power companies will use whatever is cheapest

I think that, in general, a power company is going to use whatever it thinks is cheapest. And of course, it's going to focus on short-term costs rather than the long-term implications of that method of energy generation.

But what is cheapest? Well, it turns out that the energy companies are really good at figuring out ways to convince politicians to subsidize their particular flavor of energy, such that it is now economically feasible for them to go that route. I've heard that nuclear is one example, where if there were no subsidies then there would be no proposals for new nuclear plants. So nuclear is "cheapest" in some cases, but only because there is not a level playing field.

I think that the solution to many of our problems remains this: kill the subsidies and may the best strategy win a fair match.