True, it is more complex than it might seem at first glance. One of my EE classes had us go out to a power plant to tour it and they talked about some of the complexity (because grid wide you get larger swings). They used to count on something like 80% of the households turning on the oven at 5PM while dinner was being prepared. They had actuarial staff that really dug into these numbers because some conditions would require starting up a 'peaker' plant and that took 3 - 4 hours to bring online from dead stop, about 1.5 hours from a "warm" start.