Solid oxide fuel cells (“SOFCs” below) operate at relatively high temperatures has an oxide ion conductive solid electrolyte as an electrolyte and electrodes placed on both sides thereof. Fuel gas is supplied to one side thereof, and oxidizer (air, oxygen, or the like) is supplied to the other side thereof.
In such SOFCs, steam or CO2 is produced by the reaction between fuel and oxygen ions passed through the oxide ion conductive solid electrolyte, thereby generating electrical and thermal energy. The electrical energy is extracted from the SOFCs, where it is used for various electrical purposes. At the same time, thermal energy is used to raise the temperature of the fuel, SOFCs, oxidant, and the like.
It is known that fuel cell units degrade with usage over long time periods. Unexamined Patent Application 2007-87756 (Patent Document 1) sets forth solid oxide fuel cells. It is stated that in the fuel cells, degradation of the fuel cells can be reduced by adjusting the flow rate of fuel.
A fuel supply amount control device, fuel supply amount control method, and electrical power supply system are also set forth in Unexamined Patent Application 2003-217627 (Patent Document 2). In this fuel supply amount control device, the amount of fuel supplied is compensated when the electrical power extractable from a predetermined amount of fuel supplied decreases due to degradation of fuel cells.