Page - 160 - in Water, Energy, and Environment - A Primer

290MWHuntersPlantinGermany,usinganexcavatedsaltdome asthestoragecontainer.In1991a110MWplantwithacapacityof 26hourswasbuiltinMcIntosh,Alabama.Theworld’sthirdCAES project, opened in 2012,was a 2MWfacility inGaines, Texas. More recently, theUtah-based Intermountain Power Project has announced a 1.2GWCAESproject in underground salt domes, with the first 300MW to serve as storage for solar PV power. Thenext900MWwill serveas storage for anticipatednewwind energy generation. The US DOE is also supporting several proposedCAESprojects inCaliforniaandNewYork. 9.2.6 Pumpedstorage Pumped storage uses surplus, low-cost electricity, usually at night, to pump water from a lower reservoir to a higher one, and then this water is allowed to run downhill through turbines to generate electricity as needed. It is a form of hydroelectricity, but the upper reservoirs used with pumped storage are quite small when compared with conventional hydroelectric dams of similar power capacity, and generating periods are often less than half a day.Because of the large scale possible in such schemes pumped storage is – based on MW installed – the most common type of utility storage today. As of 2017 total installed global capacity was 184GW, ofwhich25GWwas in theUS (59). The round-trip efficiency of pumped storage is in the range 70–80%, but such losses are compensated for financially by its ability to offer electricity to the grid during periods of peak demandwhenelectricity prices are highest. Themaindisadvantageofpumpedstorage is theneed for sites offering both geographical height andwater availability, usually in hilly ormountainous regions. They are often areas of natural beauty, and therefore subject to public opposition. In many ways pumped storage is similar to CAES in that surplus electricity is used to store energy in a large reservoir. It Water,Energy, andEnvironment–APrimer160