1. Field of the Invention
The present invention relates to a fuel cell system using a fuel cell and battery, and more particularly, to a fuel cell system used for self-generation including cogeneration at a household or factory, and a method of operating the same.
2. Related Art of the Invention
When generators such as an engine, gas turbine and fuel cell are used for self-generation, these generators cannot perform power control capable of speedily responding to a load, which causes excess or shortage of power. It has been known to solve excess or shortage of power produced by self-generation such as a power generation system, by connecting self-generation equipment, commercial power and a load by means of a grid connect. This system only requires an amount of power generated smaller than a peak load, and therefore it has a merit of reducing an equipment cost.
However, when power is traded with a power company through the grid connect, there is a case that a purchase price from the power company is high, while a selling price for the power company is extremely low. For example, in Japan, the purchasing price is ¥25/kW, while the selling price is ¥5/kW. For this reason, under the current price system of electric power, the economical merit of self-generation for the purpose of solving the problem of excess or shortage of self-generation decreases as the amount of power traded increases.
Other means of solving power excess or shortage includes, for example, means of storing power using batteries (e.g., Japanese Patent Laid-Open No. 05-182675). The problem of power excess or shortage is solved by charging the excessive power in a battery when the amount of power generated by a fuel cell exceeds its load, and by discharging and supplying power from the battery to the load when the amount of power generated by the fuel cell falls below the load. The disclosure of Japanese Patent Laid-Open No. 05-182675 is incorporated herein by reference in its entirety.
Since this method does not involve trading of power in excess or shortage, the economical efficiency of self-generation is improved. However, a large-volume battery is required to cover a peak load, which produces a new problem of increasing a cost of equipment. Therefore, a method of employing a grid connect simultaneously with this method, reducing the size of equipment and increasing an operation rate of the equipment while reducing the amount of power traded with a power company is also often adopted.
On the other hand, a fuel cell is now a focus of attention as a high efficiency generator. Especially, a polymer electrolyte fuel cell, which operates at a low temperature of 70xc2x0 C., can quickly increase or decrease the amount of power generated and its speed of response is so high that it is expected to be used in electric vehicles when hydrogen is used as a fuel gas.
However, self-generation requires hydrogen to be generated as a fuel gas for a fuel cell using natural gas or petroleum as a raw material and it is difficult to control the amount of hydrogen generated in this hydrogen generation process at high speed. Thus, even if the power generation section is a highly responsive high polymer type fuel cell, it is difficult to operate and control the entire system in accordance with load variations.
Due to technical problems of the generator or battery, or problems with the fee system, etc., excess or shortage in the amount of power generated of self-generation has not been solved. This accounts for the fact that self-generation using a fuel cell is widely used only among hotels and semiconductor factories where there are fewer load variations and self-generation using a fuel cell is conventionally not used at households and stores where there are drastic load variations.
One of causes for power excess or shortage in self-generation using a fuel cell is slow heat response in hydrogen generation process control. The speed of response of control over the amount of power generated of the fuel cell itself is high, but increase/decrease or fluctuations in hydrogen generation by transforming carbon hydride into hydrogen cannot be accelerated.
Attempting to use a battery, especially a flood type lead acid battery for a fuel cell to solve the problem of responsivity in particular will result in technical problems of the battery itself. That is, if self-generation is performed at a household, power load fluctuates frequently and drastically, charging/discharging takes place several tens of times to several thousands of times a day and since its depth of discharge is large, thereby intensifying the deterioration of the battery.
Furthermore, due to an overcharge reaction before and after full charging, the battery produces hydrogen, which is hard to deal with. Hydrogen generated is normally discharged into an atmosphere, but for the purpose of the security, it is necessary to diffuse and so on, and then discharge it into an atmosphere in an extremely low-concentration. Thus, this equipment for diffusion and discharge entails a problem of high cost.
On the other hand, to prevent generation of hydrogen, a sealed lead acid battery may be used, but it is more expensive than a flood type, inferior in volumetric efficiency or economical efficiency, which still results in a high cost.
Moreover, an overcharge reaction reduces the amount of water as the electrolyte of the battery, and reduces the battery capacity, causing a problem of reducing the efficiency of the battery. On the other hand, there are also additional problems with the fuel cell, which requires a solution. That is, the problem is that carbon monoxide (hereinafter referred to as xe2x80x9cCOxe2x80x9d) increased when the amount of hydrogen generated in the hydrogen generation process is increased/decreased may poison the catalyst of the fuel cell. Solving this problem is also required to secure the responsivity of the power generation system.
The present invention solves the above-described problems and it is an object of the present invention to provide a low-cost, highly responsive fuel cell system capable of facilitating the handling of a battery which works in conjunction with a fuel cell, and a method of operating the same.
The 1st aspect of the present invention is a fuel cell system comprising:
a fuel cell for generating power, that (1) is supplied an oxidizer containing oxygen to a positive electrode and (2) is supplied a fuel gas containing hydrogen to a negative electrode;
a battery including at least water as an electrolyte; and
a hydrogen supply channel that supplies hydrogen generated from said battery to said fuel cell.
The 2nd aspect of the present invention is the fuel cell system according to 1st aspect, further comprising a hydrogen storage section in said hydrogen supply channel, which stores hydrogen generated from said battery.
The 3rd aspect of the present invention is the fuel cell system according to 1st or 2nd aspect, wherein said hydrogen supply channel is connected to the negative electrode of said fuel cell.
The 4th aspect of the present invention is the fuel cell system according to 1st aspect, further comprising an oxygen supply channel that extracts oxygen generated from said battery.
The 5th aspect of the present invention is the fuel cell system according to the 4th aspect, further comprising an oxygen storage section provided at a midpoint in said oxygen supply channel, which stores oxygen generated from said battery.
The 6th aspect of the present invention is the fuel cell system according to the 4th aspect, wherein said oxygen supply channel is connected to the positive electrode of said fuel cell.
The 7th aspect of the present invention is the fuel cell system according to the 4th aspect, wherein said oxygen supply channel is connected to the negative electrode of said fuel cell.
The 8th aspect of the present invention is the fuel cell system according to the 4th aspect, further comprising:
fuel gas generating means of generating said fuel gas by allowing fuel containing at least carbon to produce a steam reforming reaction with water; and
CO reducing means of reducing carbon monoxide contained in said fuel gas by converting the carbon monoxide into carbon dioxide through oxidation catalyst,
wherein said oxygen supply channel is connected to said CO reducing means.
The 9th aspect of the present invention is the fuel cell system according to the 1st aspect, further comprising a water supply channel that supplies water generated during power generation by said fuel cell to said battery.
The 10th aspect of the present invention is the fuel cell system according to any one of the 1st or 4th aspect, wherein said hydrogen and/or said oxygen is generated from said battery by allowing said battery to produce an overcharge reaction.
The 11th aspect of the present invention is the fuel cell system according to the 10th aspect, wherein said overcharge reaction is produced through output from said fuel cell.
The 12th aspect of the present invention is the fuel cell system according to the 10th aspect, wherein said overcharge reaction is produced through power from an external source in grid connect with said fuel cell.
The 13th aspect of the present invention is the fuel cell system according to the 1st aspect, wherein said battery is a flood type lead acid battery.
The 14th aspect of the present invention is the fuel cell system according to the 1st aspect, wherein said fuel cell is any one of polymer electrolyte type, direct methanol type or solid electrolytic type.
The 15th aspect of the present invention is a method of operating a fuel cell system comprising the steps of:
(a) supplying an oxidizer containing oxygen to a positive electrode of said fuel cell, supplying a fuel gas containing hydrogen to a negative electrode of said fuel cell and generating power,
(b) allowing a battery including at least water as an electrolyte to produce overcharge reaction, thereby to generate from said battery at least hydrogen for supplying to said fuel cell.
The 16th aspect of the present invention is the method of operating a fuel cell system according to the 15th aspect, wherein said overcharge reaction is produced when the output of said fuel cell is not insufficient with respect to a load of said fuel cell.
The 17th aspect of the present invention is the method of operating a fuel cell system according to the 15th aspect, wherein the step (a) includes supplying said hydrogen when the output of said fuel cell is not insufficient with respect to the load of said fuel cell.
The 18th aspect of the present invention is the method of operating a fuel cell system according to the 17th aspect, wherein the step (a) includes supplying said hydrogen when operation of said fuel cell is started.
The 19th aspect of the present invention is the method of operating a fuel cell system according to the 15th or 16th aspect, further comprising a step of supplying oxygen generated together with said hydrogen from said battery through said overcharge reaction to said fuel cell.
The 20th aspect of the present invention is the method of operating a fuel cell system according to the 15th aspect, further comprising a step of supplying water generated during power generation by said fuel cell as electrolytic water to said battery.
The 21st aspect of the present invention is the method of operating a fuel cell system according to the 15th aspect, wherein the step (b) includes producing said overcharge reaction through the output from said fuel cell or power of an external source in grid connect with said fuel cell.