2004 Volume 124 Issue 6 Pages 851-858
The Metal Hydride Intermediate-Buffer (MIB) method, which enables the load following operation of the PEFC system with reformer, has been proposed. Feasibility of this system has been already confirmed by the experiment and the result shows that metal hydride is not poisoned with impurities in reformed gas. It is expected that the MIB method improves the efficiency of PEFC system especially in low load. Efficiency improvement in low load of the PEFC system for residential use is important because the average electric power consumption in general residences is about 10-20% of the peak power. In this paper the efficiency of PEFC system with MIB method is evaluated by using the concept of exergy. The exergy efficiency of this system has been calculated and compared with the conventional system as a function of load factor. The result shows that efficiency of our system is higher especially in lower load factor, but slightly lower at the rated condition than that of the conventional. The obtained relation between the load factor and the exergy efficiency has been adapted to load demand patterns for one year measured at a residence. The results show that maximum exergy efficiency of the system with the MIB method is 4.5% higher than that of the conventional system, and the system efficiency with the MIB method is higher than the conventional system above 900W of rated power. The PEFC system for residential use is being investigated mainly about 1kW class generator. It has been clarified that the PEFC system with the MIB method has an ability to improve the efficiency at 1kW rated power and the passive load following function that the conventional systems never have.