Editing Energy storage (section)

==== Compressed air ====
[[Image:Compressed Air Loco.jpg|thumb|A [[Fireless locomotive|compressed air locomotive]] used inside a mine between 1928 and 1961]]
{{Main|Compressed air energy storage|Salt dome}}

Compressed-air energy storage (CAES) uses surplus energy to compress air for subsequent electricity generation.<ref name="NYT-2010.07.28">{{Cite news |last=Wald |first=Matthew L. |date=2010-07-27 |title=Wind Drives Growing Use of Batteries |url=https://www.nytimes.com/2010/07/28/business/energy-environment/28storage.html |access-date=2025-04-24 |work=The New York Times |language=en-US |issn=0362-4331}}</ref> Small-scale systems have long been used in such applications as propulsion of mine locomotives. The compressed air is stored in an [[underground reservoir]], such as a [[salt dome]].

Compressed-air energy storage (CAES) plants can bridge the gap between production volatility and load. CAES storage addresses the energy needs of consumers by effectively providing readily available energy to meet demand. Renewable energy sources like wind and solar energy vary. So at times when they provide little power, they need to be supplemented with other forms of energy to meet energy demand. Compressed-air energy storage plants can take in the surplus energy output of renewable energy sources during times of energy over-production. This stored energy can be used at a later time when demand for electricity increases or energy resource availability decreases.<ref>{{cite journal |last1=Keles |first1=Dogan |last2=Hartel |first2=Rupert |last3=Möst |first3=Dominik |last4=Fichtner |first4=Wolf |title=Compressed-air energy storage power plant investments under uncertain electricity prices: an evaluation of compressed-air energy storage plants in liberalized energy markets |journal=The Journal of Energy Markets |date=Spring 2012 |volume=5 |issue=1 |page=54 |id={{ProQuest|1037988494}} |doi=10.21314/JEM.2012.070 }}</ref>

[[Gas compressor|Compression]] of [[air]] creates heat; the air is warmer after compression. [[Thermal expansion|Expansion]] requires heat. If no extra heat is added, the air will be much colder after expansion. If the heat generated during compression can be stored and used during expansion, efficiency improves considerably.<ref name="NYTimes-2012.10.01" /> A CAES system can deal with the heat in three ways. Air storage can be [[adiabatic]], [[Adiabatic|diabatic]], or [[isothermal]]. Another approach uses compressed air to power vehicles.<ref name="Auto.com-2004.03.18" /><ref name="Freep-2004.03.18" />