprising the opening  22  made the temperature distribution of the cell stacks  5  closer to uniform. 
         [0144]    The module that comprised the heat insulators having the opening  22  and the attaching members  32  had a temperature difference of about 40° C. between the ends  91 / 92  and the central portion  56  of the cell stacks  5 . Installation of the attaching members  32  further made the temperature distribution of the cell stacks  5  closer to uniform. 
         [0145]    The module that comprised the heat insulators comprising the opening  29  had a temperature difference of approximately 40° C. between the ends  91 / 92  and the central portion  56  of the cell stacks  5 . Installation of the heat insulators at the upper end  101  and the lower end  102  of the side surfaces  51 / 52  of the cell stacks  5  made the temperature distribution of the cell stacks  5  closer to uniform. 
         [0146]    While at least one exemplary embodiment has been presented in the foregoing detailed description, the disclosure is not limited to the above-described embodiment or embodiments. Variations may be apparent to those skilled in the art. In carrying out the disclosure, various modifications, combinations, sub-combinations and alterations may occur in regard to the elements of the above-described embodiment insofar as they are within the technical scope of the disclosure or the equivalents thereof. The exemplary embodiment or exemplary embodiments are examples, and are not intended to limit the scope, applicability, or configuration of the disclosure in any way. Rather, the foregoing detailed description will provide those skilled in the art with a template for implementing the exemplary embodiment or exemplary embodiments. It should be understood that various changes can be made in the function and arrangement of elements without departing from the scope of the disclosure as set forth in the appended claims and the legal equivalents thereof. Furthermore, although embodiments of the disclosure have been described with reference to the accompanying drawings, it is to be noted that changes and modifications may be apparent to those skilled in the art. Such changes and modifications are to be understood as being comprised within the scope of the disclosure as defined by the claims. 
         [0147]    Terms and phrases used in this document, and variations hereof, unless otherwise expressly stated, should be construed as open ended as opposed to limiting. As examples of the foregoing: the term “including” should be read as mean “including, without limitation” or the like; the term “example” is used to provide exemplary instances of the item in discussion, not an exhaustive or limiting list thereof; and adjectives such as “conventional,” “traditional,” “normal,” “standard,” “known” and terms of similar meaning should not be construed as limiting the item described to a given time period or to an item available as of a given time, but instead should be read to encompass conventional, traditional, normal, or standard technologies that may be available or known now or at any time in the future. Likewise, a group of items linked with the conjunction “and” should not be read as requiring that each and every one of those items in the grouping be present, but rather should be read as “and/or” unless expressly stated otherwise. Similarly, a group of items linked with the conjunction “or” should not be read as requiring mutual exclusivity among that group, but rather should also be read as “and/or” unless expressly stated otherwise. Furthermore, although items, elements or components of the disclosure may be described or claimed in the singular, the plural is contemplated to be within the scope thereof unless limitation to the singular is explicitly stated. The presence of broadening words and phrases such as “one or more,” “at least,” “but not limited to” or other like phrases in some instances shall not be read to mean that the narrower case is intended or required in instances where such broadening phrases may be absent. The term “about” when referring to a numerical value or range is intended to encompass values resulting from experimental error that can occur when taking measurements.