Coal is used in (some) peaking power plants that only turn on during a surge of demand for electricity. Some also use natural gas. It's easier to spin them up/down and can deal with the strain of being used intermittently.
I work for a major American utility company and I'm not aware of coal being used to deliver peak power ("peaker plant" in the utility parlance). Coal power plants take hours to get up to operating temperature and when allowed to flame out you've significantly decreased the lifespan of the furnace. What they do instead is reduce the injection rate to maintain minimal operating temperature and run the output to ground. From that standpoint coal is very similar to nuclear: you don't simply stop a reactor. You send its output to ground. That's why coal and nuclear units are used for base load, not peak load. Natural gas units are just a turbine engine, you can spin that thing up and down as needed all day long to handle peaks. Wind and solar are auxiliary power sources - all American ISO's and RTO's require you have non-volatile power covering those units. Natural gas units are preferred to cover the these volatile units because they can be spun up so quickly. But there's a catch to that too - you have to put your natural gas order in 24 hours in advance of use and you have to pay for whatever you don't use. It's not like residential where your furnace just kicks on and gas is available and you get billed for it. Nope. You have to preorder your gas. If your wind and solar are covering the load then you're going to pay a fine for not taking all of your gas delivery. The utility business has its complexities!
taylodl|4 years ago