https://www.eia.gov/todayinenergy/detail.php?id=45956
If you shut down by day, it can take multiple hours for it to be able to provide full load... and multiple hours for it to shut down cleanly. During this time it is producing power at less than optimal rates and/or using the fossil fuels to keep the wheels spinning and in sync with the grid so that they don't have to go through a phase matching period.
(aside for coal - note that it takes more than 12 hours for a coal plant to get running from a cold start)
Wind also helps since wind makes more power at night, as does demand which is dramatically lower at night.
For coal, Great. Making coal economical is excellent. We should have banned it worldwide 20 years ago.
There's a good number of 'em: https://en.wikipedia.org/wiki/Category:Pumped-storage_hydroe...
https://www.ferc.gov/media/licensed-pumped-storage-projects-...
You'll see that most of them are in the Appalachian mountains and in the Sierra mountain range.
The one in Missouri is one of the interesting ones that isn't in either.
https://en.wikipedia.org/wiki/Taum_Sauk_Hydroelectric_Power_...
> The Taum Sauk pumped storage plant is a power station in the St. Francois mountain region of Missouri, United States about 90 miles (140 km) south of St. Louis near Lesterville, Missouri, in Reynolds County.
It has a hydraulic head of 860 feet and that represents the challenge - you need to find places in the US where you can get several hundred feet of elevation in a short distance.
Hypothetically, lets build one in Minnesota... Taum Sauk Mountain is the highest point in Missouri. The highest point in Minnesota is Eagle Mountain (in the boundary waters - you can't build there, pretend we can) ... the elevation to the top os 550 feet (about half what Taum Sauk provides) over 3.5 miles (Taum Sauk is just over 1 mile). ( https://maps.app.goo.gl/vHfWarwubaLvsf5z7 )
Much of the US is too flat for it to be useful.
That makes 300B
Eu pricing