To date, the only significant bulk electricity storage technology has been pumped storage hydroelectric technology. Distributed storage exists (e.g. local storage for UPS systems, etc.) but it is not aggregated or available for any system benefits. New storage technologies are under development and in some cases are being deployed, and could also potentially provide substantial value to the electric grid.
Electric storage is recognized to have value at all levels in the modern power system, from central generation to point of use. For example, the storage functionalities are, at Generation level – frequency control, spinning reserve, supply-ramping, demand-leveling, minimum loading; at Transmission level – stability, VAR support, power quality and transfer-leveling, and reliability; at Substation/Distribution – peak shaving, voltage support, power quality, capacity investment deferral, and reliability and at End-Use level – demand control, interruption protection, voltage support and power quality