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.
During the availability of surplus electricity, the reversible pumpturbine converts the grid power supplied by a dual purpose motorgenerator to potential energy, by pumping the water in the larger shaft to raise the heavy piston. At times of need, like during peak demand, this stored potential energy is converted back to electrical energy by allowing the piston to descend, which in the process energizes the water molecules to rotate the turbinepump blades, leading to power generation at the generatormotor end.
OK — so how much energy will be used to create this huge system and concrete piston? How is the seal going to work? Compressed air is much simpler and is already being used in storage systems like salt domes. Water is pressurised by the compressed air which acts like an accumulator — which is of course another name for a battery. Most of this type of storage system are large and capex heavy. Try to think of something more efficient and you will be a Billionaire!