Passive load following method for PEFC system with reformer and its efficiency improvement evaluated by using the concept of exergy

Abstract

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 already been confirmed experimentally and the result shows that the metal hydride is not poisoned with impurities in reformed gas. It is expected that the MIB method improves the efficiency of PEFC systems 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 to 20% of the peak power. In this paper, the PEFC system efficiency using the MIB method is evaluated by 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 the efficiency of our system is higher especially at lower load factor, but slightly lower at the rated condition than that of the conventional system. 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 900 W of rated power. The PEFC system for residential use is being investigated mainly for a 1-kW-class generator. It has been clarified that the PEFC system with the MIB method has an ability to improve the efficiency at 1 kW rated power and passive load following function that the conventional systems never have. © 2005 Wiley Periodicals, Inc. Electr Eng Jpn, 152(4): 17–26, 2005; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/eej.20148