http://www.eia.gov/todayinenergy/detail.cfm?id=7330

Current trends in the electric power market put many coal-fired generators in the United States at risk for retirement. In the Annual Energy Outlook 2012 (AEO2012) Reference case, 49 gigawatts of coal-fired capacity are retired through 2020, representing roughly one-sixth of the existing coal capacity in the U.S. and less than 5% of total electricity generation nationwide.

FWIW