The US's dependency on coal for its electricity generation, although it remains substantial, continues to fall. In 2000 it accounted for a little over 50%; now it's just under 40%. Most of the slack has been taken up by natural gas, which has grown its share of the country's electricity generation from around 16% in 2000 to 27% in 2014. Nuclear has stayed constant throughout that period, accounting for 19%.
Wind power's contribution was negligible until 2004, when a little over 6GW of installed capacity provided 0.36% of the country's electricity. But it has grown exponentially over the past decade and by the end of last year its 66GW of installed capacity supplied 4.4%.
Texas remains America's biggest wind player, its 14GW accounting for 8.3% of the state's electricity generation in 2014. However, Iowa leads the table for wind's biggest contribution to the energy mix; the mid-west state's 5.7GW of installed capacity generated 27.4% of its electricity last year. Wind also plays a significant role in South Dakota and Kansas, providing 26% and 19.4% respectively.
Although China has overtaken the US in terms of cumulative capacity, research by the American Wind Energy Association (AWEA) indicates that the US is harnessing its wind resources more efficiently, and that every year it has been the world leader in terms of electricity generated by wind since 2008.