Editing Energy storage (section)

=== Thermal ===
{{Main|Thermal energy storage|Molten salt|Seasonal thermal energy storage}}

Thermal energy storage (TES) is the temporary storage or removal of heat.

==== Sensible heat thermal ====
Sensible heat storage take advantage of [[sensible heat]] in a material to store energy.<ref>Layered Materials for Energy Storage and Conversion, Editors: Dongsheng Geng, Yuan Cheng, Gang Zhang, Royal Society of Chemistry, Cambridge 2019,</ref>

[[Seasonal thermal energy storage]] (STES) allows heat or cold to be used months after it was collected from waste energy or natural sources. The material can be stored in contained aquifers, clusters of boreholes in geological substrates such as sand or crystalline bedrock, in lined pits filled with gravel and water, or water-filled mines.<ref name=TES_BIES/> Seasonal thermal energy storage (STES) projects often have paybacks in four to six years.<ref name="Hellström" /> An example is [[Drake Landing Solar Community]] in Canada, for which 97% of the year-round heat is provided by solar-thermal collectors on garage roofs, enabled by a borehole thermal energy store (BTES).<ref name="Wong" /><ref name="DistrictEnergy.org-a" /><ref>[http://www.nrcan.gc.ca/media-room/news-release/2012/6586 Canadian Solar Community Sets New World Record for Energy Efficiency and Innovation] {{Webarchive|url=https://web.archive.org/web/20130430221347/http://www.nrcan.gc.ca/media-room/news-release/2012/6586 |date=April 30, 2013 }}, Natural Resources Canada, October 5, 2012.</ref> In Braedstrup, Denmark, [[Solar power in Denmark|the community's solar district heating system]] also uses STES, at a temperature of {{convert|65|C}}. A [[heat pump]], which runs only while surplus wind power is available. It is used to raise the temperature to {{convert|80|C|F}} for distribution. When wind energy is not available, a gas-fired boiler is used. Twenty percent of Braedstrup's heat is solar.<ref name="Solar District Heating" />

==== {{anchor|Latent heat thermal energy storage}} Latent heat thermal (LHTES) ====
Latent heat thermal energy storage systems work by transferring heat to or from a material to change its phase. A phase-change is the melting, solidifying, vaporizing or liquifying. Such a material is called a [[Phase-change material|phase change material]] (PCM). Materials used in LHTESs often have a high [[latent heat]] so that at their specific temperature, the phase change absorbs a large amount of energy, much more than sensible heat.<ref>{{cite journal |last1=Sekhara Reddy |first1=M.C. |last2=T. |first2=R.L. |last3=K. |first3=D.R |last4=Ramaiah |first4=P.V |title=Enhancement of thermal energy storage system using sensible heat and latent heat storage materials |journal=I-Manager's Journal on Mechanical Engineering |date=2015 |volume=5 |page=36 |id={{ProQuest|1718068707}} }}</ref>

A [[steam accumulator]] is a type of LHTES where the phase change is between liquid and gas and uses the [[latent heat of vaporization]] of water. [[Ice storage air conditioning]] systems use off-peak electricity to store cold by freezing water into ice. The stored cold in ice releases during melting process and can be used for cooling at peak hours.

==== Cryogenic thermal energy storage ====
{{Main|Cryogenic energy storage}}

Air can be liquefied by cooling using electricity and stored as a cryogen with existing technologies. The liquid air can then be expanded through a turbine and the energy recovered as electricity. The system was demonstrated at a pilot plant in the UK in 2012.<ref name=LAES2012/>
In 2019, Highview announced plans to build a 50 MW in the North of England and northern Vermont, with the proposed facility able to store five to eight hours of energy, for a 250–400&nbsp;MWh storage capacity.<ref name=LAES2019/>

==== Carnot battery ====
{{Main|Carnot battery}}

Electrical energy can be stored thermally by resistive heating or heat pumps, and the stored heat can be converted back to electricity via [[Rankine cycle]] or [[Brayton cycle]].<ref name="DumontFrate2020"/> This technology has been studied to retrofit coal-fired power plants into fossil-fuel free generation systems.<ref name = Kraemer2019/> Coal-fired boilers are replaced by high-temperature heat storage charged by excess electricity from renewable energy sources. In 2020, [[German Aerospace Center]] started to construct the world's first large-scale Carnot battery system, which has 1,000&nbsp; MWh storage capacity.<ref name = DLR2020/>