seanmcdirmid parent
They are replacing old coal plants with more efficient cleaner designers. National security wise they still have lots of coal to work with, while most renewable energy is generated in the west where ongoing grid upgrades are needed to use it where people live (in the east).
The newer plants not only more efficient going from 30-35% of peak efficiency to something like 45%, they can also operate efficiently over wider range of power output and are faster to turn on/off.
This is very helpful to deal with variability with renewable output.