[seren]

But what kind of machine do you need to raise a hill up and down by a few meters ? Even if breaking the load in small bits, the cost and maintenance of equipment would likely be a few magnitude higher that the energy stored or saved.

[thechao]

An electric motor moves it up. An electric regenerating break (an electric generator) keeps it from going down too quickly and/or not at the right time. The particulars of maintenance and long term robustness are pretty straightforward engineering efforts. The largest steam hammers are 125 short tons, and they can operate for decades.

Why would the stresses be any greater than burying a turbine electric generator at the bottom of a hydroelectric dam? The forces would be similar, right? That's the whole point: it's just a crap load of "pressure" due to a bunch of stuff piled up on top.

[pjc50]

I'd do it with hydraulics. Turn the rock into a giant piston: https://heindl-energy.com/