I. Introduction
Since most of the electrical energies are generated from fossil fuels, power generation becomes the leading source of greenhouse gases emission. This has led to severe environmental problems and concern of global warming. Kyoto Protocol was effective on February 16, 2005 and most industrialized countries had to obey and endeavor to reduce their overall emissions of greenhouse gases at least 5% below the 1990 level in the commitment period from 2008 to 2012. in addition, the rise of oil prices has also promoted the development of renewable energy technologies. Among the renewable energy technologies, wind generation is the most mature technology that can effectively reduce environmental pollution, fossil fuel consumption, and the costs of overall electricity generation. World wind energy capacity has expanded at an annual rate of 25% during the 1990s. The total world wind turbine installation capacity has reached 93 881 MW in April 2008.