The United States is undergoing the greatest revolution in energy production in decades due to the shale-gas boom and the rise of renewable energy.
Renewable energy's share of energy production is rising rapidly. Solar, in particular, has benefited from a sharp drop in the price of photovoltaic modules as a result of a massive expansion of manufacturing capacity in recent years.
Power plants are multibillion-dollar investments and are designed to operate for decades. Thus all those natural gas-fired power plants and solar and wind farms coming online now will be fueling the economy for a good chunk of the 21st century.
The chart below shows when the capacity that we use to power the grid came online. A lot of the dirty coal plants are more than thirty years old.