There is no reason to ever build another coal plant in the United States

https://thinkprogress.org/renewable-cheaper-than-coal-589e43113faf#.9lwxa1m4k
"For the second year in a row, wind and solar accounted for roughly two-thirds of new U.S. generating capacity, while natural gas and nuclear made up most of the rest. That’s because right now, in much of the United States, wind and solar are the cheapest form of power available, according to a new report from investment bank Lazard. Analysts found that new solar or wind installations are cheaper than a new coal-fired power installation just about everywhere — even without subsidies — while the cost of renewables continues to fall rapidly."