backed with gravity hydro reservoirs ... is probably the most realistic ... in the short term. There seems to be a relative concensus among engineers that Comp

backed with gravity hydro reservoirs ... is probably the most realistic ... in the short term. There seems to be a relative concensus among engineers that Compressed Air Energy Storage (CAES) makes the most sense for grid energy storage in the longer term. http://topics.energycentral.com/centers/gentech/view/detail.cfm?aid=1404 http://topics.energycentral.com/centers/gentech/view/detail.... In Europe, a group of researchers are studying a different [from standard CAES] approach. It eliminates fuel consumption altogether, so that the system functions as a pure storage facility. They call it Advanced Adiabatic CAES. The idea for AACAES is that, in the charge cycle, hot compressed air is passed through a counter-flow heat exchanger before being sent to its storage cavern. The compressed air transfers its heat to a thermal storage fluid, which then enters a well-insulated storage tank of its own. In the discharge cycle, both flows are reversed, and the cool compressed air from the storage cavern recovers most of the heat it gave up before being stored. The now-hot compressed air exiting the heat exchanger drives an expander turbine to generate power. If the heat exchanger and thermal storage work well, then efficiencies approaching those achieved with pumped hydroelectric storage should be possible.