Coal plants are not able to rapidly start and stop like that and still operate efficiently or at peak capacity - their startup time is measured in hours not min

Coal plants are not able to rapidly start and stop like that and still operate efficiently or at peak capacity - their startup time is measured in hours not minutes. Gas (particularly OCGTs - CCGTs are usually less efficient than OCGTs if you do that with them) does that. Coal can be used in some markets seasonally (ie to supply additional baseload demand for summer AC / winter heating depending on local needs).