Mechanical Energy Storage Systems: Compressed Air and Underground Pumped Hydro

A new principle for underground pumped hydroelectric storage

“…The pressure delivered for power generation is provided directly by the hydrostatic pressure obtained from this height difference. In situations where such a height difference is not topographically available, concepts of the underground pumped hydro storage (UPHS) type have been proposed [7][8][9]. The conventional concept here is to facilitate the height difference by placing the lower reservoir in an underground cavity.…”

Can large-scale advanced-adiabatic compressed air energy storage be justified economically in an age of sustainable energy?

“…26 Because every temperature change, processing step, and complexity to which the air is subjected has an energy cost and erodes system efficiency, an AA-CAES system may have difficulties with market penetration unless ͑i͒ all obvious inefficiencies have been wrung out of it, ͑ii͒ exergy dissipation by internal irreversibilities has been minimized, 32 and ͑iii͒ its cycle efficiency demonstrably matches or betters that of the established competition, here pumped hydro at around 75%. 24 Because AA-CAES is so commonly mentioned as a major contender for bulk energy storage medium of choice, 17,20,25,30,[33][34][35] and because it has never actually been subjected to a rigorous experimental test, we believe it is important that its conceptual bases be closely examined.…”