Large quantities of electrical energy can be stored using pumped hydro or underground compressed air facilities. Such schemes can have a power rating of up to 1–2 GW with an energy capacity of 10–20 GWh. Smaller quantities of energy can be stored in batteries, flywheels and Superconducting Magnetic Energy Storage (SMES) devices [1–3]. Fuel cells convert a continuous source of chemical energy into electricity but have a similar impact on the power network as some energy storage systems (for example, flow batteries).
Figure 12.1 (also refer to Plate 9) shows the power and energy outputs of some of the electricity storage schemes that have been implemented using different technologies [1, 4, 5]. Fuel cells of a few hundred kW to several MWs are now in operation as a continuous source of power and are not shown in Figure 12.1. (Also refer to Plate 9) .
Applications of energy storage in the power system can be considered as being divided into those whose prime function is to deliver short-term power (kW) or those primarily supplying energy (kWh) over a longer period. Power quality, voltage support and some frequency support services which require short-term power support use batteries, flywheels and SMES which have a high power to energy ratio. Support for renewable energy, electrical energy shifting and end user energy management requires a large amount of energy and a discharge duration of several minutes to hours. Pumped hydro, compressed air ...