[TheLoafOfBread]

You can disconnect output, yet you need to still burn coal anyway, unless you want to damage the coal power plant.

[cinntaile]

I'm not talking about disconnecting output, I'm talking about reducing it. You don't burn as much coal, which was my original statement.

[TheLoafOfBread]

But idle = power plant still running on 80% so you are still using 80% of coal input to just keep it running on empty.

[cinntaile]

Coal plants for load following end up around 20-40%, nowhere near your 80% number. They have to, because the energy grid demands that they're capable of doing this because it's just not economical to run them at 80% when there is such variability.