The dynamic characteristics and generation efficiency of a micro-grid structured from 17 houses were examined. A gas engine generator with a power generation capacity of 3 kW installed in a house is made to correspond to the base load, and a solid-polymer-membrane-type fuel cell with a power generation capacity of I kW is installed in 16 houses. Moreover, when changing the load of a micro-grid, the correspondence takes place by controlling the number of fuel cells. Using numerical analysis, the characteristics of the power quality of a fuel cell micro-grid, and the generation efficiency of the fuel cell were examined. As a result, the relationship between the parameter of the controller and power quality and a fall in generation efficiency by a partial load was clarified. (c) 2006 International Association for Hydrogen Energy. Published by Elsevier Ltd. All rights reserved.