I also have searched the Net very extensively on this topic. Have not came across any posting. Hydro-electric energy storage in principle is the same thing and they are used widely to store massive amount of energy by the Power Utility sectors. The problem is that for it to work one requires two adjacent lakes at different heights and it's efficiency is around 70% (multiplicative of the efficiencies of hydro-turbines and pumps). I have this idea of hauling very large mass of (1000s of tons) scrap lead (from car batteries) top of grand canyon (more than a mile up) and use electirc motor /generator (could be one unit acually..I have to think). The system can store massive amount of energy in a very tiny place and the efficiency can be more than 85%. It can be used anywhere where there are such great vertical fall or even on mountain slopes (the efficiency will be slightly reduced because of friction)
