Renewable energy technologies such as wind power and photovoltaic energy are getting attentions from view points of energy conservation and environmental issue. However, fluctuation of output power of renewable energy may cause excess variation of voltage or frequency of the grid. Increase of the amount of renewable energy would violate the quality of the grid. The micro grid in which dispersed power systems compensate the variation from the renewable energy can expand the installation limit of the renewable energy by maintaining the quality of the interconnected grid. In this paper, evaluation of the ratio of gas turbines is discussed from the point of power flow stability of the grid, efficiency, economy and CO2 emission in a daily load curve. In addition to the discussion in a daily load curve, the number of gas turbines to be in operation is discussed in this paper.
