What is ideally needed is a bulk electricity storage device which is scalable to gig watt, which is reliable, efficient and economically viable, but more importantly, it should be environmentally friendly. One such promising technology on the horizon with a capability to compete with pumped hydro and gas turbines for peaking and immediate power generation is storing energy by gravity.
A gravity storage system consist of a pair of two deep shafts one large, and the other smaller in diameter connected at the top and bottom, forming a closed formed circuit via a reversible pumpturbine, as seen in Figure 1. The shafts are filled with water, which acts as a medium for energy transfer, and the bigger shaft is fitted with a huge steel piston filled with reinforced rock and concrete. The whole device operates on the simple action of vertical motion of piston.