Coal has already been losing to other sources, albeit not necessarily renewables. The cost of natural gas has plunged and getting coal out of the ground is more expensive than it used to be as we've already pulled out the easy to get coal.

A lot of the cost issues is about comparing wattage - solar has become way more efficient than it used to be. Coal efficiency has not changed much.

https://www.bloomberg.com/news/articles/2017-01-03/for-cheap...