Capacity factor is the ratio of actual output from a power plant in a given period to its total potential capacity. Capacity factor varies depending upon the fuel and technology used.
Capacity additions in wind power have been quite volatile over the past few years due to uncertainty over tax incentive policies. Still, wind added the highest capacity in 2015.
For more information on electric generation capacity additions, you can read Generation Capacity Additions: Which Source Will Lead in 2016