If we built 43 Hoover Dams, we wouldn't need to build any other renewables at all-- the Hoover Dam doesn't just store power, it also generates it. I'm not sure of the numbers for pure pumped storage hydropower systems (I don't think "pure" systems even exist, everywhere gets some rain), but we only need enough capacity to take over when the normal grid is underproducing.

[–] Feathercrown@lemmy.world 2 points 4 months ago* (last edited 4 months ago)

To answer your actual question though, we need about 85 times our current pumped hydro capacity to transition to a fully renewable US. This seems daunting, but:

Pumped hydro is growing rapidly
It's not the only battery storage technology (heat batteries look promising imo)
Any increases in storage allow more renewables, less pollution, and overall contribute to making our future better

Pumped Hydro doesn't need to singlehandedly handle the storage load of the entire US because there are other options to use in conjunction with it and even a partial storage solution produces benefits. This is good, because Pumped Hydro is geographically limited.