Renewable energies such as wind power or photovoltaic energy are environmentally focused but the output power fluctuation of the renewable energies may cause excess variation of voltage or frequency of the grid -. Increase of the amount of renewable energies would violate the quality of the grid. The micro grid in which dispersed energies compensate the variation from the renewable energies can expand the installation limit of the renewable energies by maintaining the quality of the interconnected grid-. In this paper, how the gas turbines absorb the power variation from the wind generation and load is discussed In order to control output power, gas turbines must run at partial load operation, which results in lower efficiency. Tie-line power flow and frequency fluctuation caused by imbalance between supply and demand is also discussed. It is shown that gas turbine output control is effective method to absorb output fluctuation from load and wind farm. If the exhausted thermal energy from a gas turbine can be used for co-generation, more energy saving is expected.