Comment by shagie

Part of the pumped storage problem is "where can you do it?"

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.