Retired coal consumption is the decreased amount of used coal with respect to previous year.
Edit: You can also use less coal than previous year and that's a negative increment in mathematical analysis.
No. You can't do that and show an increase in the same chart for the same year. This is called cognitive dissonance. You're going into a mental pretzel trying to justify your claim that the chart is showing consumption, when it is only showing capacity (both the removal of power plants and addition of new ones).