Editing Energy storage (section)

==== Flywheel ====
[[File:Example of cylindrical flywheel rotor assembly.png|thumb|right|The main components of a typical flywheel]]
[[File:Flybrid Systems Kinetic Energy Recovery System.jpg|thumb|right|A Flybrid [[Kinetic Energy Recovery System]] [[Flywheel energy storage|flywheel]]. Built for use on [[Formula One|Formula 1 racing cars]], it is employed to recover and reuse kinetic energy captured during braking.]]
{{Main|Flywheel energy storage|Flywheel storage power system}}

Flywheel energy storage (FES) works by accelerating a rotor (a [[flywheel]]) to a very high speed, holding energy as [[rotational energy]]. When energy is added the rotational speed of the flywheel increases, and when energy is extracted, the speed declines, due to [[conservation of energy]].

Most FES systems use electricity to accelerate and decelerate the flywheel, but devices that directly use mechanical energy are under consideration.<ref name="Torotrak">{{Cite web |title=Wayback Machine |url=http://www.xtrac.com/pdfs/Torotrak_Xtrac_CVT.pdf |archive-url=https://web.archive.org/web/20120311124324/http://www.xtrac.com/pdfs/Torotrak_Xtrac_CVT.pdf |archive-date=March 11, 2012 |access-date=2025-04-24 |website=www.xtrac.com |url-status=dead }}</ref>

FES systems have rotors made of high strength [[carbon-fiber]] composites, suspended by [[magnetic bearing]]s and spinning at speeds from 20,000 to over 50,000&nbsp;revolutions per minute (rpm) in a vacuum enclosure.<ref name="ScienceNews">{{Cite journal| last1 = Castelvecchi| first1 = Davide| title = Spinning into control: High-tech reincarnations of an ancient way of storing energy| doi = 10.1002/scin.2007.5591712010| journal = Science News| volume = 171| issue = 20| pages = 312–313| date = May 19, 2007| url = http://sciencewriter.org/flywheels-spinning-into-control/| access-date = May 8, 2014| archive-url = https://web.archive.org/web/20140606223717/http://sciencewriter.org/flywheels-spinning-into-control/| archive-date = June 6, 2014| url-status = dead}}</ref> Such flywheels can reach maximum speed&nbsp;("charge") in a matter of minutes. The flywheel system is connected to a combination [[electric motor]]/[[electric generator|generator]].

FES systems have relatively long lifetimes (lasting decades with little or no maintenance;<ref name="ScienceNews" /> full-cycle lifetimes quoted for flywheels range from in excess of 10<sup>5</sup>, up to 10<sup>7</sup>, cycles of use),<ref name="Investire">{{Cite web |url=http://www.itpower.co.uk/investire/pdfs/flywheelrep.pdf |title=Storage Technology Report, ST6 Flywheel |access-date=May 8, 2014 |archive-url=https://web.archive.org/web/20130114062530/http://www.itpower.co.uk/investire/pdfs/flywheelrep.pdf |archive-date=January 14, 2013 |url-status=dead }}</ref> high [[specific energy]] (100–130&nbsp;W·h/kg, or 360–500 kJ/kg)<ref name="Investire" /><ref name="pddnet">{{cite web |title=Next-gen of Flywheel Energy Storage |url=http://www.pddnet.com/article-next-gen-of-flywheel-energy-storage/ |publisher=Product Design & Development |access-date=May 21, 2009 |url-status=dead |archive-url=https://web.archive.org/web/20100710052927/http://www.pddnet.com/article-next-gen-of-flywheel-energy-storage/ |archive-date=July 10, 2010  }}</ref> and [[power density]].