"Yeah, that looks right. About 150 kWh. Math using approx numbers, in case anyone wants to check it:PE, Potential Energy (in joules, J)m, mass (in kilograms, kg)g, acceleration of gravity (9.8 m/s^2)h, height (in meters, m)PE = mghAssume mass m is 200,000 kg (about 200 US tons), and height h is 300 m (about 1000 ft).PE = 200,000 kg * 9.8 m/s^2 * 300 m = 588,000,000 JThen to convert J to kWh,1 J = 1 Ws = 1 / 3,600 Wh =  1 / 3,600,000 kWhSo, PE = 588,000,000 / 3,600,000 = 163 kWhI’m ignoring efficiency losses, but I think that’s in the noise for our approximate numbers here. Pumped hydro also needs similar mass and/or height, but when you think of it as two big ponds and a few pipes with pumps, it starts to sound much more feasible, even if the efficiency is a little worse. A 1 acre pond that is 6 feet deep contains about 10X more mass than the example above, just for reference. "

"But if you do the math on something like a whole-house backup, it seems a little tricky. Assume you have a 100 foot (30 meter) tall hill to work with (which is very tall for someone's backyard). And you want to store 15 kWh (about half of a typical US home's daily electricity usage). You would need about 220 US tons (200,000 kg) of mass. Flipping it around a bit: 1 US ton lifted 100 feet is about 75 Wh. I'm not sure if you can even buy a battery pack with an AC outlet that small - they seem to start around 200 Wh. 75 Wh is one common powertool battery that you can buy for ~$50.Math checked with https://www.calculatorsoup.com/calculators/physics/gravitational-potential.php and https://www.omnicalculator.com/physics/potential-energy."