The rush to install wind capacity comes ahead of the expiration of the wind Production Tax Credit (PTC) on 31 December.
The 12GW would account for 45% of total additions of the electricity plants in America in 2012.
It would also exceed capacity additions from any other single fuel source, including natural gas, which comprised the leading new fuel source in 2010 and 2011.
This month is especially busy. As of 30 November, a little over 6GW had been completed in 2012. Another 6GW was expected to be added in December, said EIA.