According to this article in The NY Times, the old coal plants are hooked into the existing power grid and contain the generators needed to link solar and wind turbines. Many projects have been stated where power plants are decommissioned.
The US can be 80% renewable energy by 2030. These old facilities provide the linkage Solar and Wind Turbines need to power our homes and factories. New jobs will be created! Some plants have already started the transition. Kudos.