A bit of Googling brings me to http://reneweconomy.com.au/2015/solar-grid-parity-world-2017:

Investment bank Deutsche Bank is predicting that solar systems will be at grid parity in up to 80 per cent of the global market within 2 years, and says the collapse in the oil price will do little to slow down the solar juggernaut.

Over the last decades solar doubled price efficiency roughly every 7 years. Batteries also get exponentially cheaper.

Coal doesn't get cheaper but a little more expensive. It also easy to make it more expensive by creating higher environmental standards and cutting coal subsidies if there's political desire to do so.