Coal hasn't been economical for at least two years, in the sense that the capital cost of new PV is less than the operating cost of existing coal. The problem

Coal hasn't been economical for at least two years, in the sense that the capital cost of new PV is less than the operating cost of existing coal. The problem is that developing countries like China and India are so desperately short of electricity (growth in demand is so high) that any new builds just add to existing production rather than replacing it. - Governments will prop up uneconomic generators to maintain total supply. I don't know how to scale up PV and wind quickly enough to just replace coal in this situation. Edit: the Chinese experiments with thorium molten salt and pebble-bed high temperature fission reactors are interesting here. If they can easily swap out coal furnaces with nuclear reactors and retain the other 80% of the power stations, they'll get great benefits in air quality and and emissions while making use of of their investment in thermal generation.