h2g2 The Hitchhiker's Guide to the Galaxy: Earth Edition

One omission in this fine entry is the use of jet engines attached to the generator. Because it takes many hours or even days to bring a steam unit on line, or shut one down, and we all have these habits that require massive amounts of power near dawn for showers and breakfast, then again at dusk when we again like to shower and cook supper, followed by several hours when we turn off all our lights and other appliances while we sleep. Since A.C. power can not be stored it must be produced as needed. To keep the supply of power available most steam power plants use a battery of jet engines not unlike those used on commercial airliners attached to smaller generators which can be brought on line in a few minutes, and shut down as quickly when the demand is reduced.

Fascinating! I hadn't heard of that.

It has been many years since I was involved with steam generation, I spent most of the seventies drafting for the fine people who brought us Three Mile Island ( in their Fossil Power Group ). After the lay-offs following I did one project designing the stacking units, basically giant mufflers, that were sold to Florida Power and Light near Miami for their peak load units.
As I recall the maximum throttle range on a boiler is from 75% to 100% of available steam. Below 75% there is a real danger of water droplets entering the turbine which will quickly destroy it! I don't know how much coverage it got on your side of the "pond" but the summer before last there where serious power shortages in California due to the high use of air-conditioners in unusual heat waves, they did not have enough peak units ready for the massive increase in demand.