From 2005 to 2009, the annual growth in U.S. wind capacity averaged 40%. Since 2006, 36% of total electric power industry capacity additions have been wind generators. The economic downturn and an uncertain regulatory environment (particularly relating to the renewal of production and investment tax credits) contributed to a lower level of wind capacity additions in 2010.
Recent wind development is driven by State-level renewable portfolio standards (or similar legislation), as well as a Federal production tax credit and grants. The PTC was established by the Energy Policy Act of 1992 to stimulate use of renewable technologies for power production. At the present time, the PTC provides a 10-year credit of 1.9¢/kWh (adjusted upwards, in future years, for inflation) for wind,While wind power is attractive due to its lack of emissions and low operating costs, its intermittency and sudden changes in production create challenges for grid operators and planners. (EIA, Dr. Ryan Wiser, Scientist, Lawrence Berkeley National Laboratory)