An independent micro-grid connected with renewable energy has the potential to reduce energy costs, and reduce the amount of greenhouse gas discharge. However, the frequency and voltage of a micro-grid may not be stable over a long time due to the input of unstable renewable energy, and changes in short-period power load that are difficult to predict. Thus, when planning the installation of a micro-grid, it is necessary to investigate the dynamic characteristics of the power. About the micro-grid composed from 10 houses, a 2.5 kW proton exchange membrane fuel cell is installed in one building, and it is assumed that this fuel cell operated corresponding to a base load. A 1 kW PEM-FC is installed in other seven houses, in addition a 1.5 kW wind turbine generator is installed. The micro-grid to investigate connects these generating equipments, and supplies the power to each house. The dynamic characteristics of this micro-grid were investigated in numerical analysis, and the cost of fuel consumption and efficiency was also calculated. Moreover, the stabilization time of the micro-grid and its dynamic characteristics accompanied by wind-power generation and fluctuation of the power load were studied. Copyright C 2007 John Wiley & Sons, Ltd.