The emerging energy crisis results from a high-price of crude-oil has drawn attention about renewable energy all over the world. Thailand is a developing country located at the heart of Southeast Asia with about 66 million of population as of 2006. The ESI structure under the government of Thailand has been managed by the Electricity Generating Authority of Thailand (EGAT), Metropolitan Electricity Authority (MEA), and Provincial Electricity Authority (PEA) for almost 50 years. According to the 2004 Power Development Plan (PDP), the country would have generation reserve at a marginal of 15 percent. Due to the rapid economic growth and difficulty in building new centralized generating facilities, this has the potential to create a security issue of electricity energy shortage and may develop a severe system blackout. Renewable energy issues have been widely discussed and debated over the country. Although solar energy is the most prominent renewable energy source due to the appropriated geographic of Thailand, it still considered as a low-density energy source which requires a large area of installation. Therefore, for the long term investment, wind power seem to be a good candidacy since it is quick to get permission, need no fuel cost, and environmental friendly. Therefore, this paper investigates the impact of penetration level of wind powered generation to be integrated into Thailand system. System stability has been observed in various system configurations change due to different control strategies of wind farms. The economics analysis of wind farm investment has been also considered.