> it would probably be too expensive to have a power plant just sitting there idle when the price isn't "high enough" This is exactly what is done, and pretty

> it would probably be too expensive to have a power plant just sitting there idle when the price isn't "high enough" This is exactly what is done, and pretty much inevitably must be done - grids need spare capacity that can be relied on to spin up rapidly when demanded, that's usually done by gas turbine plants.