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{{Short description|Large scale electricity supply management}}
{{Portalpar|Sustainable development|Sustainable development.svg}}
{{good article}}
[[Image:Stwlan.dam.jpg|thumb|right|The upper reservoir of [[Ffestiniog]], a [[Pumped-storage hydroelectricity|pumped storage power station]] ]]
{{Redirect|Grid storage|data storage with grid computing|Grid-oriented storage}}
{{Use dmy dates|date=October 2020}}
[[File:20241206 Grid energy storage.svg|thumb|Energy from fossil or nuclear power plants and renewable sources is stored for use by customers.]]
[[File:20241201 Power grid storage energy flow - daily.svg|thumb|Diagram showing flow of energy between energy storage facilities and power grids, as a function of time over a 24 hour period]]


'''Grid energy storage''', also known as '''large-scale energy storage''', are technologies connected to the [[electrical power grid]] that [[Energy storage|store energy]] for later use. These systems help balance supply and demand by storing excess electricity from [[Variable renewable energy|variable renewables]] such as [[Solar power|solar]] and inflexible sources like [[nuclear power]], releasing it when needed. They further provide [[Ancillary services (electric power)|essential grid services]], such as helping to [[Black start|restart the grid]] after a [[power outage]].
'''Grid energy storage''' lets [[electric power generation|electric energy producers]] send excess electricity over the [[electric power transmission|electricity transmission grid]] to [[energy storage|temporary electricity storage sites]] that become energy producers when electricity demand is greater, optimizing the production by storing off-peak power for use during peak times. Also, [[photovoltaic]] and [[Wind power|wind turbine]] users can avoid the necessity of having [[Battery (electricity)|battery]] storage by connecting to the grid, which effectively becomes a giant battery. Photovoltaic operations can store electricity for night time use, and wind power can be stored for calm times.


{{As of|2023}}, the largest form of grid storage is [[pumped-storage hydroelectricity]], with [[Battery energy storage system|utility-scale batteries]] and behind-the-meter batteries coming second and third.{{sfn|Cozzi|Petropoulos|Wanner|2024|p=68}} [[Lithium-ion battery|Lithium-ion batteries]] are highly suited for shorter duration storage up to 8 hours. [[Flow battery|Flow batteries]] and [[Compressed-air energy storage|compressed air energy storage]] may provide storage for medium duration. Two forms of storage are suited for long-duration storage: [[green hydrogen]], produced via [[electrolysis]] and [[thermal energy storage]].{{Sfn|IPCC AR6 WG3 Ch6|2022|pp=653, 656}}
Grid energy storage is closely related to [[distributed generation]]. For distributed generation to function correctly, specialized technical and economic arrangements (such as [[net metering]] and [[vehicle-to-grid]] power systems) may be needed, and often require regulatory support.


Energy storage is one option to making grids more flexible. An other solution is the use of more [[Dispatchable generation|dispatchable power plants]] that can change their output rapidly, for instance [[peaking power plant]]s to fill in supply gaps. [[Demand response]] can shift load to other times and [[Interconnector|interconnections]] between regions can balance out fluctuations in renewables production.{{Sfn|IPCC AR6 WG3 Ch6|2022|p=651}}
== Example ==


The price of storage technologies typically [[Experience curve|goes down with experience]]. For instance, lithium-ion batteries have been getting some 20% cheaper for each doubling of worldwide capacity.{{Sfn|Schmidt|Staffell|2023|p=92}} Systems with under 40% variable renewables need only short-term storage. At 80%, medium-duration storage becomes essential and beyond 90%, long-duration storage. The economics of long-duration storage is challenging, and alternative flexibility options like demand response may be more economic.
A large expensive [[nuclear power plant|nuclear]] or [[coal plant]] can optimally run at full power 24/7, including overnight when businesses and households need about half their daily electricity maximum. The cheap nightly electricity on the grid is used by a [[pumped-storage hydroelectricity|pumped-storage hydroelectric power plant]] to push water hundreds of feet uphill from a lower storage lake to an upper storage lake, effectively storing the electricity as higher elevation water. When electricity demand begins peaking in the afternoon and whenever rapid supply adjustments are needed, the [[pumped-storage hydroelectricity|pumped water storage power plant]] becomes an electricity producer by sending water downhill from the upper to lower lakes through a turbine that generates electricity.


{{toclimit|3}}

==Roles in the power grid==
Any [[grid (electricity)|electrical power grid]] must match electricity production to consumption, both of which vary significantly over time. Energy derived from [[Solar power|solar]] and [[Wind power|wind sources]] varies with the weather on time scales ranging from less than a second to weeks or longer. [[Nuclear power]] is less flexible than [[Fossil fuel|fossil fuels]], meaning it cannot easily match the variations in demand. Thus, [[low-carbon electricity]] without storage presents special challenges to [[Electric utility|electric utilities]].{{Sfn|Schmidt|Staffell|2023|p=8}}

Electricity storage is one of the three key ways to replace flexibility from [[Fossil fuel|fossil fuels]] in the grid. Other options are [[demand-side response]], in which consumers change when they use electricity or how much they use. For instance, households may have [[Dynamic pricing#Time-based utility pricing|cheaper night tariffs]] to encourage them to use electricity at night. Industry and commercial consumers can also change their demand to meet supply. Improved [[Electric power transmission|network interconnection]] smooths the variations of renewables production and demand. When there is little wind in one location, another might have a surplus of production. Expansion of [[Transmission line|transmission lines]] usually takes a long time.{{Sfn|Schmidt|Staffell|2023|pp=10-11}}
{| class="wikitable"
|+Potential roles of energy storage in the grid{{sfn|Schmidt|Staffell|2023|pp=74-76}}{{sfn|Cozzi|Petropoulos|Wanner|2024|p=36}}
!
!Consumption
!Network
!Generation
|-
! Short-term flexibility
|Increased use [[Rooftop solar power|rooftop solar]], cost reductions from [[Dynamic pricing#Time-based|time-based]] rates
|[[Transmission congestion|Congestion]] relief
|Renewables integration (smoothing, [[arbitrage]])
|-
! Essential grid services
|Backup power during outages
|[[Frequency regulation]]
|[[Black start]]
|-
! System reliability and planning
|Creation of [[mini-grids]]
|Savings in transmission and [[Electric power distribution|distribution network]]
|Meeting [[peak demand]]
|}
Energy storage has a large set of roles in the electricity grid and can therefore provide many different services. For instance, it can [[arbitrage]] by keeping it until the [[Electricity pricing|electricity price]] rises, it can help make the grid more stable, and help reduce investment into transmission infrastructure.{{Sfn|Armstrong|Chiang|2022|pp=6-7}} The type of service provided by storage depends on who manages the technology, whether the technology is based alongside generation of electricity, within the network, or at the side of [[Electric energy consumption|consumption]].{{sfn|Cozzi|Petropoulos|Wanner|2024|p=36}}

Providing short-term flexibility is a key role for energy storage. On the generation side, it can help with the integration of [[variable renewable energy]], storing it when there is an oversupply of wind and solar and electricity prices are low. More generally, it can exploit the changes in prices of electricity over time in the [[wholesale market]], charging when electricity is cheap and selling when it is expensive. It can further help with [[grid congestion]] (where there is insufficient capacity on [[transmission lines]]). Consumers can use storage to use more of their self-produced electricity (for instance from [[rooftop solar power]]).{{sfn|Cozzi|Petropoulos|Wanner|2024|p=36}}{{sfn|Schmidt|Staffell|2023|pp=74-76}}

Storage can also be used to provide [[ancillary services|essential grid services]]. On the generation side, storage can smooth out the variations in production, for instance for solar and wind. It can assist in a [[black start]] after a [[power outage]]. On the network side, these include [[frequency regulation]] (continuously) and [[frequency response]] (after unexpected changes in supply or demand). On the consumption side, storage can help to improve the [[Electric power quality|quality of the delivered electricity]] in less stable grids.{{sfn|Cozzi|Petropoulos|Wanner|2024|p=36}}{{sfn|Schmidt|Staffell|2023|pp=74-75}}

Investment in storage may make some investments in the transmission and [[distribution network]] unnecessary, or may allow them to be scaled down. Additionally, storage can ensure there is sufficient capacity to meet [[peak demand]] within the electricity grid. Finally, in off-grid home systems or [[Mini-grid|mini-grids]], electricity storage can help provide [[energy access]] in areas that were previously not connected to the electricity grid.{{sfn|Cozzi|Petropoulos|Wanner|2024|p=36}}
==Forms==
==Forms==
[[File:20240706 Energy storage - renewable energy - battery - 100 ms.gif |thumb |Energy from sunlight or other renewable energy is converted to potential energy for storage in devices such as electric batteries. The stored potential energy is later converted to electricity that is added to the power grid, even when the original energy source is not available.]]
===Pumped water===
''Main article: [[Pumped-storage hydroelectricity]]''


Electricity can be stored directly for a short time in capacitors, somewhat longer electrochemically in [[Electric battery|batteries]], and much longer chemically (e.g. hydrogen), mechanically (e.g. pumped hydropower) or as heat.{{Sfn|Schmidt|Staffell|2023|p=33}} The first pumped hydroelectricity was constructed at the end of the 19th century around [[Alps|the Alps]] in Italy, Austria, and Switzerland. The technique rapidly expanded during the 1960s to 1980s [[History of nuclear power#Development and early opposition to nuclear power|nuclear boom]], due to nuclear power's inability to quickly adapt to changes in electricity demand. In the 21st century, interest in storage surged due to the rise of [[Sustainable energy|sustainable energy sources]], which are often weather-dependent.<ref>{{Cite journal |last1=Mitali |first1=J. |last2=Dhinakaran |first2=S. |last3=Mohamad |first3=A. A. |date=2022 |title=Energy storage systems: a review |url=https://linkinghub.elsevier.com/retrieve/pii/S277268352200022X |journal=Energy Storage and Saving |volume=1 |issue=3 |pages=166–216 |doi=10.1016/j.enss.2022.07.002 |issn=2772-6835}}</ref> Commercial batteries have been available for over a century,<ref>{{Cite journal |last=Gür |first=Turgut M. |date=2018-10-10 |title=Review of electrical energy storage technologies, materials and systems: challenges and prospects for large-scale grid storage |url=https://pubs.rsc.org/en/content/articlelanding/2018/ee/c8ee01419a |journal=Energy & Environmental Science |language=en |volume=11 |issue=10 |pages=2696–2767 |doi=10.1039/C8EE01419A |issn=1754-5706}}</ref> their widespread use in the power grid is more recent, with only 1 GW available in 2013.{{Sfn|Cozzi|Petropoulos|Wanner|2024|p=32}}
In many places, pumped storage hydroelectricity is used to even out the daily generating load, by pumping water to a high storage reservoir during off-peak hours and weekends, using the excess base-load capacity from coal or nuclear sources. During peak hours, this water can be used for [[hydroelectric]] generation, often as a high value rapid-response reserve to cover transient peaks in demand. Pumped storage recovers about 75% of the energy consumed, and is currently the most cost effective form of mass power storage. The chief problem with pumped storage is that it usually requires two nearby reservoirs at considerably different heights, and often requires considerable capital expenditure.


=== Batteries ===
Pumped water systems can come on-line very quickly, typically within 15 seconds, <ref>[http://www.fhc.co.uk/dinorwig.htm]</ref> which makes these systems very efficient at soaking up variability in electrical ''demand'' from consumers. There is over 90 GW of pumped storage in operation around the world, which is about 3% of ''instantaneous'' global generation capacity. However, due to their limited total energy capacity, pumped storage systems are not so useful for covering for electrical ''supply'' outages. Most pumped water storage systems hold just five or six hours of generating capacity,<ref>[http://www.fhc.co.uk/dinorwig.htm]</ref> and are already fully utilised in smoothing out demand variations. If generating capacity was lost to the grid, for instance during windless days, pumped water storage systems could never make up the difference. For instance, the [[Dinorwig power station|Dinorwig]] storage system can provide 5% of UK power generation (2.9 gw) for up to 5 hours before it runs out of water (total capacity of 14.5 [[Watt-hour|gwh]]). If the UK was entirely dependent on wind power, a wind outage lasting just two days would require 140 storage stations with the same generating capacity as Dinorwig to maintain normal power supplies (assuming average UK demand of 1,000 gwh/day).<ref>[http://www.cslforum.org/uk.htm]</ref>
{{Main|Battery energy storage system}}
[[File:Light-plant-Fig1198-Page989-Ch45-Hawkins-Electrical-Guide.png|thumb|A 900 watt direct current light plant using 16 separate [[lead acid battery]] cells (32 volts) from 1917.<ref name="Hawkins1917">{{cite book|first=Nehemiah |last=Hawkins|title=Hawkins Electrical Guide ...: Questions, Answers & Illustrations; a Progressive Course of Study for Engineers, Electricians, Students and Those Desiring to Acquire a Working Knowledge of Electricity and Its Applications; a Practical Treatise|url={{google books |plainurl=y |id=yyEVAAAAYAAJ|page=989}}|year=1917|publisher=T. Audel & Company|pages=989–}}</ref>]]
==== Lithium-ion batteries ====
Lithium-ion batteries are the most commonly used batteries for grid applications, {{As of|2024|lc=y}}, following the application of batteries in electric vehicles (EVs). In comparison with EVs, grid batteries require less [[energy density]], meaning that more emphasis can be put on costs, the ability to charge and discharge often and lifespan. This has led to a shift towards [[Lithium iron phosphate battery|lithium iron phosphate batteries]] (LFP batteries), which are cheaper and last longer than traditional lithium-ion batteries.{{Sfn|Cozzi|Petropoulos|Wanner|2024|p=45}}


Costs of batteries are declining rapidly; from 2010 to 2023 costs fell by 90%.{{Sfn|Cozzi|Petropoulos|Wanner|2024|p=18}} {{As of|2024}}, utility-scale systems account for two thirds of added capacity, and home applications (behind-the-meter) for one third.{{Sfn|Cozzi|Petropoulos|Wanner|2024|p=20}} Lithium-ion batteries are highly suited to short-duration storage (<8h) due to cost and degradation associated with high [[State of charge|states of charge]].{{Sfn|Cozzi|Petropoulos|Wanner|2024|p=45-46}}
Traditional hydroelectric dam configurations are far more common than pumped storage; in this configuration, release is delayed until needed. The net effect is the same as pumped storage, but without the round-trip efficiency loss. Additionally a new concept in pumped-storage is utilizing [[wind energy]] to pump water. [[Wind turbine]]s that direct drive water pumps for an 'energy storing wind dam' can make this a more efficient process, but are again limited in total capacity. Such systems can only cover for windless periods of a few hours.


===== Electric vehicles =====
===Batteries ===
{{Main|Battery (electricity)}}
{{Main|Vehicle-to-grid|}}
[[File:Nissan Leaf aan Amsterdamse laadpaal.jpg|thumb|Batteries from old electric cars, such as this [[Nissan Leaf]], can be reused but as of 2024 it is not known whether grid storage or behind the meter storage will be the best application.<ref>{{Cite web |date=2024-04-30 |title=Nissan and Ecobat to give used EV batteries a second life beyond the car |url=https://uk.nissannews.com/en-GB/releases/nissan-and-ecobat-to-give-used-ev-batteries-a-second-life-beyond-the-car |access-date=2024-11-21 |website=Official Great Britain Newsroom |language=en-GB}}</ref>|alt=A Nissan Leaf charging]]
The [[electric vehicle]] fleet has a large overall battery capacity, which can potentially be used for grid energy storage. This could be in the form of [[vehicle-to-grid]] (V2G), where cars store energy when they are not in use, or by [[repurposing]] batteries from cars at the end of the vehicle's life. Car batteries typically range between 33 and 100 kWh;<ref>{{Cite journal |last1=Xu |first1=Chengjian |last2=Behrens |first2=Paul |last3=Gasper |first3=Paul |last4=Smith |first4=Kandler |last5=Hu |first5=Mingming |last6=Tukker |first6=Arnold |last7=Steubing |first7=Bernhard |date=2023-01-17 |title=Electric vehicle batteries alone could satisfy short-term grid storage demand by as early as 2030 |url=http://dx.doi.org/10.1038/s41467-022-35393-0 |journal=Nature Communications |volume=14 |issue=1 |page=119 |doi=10.1038/s41467-022-35393-0 |pmid=36650136 |issn=2041-1723|pmc=9845221 |bibcode=2023NatCo..14..119X }}</ref> for comparison, a typical upper-middle-class household in Spain might use some 18 kWh in a day.<ref>{{Cite journal |last1=García-Vázquez |first1=Carlos Andrés |last2=Espinoza-Ortega |first2=Hernán |last3=Llorens-Iborra |first3=Francisco |last4=Fernández-Ramírez |first4=Luis M. |date=2022-11-01 |title=Feasibility analysis of a hybrid renewable energy system with vehicle-to-home operations for a house in off-grid and grid-connected applications |url=https://linkinghub.elsevier.com/retrieve/pii/S2210670722004371 |journal=Sustainable Cities and Society |volume=86 |pages=104124 |doi=10.1016/j.scs.2022.104124 |bibcode=2022SusCS..8604124G |issn=2210-6707}}</ref> By 2030, batteries in electric vehicles may be able to meet all short-term storage demand globally.<ref>{{Cite journal |last1=Xu |first1=Chengjian |last2=Behrens |first2=Paul |last3=Gasper |first3=Paul |last4=Smith |first4=Kandler |last5=Hu |first5=Mingming |last6=Tukker |first6=Arnold |last7=Steubing |first7=Bernhard |date=2023-01-17 |title=Electric vehicle batteries alone could satisfy short-term grid storage demand by as early as 2030 |journal=Nature Communications |language=en |volume=14 |issue=1 |pages=119 |doi=10.1038/s41467-022-35393-0 |pmid=36650136 |issn=2041-1723|pmc=9845221 |bibcode=2023NatCo..14..119X }}</ref>


{{As of|2024}}, there have been more than 100 V2G pilot projects globally.<ref name=":0">{{Cite journal |last1=Aguilar Lopez |first1=Fernando |last2=Lauinger |first2=Dirk |last3=Vuille |first3=François |last4=Müller |first4=Daniel B. |date=2024-05-16 |title=On the potential of vehicle-to-grid and second-life batteries to provide energy and material security |url=http://dx.doi.org/10.1038/s41467-024-48554-0 |journal=Nature Communications |volume=15 |issue=1 |page=4179 |doi=10.1038/s41467-024-48554-0 |pmid=38755161 |issn=2041-1723|pmc=11099178 |bibcode=2024NatCo..15.4179A }}</ref> The effect of V2G charging on battery life can be positive or negative. Increased cycling of batteries can lead to faster degradation, but due to better management of the [[state of charge]] and gentler charging and discharing, V2G might instead increase the lifetime of batteries.<ref name=":0" /><ref>{{Cite journal |last1=Bhoir |first1=Shubham |last2=Caliandro |first2=Priscilla |last3=Brivio |first3=Claudio |date=2021-12-01 |title=Impact of V2G service provision on battery life |url=https://linkinghub.elsevier.com/retrieve/pii/S2352152X21008781 |journal=Journal of Energy Storage |volume=44 |pages=103178 |doi=10.1016/j.est.2021.103178 |bibcode=2021JEnSt..4403178B |issn=2352-152X}}</ref> Second-hand batteries may be useable for stationary grid storage for roughly 6 years, when their capacity drops from roughly 80% to 60% of the initial capacity. [[Lithium iron phosphate battery|LFP batteries]] are particularly suitable for reusing, as they degrade less than other lithium-ion batteries and recycling is less attractive as their materials are not as valuable.<ref name=":0" />
Battery storage was used in the very early days of electric power networks, but is appearing again. Many "off-the-grid" domestic systems rely on battery storage, as well as most [[telephone]] systems, but means of storing large amounts of electricity as such in giant batteries or by other electrical means have not yet been put to general use. Batteries are generally expensive, have maintenance problems, and have limited lifespans. One possible technology for large-scale storage are large-scale [[flow battery|flow batteries]]. [[NaS battery|Sodium-sulfur batteries]] could also be inexpensive to implement on a large scale and have been used for grid storage in Japan and in the United States[http://www.appalachianpower.com/news/releases/viewrelease.asp?releaseID=281]. [[Vanadium redox battery|Vanadium redox batteries]] and other types of flow batteries are also beginning to be used for energy storage including the averaging of generation from wind turbines. Battery storage has relatively high efficiency, as high as 90% or better.


==== Other battery types ====
When [[plug-in hybrid]] vehicles are mass-produced <ref>http://www.newscientist.com/article.ns?id=dn7081 , http://www.toshiba.co.jp/about/press/2005_03/pr2901.htm </ref> these mobile energy sinks could be utilized for their energy storage capabilities. [[Vehicle-to-grid]] technology can be employed, turning each vehicle with its 20 to 50 kWh [[battery pack]] into a distributed load-balancing device or emergency power source. This represents 2 to 5 days per vehicle of average household requirements of 10 kWh per day, assuming annual consumption of 3650 kWh. This quantity of energy is equivalent to between 40 and 300 miles of range in such vehicles consuming 0.5 to 0.16 kWh per mile. These figures can be achieved even in home-made [[electric vehicle conversion]]s. Some electric utilities plan to use old plug-in vehicle batteries (sometimes resulting in a giant battery) to store electricity <ref name="woody">Woody, Todd. [http://blogs.business2.com/greenwombat/2007/06/photo_green_wom.html "PG&E's Battery Power Plans Could Jump Start Electric Car Market."] (Blog). ''Green Wombat'', [[2007]]-[[06-12]]. Retrieved on [[2007]]-[[08-19]] </ref> <ref>http://www.planetark.com/dailynewsstory.cfm/newsid/44343/story.htm</ref>
In redox [[flow battery|flow batteries]], energy is stored in liquids, which are placed in two separate tanks. When charging or discharging, the liquids are pumped into a cell with the electrodes. The amount of energy stored (as set by the size of the tanks) can be adjusted separately from the power output (as set by the speed of the pumps).{{sfn|Cozzi|Petropoulos|Wanner|2024|p=46}} Flow batteries have the advantages of low capital cost for charge-discharge duration over 4 h, and of long durability (many years). Flow batteries are inferior to [[lithium-ion batteries]] in terms of [[Energy efficiency (physics)|energy efficiency]], averaging efficiencies between 60% and 75%. [[Vanadium redox battery|Vanadium redox batteries]] is most commercially advanced type of flow battery, with roughly 40 companies making them {{As of|2022|lc=y}}.<ref>{{Cite journal |last=Tolmachev |first=Yuriy V. |date=2023-03-01 |title=Review—Flow Batteries from 1879 to 2022 and Beyond |url=https://iopscience.iop.org/article/10.1149/1945-7111/acb8de |journal=Journal of the Electrochemical Society |volume=170 |issue=3 |pages=030505 |bibcode=2023JElS..170c0505T |doi=10.1149/1945-7111/acb8de |issn=0013-4651}}</ref>


[[Sodium-ion battery|Sodium-ion batteries]] are possible alternative to lithium-ion batteries, as they rely on cheaper materials and less on critical materials. It has a lower energy density, and possibly a shorter lifespan. If produced at the same scale as lithium-ion batteries, they may become 20% to 30% cheaper.{{Sfn|Cozzi|Petropoulos|Wanner|2024|p=46}} [[Iron-air batteries]] may be suitable for even longer duration storage than flow batteries (weeks), but the technology is not yet mature.{{Sfn|Cozzi|Petropoulos|Wanner|2024|p=47}}


{| class="wikitable sortable" style="width: auto; text-align: center; table-layout: fixed;"
===Compressed air===
|+Technology comparison{{Sfn|Cozzi|Petropoulos|Wanner|2024|p=47}}
''Main article: [[Compressed air energy storage]]''
|-
! scope="col" | Technology
! scope="col" | Less than 4h
! scope="col" | 4h to 8h
! scope="col" | Days
! scope="col" | Weeks
! scope="col" | Seasons
|-
! scope="row" | [[Lithium-ion battery|Lithium-ion]]
| {{Yes}}
| {{Yes}}
| {{No}}
| {{No}}
| {{No}}
|-
! scope="row" | [[Sodium-ion battery|Sodium-ion]]
| {{Yes}}
| {{Yes}}
| {{No}}
| {{No}}
| {{No}}
|-
! scope="row" | [[Vanadium redox battery|Vanadium flow]]
| {{Maybe}}
| {{Yes}}
| {{Yes}}
| {{No}}
| {{No}}
|-
! scope="row" | [[Metal–air electrochemical cell|Iron-air]]
| {{No}}
| {{No}}
| {{Maybe}}
| {{Yes}}
| {{No}}
|}


=== Electrical ===
Another grid energy storage method is to use off-peak electricity to [[compressed air|compress air]], which is usually stored in an old [[mining|mine]] or some other kind of geological feature. When electricity demand is high, the compressed air is heated with a small amount of [[natural gas]] and then goes through expanders to generate electricity.
Storage in [[Supercapacitor|supercapacitors]] works well for applications where a lot of power is needed for short amount of time. In the power grid, they are therefore mostly used in short-term frequency regulation.{{Sfn|Schmidt|Staffell|2023|pp=54-55}}


===Hydrogen and chemical storage===
===Thermal===
''Main article: [[Thermal energy storage]]''


{{Main|Hydrogen economy|Hydrogen storage}}
Off-peak electricity can be used to make [[ice]] from water, and the ice can be stored until the next day, when it is used to cool either the air in a large building, thereby shifting that demand off-peak, or the intake air of a [[gas turbine]] [[electrical generator|generator]], thereby increasing the on-peak generation capacity.


{{See also|Combined cycle hydrogen power plant}}Various [[power-to-gas]] technologies exist that can convert excess electricity into an easier to store chemical. The lowest cost and most efficient one is [[hydrogen]]. However, it is easier to use synthetic [[methane]] with existing infrastructure and appliances, as it is very similar to natural gas.{{Sfn|Letcher|2022|p=606}}
=== Flywheel ===
''Main article: [[Flywheel energy storage]]''


{{As of|2024}}, there have been a number of demonstration plants where hydrogen is burned in [[Gas turbine|gas turbines]], either co-firing with natural gas, or on its own. Similarly, a number of [[Coal-fired power station|coal plants]] have demonstrated it is possible to co-fire [[ammonia]] when burning coal. In 2022, there was also a small pilot to burn pure ammonia in a gas turbine.{{Sfn|Remme|Bermudez Menendez|2024|pp=54-55}} A portion of existing gas turbines are capable of co-firing hydrogen, which means there is, as a lower estimate, 80 GW of capacity ready to burn hydrogen.{{Sfn|Remme|Bermudez Menendez|2024|p=57}}
Mechanical inertia is the basis of this storage method. A heavy rotating disc is accelerated by an [[electric motor]], which acts as a generator on reversal, slowing down the disc and producing electricity. Electricity is stored as the [[kinetic energy]] of the disc. [[Friction]] must be kept to a minimum to prolong the storage time. This is often achieved by placing the flywheel in a vacuum and using [[magnetic bearing]]s, tending to make the method expensive. Larger flywheel speeds allow greater storage capacity but require strong materials such as [[steel]] or [[composite material]]s to resist the [[centrifugal]] forces (or rather, to provide [[centripetal force]]s). The use of [[carbon nanotube]]s as a flywheel material is being researched{{Fact|date=October 2007}}. The ranges of power and energy storage technically and economically achievable, however, tend to make flywheels unsuitable for general power system application; they are probably best suited to load-leveling applications on railway power systems and for improving [[power quality]] in [[renewable energy]] systems. One application that currently uses flywheel storage is applications that require very high bursts of power for very short durations such as [[tokamak]] and [[laser]] experiments where a motor generator is spun up to operating speed and may actually come to a stop in one revolution. Flywheel storage is also currently used to provide [[Uninterruptible Power Supply#Rotary|Uninterruptible Power Supply]] systems (such as those in large [[Data Center|datacenters]]) the ride-through power necessary during transfer. (That is, the relatively brief amount of time between a loss of power to the mains and the warm-up of an alternate source, such as a [[diesel generator]].)


==== Hydrogen ====
=== Superconducting magnetic energy ===
[[Hydrogen]] can be used as a long-term storage medium.{{Sfn|Smith|2023|p=5}} [[Green hydrogen]] is produced from the [[electrolysis of water]] and converted back into electricity in an [[internal combustion engine]], or a [[fuel cell]], with a round-trip efficiency of roughly 41%.{{Sfn|Smith|2023|p=14}} Together with thermal storage, it is expected to be best suited to seasonal energy storage.{{Sfn|IPCC AR6 WG3 Ch6|2022|p=653}}
''Main article: [[Superconducting magnetic energy storage]]''


Hydrogen can be stored aboveground in tanks or underground in larger quantities. Underground storage is easiest in [[salt cavern]]s, but only a certain number of places have suitable geology.{{Sfn|Armstrong|Chiang|2022|p=150}} Storage in porous rocks, for instance in empty [[Gas field|gas fields]] and some [[aquifer]]s, can store hydrogen at a larger scale, but this type of storage may have some drawbacks. For instance, some of the hydrogen may leak, or react into [[H2S|H<sub>2</sub>S]] or [[methane]].<ref>{{Cite journal |last1=Miocic |first1=Johannes |last2=Heinemann |first2=Niklas |last3=Edlmann |first3=Katriona |last4=Scafidi |first4=Jonathan |last5=Molaei |first5=Fatemeh |last6=Alcalde |first6=Juan |date=2023-08-30 |title=Underground hydrogen storage: a review |url=https://www.lyellcollection.org/doi/10.1144/SP528-2022-88 |journal=Geological Society, London, Special Publications |language=en |volume=528 |issue=1 |pages=73–86 |doi=10.1144/SP528-2022-88 |issn=0305-8719|hdl=10261/352537 |hdl-access=free }}</ref>
Superconducting magnetic energy storage (SMES) systems store energy in the [[magnetic field]] created by the flow of [[direct current]] in a [[Superconductivity|superconducting]] coil which has been [[cryogenics|cryogenically]] cooled to a temperature below its superconducting critical temperature. A typical SMES system includes three parts: superconducting [[coil]], power conditioning system and cryogenically cooled refrigerator. Once the superconducting coil is charged, the current will not decay and the magnetic energy can be stored indefinitely. The stored energy can be released back to the network by discharging the coil. The power conditioning system uses an [[inverter (electrical)|inverter]]/[[rectifier]] to transform [[alternating current]] (AC) power to direct current or convert DC back to AC power. The inverter/rectifier accounts for about 2-3% energy loss in each direction. SMES loses the least amount of [[electricity]] in the energy storage process compared to other methods of storing energy. SMES systems are highly efficient; the round-trip efficiency is greater than 95%. The high cost of superconductors is the primary limitation for commercial use of this energy storage method.


====Ammonia ====
Due to the energy requirements of [[refrigeration]], and the limits in the total energy able to be stored, SMES is currently used for short duration energy storage. Therefore, SMES is most commonly devoted to improving [[power quality]]. If SMES were to be used for [[public utility|utilities]] it would be a [[day|diurnal]] storage device, charged from [[base load power plant|base load]] power at night and meeting [[peaking power plant|peak loads]] during the day.


Hydrogen can be converted into ammonia in a reaction with [[nitrogen]] in the [[Haber-Bosch process]]. Ammonia, a gas at room temperature, is more expensive to produce than hydrogen. However, it can be stored more cheaply than hydrogen. Tank storage is usually done at between one and ten [[Bar (unit)|times atmospheric pressure]] and at a temperature of {{Convert|-30|C|F}}, in liquid form.{{Sfn|Smith|2023|p=18}} Ammonia has [[Ammonia#Applications|multiple uses]] besides being an energy carrier: it is the basis for the production of many chemicals; the most common use is for fertilizer.<ref>{{cite web |last1=Service |first1=Robert F. |date=2018-07-12 |title=Ammonia—a renewable fuel made from sun, air, and water—could power the globe without carbon |url=https://www.science.org/content/article/ammonia-renewable-fuel-made-sun-air-and-water-could-power-globe-without-carbon |access-date=2021-04-15 |website=Science {{!}} AAAS |language=en}}</ref> It can be used for power generation directly, or converted back to hydrogen first. Alternatively, it has potential applications as a fuel in [[shipping]].<ref>{{Cite web |date=2020 |title=Green ammonia |url=https://royalsociety.org/news-resources/projects/low-carbon-energy-programme/green-ammonia/ |access-date=2024-11-23 |website=Royal Society |language=en}}</ref>
===Hydrogen===
''Main article: [[Hydrogen economy]]''


====Methane====
[[Hydrogen]] is not a primary energy source, but a portable energy storage method, because it must first be manufactured by other energy sources in order to be used. However, as a storage medium, it may be a significant factor in using renewable energies. See [[hydrogen storage]]. [http://www.plugpower.com/news/customer.cfm] Hydrogen may be used in conventional [[internal combustion engine]]s, or in [[fuel cell]]s which convert chemical energy directly to electricity without flames, similar to the way the human body burns fuel. Making hydrogen requires either reforming natural gas with steam, or, for a possibly renewable and more ecologic source, ''the [[electrolysis of water]]'' into hydrogen and [[oxygen]]. The former process has [[carbon dioxide]] as a by-product. With electrolysis, the greenhouse burden depends on the source of the power.


It is possible to further convert hydrogen into [[methane]] via the [[Sabatier reaction]], a chemical reaction which combines {{CO2}} and H<sub>2</sub>. While the reaction that converts CO from [[gasified coal]] into {{CH4}} is mature, the process to form methane out of {{CO2}} is less so. Efficiencies of around 80% one-way can be achieved, that is, some 20% of the energy in hydrogen is lost in the reaction.{{Sfn|Letcher|2022|p=602}}
With intermittent renewables such as solar and wind, the output may be fed directly into an electricity grid. At penetrations below 20% of the grid demand, this does not severely change the economics; but beyond about 20% of the total demand, external storage will become important. If these sources are used for electricity to make hydrogen, then they can be utilized fully whenever they are available, opportunistically. Broadly speaking, it does not matter when they cut in or out, the hydrogen is simply stored and used as required. A community based pilot program using [[wind turbines]] and hydrogen generators is being developed undertaken from 2007 for five years in the remote community of [[Ramea, Newfoundland and Labrador]].<ref>[http://www.ieawind.org/wnd_info/KWEA_pdf/Oprisan_KWEA_.pdf Introduction of Hydrogen Technologies to Ramea Island]</ref>
=== Mechanical ===


==== Flywheel ====
Nuclear advocates note that using nuclear power to manufacture hydrogen would help solve plant inefficiencies. Here the plant would be run continuously at full capacity, with perhaps all the output being supplied to the grid in peak periods, and any not needed to meet demand being used to make hydrogen at other times. This would mean far better efficiency for the nuclear power plants. High temperature (950-1,000°C) gas cooled nuclear reactors have the potential to separate hydrogen from water by thermochemical means using nuclear heat (i.e. without using electrolysis).
{{Main|Flywheel storage power system|Flywheel energy storage}}
[[File:G2 front2.jpg|thumb|upright|NASA G2 flywheel|alt=a metal casing with wires, roughtly cyclindrically shaped]]


Flywheels store energy in the form of mechanical energy. They are suited to supplying high levels of electricity over minutes and can also be charged rapidly. They have a long lifetime and can be used in settings with widely varying temperatures. The technology is mature, but more expensive than batteries and supercapacitors and not used frequently.{{Sfn|IPCC AR6 WG3 Ch6|2022|p=655}}
The efficiency for hydrogen storage is typically 50 to 60% overall, which is lower than pumped storage systems or batteries. About 50 kWh (180 MJ) is required to produce a kilogram of hydrogen by electrolysis, so the cost of the electricity clearly is crucial, even for hydrogen uses other than storage for electrical generation. At $0.03/kWh, common off-peak high-voltage line rate in the [[United States|U.S.]], this means hydrogen costs $1.50 a kilogram for the electricity, equivalent to $1.50 a US gallon for [[gasoline]] if used in a fuel cell vehicle. Other costs would include the electrolyzer plant, [[gas compressor|compressors]], [[liquefaction]], storage and transportation, which will be significant.


==== Pumped hydro ====
==Economics== <!-- Although related to the rest of the article, i think this section, especially the second paragraph, deserves an article in itself -->
{{Main|Pumped-storage hydroelectricity}}
[[File:Taiwan Power Ccopany Mingtan Power Station.JPG|thumb|[[Mingtan Pumped-Storage Hydro Power Plant]] dam in [[Nantou County|Nantou]], Taiwan]]


In 2023, pumped hydroelectric storage (PHS) was the largest storage technology, with a worldwide capacity of 181 [[Watt|GW]], compared to some 55{{nbsp}}GW of storage in utility-scale batteries and 33{{nbsp}}GW of behind-the-meter batteries.<ref>{{Cite web |title=Global installed energy storage capacity by scenario, 2023 and 2030 – Charts – Data & Statistics |url=https://www.iea.org/data-and-statistics/charts/global-installed-energy-storage-capacity-by-scenario-2023-and-2030 |access-date=2024-08-25 |website= |publisher=International Energy Agency |language=en-GB}}</ref> PHS is well suited to evening out daily variations, pumping water to a high storage reservoir during off-peak hours, and using this water during peak times for [[hydroelectric]] generation.{{Sfn|IPCC AR6 WG3 Ch6|2022|p=654}} The efficiency of PHS ranges between 75% and 85%, and the response time is fast, between seconds and minutes.<ref>{{Cite journal |last1=Javed |first1=Muhammad Shahzad |last2=Ma |first2=Tao |last3=Jurasz |first3=Jakub |last4=Amin |first4=Muhammad Yasir |date=2020-04-01 |title=Solar and wind power generation systems with pumped hydro storage: Review and future perspectives |url=https://linkinghub.elsevier.com/retrieve/pii/S0960148119318592 |journal=Renewable Energy |volume=148 |pages=176–192 |doi=10.1016/j.renene.2019.11.157 |bibcode=2020REne..148..176J |issn=0960-1481}}</ref>
Generally speaking, energy storage is economical when the [[marginal cost]] of electricity varies more than the costs of storing and retrieving the energy plus the price of energy lost in the process. For instance, assume a [[pumped-storage hydroelectricity|pumped-storage reservoir]] can pump to its upper reservoir water equivalent to 1,200 [[MWh]] during the night, for $15 per MWh, at a total cost of $18,000. The next day, all of the stored energy can be sold at the peak hours for $40 per MWh, but from the 1,200 MWh pumped 50 were lost due to evaporation and seeping in the reservoir. 1,150 MWh are sold for $46,000, for a final profit of $28,000.


PHS systems can only be built in limited locations. However, other pumped storage systems can be made, for instance by using deep [[salt cavern]]s or by constructing a hollow structure on the [[seabed]], with the sea itself serving as the upper reservoir.{{Sfn|IPCC AR6 WG3 Ch6|2022|p=654}} PHS construction can be costly, takes relatively long and can be disruptive for the environment and people living nearby.{{Sfn|IPCC AR6 WG3 Ch6|2022|p=654}} The efficiency of pumped hydro can be increased by placing [[Floating solar|floating solar panels]] on top, which prevent evaporation. This also improves the efficiency of the solar panels, as they are constantly cooled.{{Sfn|IRENA|2020|p=7}}
However, the marginal cost of electricity varies because of the varying operational and fuel costs of different classes of generators. At one extreme, [[base load power plant]]s such as [[coal power|coal]]-fired power plants and [[nuclear power]] plants are low marginal cost generators, as they have high capital and maintenance costs but low fuel costs. At the other extreme, [[peaking power plant]]s such as [[gas turbine]] [[Natural gas#Power generation|natural gas]] plants burn expensive fuel but are cheaper to build, operate and maintain. To minimize the total operational cost of generating power, base load generators are dispatched most of the time, while peak power generators are dispatched only when necessary, generally when energy demand peaks. This is called "economic dispatch".


==== Hydroelectric dams ====
Demand for [[electricity]] from the world's various grids varies over the course of the day and from season to season. For the most part, variation in electric demand is met by varying the amount of electrical energy supplied from primary sources. Increasingly, however, operators are storing lower-cost energy produced at night, then releasing it to the grid during the peak periods of the day when it is more valuable.<ref>[http://www.eia.doe.gov/emeu/aer/pdf/pages/sec8_8.pdf Energy Information Administration / Annual Energy Review 2006], Table 8.2a</ref> In areas where hydroelectric dams exist, release can be delayed until demand is greater; this form of storage is common and can make use of existing reservoirs. This is not storing "surplus" energy produced elsewhere, but the net effect is the same - although without the efficiency losses. Renewable supplies with variable production, like [[wind power|wind]] and [[solar power]], tend to increase the net variation in electric load, increasing the opportunity for grid energy storage.
[[File:FeiCueiReservoir.jpg|thumb|[[Feitsui Dam|Fetsui hydroelectric dam]] in [[New Taipei]], Taiwan]]


[[Hydroelectric dams]] with large reservoirs can also be operated to provide peak generation at times of peak demand. Water is stored in the reservoir during periods of low demand and released through the plant when demand is higher. While technically no electricity is stored, the net effect is the similar as pumped storage. The amount of storage available in hydroelectric dams is much larger than in pumped storage. Upgrades may be needed so that these dams can respond to variable demand. For instance, additional investment may be needed in transmission lines, or additional turbines may need to be installed to increase the peak output from the dam.{{Sfn|Armstrong|Chiang|2022|pp=69-70}}
=== Load Levelling ===


Dams usually have multiple purposes. As well as energy generation, they often play a role in [[flood defense]] and protection of ecosystems, recreation, and they supply water for [[irrigation]]. This means it is not always possible to change their operation much, but even with low flexibility, they may still play an important role in responding to changes in wind and solar production.{{Sfn|Armstrong|Chiang|2022|pp=69}}
The demand for electricity from consumers and industry is constantly changing, broadly within the following categories:<br>
*Seasonal (during dark winters more electric lighting and heating is required, while in other climates hot weather boosts the requirement for air conditioning)
*Weekly (most industry closes at the weekend, lowering demand)
*Daily (such as the peak as everyone arrives home and switches the television on)
*Hourly (one method for estimating television viewing figures in the United Kingdom is to measure the power spike when advertisements are shown and everyone goes to switch the kettle on)
*Transient (fluctuations due to individual's actions, differences in power transmission efficiency and other small factors that need to be accounted for)


==== Gravity ====
There are currently three main methods for dealing with changing demand:<br>
{{Main|Energy storage#Solid mass gravitational}}
*Electrical devices generally having a working [[voltage]] range that they require, commonly 110-120V or 220-240V. Minor variations in load are automatically smoothed by slight variations in the voltage available across the system.
*Power plants can be run below their normal output, with the facility to increase the amount they generate almost instantaneously. This is termed 'Spinning Reserve'.
*Additional power plants can be brought online to provide a larger generating capacity. Typically, these would be combustion gas turbines, which can be started in a matter of minutes.


Alternative [[Gravity battery|methods that use gravity]] include storing energy by moving large solid masses upward against gravity. This can be achieved inside old mine shafts<ref>{{Cite web |date=21 October 2019 |title=How UK's disused mine shafts could be used to store renewable energy |url=http://www.theguardian.com/environment/2019/oct/21/how-uks-disused-mine-shafts-plan-to-store-renewable-energy |website=The Guardian}}</ref> or in specially constructed towers where heavy weights are [[winch]]ed up to store energy and allowed a controlled descent to release it.<ref>{{Cite web |last=Gourley |first=Perry |date=31 August 2020 |title=Edinburgh firm behind incredible gravity energy storage project hails milestone |url=https://www.edinburghnews.scotsman.com/business/edinburgh-firm-behind-incredible-gravity-energy-storage-project-hails-milestone-2955863 |access-date=2020-09-01 |website=www.edinburghnews.scotsman.com |language=en}}</ref><ref name="quartz">{{cite news |author=Akshat Rathi |date=August 18, 2018 |title=Stacking concrete blocks is a surprisingly efficient way to store energy |url=https://qz.com/1355672/stacking-concrete-blocks-is-a-surprisingly-efficient-way-to-store-energy/ |work=Quartz}}</ref>
The problem with relying on these last two methods in particular is that they are expensive, because they leave expensive generating equipment unused much of the time, and because plants running below maximum output usually produce at less than their best efficiency. Grid energy storage is used to shift load from peak to off-peak hours. Power plants are able to run closer to their peak efficiency for much of the year.


===Energy demand management===
====Compressed air ====
{{Main|Compressed-air energy storage}}
''Main article: [[Energy demand management]]''


Compressed air energy storage (CAES) stores electricity by compressing air. The compressed air is typically stored in large underground caverns. The expanding air can be used to drive turbines, converting the energy back into electricity. As [[Adiabatic cooling|air cools when expanding]], some heat needs to be added in this stage to prevent freezing. This can be provided by a low-carbon source, or in the case of advanced CAES, by reusing the heat that is released when air is compressed. {{As of|2023}}, there are three advanced CAES project in operation in China.{{Sfn|Smith|2023|p=19}} Typical efficiencies of advanced CAES are between 60% and 80%.<ref>{{Cite journal |last1=Zhang |first1=Xinjing |last2=Gao |first2=Ziyu |last3=Zhou |first3=Bingqian |last4=Guo |first4=Huan |last5=Xu |first5=Yujie |last6=Ding |first6=Yulong |last7=Chen |first7=Haisheng |date=2024 |title=Advanced Compressed Air Energy Storage Systems: Fundamentals and Applications |journal=Engineering |volume=34 |pages=246–269 |doi=10.1016/j.eng.2023.12.008 |issn=2095-8099 |doi-access=free}}</ref>
The easiest way to deal with varying electrical loads is to decrease the difference between varying generation and demand. This is referred to as demand side management (DSM). For decades, utilities have sold off-peak power to large consumers at lower rates, to encourage these users to shift their loads to off-peak hours, in the same way that telephone companies do with individual customers. Usually, these time-dependent prices are negotiated ahead of time. In an attempt to save more money, some utilities are experimenting with selling electricity at minute-by-minute [[spot price]]s, which allow those users with monitoring equipment to detect demand peaks as they happen, and shift demand to save both the user and the utility money. Demand side management can be manual or automatic and is not limited to large industrial customers. In residential and small business applications, for example, appliance control modules can reduce energy usage of [[water heating|water heaters]], [[air conditioning]] units, and other devices during these periods by turning them off for some portion of the peak demand time or by reducing the power that they draw. Energy demand management includes more than reducing overall energy use or shifting loads to off-peak hours. A particularly effective method of energy demand management is the installation of more [[energy conversion efficiency|energy efficient]] equipment. For example, many utilities give rebates for the purchase of [[thermal insulation|insulation]], [[weatherstripping]], and appliances and [[light bulb]]s that are energy efficient. Companies with factories and large buildings can also install such products, but they can also buy energy efficient industrial equipment, like [[boiler]]s, or use more efficient processes to produce products. Companies may get incentives like rebates or low interest loans from utilities or the government for the installation of energy efficient industrial equipment.


=== Portability ===
==== Liquid air or {{CO2}} ====
{{Main|Cryogenic energy storage|}}
This is the area of greatest success for current energy storage technologies. Single-use and rechargeable batteries are ubiquitous, and provide power for devices with demands as varied as digital watches and cars. Advances in battery technology have generally been slow, however, with much of the advance in battery life that consumers see being attributable to efficient power management rather than increased storage capacity. This has become an issue as pressure grows for alternatives to the [[internal combustion engine]] in cars and other means of transport. These uses require far more [[energy density]] (the amount of energy stored in a given volume or weight) than current battery technology can deliver. Liquid [[hydrocarbon]] fuel (such as [[gasoline]],ethanol/[[petrol]] and [[diesel]]) have much higher energy densities.


Another electricity storage method is to compress and cool air, turning it into [[liquid air]], which can be stored and expanded when needed, turning a turbine to generate electricity. This is called liquid air energy storage (LAES).{{Sfn|Smith|2023|p=20}} The air would be cooled to temperatures of {{Convert|-196|C|F}} to become liquid. Like with compressed air, heat is needed for the expansion step. In the case of LAES, low-grade industrial heat can be used for this.{{Sfn|IPCC AR6 WG3 Ch6|2022|p=655}} Energy efficiency for LAES lies between 50% and 70%. {{As of|2023}}, LAES is moving from pre-commercial to commercial.<ref>{{Cite journal |last1=Liang |first1=Ting |last2=Zhang |first2=Tongtong |last3=Lin |first3=Xipeng |last4=Alessio |first4=Tafone |last5=Legrand |first5=Mathieu |last6=He |first6=Xiufen |last7=Kildahl |first7=Harriet |last8=Lu |first8=Chang |last9=Chen |first9=Haisheng |last10=Romagnoli |first10=Alessandro |last11=Wang |first11=Li |last12=He |first12=Qing |last13=Li |first13=Yongliang |last14=Yang |first14=Lizhong |last15=Ding |first15=Yulong |date=2023 |title=Liquid air energy storage technology: a comprehensive review of research, development and deployment |url=https://iopscience.iop.org/article/10.1088/2516-1083/aca26a/meta |journal=Progress in Energy |language=en |volume=5 |issue=1 |pages=012002 |doi=10.1088/2516-1083/aca26a |bibcode=2023PrEne...5a2002L |issn=2516-1083}}</ref> An alternative is the compression of {{Chem|CO|2}} to store electricity.{{Sfn|Schmidt|Staffell|2023|p=64}}
=== Reliability ===

Virtually all devices that operate on electricity are adversely affected by the sudden removal of their power supply. Solutions such as UPS ([[Uninterruptible power supply|uninterruptible power supplies]]) or backup generators are available, but these are expensive. Efficient methods of power storage would allow for devices to have a built-in backup for power cuts, and also reduce the impact of a failure in a generating station. Examples of this are currently available using [[fuel cell]]s and flywheels.
===Thermal===
{{Main|Thermal energy storage}}

Electricity can be directly stored thermally with a [[Carnot battery]]. A Carnot battery is a type of energy storage system that stores electricity in heat storage and converts the stored heat back to electricity via [[thermodynamic cycle]]s (for instance, a turbine). While less efficient than pumped hydro or battery storage, this type of system is expected to be cheap and can provide long-duration storage.<ref name="DumontFrate2020">{{cite journal |last1=Dumont |first1=Olivier |last2=Frate |first2=Guido Francesco |last3=Pillai |first3=Aditya |last4=Lecompte |first4=Steven |last5=De paepe |first5=Michel |last6=Lemort |first6=Vincent |year=2020 |title=Carnot battery technology: A state-of-the-art review |journal=Journal of Energy Storage |volume=32 |pages=101756 |bibcode=2020JEnSt..3201756D |doi=10.1016/j.est.2020.101756 |issn=2352-152X |s2cid=225019981 |hdl-access=free |hdl=2268/251473}}</ref>{{Sfn|Vandersickel|Gutierrez|2023|p=107}} A [[pumped-heat electricity storage]] system is a Carnot battery that uses a [[reversible heat pump]] to convert the electricity into heat.<ref>{{Cite journal |last1=Benato |first1=Alberto |last2=Stoppato |first2=Anna |date=2018-06-01 |title=Pumped Thermal Electricity Storage: A technology overview |url=https://linkinghub.elsevier.com/retrieve/pii/S2451904917303700 |journal=Thermal Science and Engineering Progress |volume=6 |pages=301–315 |doi=10.1016/j.tsep.2018.01.017 |bibcode=2018TSEP....6..301B |issn=2451-9049}}</ref> It usually stores the energy in both a hot and cold reservoir. To achieve decent efficiencies (>50%), the temperature ratio between the two must reach a factor of 5.<ref>{{Cite journal |last1=Albertus |first1=Paul |last2=Manser |first2=Joseph S. |last3=Litzelman |first3=Scott |date=2020 |title=Long-Duration Electricity Storage Applications, Economics, and Technologies |url=https://linkinghub.elsevier.com/retrieve/pii/S2542435119305392 |journal=Joule |volume=4 |issue=1 |pages=21–32 |doi=10.1016/j.joule.2019.11.009 |bibcode=2020Joule...4...21A |issn=2542-4351}}</ref>

Thermal energy storage is also used in combination with [[concentrated solar power]] (CSP). In CSP, solar energy is first converted into heat, and then either directly converted into electricity or first stored. The energy is released when there is little or no sunshine.<ref>{{Cite journal |last1=Pelay |first1=Ugo |last2=Luo |first2=Lingai |last3=Fan |first3=Yilin |last4=Stitou |first4=Driss |last5=Rood |first5=Mark |date=2017-11-01 |title=Thermal energy storage systems for concentrated solar power plants |url=https://www.sciencedirect.com/science/article/abs/pii/S1364032117304021 |journal=Renewable and Sustainable Energy Reviews |volume=79 |pages=82–100 |doi=10.1016/j.rser.2017.03.139 |bibcode=2017RSERv..79...82P |issn=1364-0321}}</ref> This means that CSP can be used as a [[Dispatchable generation|dispatchable (flexible)]] form of generation. The energy in a CSP system can for instance be stored in [[Molten-salt battery|molten salts]] or in a solid medium such as sand.<ref>{{Cite web |title=Thermal Storage System Concentrating Solar-Thermal Power Basics |url=https://www.energy.gov/eere/solar/thermal-storage-system-concentrating-solar-thermal-power-basics |access-date=2024-11-17 |website=Energy.gov |language=en}}</ref>

Finally, [[Heating, ventilation, and air conditioning|heating and cooling systems]] in [[buildings]] can be controlled to store thermal energy in either the building's mass or dedicated thermal storage tanks. This thermal storage can provide load-shifting or even more complex [[ancillary services]] by increasing power consumption (charging the storage) during off-peak times and lowering power consumption (discharging the storage) during higher-priced peak times.<ref>{{cite journal |last1=Lee |first1=Zachary E. |first2=Qingxuan |last2=Sun |first3=Zhao |last3=Ma |first4=Jiangfeng |last4=Wang |first5=Jason S. |last5=MacDonald |first6=K. Max |last6=Zhang |title=Providing Grid Services With Heat Pumps: A Review |journal=Journal of Engineering for Sustainable Buildings and Cities |date=Feb 2020 |volume=1 |issue=1 |doi=10.1115/1.4045819 |s2cid=213898377 |url=https://escholarship.org/uc/item/4w97v0wb |doi-access=free }}</ref>

==Economics==

=== Costs ===
[[File:Battery-cost-learning-curve.png|thumb|upright=1.5| [[Experience curve]] of lithium-ion batteries: the price of batteries dropped by 97% in three decades.<ref>{{Cite journal |last1=Ziegler |first1=Micah S. |last2=Trancik |first2=Jessika E. |date=2021 |title=Re-examining rates of lithium-ion battery technology improvement and cost decline |url=http://xlink.rsc.org/?DOI=D0EE02681F |journal=Energy & Environmental Science |language=en |volume=14 |issue=4 |pages=1635–1651 |arxiv=2007.13920 |doi=10.1039/D0EE02681F |issn=1754-5692 |s2cid=220830992 |doi-access=free}}</ref><ref>{{Cite web |title=The price of batteries has declined by 97% in the last three decades |url=https://ourworldindata.org/battery-price-decline |access-date=2022-04-26 |website=Our World in Data}}</ref>|alt=log-log graph of cumulative capacity and battery costs showing a near-linear downwards line, starting in 1992.]]
The [[levelized cost of storage|levelized cost of storing electricity]] (LCOS) is a measure of the lifetime costs of storing electricity per [[MWh]] of electricity discharged. It includes investment costs, but also operational costs and charging costs.{{sfn|Schmidt|Staffell|2023|pp=131, 136}} It depends highly on storage type and purpose; as subsecond-scale [[Utility frequency|frequency regulation]], minute/hour-scale peaker plants, or day/week-scale season storage.<ref>{{cite web |url=http://www.utilitydive.com/news/some-energy-storage-already-cost-competitive-new-valuation-study-shows/409641/|title=Some energy storage already cost competitive, new valuation study shows|date=24 November 2015|work=Utility Dive |access-date=15 October 2016 |url-status=live |archive-url=https://web.archive.org/web/20161018235841/http://www.utilitydive.com/news/some-energy-storage-already-cost-competitive-new-valuation-study-shows/409641/ |archive-date=18 October 2016}}</ref><ref>{{cite web |title=Lazard's Levelized Cost of Storage Analysis |url=https://www.lazard.com/media/2391/lazards-levelized-cost-of-storage-analysis-10.pdf |access-date=2 February 2017 |url-status=live |archive-url=https://web.archive.org/web/20170202184057/https://www.lazard.com/media/2391/lazards-levelized-cost-of-storage-analysis-10.pdf |archive-date=2 February 2017}}</ref><ref>{{cite journal |last1=Lai |first1=Chun Sing |last2=McCulloch |first2=Malcolm D. |title=Levelized cost of electricity for solar photovoltaic and electrical energy storage |journal=Applied Energy |date=March 2017 |volume=190 |pages=191–203 |doi=10.1016/j.apenergy.2016.12.153 |bibcode=2017ApEn..190..191L |s2cid=113623853 |url=http://bura.brunel.ac.uk/handle/2438/22670 }}</ref>

For power applications (for instance around [[ancillary services]] or [[black start]]s), a similar metric is the [[annuitized capacity cost]] (ACC), which measures the lifetime costs per kW. ACC is lowest when there are few cycles (<300) and when the discharge is less than one hour. This is because the technology is reimbursed only when it provides spare capacity, not when it is discharged.{{sfn|Schmidt|Staffell|2023|pp=137, 150-151}}

The cost of storage is coming down following technology-dependent [[Experience curve effects|experience curves]], the price drop for each doubling in cumulative capacity (or experience). Lithium-ion battery prices fast: the price utitlities pay for them falls 19% with each doubling of capacity. Hydrogen production via electrolysis has a similar learning rate, but it is much more uncertain. Vanadium-flow batteries typically get 14% cheaper for each doubling of capacity. Pumped hydropower has not seen prices fall much with increased experience.{{Sfn|Schmidt|Staffell|2023|p=92}}

===Market and system value===
There are four categories of services which provide economic value for storage: those related to power quality (such as frequency regulation), reliability (ensuring peak demand can be met), better use of assets in the system (e.g. avoiding transmission investments) and [[arbitrage]] (exploiting price differences over time). Before 2020, most value for storage was in providing power quality services. Arbitrage is the service with the largest economic potential for storage applications.{{sfn|Schmidt|Staffell|2023|p=|pp=177, 179}}
{| class="wikitable"
|+Storage requirements based on the share of variable renewable energy (VRE). For energy storage, this is the energy stored at a given time, not the total over the year{{Sfn|Schmidt|Staffell|2023|p=227}}
!VRE share
!Power (% of peak demand)
!Energy storage (% of annual demand)
|-
|50%
|Less than 20%
|0.02%
|-
|80%
|20–50%
|0.03–0.1%
|-
|90%
|25–75%
|0.05–0.2%
|}
In systems with under 40% of variable renewables, only short-term storage (of less than 4 hours) is needed for integration. When the share of variable renewables climbs to 80%, medium-duration storage (between 4 and 16 hours, for instance [[Compressed-air energy storage|compressed air]]) is needed. Above 90%, large-scale [[long-duration storage]] is required.{{Sfn|Schmidt|Staffell|2023|p=241}} The economics of long-duration storage is challenging even then, as the costs are high. Alternative flexibility options, such as demand response, network expansions or flexible generation ([[Geothermal energy|geothermal]] or fossil gas with [[carbon capture and storage]]) may be lower-cost.{{Sfn|Schmidt|Staffell|2023|p=247}}

Like with renewables, storage will "[[Market cannibalisation|cannibalise]]" its own income, but even more strongly. That is, with more storage on the market, there is less of an opportunity to do arbitrage or deliver other services to the grid.{{Sfn|Schmidt|Staffell|2023|p=261}} How markets are designed impacts revenue potential too. The income from arbitrage is quite variable between years, whereas markets that have [[capacity payments]] likely show less volatility.{{Sfn|Schmidt|Staffell|2023|p=215}}

Electricity storage is not 100% efficient, so more electricity needs to be bought than can be sold. This implies that if there is only a small variation in price, it may not be economical to charge and discharge. For instance, if the storage application is 75% efficient, the price at which the electricity is sold needs to be at least 1.33 higher than the price for which it was bought.{{Sfn|Schmidt|Staffell|2023|p=191}} Typically, electricity prices vary most between day and night, which means that storage up to 8 hours has relatively high potential for profit.{{Sfn|Schmidt|Staffell|2023|p=176}}


==See also==
==See also==
{{portal|Energy}}
{{Portal|Energy}}
{{div col|colwidth=18em}}
*[[Grid-tied electrical system]]
* [[Distributed generation]]
*[[Battery-to-grid]]
* [[Energy storage as a service]] (ESaaS)
*[[Distributed generation]]
*[[Energy storage]]
* [[List of energy storage projects]]
* [[Power-to-X]]
*[[Virtual power plant]]
* [[United States Department of Energy International Energy Storage Database|U.S. Department of Energy International Energy Storage Database]], a list of grid energy storage projects
*[[Wind farm]]
* [[Virtual power plant]]
{{div col end}}


==References==
==References==
{{reflist}}
{{reflist|30em}}

=== Cited sources ===
* {{cite book |title=The Future of Energy Storage: An Interdisciplinary MIT Study |url=https://energy.mit.edu/wp-content/uploads/2022/05/The-Future-of-Energy-Storage.pdf |last1=Armstrong |first1=Robert |last2=Chiang |first2=Yet-Ming |publisher=Massachusetts Institute of Technology |year=2022 |isbn=978-0-578-29263-2}}
* {{Cite book |last1=Cozzi |first1=Laura |url=https://iea.blob.core.windows.net/assets/cb39c1bf-d2b3-446d-8c35-aae6b1f3a4a0/BatteriesandSecureEnergyTransitions.pdf |title=Batteries and Secure Energy Transitions |last2=Petropoulos |first2=Apostolos |last3=Wanner |first3=Brent |date=April 2024 |publisher=International Energy Agency}}
* {{Cite book | url=https://iea.blob.core.windows.net/assets/3ece5ee4-7537-4992-8ba6-b83c994c3fd4/GlobalHydrogenReview2024.pdf|title=Global Hydrogen Review 2024|date=October 2024|publisher=International Energy Agency|last1=Remme |first1=Uwe|last2=Bermudez Menendez|first2=Jose Miguel|display-authors=etal}}
*{{cite report |ref= {{harvid|IPCC AR6 WG3 Ch6|2022}}
|chapter-url= https://ipcc.ch/report/ar6/wg3/downloads/report/IPCC_AR6_WGIII_Chapter06.pdf
|chapter= Chapter 6: Energy Systems
|display-authors= 4
|last1= Clarke |first1= L.
|last2= Wei |first2= Y.-M.
|last3= De La Vega Navarro |first3= A.
|last4= Garg |first4= A.
|last5= Hahmann |first5= A.N.
|last6= Khennas |first6= S.
|last7= Azevedo |first7= I.M.L.
|last8= Löschel |first8= A.
|last9= Singh |first9= A.K.
|last10= Steg |first10= L.
|last11= Strbac |first11= G.
|last12= Wada |first12= K.
|title=Climate Change 2022: Mitigation of Climate Change. Contribution of Working Group III to the Sixth Assessment Report of the Intergovernmental Panel on Climate Change
|doi=10.1017/9781009157926.008
}}
* {{cite book | isbn=978-92-9260-180-5|author-last1=IRENA|year=2020 |title=Innovation landscape brief: Innovative operation of pumped hydropower storage|publisher = International Renewable Energy Agency|location=Abu Dhabi}}
* {{Cite book |title=Storing energy: with special reference to renewable energy sources |date=2022 |publisher=Elsevier |isbn=978-0-12-824510-1 |editor-last=Letcher |editor-first=Trevor M. |edition=Second|location=Amsterdam Oxford Cambridge, MA}}
* {{Cite book |last1=Schmidt |first1=Oliver |title=Monetizing energy storage: a toolkit to assess future cost and value |last2=Staffell |first2=Iain |date=2023 |publisher=Oxford University Press |isbn=978-0-19-288817-4 |location=Oxford, United Kingdom|url=https://academic.oup.com/book/55104}}
* {{cite book |title=Large-scale electricity storage |url=https://royalsociety.org/-/media/policy/projects/large-scale-electricity-storage/large-scale-electricity-storage-policy-briefing.pdf |publisher=Royal Society |year=2023 |isbn=978-1-78252-666-7 |last1=Smith |first1=Chris Llewellyn}}
*{{cite report
|last1 = Vandersickel | first1=Annelies
|last2 = Gutierrez |first2 = Andrea
| title = Task 36 Carnot Batteries Final Report
| url=https://iea-es.org/publications/final-report-task-36/
| publisher = Technology Collaboration Programme Energy Storage, International Energy Agency
| date = 2023
| accessdate = 29 October 2024
}}

==External links==
==External links==
* [https://www.gov.uk/government/publications/benefits-of-long-duration-electricity-storage UK Government report on the Benefits of long-duration electricity storage (Aug 2022)]
*[http://www.electricitystorage.org/technologies.htm Electricity storage technologies]

*Graphical comparisons of different energy storage systems:
{{Electricity grid modernization|state=expanded}}
**[http://www.electricitystorage.org/pix/photo_ESAratings.gif System power ratings]
{{Electricity generation}}
**[http://www.electricitystorage.org/pix/photo_EnergyDensity.gif Energy density]
{{emerging technologies|energy=yes}}
**[http://www.electricitystorage.org/pix/photo_ESACost.gif Cost per unit]
**[http://www.electricitystorage.org/pix/Photo_ESAEfficiency2.gif Efficiency]
**[http://www.electricitystorage.org/pix/photo_ESApercycle.gif Capital cost per cycle]
**[http://www.abb.com/cawp/seitp202/0B6D46A05BBC3A27C1256FF2002FD2A0.aspx A large grid-connected nickel-cadmium battery]


[[Category:Energy storage]]
[[Category:Grid energy storage| ]]
[[Category:Power engineering]]
[[Category:Power engineering]]

Latest revision as of 13:28, 18 December 2024

Energy from fossil or nuclear power plants and renewable sources is stored for use by customers.
Diagram showing flow of energy between energy storage facilities and power grids, as a function of time over a 24 hour period

Grid energy storage, also known as large-scale energy storage, are technologies connected to the electrical power grid that store energy for later use. These systems help balance supply and demand by storing excess electricity from variable renewables such as solar and inflexible sources like nuclear power, releasing it when needed. They further provide essential grid services, such as helping to restart the grid after a power outage.

As of 2023, the largest form of grid storage is pumped-storage hydroelectricity, with utility-scale batteries and behind-the-meter batteries coming second and third.[1] Lithium-ion batteries are highly suited for shorter duration storage up to 8 hours. Flow batteries and compressed air energy storage may provide storage for medium duration. Two forms of storage are suited for long-duration storage: green hydrogen, produced via electrolysis and thermal energy storage.[2]

Energy storage is one option to making grids more flexible. An other solution is the use of more dispatchable power plants that can change their output rapidly, for instance peaking power plants to fill in supply gaps. Demand response can shift load to other times and interconnections between regions can balance out fluctuations in renewables production.[3]

The price of storage technologies typically goes down with experience. For instance, lithium-ion batteries have been getting some 20% cheaper for each doubling of worldwide capacity.[4] Systems with under 40% variable renewables need only short-term storage. At 80%, medium-duration storage becomes essential and beyond 90%, long-duration storage. The economics of long-duration storage is challenging, and alternative flexibility options like demand response may be more economic.

Roles in the power grid

[edit]

Any electrical power grid must match electricity production to consumption, both of which vary significantly over time. Energy derived from solar and wind sources varies with the weather on time scales ranging from less than a second to weeks or longer. Nuclear power is less flexible than fossil fuels, meaning it cannot easily match the variations in demand. Thus, low-carbon electricity without storage presents special challenges to electric utilities.[5]

Electricity storage is one of the three key ways to replace flexibility from fossil fuels in the grid. Other options are demand-side response, in which consumers change when they use electricity or how much they use. For instance, households may have cheaper night tariffs to encourage them to use electricity at night. Industry and commercial consumers can also change their demand to meet supply. Improved network interconnection smooths the variations of renewables production and demand. When there is little wind in one location, another might have a surplus of production. Expansion of transmission lines usually takes a long time.[6]

Potential roles of energy storage in the grid[7][8]
Consumption Network Generation
Short-term flexibility Increased use rooftop solar, cost reductions from time-based rates Congestion relief Renewables integration (smoothing, arbitrage)
Essential grid services Backup power during outages Frequency regulation Black start
System reliability and planning Creation of mini-grids Savings in transmission and distribution network Meeting peak demand

Energy storage has a large set of roles in the electricity grid and can therefore provide many different services. For instance, it can arbitrage by keeping it until the electricity price rises, it can help make the grid more stable, and help reduce investment into transmission infrastructure.[9] The type of service provided by storage depends on who manages the technology, whether the technology is based alongside generation of electricity, within the network, or at the side of consumption.[8]

Providing short-term flexibility is a key role for energy storage. On the generation side, it can help with the integration of variable renewable energy, storing it when there is an oversupply of wind and solar and electricity prices are low. More generally, it can exploit the changes in prices of electricity over time in the wholesale market, charging when electricity is cheap and selling when it is expensive. It can further help with grid congestion (where there is insufficient capacity on transmission lines). Consumers can use storage to use more of their self-produced electricity (for instance from rooftop solar power).[8][7]

Storage can also be used to provide essential grid services. On the generation side, storage can smooth out the variations in production, for instance for solar and wind. It can assist in a black start after a power outage. On the network side, these include frequency regulation (continuously) and frequency response (after unexpected changes in supply or demand). On the consumption side, storage can help to improve the quality of the delivered electricity in less stable grids.[8][10]

Investment in storage may make some investments in the transmission and distribution network unnecessary, or may allow them to be scaled down. Additionally, storage can ensure there is sufficient capacity to meet peak demand within the electricity grid. Finally, in off-grid home systems or mini-grids, electricity storage can help provide energy access in areas that were previously not connected to the electricity grid.[8]

Forms

[edit]
Energy from sunlight or other renewable energy is converted to potential energy for storage in devices such as electric batteries. The stored potential energy is later converted to electricity that is added to the power grid, even when the original energy source is not available.

Electricity can be stored directly for a short time in capacitors, somewhat longer electrochemically in batteries, and much longer chemically (e.g. hydrogen), mechanically (e.g. pumped hydropower) or as heat.[11] The first pumped hydroelectricity was constructed at the end of the 19th century around the Alps in Italy, Austria, and Switzerland. The technique rapidly expanded during the 1960s to 1980s nuclear boom, due to nuclear power's inability to quickly adapt to changes in electricity demand. In the 21st century, interest in storage surged due to the rise of sustainable energy sources, which are often weather-dependent.[12] Commercial batteries have been available for over a century,[13] their widespread use in the power grid is more recent, with only 1 GW available in 2013.[14]

Batteries

[edit]
A 900 watt direct current light plant using 16 separate lead acid battery cells (32 volts) from 1917.[15]

Lithium-ion batteries

[edit]

Lithium-ion batteries are the most commonly used batteries for grid applications, as of 2024, following the application of batteries in electric vehicles (EVs). In comparison with EVs, grid batteries require less energy density, meaning that more emphasis can be put on costs, the ability to charge and discharge often and lifespan. This has led to a shift towards lithium iron phosphate batteries (LFP batteries), which are cheaper and last longer than traditional lithium-ion batteries.[16]

Costs of batteries are declining rapidly; from 2010 to 2023 costs fell by 90%.[17] As of 2024, utility-scale systems account for two thirds of added capacity, and home applications (behind-the-meter) for one third.[18] Lithium-ion batteries are highly suited to short-duration storage (<8h) due to cost and degradation associated with high states of charge.[19]

Electric vehicles
[edit]
A Nissan Leaf charging
Batteries from old electric cars, such as this Nissan Leaf, can be reused but as of 2024 it is not known whether grid storage or behind the meter storage will be the best application.[20]

The electric vehicle fleet has a large overall battery capacity, which can potentially be used for grid energy storage. This could be in the form of vehicle-to-grid (V2G), where cars store energy when they are not in use, or by repurposing batteries from cars at the end of the vehicle's life. Car batteries typically range between 33 and 100 kWh;[21] for comparison, a typical upper-middle-class household in Spain might use some 18 kWh in a day.[22] By 2030, batteries in electric vehicles may be able to meet all short-term storage demand globally.[23]

As of 2024, there have been more than 100 V2G pilot projects globally.[24] The effect of V2G charging on battery life can be positive or negative. Increased cycling of batteries can lead to faster degradation, but due to better management of the state of charge and gentler charging and discharing, V2G might instead increase the lifetime of batteries.[24][25] Second-hand batteries may be useable for stationary grid storage for roughly 6 years, when their capacity drops from roughly 80% to 60% of the initial capacity. LFP batteries are particularly suitable for reusing, as they degrade less than other lithium-ion batteries and recycling is less attractive as their materials are not as valuable.[24]

Other battery types

[edit]

In redox flow batteries, energy is stored in liquids, which are placed in two separate tanks. When charging or discharging, the liquids are pumped into a cell with the electrodes. The amount of energy stored (as set by the size of the tanks) can be adjusted separately from the power output (as set by the speed of the pumps).[26] Flow batteries have the advantages of low capital cost for charge-discharge duration over 4 h, and of long durability (many years). Flow batteries are inferior to lithium-ion batteries in terms of energy efficiency, averaging efficiencies between 60% and 75%. Vanadium redox batteries is most commercially advanced type of flow battery, with roughly 40 companies making them as of 2022.[27]

Sodium-ion batteries are possible alternative to lithium-ion batteries, as they rely on cheaper materials and less on critical materials. It has a lower energy density, and possibly a shorter lifespan. If produced at the same scale as lithium-ion batteries, they may become 20% to 30% cheaper.[26] Iron-air batteries may be suitable for even longer duration storage than flow batteries (weeks), but the technology is not yet mature.[28]

Technology comparison[28]
Technology Less than 4h 4h to 8h Days Weeks Seasons
Lithium-ion Yes Yes No No No
Sodium-ion Yes Yes No No No
Vanadium flow Maybe Yes Yes No No
Iron-air No No Maybe Yes No

Electrical

[edit]

Storage in supercapacitors works well for applications where a lot of power is needed for short amount of time. In the power grid, they are therefore mostly used in short-term frequency regulation.[29]

Hydrogen and chemical storage

[edit]

Various power-to-gas technologies exist that can convert excess electricity into an easier to store chemical. The lowest cost and most efficient one is hydrogen. However, it is easier to use synthetic methane with existing infrastructure and appliances, as it is very similar to natural gas.[30]

As of 2024, there have been a number of demonstration plants where hydrogen is burned in gas turbines, either co-firing with natural gas, or on its own. Similarly, a number of coal plants have demonstrated it is possible to co-fire ammonia when burning coal. In 2022, there was also a small pilot to burn pure ammonia in a gas turbine.[31] A portion of existing gas turbines are capable of co-firing hydrogen, which means there is, as a lower estimate, 80 GW of capacity ready to burn hydrogen.[32]

Hydrogen

[edit]

Hydrogen can be used as a long-term storage medium.[33] Green hydrogen is produced from the electrolysis of water and converted back into electricity in an internal combustion engine, or a fuel cell, with a round-trip efficiency of roughly 41%.[34] Together with thermal storage, it is expected to be best suited to seasonal energy storage.[35]

Hydrogen can be stored aboveground in tanks or underground in larger quantities. Underground storage is easiest in salt caverns, but only a certain number of places have suitable geology.[36] Storage in porous rocks, for instance in empty gas fields and some aquifers, can store hydrogen at a larger scale, but this type of storage may have some drawbacks. For instance, some of the hydrogen may leak, or react into H2S or methane.[37]

Ammonia

[edit]

Hydrogen can be converted into ammonia in a reaction with nitrogen in the Haber-Bosch process. Ammonia, a gas at room temperature, is more expensive to produce than hydrogen. However, it can be stored more cheaply than hydrogen. Tank storage is usually done at between one and ten times atmospheric pressure and at a temperature of −30 °C (−22 °F), in liquid form.[38] Ammonia has multiple uses besides being an energy carrier: it is the basis for the production of many chemicals; the most common use is for fertilizer.[39] It can be used for power generation directly, or converted back to hydrogen first. Alternatively, it has potential applications as a fuel in shipping.[40]

Methane

[edit]

It is possible to further convert hydrogen into methane via the Sabatier reaction, a chemical reaction which combines CO2 and H2. While the reaction that converts CO from gasified coal into CH4 is mature, the process to form methane out of CO2 is less so. Efficiencies of around 80% one-way can be achieved, that is, some 20% of the energy in hydrogen is lost in the reaction.[41]

Mechanical

[edit]

Flywheel

[edit]
a metal casing with wires, roughtly cyclindrically shaped
NASA G2 flywheel

Flywheels store energy in the form of mechanical energy. They are suited to supplying high levels of electricity over minutes and can also be charged rapidly. They have a long lifetime and can be used in settings with widely varying temperatures. The technology is mature, but more expensive than batteries and supercapacitors and not used frequently.[42]

Pumped hydro

[edit]
Mingtan Pumped-Storage Hydro Power Plant dam in Nantou, Taiwan

In 2023, pumped hydroelectric storage (PHS) was the largest storage technology, with a worldwide capacity of 181 GW, compared to some 55 GW of storage in utility-scale batteries and 33 GW of behind-the-meter batteries.[43] PHS is well suited to evening out daily variations, pumping water to a high storage reservoir during off-peak hours, and using this water during peak times for hydroelectric generation.[44] The efficiency of PHS ranges between 75% and 85%, and the response time is fast, between seconds and minutes.[45]

PHS systems can only be built in limited locations. However, other pumped storage systems can be made, for instance by using deep salt caverns or by constructing a hollow structure on the seabed, with the sea itself serving as the upper reservoir.[44] PHS construction can be costly, takes relatively long and can be disruptive for the environment and people living nearby.[44] The efficiency of pumped hydro can be increased by placing floating solar panels on top, which prevent evaporation. This also improves the efficiency of the solar panels, as they are constantly cooled.[46]

Hydroelectric dams

[edit]
Fetsui hydroelectric dam in New Taipei, Taiwan

Hydroelectric dams with large reservoirs can also be operated to provide peak generation at times of peak demand. Water is stored in the reservoir during periods of low demand and released through the plant when demand is higher. While technically no electricity is stored, the net effect is the similar as pumped storage. The amount of storage available in hydroelectric dams is much larger than in pumped storage. Upgrades may be needed so that these dams can respond to variable demand. For instance, additional investment may be needed in transmission lines, or additional turbines may need to be installed to increase the peak output from the dam.[47]

Dams usually have multiple purposes. As well as energy generation, they often play a role in flood defense and protection of ecosystems, recreation, and they supply water for irrigation. This means it is not always possible to change their operation much, but even with low flexibility, they may still play an important role in responding to changes in wind and solar production.[48]

Gravity

[edit]

Alternative methods that use gravity include storing energy by moving large solid masses upward against gravity. This can be achieved inside old mine shafts[49] or in specially constructed towers where heavy weights are winched up to store energy and allowed a controlled descent to release it.[50][51]

Compressed air

[edit]

Compressed air energy storage (CAES) stores electricity by compressing air. The compressed air is typically stored in large underground caverns. The expanding air can be used to drive turbines, converting the energy back into electricity. As air cools when expanding, some heat needs to be added in this stage to prevent freezing. This can be provided by a low-carbon source, or in the case of advanced CAES, by reusing the heat that is released when air is compressed. As of 2023, there are three advanced CAES project in operation in China.[52] Typical efficiencies of advanced CAES are between 60% and 80%.[53]

Liquid air or CO2

[edit]

Another electricity storage method is to compress and cool air, turning it into liquid air, which can be stored and expanded when needed, turning a turbine to generate electricity. This is called liquid air energy storage (LAES).[54] The air would be cooled to temperatures of −196 °C (−320.8 °F) to become liquid. Like with compressed air, heat is needed for the expansion step. In the case of LAES, low-grade industrial heat can be used for this.[42] Energy efficiency for LAES lies between 50% and 70%. As of 2023, LAES is moving from pre-commercial to commercial.[55] An alternative is the compression of CO
2
to store electricity.[56]

Thermal

[edit]

Electricity can be directly stored thermally with a Carnot battery. A Carnot battery is a type of energy storage system that stores electricity in heat storage and converts the stored heat back to electricity via thermodynamic cycles (for instance, a turbine). While less efficient than pumped hydro or battery storage, this type of system is expected to be cheap and can provide long-duration storage.[57][58] A pumped-heat electricity storage system is a Carnot battery that uses a reversible heat pump to convert the electricity into heat.[59] It usually stores the energy in both a hot and cold reservoir. To achieve decent efficiencies (>50%), the temperature ratio between the two must reach a factor of 5.[60]

Thermal energy storage is also used in combination with concentrated solar power (CSP). In CSP, solar energy is first converted into heat, and then either directly converted into electricity or first stored. The energy is released when there is little or no sunshine.[61] This means that CSP can be used as a dispatchable (flexible) form of generation. The energy in a CSP system can for instance be stored in molten salts or in a solid medium such as sand.[62]

Finally, heating and cooling systems in buildings can be controlled to store thermal energy in either the building's mass or dedicated thermal storage tanks. This thermal storage can provide load-shifting or even more complex ancillary services by increasing power consumption (charging the storage) during off-peak times and lowering power consumption (discharging the storage) during higher-priced peak times.[63]

Economics

[edit]

Costs

[edit]
log-log graph of cumulative capacity and battery costs showing a near-linear downwards line, starting in 1992.
Experience curve of lithium-ion batteries: the price of batteries dropped by 97% in three decades.[64][65]

The levelized cost of storing electricity (LCOS) is a measure of the lifetime costs of storing electricity per MWh of electricity discharged. It includes investment costs, but also operational costs and charging costs.[66] It depends highly on storage type and purpose; as subsecond-scale frequency regulation, minute/hour-scale peaker plants, or day/week-scale season storage.[67][68][69]

For power applications (for instance around ancillary services or black starts), a similar metric is the annuitized capacity cost (ACC), which measures the lifetime costs per kW. ACC is lowest when there are few cycles (<300) and when the discharge is less than one hour. This is because the technology is reimbursed only when it provides spare capacity, not when it is discharged.[70]

The cost of storage is coming down following technology-dependent experience curves, the price drop for each doubling in cumulative capacity (or experience). Lithium-ion battery prices fast: the price utitlities pay for them falls 19% with each doubling of capacity. Hydrogen production via electrolysis has a similar learning rate, but it is much more uncertain. Vanadium-flow batteries typically get 14% cheaper for each doubling of capacity. Pumped hydropower has not seen prices fall much with increased experience.[4]

Market and system value

[edit]

There are four categories of services which provide economic value for storage: those related to power quality (such as frequency regulation), reliability (ensuring peak demand can be met), better use of assets in the system (e.g. avoiding transmission investments) and arbitrage (exploiting price differences over time). Before 2020, most value for storage was in providing power quality services. Arbitrage is the service with the largest economic potential for storage applications.[71]

Storage requirements based on the share of variable renewable energy (VRE). For energy storage, this is the energy stored at a given time, not the total over the year[72]
VRE share Power (% of peak demand) Energy storage (% of annual demand)
50% Less than 20% 0.02%
80% 20–50% 0.03–0.1%
90% 25–75% 0.05–0.2%

In systems with under 40% of variable renewables, only short-term storage (of less than 4 hours) is needed for integration. When the share of variable renewables climbs to 80%, medium-duration storage (between 4 and 16 hours, for instance compressed air) is needed. Above 90%, large-scale long-duration storage is required.[73] The economics of long-duration storage is challenging even then, as the costs are high. Alternative flexibility options, such as demand response, network expansions or flexible generation (geothermal or fossil gas with carbon capture and storage) may be lower-cost.[74]

Like with renewables, storage will "cannibalise" its own income, but even more strongly. That is, with more storage on the market, there is less of an opportunity to do arbitrage or deliver other services to the grid.[75] How markets are designed impacts revenue potential too. The income from arbitrage is quite variable between years, whereas markets that have capacity payments likely show less volatility.[76]

Electricity storage is not 100% efficient, so more electricity needs to be bought than can be sold. This implies that if there is only a small variation in price, it may not be economical to charge and discharge. For instance, if the storage application is 75% efficient, the price at which the electricity is sold needs to be at least 1.33 higher than the price for which it was bought.[77] Typically, electricity prices vary most between day and night, which means that storage up to 8 hours has relatively high potential for profit.[78]

See also

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References

[edit]
  1. ^ Cozzi, Petropoulos & Wanner 2024, p. 68.
  2. ^ IPCC AR6 WG3 Ch6 2022, pp. 653, 656.
  3. ^ IPCC AR6 WG3 Ch6 2022, p. 651.
  4. ^ a b Schmidt & Staffell 2023, p. 92.
  5. ^ Schmidt & Staffell 2023, p. 8.
  6. ^ Schmidt & Staffell 2023, pp. 10–11.
  7. ^ a b Schmidt & Staffell 2023, pp. 74–76.
  8. ^ a b c d e Cozzi, Petropoulos & Wanner 2024, p. 36.
  9. ^ Armstrong & Chiang 2022, pp. 6–7.
  10. ^ Schmidt & Staffell 2023, pp. 74–75.
  11. ^ Schmidt & Staffell 2023, p. 33.
  12. ^ Mitali, J.; Dhinakaran, S.; Mohamad, A. A. (2022). "Energy storage systems: a review". Energy Storage and Saving. 1 (3): 166–216. doi:10.1016/j.enss.2022.07.002. ISSN 2772-6835.
  13. ^ Gür, Turgut M. (10 October 2018). "Review of electrical energy storage technologies, materials and systems: challenges and prospects for large-scale grid storage". Energy & Environmental Science. 11 (10): 2696–2767. doi:10.1039/C8EE01419A. ISSN 1754-5706.
  14. ^ Cozzi, Petropoulos & Wanner 2024, p. 32.
  15. ^ Hawkins, Nehemiah (1917). Hawkins Electrical Guide ...: Questions, Answers & Illustrations; a Progressive Course of Study for Engineers, Electricians, Students and Those Desiring to Acquire a Working Knowledge of Electricity and Its Applications; a Practical Treatise. T. Audel & Company. pp. 989–.
  16. ^ Cozzi, Petropoulos & Wanner 2024, p. 45.
  17. ^ Cozzi, Petropoulos & Wanner 2024, p. 18.
  18. ^ Cozzi, Petropoulos & Wanner 2024, p. 20.
  19. ^ Cozzi, Petropoulos & Wanner 2024, p. 45-46.
  20. ^ "Nissan and Ecobat to give used EV batteries a second life beyond the car". Official Great Britain Newsroom. 30 April 2024. Retrieved 21 November 2024.
  21. ^ Xu, Chengjian; Behrens, Paul; Gasper, Paul; Smith, Kandler; Hu, Mingming; Tukker, Arnold; Steubing, Bernhard (17 January 2023). "Electric vehicle batteries alone could satisfy short-term grid storage demand by as early as 2030". Nature Communications. 14 (1): 119. Bibcode:2023NatCo..14..119X. doi:10.1038/s41467-022-35393-0. ISSN 2041-1723. PMC 9845221. PMID 36650136.
  22. ^ García-Vázquez, Carlos Andrés; Espinoza-Ortega, Hernán; Llorens-Iborra, Francisco; Fernández-Ramírez, Luis M. (1 November 2022). "Feasibility analysis of a hybrid renewable energy system with vehicle-to-home operations for a house in off-grid and grid-connected applications". Sustainable Cities and Society. 86: 104124. Bibcode:2022SusCS..8604124G. doi:10.1016/j.scs.2022.104124. ISSN 2210-6707.
  23. ^ Xu, Chengjian; Behrens, Paul; Gasper, Paul; Smith, Kandler; Hu, Mingming; Tukker, Arnold; Steubing, Bernhard (17 January 2023). "Electric vehicle batteries alone could satisfy short-term grid storage demand by as early as 2030". Nature Communications. 14 (1): 119. Bibcode:2023NatCo..14..119X. doi:10.1038/s41467-022-35393-0. ISSN 2041-1723. PMC 9845221. PMID 36650136.
  24. ^ a b c Aguilar Lopez, Fernando; Lauinger, Dirk; Vuille, François; Müller, Daniel B. (16 May 2024). "On the potential of vehicle-to-grid and second-life batteries to provide energy and material security". Nature Communications. 15 (1): 4179. Bibcode:2024NatCo..15.4179A. doi:10.1038/s41467-024-48554-0. ISSN 2041-1723. PMC 11099178. PMID 38755161.
  25. ^ Bhoir, Shubham; Caliandro, Priscilla; Brivio, Claudio (1 December 2021). "Impact of V2G service provision on battery life". Journal of Energy Storage. 44: 103178. Bibcode:2021JEnSt..4403178B. doi:10.1016/j.est.2021.103178. ISSN 2352-152X.
  26. ^ a b Cozzi, Petropoulos & Wanner 2024, p. 46.
  27. ^ Tolmachev, Yuriy V. (1 March 2023). "Review—Flow Batteries from 1879 to 2022 and Beyond". Journal of the Electrochemical Society. 170 (3): 030505. Bibcode:2023JElS..170c0505T. doi:10.1149/1945-7111/acb8de. ISSN 0013-4651.
  28. ^ a b Cozzi, Petropoulos & Wanner 2024, p. 47.
  29. ^ Schmidt & Staffell 2023, pp. 54–55.
  30. ^ Letcher 2022, p. 606.
  31. ^ Remme & Bermudez Menendez 2024, pp. 54–55.
  32. ^ Remme & Bermudez Menendez 2024, p. 57.
  33. ^ Smith 2023, p. 5.
  34. ^ Smith 2023, p. 14.
  35. ^ IPCC AR6 WG3 Ch6 2022, p. 653.
  36. ^ Armstrong & Chiang 2022, p. 150.
  37. ^ Miocic, Johannes; Heinemann, Niklas; Edlmann, Katriona; Scafidi, Jonathan; Molaei, Fatemeh; Alcalde, Juan (30 August 2023). "Underground hydrogen storage: a review". Geological Society, London, Special Publications. 528 (1): 73–86. doi:10.1144/SP528-2022-88. hdl:10261/352537. ISSN 0305-8719.
  38. ^ Smith 2023, p. 18.
  39. ^ Service, Robert F. (12 July 2018). "Ammonia—a renewable fuel made from sun, air, and water—could power the globe without carbon". Science | AAAS. Retrieved 15 April 2021.
  40. ^ "Green ammonia". Royal Society. 2020. Retrieved 23 November 2024.
  41. ^ Letcher 2022, p. 602.
  42. ^ a b IPCC AR6 WG3 Ch6 2022, p. 655.
  43. ^ "Global installed energy storage capacity by scenario, 2023 and 2030 – Charts – Data & Statistics". International Energy Agency. Retrieved 25 August 2024.
  44. ^ a b c IPCC AR6 WG3 Ch6 2022, p. 654.
  45. ^ Javed, Muhammad Shahzad; Ma, Tao; Jurasz, Jakub; Amin, Muhammad Yasir (1 April 2020). "Solar and wind power generation systems with pumped hydro storage: Review and future perspectives". Renewable Energy. 148: 176–192. Bibcode:2020REne..148..176J. doi:10.1016/j.renene.2019.11.157. ISSN 0960-1481.
  46. ^ IRENA 2020, p. 7.
  47. ^ Armstrong & Chiang 2022, pp. 69–70.
  48. ^ Armstrong & Chiang 2022, pp. 69.
  49. ^ "How UK's disused mine shafts could be used to store renewable energy". The Guardian. 21 October 2019.
  50. ^ Gourley, Perry (31 August 2020). "Edinburgh firm behind incredible gravity energy storage project hails milestone". www.edinburghnews.scotsman.com. Retrieved 1 September 2020.
  51. ^ Akshat Rathi (18 August 2018). "Stacking concrete blocks is a surprisingly efficient way to store energy". Quartz.
  52. ^ Smith 2023, p. 19.
  53. ^ Zhang, Xinjing; Gao, Ziyu; Zhou, Bingqian; Guo, Huan; Xu, Yujie; Ding, Yulong; Chen, Haisheng (2024). "Advanced Compressed Air Energy Storage Systems: Fundamentals and Applications". Engineering. 34: 246–269. doi:10.1016/j.eng.2023.12.008. ISSN 2095-8099.
  54. ^ Smith 2023, p. 20.
  55. ^ Liang, Ting; Zhang, Tongtong; Lin, Xipeng; Alessio, Tafone; Legrand, Mathieu; He, Xiufen; Kildahl, Harriet; Lu, Chang; Chen, Haisheng; Romagnoli, Alessandro; Wang, Li; He, Qing; Li, Yongliang; Yang, Lizhong; Ding, Yulong (2023). "Liquid air energy storage technology: a comprehensive review of research, development and deployment". Progress in Energy. 5 (1): 012002. Bibcode:2023PrEne...5a2002L. doi:10.1088/2516-1083/aca26a. ISSN 2516-1083.
  56. ^ Schmidt & Staffell 2023, p. 64.
  57. ^ Dumont, Olivier; Frate, Guido Francesco; Pillai, Aditya; Lecompte, Steven; De paepe, Michel; Lemort, Vincent (2020). "Carnot battery technology: A state-of-the-art review". Journal of Energy Storage. 32: 101756. Bibcode:2020JEnSt..3201756D. doi:10.1016/j.est.2020.101756. hdl:2268/251473. ISSN 2352-152X. S2CID 225019981.
  58. ^ Vandersickel & Gutierrez 2023, p. 107.
  59. ^ Benato, Alberto; Stoppato, Anna (1 June 2018). "Pumped Thermal Electricity Storage: A technology overview". Thermal Science and Engineering Progress. 6: 301–315. Bibcode:2018TSEP....6..301B. doi:10.1016/j.tsep.2018.01.017. ISSN 2451-9049.
  60. ^ Albertus, Paul; Manser, Joseph S.; Litzelman, Scott (2020). "Long-Duration Electricity Storage Applications, Economics, and Technologies". Joule. 4 (1): 21–32. Bibcode:2020Joule...4...21A. doi:10.1016/j.joule.2019.11.009. ISSN 2542-4351.
  61. ^ Pelay, Ugo; Luo, Lingai; Fan, Yilin; Stitou, Driss; Rood, Mark (1 November 2017). "Thermal energy storage systems for concentrated solar power plants". Renewable and Sustainable Energy Reviews. 79: 82–100. Bibcode:2017RSERv..79...82P. doi:10.1016/j.rser.2017.03.139. ISSN 1364-0321.
  62. ^ "Thermal Storage System Concentrating Solar-Thermal Power Basics". Energy.gov. Retrieved 17 November 2024.
  63. ^ Lee, Zachary E.; Sun, Qingxuan; Ma, Zhao; Wang, Jiangfeng; MacDonald, Jason S.; Zhang, K. Max (February 2020). "Providing Grid Services With Heat Pumps: A Review". Journal of Engineering for Sustainable Buildings and Cities. 1 (1). doi:10.1115/1.4045819. S2CID 213898377.
  64. ^ Ziegler, Micah S.; Trancik, Jessika E. (2021). "Re-examining rates of lithium-ion battery technology improvement and cost decline". Energy & Environmental Science. 14 (4): 1635–1651. arXiv:2007.13920. doi:10.1039/D0EE02681F. ISSN 1754-5692. S2CID 220830992.
  65. ^ "The price of batteries has declined by 97% in the last three decades". Our World in Data. Retrieved 26 April 2022.
  66. ^ Schmidt & Staffell 2023, pp. 131, 136.
  67. ^ "Some energy storage already cost competitive, new valuation study shows". Utility Dive. 24 November 2015. Archived from the original on 18 October 2016. Retrieved 15 October 2016.
  68. ^ "Lazard's Levelized Cost of Storage Analysis" (PDF). Archived (PDF) from the original on 2 February 2017. Retrieved 2 February 2017.
  69. ^ Lai, Chun Sing; McCulloch, Malcolm D. (March 2017). "Levelized cost of electricity for solar photovoltaic and electrical energy storage". Applied Energy. 190: 191–203. Bibcode:2017ApEn..190..191L. doi:10.1016/j.apenergy.2016.12.153. S2CID 113623853.
  70. ^ Schmidt & Staffell 2023, pp. 137, 150–151.
  71. ^ Schmidt & Staffell 2023, pp. 177, 179.
  72. ^ Schmidt & Staffell 2023, p. 227.
  73. ^ Schmidt & Staffell 2023, p. 241.
  74. ^ Schmidt & Staffell 2023, p. 247.
  75. ^ Schmidt & Staffell 2023, p. 261.
  76. ^ Schmidt & Staffell 2023, p. 215.
  77. ^ Schmidt & Staffell 2023, p. 191.
  78. ^ Schmidt & Staffell 2023, p. 176.

Cited sources

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