Stirling engines would definitely be the future, if cheap energy was at all a priority. They just need a heat differential, whether solar, water, or whatever. They can even be run in colder conditions, so long as the gaseous properties are in balance. There is a lot of work that needs to be done on them, but at present they can even be used to convert otherwise "lost" energy (heat) into useful energy.
Anyway, this will probably never happen in a world where money dominates. However ineffective coal, fossil fuel, or any other source of non-renewable energy is, it is still highly profitable.