If you're worried strictly about profits, and not a strong desire to avoid CO2 emissions, we can imagine a carbon tax. $100 per ton would cost a coal plant 10¢/kWh on top of operating costs. So if a carbon-free source gets even close for operating costs, then that's a lot of money to fund a backup plant and still come out ahead.

And this doesn't really require a tax. We could imagine an electrical company pricing out their aversion to carbon in cents per kWh out of their own volition or because of customer demand.