Given that there are no great ways to store large amounts of power at utility scale, the first thing to know is that demand and supply have to always match. (Th

Given that there are no great ways to store large amounts of power at utility scale, the first thing to know is that demand and supply have to always match. (There's mechanical inertia in the grid, pumped storage, and batteries, but those are modest in capacity and mostly short-term storage.) So, absent ways to support the full demand, the grid essentially slows down. You can see this if you look at the frequency of the current at the wall outlet - the nominal 60Hz will dip, and it will also dip across the entire rest of the grid. (In this case, across the entire state of Texas.) The next thing you need to know is that the rotational speed of the generators on the grid are bound to the grid's operating frequency. The frequency lags, and so does the speed of all the generators and sychronous motors connected to the grid. (In this case, across the entire state of Texas.) What happens then is that each generator with the capacity to do so will throttle up, try to hold the 60Hz, fail to do so, and potentially do things like jump poles. This is where a rotating assembly trying to maintain 60Hz on, say, a 58Hz grid, mechanically skips cycles, and jumps forward suddenly, and potentially catastrophically. It can literally physically destroy equipment. So what happens instead is that the generator trips, goes offline to protect itself, and the overall load imbalance problem gets worse. This is why grid operators pay a great deal of attention to the amount of reserve generating capacity they have online at any moment. Some of this means the ability to turn on a generator that's completely off, but it's also very important that there be enough generation with the capability of throttling up quickly to deal with short term transient failures (like other generation tripping offline, etc.).