JPH0624135B2 - Fuel cell power generation system - Google Patents

Description

Description: TECHNICAL FIELD OF THE INVENTION The present invention relates to a fuel cell power generation system, and more particularly to an improvement of a fuel cell power generation system including a cooling water system for removing heat generated by the fuel cell.

[Technical background of the invention]

A fuel cell is a device that directly oxidizes the chemical energy of the fuel in an electrochemical process to directly convert the energy released along with the oxidation reaction into electrical energy. The power generation system using this fuel cell is expected to reach a power generation efficiency of 40 to 50% even on a comparatively small scale, and far surpass the new thermal power. Furthermore, SOx, N, which is a pollution factor that has become a big social problem in recent years,
In principle, high energy conversion efficiency can be expected, such as extremely low Ox emissions, no need for a large amount of cooling water because the power generator does not include a combustion cycle, and low vibration noise, as well as environments such as noise and exhaust gas. Since there are few questions and answers, and because it has characteristics such as good responsiveness to load fluctuations, expectations for and interest in research on its development and practical application are high.

In addition, since this fuel cell power generation system can be modularized, the construction work period is short. Furthermore, since the exhaust heat temperature of the fuel cell body is in a range that can be used as a heat source for hot water supply, etc., and it has high efficiency such as the ability to create a heat supply power generation system, it can be used as a large-scale power generation system to partially replace future thermal power generation. Is also expected and interested.

A small-scale fuel cell power generation system like this has already been prototyped and is in the stage of experimental operation. But,
The biggest technical problems in the practical application of a large-capacity fuel cell power generation system are the miniaturization of individual fuel cells by increasing the capacity of a single unit, and how efficiently multiple fuel cells can be installed and their installation space. Of the fuel gas cooling system and the efficiency of the connection system of various terminals and electronic terminals of the fuel gas cooling system.

By the way, a cross-sectional model diagram showing the principle of such a fuel cell is shown in FIG.
As shown in the figure. That is, a unit cell in which an electrolyte layer 2 impregnated with an electrolytic solution such as phosphoric acid is interposed between a pair of porous electrodes 1 is formed, and hydrogen gas H, which is a fuel gas, is formed on both end faces of the unit cell. And air A, which is an oxidant gas, are continuously supplied. By doing so, the reaction product and the reaction residue L are continuously removed to the outside, so that power generation is continued for a long time.

The basic configuration of such a fuel cell is as shown in FIG. That is, a positive electrode 4 and a negative electrode 5 are arranged on both sides of the electrolyte matrix layer 3 to form a rectangular plate-shaped unit cell, and a large number of unit cells are connected in series in order to use the unit cell as a power generator. And then stacked,
An interconnector 6 having a groove for supplying gas is arranged between these unit cells, and the unit cells are alternately stacked. The interconnector 6 is provided with a plurality of grooves that open on two opposite side edges, and the hydrogen gas flow path 7 and the air flow path 8 whose channels are the grooves on one side face are arranged in directions orthogonal to each other. It is arranged.

By the way, the fuel cell N currently under development is the 7th
As shown in FIGS. (A) and (b), a cell stack 9 is constructed by stacking a plurality of the above-mentioned unit cells in a square pole shape, and a manifold 10 for supplying a reaction gas is attached to the side surfaces of the four sides. There is. The manifold 10 includes a hydrogen gas supply pipe 11, a hydrogen gas discharge pipe 12, and an air supply pipe 1, respectively.
3 and the air discharge pipe 14 are connected to each other, and the hydrogen gas and the air are designed to flow in the cell stack 9 in the directions of arrows A and B in the drawing. Further, the higher the operating temperature of the cell stack 9 is from the viewpoint of reaction theory, but it is desirable to maintain the operating temperature at around 200 ° C. from the viewpoint of controlling the heat resistance of the constituent materials and the vapor pressure of the electrolyte. Therefore, the cooling water is circulated through the conduit (cooling pipe) embedded in the cell stack 9 to cool the fuel at the time of starting the fuel cell and the heat generated during the operation. That is, in this type of fuel cell, the cooling water supply pipe 15 and the cooling water discharge pipe 16 are arranged as shown in FIG. 7 (a), and the cooling water flows in the cell stack 9 as shown by a broken line C in the drawing. It circulates. Further, the output of the fuel cell N is direct current, and from the power terminal (plus pole) 17 and the power terminal (minus pole) 18 arranged at the upper and lower ends of the cell stack 9,
It is drawn out of the tank 21 via the connection conductor 19 and the bushing 20.

The main body of the fuel cell as described above is housed in the tank 21, and the tank 21 is filled with nitrogen gas or the like in order to suppress the leakage of the reaction gas from the manifold 10 or the like. A heat insulating material 22 is attached to the inner surface of the tank 21 in order to keep the cell stack 9 at an appropriate temperature and to effectively utilize the generated heat during operation through the cooling pipe without radiating the heat to the outside. There is.

[Problems of background technology]

Now, a fuel cell generates a direct current voltage by an electrochemical reaction, and heat is generated by the reaction. In order to operate this fuel cell efficiently and appropriately, it is necessary to control the temperature of the cell stack at a constant level, and for that purpose, a cooling water system is provided for cooling with water. Also, since many fuel cells are connected in series or in parallel with unit cells or cell stacks, it is necessary to balance the flow rate of cooling water in order to obtain a uniform temperature distribution. For this purpose, throttle the water passage. Can be used. However, when there are a large number of cooling systems connected in parallel, the number of throttles also increases, and there is a risk of problems such as increased cost and reduced reliability due to the space occupied by them or the increase in the number of joints during manufacturing. is there.

On the other hand, the cooling water system of the fuel cell power generation system is provided with an insulating joint because it is necessary to electrically insulate the DC voltage generated in the fuel cell. Since the flow rate to each fuel cell is the same as the flow rate inside this insulating joint, a method of balancing the flow rate at the insulating joint portion can be considered. That is, if the throttle is provided in the joint fitting in the insulating joint, the above-mentioned problems can be solved. However, some of the insulating joints may be applied with a DC voltage of about 300 V in the cell stack and several thousand V between the cell stacks. When a DC voltage is applied to the insulation joint in this way, the corrosion products generated in the cooling water pipes, etc. adhere to the inner surface of the joint fitting where the voltage has a positive polarity (regardless of the water flow direction). It turned out to be. Note that this relationship is shown in the table below, and in the table, the leakage current of the joint fitting to which the voltage on the plus side is applied is expressed as plus (+).
The deposit adheres to the inner surface of the fitting in the shape of a sharp orifice, which increases water resistance, resulting in a decrease in the amount of cooling water and a decrease in cooling capacity. Depending on the amount of this adhesion, the flow rate of the cooling water may be unbalanced, or if it adheres to the above-mentioned narrowed part of the water passage, even if the amount of adhesion is small, it may become blocked. Overheating, which leads to a decrease in fuel cell performance and a reduction in life. Of the two problems described above, the latter problem is particularly the main problem.

[Object of the invention] The object of the present invention is to minimize the imbalance of the cooling water flow rate by eliminating the risk of clogging of the cooling water system due to the adhesion of corrosion products, and to ensure the localized heat due to the flow rate reduction. It is an object of the present invention to provide a small-sized, inexpensive and highly reliable fuel cell power generation system capable of preventing and improving the fuel cell performance and extending the life of the fuel cell, and performing highly efficient and stable cell operation.

[Outline of Invention]

In order to achieve the above object, in the present invention, while accommodating in a tank a cell stack formed by stacking a plurality of unit cells each having a pair of porous electrodes sandwiching an electrolyte layer impregnated with an electrolyte A fuel cell configured to supply a fuel gas to one electrode and an oxidant gas to the other electrode to extract electric energy from between the electrodes by an electrochemical reaction occurring at this time, and an inside of a cell stack. A plurality of cooling pipes are embedded in the cooling pipe, and cooling water supply and discharge pipes are connected to the cooling pipes to circulate the cooling water, and the cooling pipe and the cooling water supply pipe are connected. Insulation for electrical insulation consisting of first and second tubular joint fittings and insulating pipes connecting these joint fittings to each other and to the respective connecting portions between the cooling pipe and the cooling water discharge pipe. With a fitting In the fuel cell power generation system including the formed cooling water system, the second joint is provided in the second joint where the voltage has a polarity on the plus side of the opposing first joint in the insulating joint. A flow distribution distributor is provided at a position where the distance from the tip of the metal fitting facing the first fitting fitting is equal to or larger than the inner diameter of the second fitting fitting.

Here, particularly, the throttle of only the second joint fitting of the insulating joint provided in the connecting portion between the cooling pipe and the cooling water supply pipe is provided.

Further, a throttle is provided in the second joint fitting of each insulating joint provided in the connection portion between the cooling pipe and the cooling water supply pipe and between the cooling pipe and the cooling water discharge pipe. .

[Embodiment of the Invention] In the present invention, in a fuel cell water cooling system in which a plurality of cooling pipes are embedded in a cell stack, clogging of the cooling water system can be prevented by attaching throttles for flow distribution at appropriate places. In addition to preventing it, the structure is rationalized.

That is, the throttle in the present invention is a joint metal fitting on the opposite side of the joint metal fittings at both ends of an insulating joint that is connected to electrically insulate between the cooling pipe and the cooling water supply or cooling water discharge pipe. Install it in the fitting (anode fitting) on the side where a positive voltage is applied. The "diaphragm" is attached at a position where the distance from the tip (the end facing the joint fitting on the opposite side) is longer than the inner diameter of the joint fitting. The length of the fitting is usually 5 to 15 times the inner diameter.

Here, the reason why the "diaphragm" is attached to such a position is as follows.

(A) In the anode fittings of the insulation joint of the fuel cell water cooling system (joint fittings to which a positive voltage is applied to the joint fittings on the opposite side of the joint fittings at both ends of the insulation joint), use cooling water piping, etc. The generated corrosion products adhere intensively to the tip of the metal fitting, and the part that adheres is limited to the distance from the tip of the metal fitting (the end facing the fitting metal fitting on the opposite side) to the distance corresponding to the inner diameter of the metal fitting. I was able to confirm that.

Therefore, the "diaphragm" attached at a position farther from the tip of the insulating fitting anode metal fitting than the distance corresponding to the inner diameter of the fitting,
Corrosion products contained in the incoming cooling water do not adhere, eliminating the risk of clogging.

(B) If there are many cooling pipes, the number of throttles required will also increase. Therefore, by mounting these throttles in the joint fittings of the insulation joint, the space of the cooling water system and the number of joints can be reduced, and the reliability can be improved. Can be improved, miniaturized, and cost can be reduced.

An embodiment of the present invention shown in the drawings based on the above concept will be described below. FIG. 1 shows an example of the configuration of a fuel cell power generation system according to the present invention.
A fuel cell power generation system consisting of two cell stacks is shown. In the figure, the same parts as those in FIGS. 7 (a) and 7 (b) are designated by the same reference numerals, and the description thereof will be omitted. Only different parts will be described here.

The cooling water system will be described first in the figure. Each of the plurality of cooling pipes 26 buried in each cell stack 9 is connected to the header 25 on the supply and discharge sides at each end thereof. In addition, the header 25 on the supply side is an insulating joint 27a.
The discharge side header 25 is connected to the discharge side manifold 24 via an insulating joint 27b. Further, in the supply-side manifold 23, the upper and lower cell stacks 9 are connected to the cooling water supply pipe 15 via insulating joints 27b, respectively. Further, the discharge side manifold 24 is connected to the cooling water discharge pipe 16 through the insulating joint 27b in both the upper and lower cell stacks 9, respectively. On the other hand, the cooling water enters from the cooling water supply pipe 15 side, is heated by the cooling pipe 26, and flows to the cooling water discharge pipe 16 side. The heated cooling water may flow as a fluid containing a part of steam, that is, a so-called two-phase flow, but the cooling water containing this heat is cooled in the steam separator 31 and adjusted to an appropriate temperature. After cooling water pipe 2
A circulating pump 28 passes the cooling water pipe 9 through the cooling water pipe 30 to the cooling water supply pipe 15. By circulating the cooling water in this way, the fuel cell is kept at an appropriate temperature.

On the other hand, the insulating joints 27a and 27b in the figure are provided to electrically insulate the pipes connected thereto, and are indispensable for the pipes for the cooling water of the fuel cell for generating the DC voltage. It is a thing. By using the insulating joints 27a and 27b, it is possible to keep the pipes connected thereto at different potentials. Also, FIG. 2 (a)
Shows an enlarged view of the insulating joint 27a in FIG. 1, and FIG. 7B shows its sectional configuration. The insulating joint 27a has a direction, and the direction is determined by the direction of current flow, in other words, the polarity of voltage. That is, the insulating joint 27a is composed of two tubular joint fittings, namely cathode and anode fittings 34 and 35, and these cathode and anode fittings 3.
4, 35 are connected to each other by a Teflon insulation tube 33, and the cathode fittings 3 facing each other in the insulation joint 27a.
In the anode metal fitting 3 in which the voltage has a positive polarity with respect to 4, the distance 1 from the tip of the anode metal fitting 35 facing the cathode metal fitting 34 is equal to or larger than the inner diameter of the anode metal fitting 35.
A throttle for distributing the flow rate is provided as shown in the figure for improving the flow rate balance. The lengths of the cathode and anode fittings 34 and 35 are usually 5 to 15 times the inner diameter of each fitting. The insulating joint 27b similarly includes cathodes, anode fittings 34 and 35, and a Teflon insulating tube 33, and does not have the throttle for distributing the flow rate. Here, as the material of the cathode fitting 34, a metal used for general piping (carbon steel, stainless steel, copper, copper alloy, etc.) can be used. On the other hand, as the material of the anode fitting 35, it is preferable to use a metal (high nickel, high chromium alloy such as stainless steel) that is unlikely to cause electrolytic corrosion due to direct current, other than copper and copper alloys or carbon steel.

Next, the electrical connection will be described. In FIG. 1, between the lower cell stack 9 and the upper cell stack 9,
Alternatively, a large number of cell stacks exist between the terminals of the lower cell stack 9 and the lower load 32, or between the upper cell stack 9 and the upper load 32, and the respective power terminals (plus pole) 17 And the power terminal (minus pole) 18
All cell stacks are connected in series. Finally, the power terminal (minus pole) 18 of the uppermost cell stack is connected to the upper load 32, and the power terminal (plus pole) 17 of the lowermost cell stack is connected to the lower load 32. There is. On the other hand, the power terminal (plus pole) 17 of the upper cell stack 9 is connected to the supply side manifold 23 and the discharge side manifold 24, and the power terminal (minus pole) 18 of the lower cell stack 9 is the supply side manifold 23.
And the discharge side manifold 24. Further, the cooling water supply pipe 15, the cooling water discharge pipe 16, the cooling water pipes 29 and 30, the steam separator 31, and the circulation pump 28 of the cooling water system are electrically connected and grounded to the ground.
Here, between cell stacks and between cell stacks 9 and loads 3
Since a large current flows between the two, it is necessary to connect with a power line, but a large current is required for the electric wire between the power terminal (plus pole) 17 or the power terminal (minus pole) 18 and the supply side manifold 23 and the discharge side manifold 24. Does not flow, so there is no need to use power lines. That is, the leakage current of the insulating joints 27a and 27b flows through this electric wire.

In the fuel cell power generation system including the cooling water system configured as described above, the supply side insulating joint 27a connected to the upper cell stack 9 is positive on the upstream side in the cooling water flowing direction. The insulating joint 27a on the supply side connected to the lower cell stack 9 has a minus side on the upstream side in the cooling water flow direction. Insulation joint 27 on the supply side of the upper cell stack 9 in which the upstream side is positive
In the case of a, the corrosion product is attached to the upstream side, and the insulating joint 27 on the supply side of the lower cell stack 9 is negative on the upstream side.
In a, corrosion products adhere to the inner surface of the fitting on the downstream side.

As a result of the experiment, as shown in FIG. 3, the adhesion position in this case has a ratio of the distance from the tip end to the adhesion position of 0.05 to 0.
It turned out to be 95. Therefore, the distance l from the tip of the anode fitting 35 shown in FIG.
If the inner diameter is 5 or more, the corrosion product adhering to the orifice can be adhered to a portion other than the throttle. When the cross-sectional shape in the joint fitting is not circular, the attachment position is determined by the position with the smallest diameter, so in this case, the diaphragm position can be determined based on the position with the smallest inner diameter. Further, when the shape is complicated, it is appropriate to use the equivalent diameter obtained from the cross-sectional area.

In this way, the corrosion product is the anode metal fitting 3 other than the narrowed portion.
Although it adheres to the inside of No. 5, since this part has a large inner diameter, the decrease in the inner diameter due to the adhesion is small, and the orifice resistance due to the adhered matter is proportional to the reduction rate of the cross-sectional area of the throttle. The rate of increase in resistance is very small. In particular, when adhering close to the narrowed portion, the resistance hardly increases due to the adhering.

As described above, in a fuel cell, the required current capacity is usually obtained by stacking a large number of unit cells. Therefore, the number of cooling pipes, the number of insulating joints, the size, the length, etc., of the fuel cell are the space of the whole cell. It is very effective for In this respect, in the fuel cell power generation system according to the present embodiment, the throttle used as a method for improving the flow rate balance of the cooling water is
Since the insulating joint 27a is installed in the anode fitting 35, the space of the cooling water system and the number of joints can be reduced, and the reliability can be improved, the size can be reduced, and the cost can be reduced.

In addition, by attaching the corrosion product to the part without the restriction in the vicinity of it, the risk of clogging due to the adhesion of the corrosion product can be eliminated, and the increase in the flow path resistance due to the attachment can be suppressed to a low level. It is possible to prevent local overheating due to a decrease in the flow rate of the fuel cell, and it is possible to operate a highly efficient and stable fuel cell.

The present invention is not limited to the above-mentioned embodiments, but can be modified in various ways without departing from the scope of the invention.

(A) In the above embodiment, the throttle is provided only in the joint fitting of the insulating joint provided in the connecting portion between the supply side manifold 23 and the cooling water supply header 25, but as shown in FIG. The upstream side in the cooling water flow direction in each of the insulating joints provided at the connection portions between the supply side manifold 23 and the cooling water supply header 25 and between the discharge side manifold 24 and the cooling water discharge header 25. Even if a diaphragm is provided in the joint fitting, the same effect as described above can be obtained. In this case, the respective insulation joints 27a provided on the supply side and the discharge side are provided in the anode metal fitting 35 in which the voltage has a positive polarity with respect to the facing cathode metal fitting 34 in the insulation joint 27a, as described above.
A flow distribution diaphragm is provided at a position excluding a portion where the distance from the end of the anode fitting 35 facing the cathode fitting 34 is equal to the inner diameter of the anode fitting 35.

(B) In the above embodiment, the supply side manifold 23 may be connected to the power terminal (plus) 17 and the outlet side manifold 24 may be connected to the power terminal (minus) 18, and the same polarity may be used. Connection is also possible. In any case, if the cathode metal fitting 34 in the insulating joint 27a is connected to the low voltage side and the anode metal fitting 35 is connected to the high voltage side, the same operation and effect as described above can be obtained. .

(C) In the above embodiment, the case where the present invention is applied to the fuel cell power generation system composed of two cell stacks has been described.
The present invention can be similarly applied to a fuel cell power generation system including one or more cell stacks.

〔The invention's effect〕

As described above, according to the present invention, while accommodating a cell stack formed by stacking a plurality of unit cells having a pair of porous electrodes sandwiching an electrolyte layer impregnated with an electrolyte in a tank, Fuel gas is supplied to one electrode and oxidant gas is supplied to the other electrode, respectively, and a fuel cell configured to extract electric energy from between the electrodes by an electrochemical reaction occurring at this time, and inside the cell stack. A plurality of cooling pipes are buried, and cooling water supply and discharge pipes are connected to the cooling pipes to circulate the cooling water, and between the cooling pipes and the cooling water supply pipe. And an insulating joint for electrical insulation, which comprises first and second tubular joint fittings and insulating pipes connecting the respective joint fittings to each other at respective connecting portions between the cooling pipe and the cooling water discharge pipe. Configured with In the fuel cell power generation system comprising a cooling water system was, first voltage to the first joint fittings facing the insulating joint is positive polarity side 2
In this joint fitting, a throttle for flow distribution is provided at a position where the distance from the tip of the second fitting fitting facing the first fitting fitting is equal to or larger than the inner diameter of the second fitting fitting. Therefore, the risk of clogging of the cooling water system due to the adhesion of corrosion products is eliminated, the unbalance of the cooling water flow rate is minimized, and the local overheating due to the flow rate decrease is reliably prevented and the fuel cell performance is improved. It is possible to provide a small-sized, inexpensive and highly reliable fuel cell power generation system capable of achieving a long life and stable and highly efficient battery operation.

[Brief description of drawings]

FIG. 1 is a configuration diagram showing an embodiment of a fuel cell of the present invention, FIGS. 2 (a) and 2 (b) are enlarged views and sectional views showing insulating joints applied to the embodiment, respectively, and FIG. FIG. 4 is a characteristic diagram showing the range of deposition of products, FIG. 4 is a configuration diagram showing another embodiment of the present invention, FIG. 5 is a cross-sectional model diagram showing the principle of a fuel cell, and FIG.
FIG. 7 is a vertical cross-sectional perspective view showing the basic structure of a fuel cell, FIG. 7 (a) is a plan view showing the schematic structure of a fuel cell currently under development, and FIG. 7 (b) is also its vertical cross-sectional view. Is. N ... Fuel cell, 1 ... Porous electrode, 2 ... Electrolyte layer,
3 ... Electrolyte matrix, 4 ... Positive electrode, 5 ... Negative electrode,
6 ... Interconnector, 7 ... Hydrogen gas passage, 8 ... Air passage, 9 ... Cell stack, 10 ... Manifold,
11 ... Hydrogen gas supply pipe, 12 ... Hydrogen gas discharge pipe, 1
3 ... Air supply pipe, 14 ... Air discharge pipe, 15 ... Cooling water supply pipe, 16 ... Cooling water discharge pipe, 17 ... Power terminal (plus pole), 18 ... Power terminal (minus pole), 19
...... Connecting conductor, 20 ... Bushing, 21 ... Tank,
22 ... Insulating material, 23 ... Supply side manifold, 24 ...
… Discharge side manifold, 25 …… Header, 26 …… Cooling pipe, 27a …… (with throttle) insulation joint, 27b ……
(No throttle) Insulation joint, 28 ... Circulation pump, 29 ...
Cooling water pipe, 30 ... Cooling water pipe, 31 ... Steam separator, 32 ... Load, 33 ... Teflon insulation pipe, 34 ...
Cathode fitting, 35 ... (with diaphragm) anode fitting, 36 ... Piping, A ... Air, H ... Hydrogen, L ... Reaction product and reaction residue.

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Sumio Yamamoto 2-4 Suehiro-cho, Tsurumi-ku, Yokohama-shi, Kanagawa Toshiba Keihin Plant (72) Inventor Kiyoshi Fukui 2-cue, Suehiro-cho, Tsurumi-ku, Yokohama-shi, Kanagawa Address: Toshiba Keihin Office (56) References JP-A-52-13637 (JP, A) JP-A-60-154473 (JP, A)

Claims (3)

[Claims] 1. A cell stack formed by stacking a plurality of unit cells having a pair of porous electrodes sandwiching an electrolyte layer impregnated with an electrolyte is housed in a tank, and fuel gas is supplied to one of the electrodes. Further, a fuel cell configured to supply an oxidant gas to the other electrode and to extract electric energy from between the electrodes by an electrochemical reaction that occurs at this time, and a plurality of cooling tubes inside the cell stack. And a pipe for supplying cooling water and a pipe for discharging cooling water are respectively connected to the cooling pipe to circulate the cooling water, and between the cooling pipe and the cooling water supply pipe and the cooling pipe. Insulating joints for electrical insulation, each of which is composed of first and second tubular fittings and insulating pipes connecting the fittings to each other, are provided at respective connecting portions between the cooling water discharge pipe and the cooling water discharge pipe. Configured cooling water In a fuel cell power generation system including a second joint metal fitting, the second joint metal fitting is provided in a second joint metal fitting in which the voltage has a polarity on the positive side with respect to the first joint metal fitting facing in the insulating joint. The fuel cell power generation system is characterized in that a throttle for distributing the flow rate is provided at a position where the distance from the tip end on the opposite side to the first joint fitting is equal to or larger than the inner diameter dimension of the second joint fitting. 2. A throttle is provided only in a second joint fitting of an insulating joint provided in a connecting portion between the cooling pipe and the cooling water supply pipe. The fuel cell power generation system according to the item 1). 3. A throttle is provided in the second joint fitting of each insulation joint provided at the connecting portion between the cooling pipe and the cooling water supply pipe and between the cooling pipe and the cooling water discharge pipe. Claims (1) characterized in that
A fuel cell power generation system according to item.