Seite - 159 - in Water, Energy, and Environment - A Primer

device has three parts, a coil of wire that can become superconducting, a cryogenic cooler that cools the superconducting wire below its transition temperature at which it loses its electrical resistance, andpower conditioning circuitry that allows for charging anddischarging the coil. Its advantages are ultra-fast charge and discharge times, no moving parts, nearly unlimited cycling capability, and an energy recovery rate greater than 95%. Disadvantages are the cost of the specializedwire, the need for continuous cooling to very low temperatures, large-area coils needed for appreciable energy storage, and the possibility of a sudden, large energy release if thewire’s superconducting state is lost. SMESdevices are often used to provide grid stability in distribution systems and for power quality at manufacturing plants requiring ultra-clean power (e.g., microchip production lines). At present 1MWh SMES units are common and a 20MWh engineering testmodel is under development. 9.2.5 Compressedairenergystorage (CAES) Compressedairenergystorage(CAES)utilizessurpluselectricity tocompressair tohighpressures inundergroundcavernsorother large storage vessels, which can then be heated and released as needed topower expansion turbines that generate electricity. OneinterestingfeatureofCAESisthat,whilebeingcompressed fromatmosphericpressure(14.7psi/101kPa)tostoragepressures ofabout1000psi, theairheatsupstrongly (tomore than1000°F, 538°C).Someofthisheatcanberemovedbycoolingtoprotectthe multi-stage air compressors, or stored thermally and used for subsequent adiabatic expansion of the stored air. Energy is also added to the compressed air during the expansion/power generation cycle by heating with natural gas. Gases other than air, for example, carbondioxide, canbeusedaswell. CAES systems were first built in the 1870s in Europe and Argentina. The first utility-scale CAES project was the 1978 Energystorage 159