This idea is for an alternative to large scale energy storage. Sorry for the double and confusing post (https://www.physicsforums.com/showthread.php?t=179768), I should have posted here in the first place. As far as I can understand, pumped-storage hydroelectricity is the main technology used for grid energy storage. The efficiency of this procedure is about 70%-85%. Is it possible to use solid materials instead of water? I am not sure how, I am not an engineer. Lifting these objects with an elevator motor, seems the easy part. If these objects were let to fall down afterwards, wouldn't they turn the motor, so that it could produce some electricity back? Probably yes, because I read about regeneration (or 'four-quadrant motor operation') with counterweights and other stuff I cannot understand at http://www.aceee.org/buildings/coml_equp/elevators.pdf (page 5) which seems to be a similar concept. Could you make a rough estimation of the round-trip efficiency of this procedure? Does it worth to compare this with pumped-hydro and investigating it further?