There might be one reason they let this spin up and down.
We mostly power the grid through a bunch of constantly humming systems, but our usage has all kinds of peaks (diurnal, seasonal... the British grid has a massive peak right around the time Eastenders ends and everyone puts on a kettle[1]).
If you are adding some power to the baseline, that's helpful. If you're promising the grid you can add some power during one of the daily or seasonal peaks, that's almost as valuable as adding a new source of always-on power. By providing energy for even just six hours a day, you might save the grid from requiring a new always-on plant. So in terms of opportunity costs, even by being twice as expensive moment to moment, you're still cutting costs in half (unless everyone followed your strategy).
So there's probably some number of hours of shutdown where it's worth the coal, some number where it's not, all contingent on what plants are nearby, and how close your customers typically are.
Related but tangential, one of the unintended benefits of electric cars would be adding a bunch of consumption at night, smoothing the diurnal cycle, letting us pursue more lower-cost always-on generation. (This is before you even consider distributed storage proposals that let the grid draw from parked cars in emergencies.)
Predictability is almost as good as a natural resource.
There might be one reason they let this spin up and down.
We mostly power the grid through a bunch of constantly humming systems, but our usage has all kinds of peaks (diurnal, seasonal... the British grid has a massive peak right around the time Eastenders ends and everyone puts on a kettle[1]).
If you are adding some power to the baseline, that's helpful. If you're promising the grid you can add some power during one of the daily or seasonal peaks, that's almost as valuable as adding a new source of always-on power. By providing energy for even just six hours a day, you might save the grid from requiring a new always-on plant. So in terms of opportunity costs, even by being twice as expensive moment to moment, you're still cutting costs in half (unless everyone followed your strategy).
So there's probably some number of hours of shutdown where it's worth the coal, some number where it's not, all contingent on what plants are nearby, and how close your customers typically are.
Related but tangential, one of the unintended benefits of electric cars would be adding a bunch of consumption at night, smoothing the diurnal cycle, letting us pursue more lower-cost always-on generation. (This is before you even consider distributed storage proposals that let the grid draw from parked cars in emergencies.)
Predictability is almost as good as a natural resource.
[1] http://www.bbc.co.uk/britainfromabove/stories/people/teatime...