Regenerative elevators do exist. I've no idea what they cost, but, shooting from the hip, I'm guessing they aren't worth the added price on any but the biggest

Regenerative elevators do exist. I've no idea what they cost, but, shooting from the hip, I'm guessing they aren't worth the added price on any but the biggest buildings. Any weight difference due to meatsacks in the elevator will be relatively small compared to what a drum full of concrete weights. Going off the math in TFA, and assuming your average meatsack weighs 75kg, lifting one of them 15 meters up (so, roughly, to the top floor of a 6 story building) stores about half a smartphone battery worth of potential energy. So you probably want to be lifting them much more than 15 meters - and be packing your elevator cars full of them - if you want to pay off the cost of the fancy regenerative kit in any reasonable amount of time.