NREL, Dec. 2016.
http://www.nrel.gov/docs/fy17osti/67058.pdf

"Over the past decade, wind power has become one of the fastest growing sources of electricity generation in the United States. Cumulative wind capacity grew from about 9 gigawatts (GW) in 2005 to approximately 74 GW by year-end 2015. ....This trend indicates a clear increasing role for wind; however, significant variability in historical annual wind installations has occurred with year-to-year fluctuations in wind deployment strongly correlated to changes in energy policies, particularly the wind production tax credit (PTC) policy."