The energy stored is mass x height x gravity.
To be generous let’s say they can move 1,000,000 kg through 1000m and gravity is ~10 gm/s^2.
That’s 10 billion joules = 2777kWh, ignoring all loses.
Or 200 Tesla power walls.
That’s a lot of deep holes to dig to gain the difference between electricity at low prices and high prices.
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