One question that has always concerned me is the extent to which individuals in an industry will demand that their job be saved (usually by government subsidy) even as it becomes redundant. Coal is bad for the environment, period, there is no room for discussion on this. Renewable energy can be incredibly good for the environment, given enough time for research and investment. So, all things being equal, renewable energy will replace coal all on it's own.
I know what you're going to say--people like Hillary are going to artificially prop up renewable energy and thus drive coal out faster than the Market would. Well, isn't that a just little bit fair considering that Ford, Chrysler and GM bought up all the patents for electric cars so that no one could invest in them and thus drive out the gasoline and diesel combustion engines? It made these "robber barons" quite a lot of money to stifle innovation and they weren't the only ones doing this!
Can you imagine where we'd be with electric vehicles and the batteries that power them if the Free Market had been allowed to operate properly over the past 100 years? Have you noticed that new "green" building standards are awfully similar to building practices of 100 years ago? Lots of large windows to let in light, heat, or air depending on the needs of the building. Cheap energy prices and the invention of the air conditioner caused a boom in less efficient housing that we're now tearing down to replace with what are essentially older designs.