Editing IPCC:AR6/WGIII/Chapter-6 (section)

=== 6.4.4 Energy Storage for Low-carbon Grids ===

<div id="h2-9-siblings" class="h2-siblings"></div>

Energy storage technologies make low-carbon electricity systems more cost-effective, allowing VRE technologies to replace more expensive firm low-carbon generation technologies (Carbon Trust 2016) and reducing investment costs in backup generation, interconnection, transmission, and distribution network upgrades ( ''high confidence'' ). Energy system decarbonisation relies on increased electrification ( [[#6.6.2.3|Section 6.6.2.3]] ). Meeting increasing demands with variable renewable sources presents challenges and could lead to costly infrastructure reinforcements. Energy storage enables electricity from variable renewables to be matched against evolving demands across both time and space, using short-, medium- and long-term storage of excess energy for delivery later or at a different location. In 2017, an estimated 4.67 TWh (0.017 EJ) of electricity storage was in operation globally ( [[#IRENA--2017b|IRENA 2017b]] ). If the integration of renewables is doubled from 2014 levels by 2030, the total capacity of global electricity storage could triple, reaching 11.89–15.27 TWh (0.043–0.055 EJ) ( [[#IRENA--2017b|IRENA 2017b]] ).

Energy storage technologies can provide a range of different grid services (Table 6.5). Energy storage enhances security of supply by providing real-time system regulation services (voltage support, frequency regulation, fast reserve, and short-term reserve). A greater proportion of variable renewable sources reduces system inertia, requiring more urgent responses to changes in system frequency, which rapid response storage technologies can provide (stability requires responses within sub-second time scale for provision of frequency and voltage control services). Energy storage also provides intermittent renewable sources with flexibility, allowing them to contribute a greater proportion of electrical energy and avoiding curtailment (capacity firming). Investment costs in backup generation, interconnection, transmission, and distribution network upgrades can thus be reduced (upgrade deferral), meaning that less low-carbon generation will need to be built while still reducing emissions. In the event of an outage, energy storage reserves can keep critical services running (islanding) and restart the grid (black start). The ability to store and release energy as required provides a range of market opportunities for buying and selling of energy (arbitrage).

'''Table 6.5 | Suitability of low-carbon energy storage technologies, interms of the grid services they can provide, and overall features such as technology maturity: where Low represents an emerging technology; Med represents a maturing technology; and High a fully mature technology.''' The opportunity for the cost of a technology to reduce over the next decade is represented by Low, Med and High and the lifetime of installations by: Long, for projects lasting more than 25 years; Med for those lasting 15–25 years; Short, for those lasting less than 15 years.

{| class="wikitable"
|-
| Suitability factor

| PHS

| CAES

| LAES

| TES

| FES

| LiB

| Scap

| RFB

| PtX

| RHFC

|-
| ''Upgrade deferral''

| ''''''

| ''''''

| ''''''

| ''''''

| ''''''

| ''''''

| ''''''

| ''''''

| ''''''

| ''''''

|-
| ''Energy arbitrage''

| ''''''

| ''''''

| ''''''

| ''''''

|
| ''''''

|
| ''''''

| ''''''

| ''''''

|-
| ''Capacity firming''

| ''''''

| ''''''

| ''''''

| ''''''

| ''''''

| ''''''

|
| ''''''

| ''''''

| ''''''

|-
| ''Seasonal storage''

|
| ''''''

|
| ''''''

| ''''''

|-
| ''Stability''

| ''''''

|
| ''''''

| ''''''

| ''''''

| ''''''

| ''''''

| ''''''

|-
| ''Frequency regulation''

| ''''''

| ''''''

| ''''''

|
| ''''''

| ''''''

| ''''''

| ''''''

| ''''''

| ''''''

|-
| ''Voltage support''

| ''''''

| ''''''

| ''''''

|
| ''''''

| ''''''

| ''''''

| ''''''

| ''''''

| ''''''

|-
| ''Black start''

| ''''''

| ''''''

| ''''''

|
| ''''''

|
| ''''''

| ''''''

| ''''''

|-
| ''Short-term reserve''

| ''''''

| ''''''

| ''''''

|
| ''''''

|
| ''''''

| ''''''

| ''''''

|-
| ''Fast reserve''

| ''''''

| ''''''

| ''''''

|
| ''''''

| ''''''

|
| ''''''

| ''''''

| ''''''

|-
| ''Islanding''

|
| ''''''

| ''''''

| ''''''

|
| ''''''

|
| ''''''

| ''''''

| ''''''

|-
| ''Uninterruptible power supply''

|
| ''''''

| ''''''

| ''''''

| ''''''

|
| ''''''

|-
| Maturity

| High

| High

| Med

| Low

| High

| Med

| Low

| Low

| Low

| Low

|-
| Opportunity to reduce costs

| Low

| Low

| Low

| Med

| Med

| High

| High

| High

| Med

| High

|-
| Lifetime

| Long

| Long

| Long

| Long

| Med

| Short

| Med

| Med

| Med

| Short

|-
| Roundtrip efficiency

| 60–80%

| 30–60%

| 55–90%

| 70–80%

| 90%

| &gt;95%

| &gt;95%

| 80–90%

| 35–60%

| &lt;30%

|}

Note: PHS – Pumped Hydroelectric Storage; CAES – Compressed Air Energy Storage; LAES – Liquid Air Energy Storage; TES – Thermal Energy Storage; FES – Flywheel Energy Storage; LIB – Li-ion Batteries; Scap – Supercapacitors; RFB – Redox Flow Batteries; RHFC – Reversible Hydrogen Fuel Cells; PtX – Power to fuels. Source: PHS – [[#Barbour--2016|Barbour et al. 2016]] , Yang 2016, [[#IRENA--2017b|IRENA 2017b]] ; CAES – [[#Luo--2014|Luo et al. 2014]] , [[#Brandon--2015|Brandon et al. 2015]] , [[#IRENA--2017b|IRENA 2017b]] ; LAES – [[#Luo--2014|Luo et al. 2014]] , Highview 2019; TES – [[#Brandon--2015|Brandon et al. 2015]] , [[#Gallo--2016|Gallo et al. 2016]] , [[#Smallbone--2017|Smallbone et al. 2017]] ; FES – [[#IRENA--2017b|IRENA 2017b]] , [[#Yulong--2017|Yulong et al. 2017]] ; LIB – [[#IRENA--2015|IRENA 2015]] b, [[#Hammond--2015|Hammond and Hazeldine 2015]] , [[#Nykvist--2015|Nykvist and Nilsson 2015]] , Staffell, I. and Rustomji, M. et al. 2016, [[#IRENA--2017b|IRENA 2017b]] , [[#Schmidt--2017|Schmidt et al. 2017]] c, [[#May--2018|May et al. 2018]] ; Scap – [[#Brandon--2015|Brandon et al. 2015]] , [[#Gur--2018|Gur 2018]] ; RFB – [[#IRENA--2017b|IRENA 2017b]] ; RHFC – IEA 2015, [[#Gur--2018|Gur 2018]] .

No single, sufficiently mature energy storage technology can provide all the required grid services – a portfolio of complementary technologies working together can provide the optimum solution ( ''high confidence'' ). Different energy storage technologies can provide these services and support cost-effective energy system decarbonisation (Carbon Trust 2016). To achieve very low-carbon systems, significant volumes of storage will be required (Strbac et al. 2015a; [[#6.4.3.2|Section 6.4.3.2]] ). There are few mature global supply chains for many of the less-developed energy storage technologies. This means that, although costs today may be relatively high, there are significant opportunities for future cost reductions, both through technology innovation and through manufacturing scale. Adding significant amounts of storage will reduce the price variation and, therefore, the profitability of additional and existing storage, increasing investment risk.

Energy storage extends beyond electricity storage and includes technologies that can store energy as heat, cold, and both liquid and gaseous fuels. Energy storage is a conversion technology, enabling energy to be converted from one form to another. This diversification improves the overall resilience of energy systems, with each system being able to cover supply shortfalls in the others. For example, storage can support the electrification of heating or cooling, as well as transport through electric vehicles, powered by batteries or by fuel cells. Storage significantly reduces the need for costly reinforcement of local distribution networks through smart charging schemes and the ability to flow electricity back to the grid (e.g., through vehicle-to-grid). By capturing otherwise wasted energy streams, such as heat or cold, energy storage improves the efficiency of many systems, such as buildings, data centres and industrial processes.

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==== 6.4.4.1 Energy Storage Technologies ====

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'''Pumped hydroelectric storage (PHS).''' PHS makes use of gravitational potential energy, using water as the medium. Water is pumped into an elevated reservoir using off-peak electricity and stored for later release when electricity is needed. These closed-loop hydropower plants have been in use for decades and account for 97% of worldwide electricity storage capacity ( [[#IRENA--2017b|IRENA 2017b]] ; [[#IEA--2018b|IEA 2018b]] ). PHS is best suited to balancing daily energy needs at a large scale, and advances in the technology now allow rapid response and power regulation in both generating and pumping mode ( [[#Valavi--2018|Valavi and Nysveen 2018]] ; [[#Dong--2019|Dong et al. 2019]] ; [[#Kougias--2019|Kougias et al. 2019]] ). The construction itself can cause disruption to the local community and environment ( [[#Hayes--2019|Hayes et al. 2019]] ), the initial investment is costly, and extended construction periods delay return on investment ( [[#6.4.2.3|Section 6.4.2.3]] ). In addition, locations for large-scale PHS plants are limited.

Advanced pump-turbines are being developed, allowing both reversible and variable-speed operation, supporting frequency control and grid stability with improved round-trip efficiencies ( [[#Ardizzon--2014|Ardizzon et al. 2014]] ). New possibilities are being explored for small-scale PHS installations and expanding the potential for siting ( [[#Kougias--2019|Kougias et al. 2019]] ). For example, in underwater PHS, the upper reservoir is the sea, and the lower is a hollow deposit at the seabed. Seawater is pumped out of the deposit to store off-peak energy and re-enters through turbines to recharge it ( [[#Kougias--2019|Kougias et al. 2019]] ). Using a similar concept, underground siting in abandoned mines and caverns could be developed reasonably quickly ( [[#IEA--2020h|IEA 2020h]] ). Storage of energy as gravitational potential can also be implemented using materials other than water, such as rocks and sand. Pumped technology is a mature technology ( [[#Rehman--2015|Rehman et al. 2015]] ; [[#Barbour--2016|Barbour et al. 2016]] ) and can be important in supporting the transition to future low-carbon electricity grids ( [[#IHA--2021|IHA 2021]] ).

'''Batteries.''' There are many types of batteries, all having unique features and suitability, but their key feature is their rapid response time. A rechargeable battery cell is charged by using electricity to drive ions from one electrode to another, with the reverse occurring on discharge, producing a usable electric current ( [[#Crabtree--2015|Crabtree et al. 2015]] ). While lead-acid batteries (LABs) have been widely used for automotive and grid applications for decades ( [[#May--2018|May et al. 2018]] ), LIBs are increasingly being used in grid-scale projects ( [[#Crabtree--2015|Crabtree et al. 2015]] ), displacing LABs. The rapid response time of batteries makes them suitable for enhanced frequency regulation and voltage support, enabling the integration of variable renewables into electricity grids ( [[#Strbac--2016|Strbac and Aunedi 2016]] ). Batteries can provide almost all electricity services, except for seasonal storage. LIBs, in particular, can store energy and power in small volumes and with low weight, making them the default choice for EVs ( [[#Placke--2017|Placke et al. 2017]] ). EV batteries are expected to form a distributed storage resource as this market grows, both impacting and supporting the grid ( [[#Staffell--2016|Staffell and Rustomji 2016]] ).

Drawbacks of batteries include relatively short lifespans and the use of hazardous or costly materials in some variants. While LIB costs are decreasing ( [[#Schmidt--2017|Schmidt et al. 2017]] ; [[#Vartiainen--2020|Vartiainen et al. 2020]] ), the risk of thermal runaway, which could ignite a fire ( [[#Gur--2018|Gur 2018]] ; [[#Wang--2019a|Wang et al. 2019a]] ), concerns about long-term resource availability ( [[#Olivetti--2017|Olivetti et al. 2017]] ; [[#Sun--2017|Sun et al. 2017]] ), and concerns about global cradle-to-grave impacts ( [[#Peters--2017|Peters et al. 2017]] ; [[#Kallitsis--2020|Kallitsis et al. 2020]] ) need to be addressed.

The superior characteristics of LIBs will keep them the dominant choice for EV and grid applications in the medium term ( ''high confidence'' ). There are, however, several next-generation battery chemistries ( [[#Placke--2017|Placke et al. 2017]] ), which show promise ( ''high confidence'' ). Cost reductions through economies of scale are a key area for development. Extending the life of the battery can bring down overall costs and mitigate the environmental impacts ( [[#Peters--2017|Peters et al. 2017]] ). Understanding and controlling battery degradation is therefore important. The liquid, air-reactive electrolytes of conventional LIBs are the main source of their safety issues ( [[#Janek--2016|Janek and Zeier 2016]] ; [[#Gur--2018|Gur 2018]] ), so all-solid-state batteries, in which the electrolyte is a solid, stable material, are being developed. They are expected to be safe, be durable, and have higher energy densities ( [[#Janek--2016|Janek and Zeier 2016]] ). New chemistries and concepts are being explored, such as lithium-sulphur batteries to achieve even higher energy densities ( [[#Van%20Noorden--2014|Van Noorden 2014]] ; [[#Blomgren--2017|Blomgren 2017]] ) and sodium chemistries because sodium is more abundant than lithium ( [[#Hwang--2017|Hwang et al. 2017]] ). Cost-effective recycling of batteries will address many sustainability issues and prevent hazardous and wasteful disposal of used batteries ( [[#Harper--2019|Harper et al. 2019]] ). Post-LIB chemistries include metal sulphur, metal-air, metal ion (besides lithium) and all-solid-state batteries.

'''Compressed air energy storage (CAES).''' With CAES, off-peak electricity is used to compress air in a reservoir – either in salt caverns for large-scale or in high-pressure tanks for smaller-scale installations. The air is later released to generate electricity. While conventional CAES has used natural gas to power compression, new low-carbon CAES technologies, such as isothermal or adiabatic CAES, control thermal losses during compression and expansion ( [[#Wang--2017c|Wang et al. 2017c]] ). Fast responses and higher efficiencies occur in small-scale CAES installations, scalable to suit the application as a distributed energy store, offering a flexible, low-maintenance alternative ( [[#Luo--2014|Luo et al. 2014]] ; [[#Venkataramani--2016|Venkataramani et al. 2016]] ).

CAES is a mature technology in use since the 1970s. Although CAES technologies have been developed, there are not many installations at present ( [[#Wang--2017b|Wang et al. 2017b]] ; [[#Blanc--2020|Blanc et al. 2020]] ). While the opportunities for CAES are significant, with a global geological storage potential of about 6.5 PW ( [[#Aghahosseini--2018|Aghahosseini and Breyer 2018]] ), a significant amount of initial investment is required. Higher efficiencies and energy densities can be achieved by exploiting the hydrostatic pressure of deep water to compress air within submersible reservoirs ( [[#Pimm--2014|Pimm et al. 2014]] ). CAES is best suited to bulk diurnal electricity storage for buffering VRE sources and services, which do not need a very rapid response. In contrast to PHS, CAES has far more siting options and poses few environmental impacts.

'''Liquid air energy storage (LAES).''' LAES uses electricity to liquefy air by cooling it to –196°C and storing it in this condensed form (largely liquid nitrogen) in large, insulated tanks. To release electricity, the ‘liquid air’ is evaporated through heating, expanding to drive gas turbines. Low-grade waste heat can be utilised, providing opportunities for integrating with industrial processes to increase system efficiency. There are clear, exploitable synergies with the existing liquid gas infrastructure ( [[#Peters--2016|Peters and Sievert 2016]] ).

LAES provides bulk daily storage of electricity, with the additional advantage of being able to capture waste heat from industrial processes. This technology is in the early commercial stage ( [[#Brandon--2015|Brandon et al. 2015]] ; [[#Regen--2017|Regen 2017]] ). Advances in whole systems integration can be developed to integrate LAES with industrial processes, making use of their waste heat streams. LAES uniquely removes contaminants in the air and could potentially incorporate CO 2 capture ( [[#Taylor--2012|Taylor et al. 2012]] ).

'''Thermal energy storage (TES).''' TES refers to a range of technologies exploiting the ability of materials to absorb and store heat or cold, either within the same phase (sensible TES), through phase changes (latent TES), or through reversible chemical reactions (thermochemical TES). Pumped Thermal Energy Storage (PTES), a hybrid form of TES, is an air-driven electricity storage technology storing both heat and cold in gravel beds, using a reversible heat-pump system to maintain the temperature difference between the two beds and gas compression to generate and transfer heat ( [[#Regen--2017|Regen 2017]] ). TES technologies can store both heat and cold energy for long periods, for example, in underground water reservoirs for balancing between seasons ( [[#Dahash--2019|Dahash et al. 2019]] ; [[#Tian--2019|Tian et al. 2019]] ), storing heat and cold to balance daily and seasonal temperatures in buildings and reducing heat build-up in applications generating excessive waste heat, such as data centres and underground operations.

TES can be much cheaper than batteries and has the unique ability to capture and reuse waste heat and cold, enabling the efficiency of many industrial, buildings, and domestic processes to be greatly improved ( ''high confidence'' ). Integration of TES into energy systems is particularly important, as the global demand for cooling is expected to grow (Elzinga et al. 2014; [[#Peters--2016|Peters and Sievert 2016]] ) ''.'' Sensible TES is well developed and widely used; latent TES is less developed with few applications. Thermochemical TES is the least developed, with no application yet ( [[#Prieto--2016|Prieto et al. 2016]] ; [[#Clark--2020|Clark et al. 2020]] ). The potential for high-density storage of industrial heat for long periods in thermochemical TES ( [[#Brandon--2015|Brandon et al. 2015]] ) is high, with energy densities comparable to that of batteries ( [[#Taylor--2012|Taylor et al. 2012]] ), but material costs are currently prohibitive, ranging from hundreds to thousands of dollars per tonne.

'''Flywheel energy storage (FES).''' Flywheels are charged by accelerating a rotor/flywheel. Energy is stored in the spinning rotor’s inertia which is only decelerated by friction (minimised by magnetic bearings in a vacuum), or by contact with a mechanical, electric motor. They can reach full charge very rapidly, their state of charge can be easily determined ( [[#Amiryar--2017|Amiryar and Pullen 2017]] ), and they operate over a wide range of temperatures. While they are more expensive to install than batteries and supercapacitors, they last a long time and are best suited to stationary grid storage, providing high power for short periods (minutes). Flywheels can be used in vehicles, but not as the primary energy source.

Flywheels are a relatively mature storage technology but not widely used, despite their many advantages over electrochemical storage (Dragoni 2017). Conventional flywheels require costly, high tensile strength materials, but high-energy flywheels, using lightweight rotor materials, are being developed ( [[#Hedlund--2015|Hedlund et al. 2015]] ; [[#Amiryar--2017|Amiryar and Pullen 2017]] ).

'''Supercapacitors – also known as ultracapacitors or double layer capacitors (Scap).''' Supercapacitors consist of a porous separator sandwiched between two electrodes, immersed in a liquid electrolyte ( [[#Gur--2018|Gur 2018]] ). When a voltage is applied across the electrodes, ions in the electrolyte form electric double layers at the electrode surfaces, held by electrostatic forces. This structure forms a capacitor, storing electrical charge ( [[#Brandon--2015|Brandon et al. 2015]] ; [[#Lin--2017|Lin et al. 2017]] ) and can operate from –40°C to 65°C.

Supercapacitors can supply high peaks of power very rapidly for short periods (seconds up to minutes) and are able to fulfil the grid requirements for frequency regulation, but they would need to be hybridised with batteries for automotive applications. Their commercial status is limited by costly materials and additional power electronics required to stabilise their output ( [[#Brandon--2015|Brandon et al. 2015]] ). Progress in this area includes the development of high-energy supercapacitors, LIB-supercapacitor devices ( [[#Gonzalez--2016|Gonzalez et al. 2016]] ), and cheaper materials ( [[#Wang--2017a|Wang et al. 2017a]] ), all providing the potential to improve the economic case for supercapacitors, either by reducing manufacturing costs or extending their service portfolio.

'''Redox flow batteries (RFB).''' Redox flow batteries use two separate electrolyte solutions, usually liquids, but solid or gaseous forms may also be involved, stored in separate tanks, and pumped over or through electrode stacks during charge and discharge, with an ion-conducting membrane separating the liquids. The larger the tank, the greater the energy storage capacity, whereas more and larger cells in the stack increase the power of the flow battery. This decoupling of energy from power enables RFB installations to be uniquely tailored to suit the requirements of any given application. There are two commercially available types today: vanadium and zinc bromide, and both operate at near ambient temperatures, incurring minimal operational costs.

RFBs respond rapidly and can perform all the same services as LIBs, except for onboard electricity for EVs. Lower cost chemistries are emerging, to enable cost-effective bulk energy storage ( [[#Brandon--2015|Brandon et al. 2015]] ). A new membrane-free design eliminates the need for a separator and also halves the system requirements, as the chemical reactions can coexist in a single electrolyte solution ( [[#Navalpotro--2017|Navalpotro et al. 2017]] ; [[#Arenas--2018|Arenas et al. 2018]] ).

'''Power to fuels (PtX)''' (see also [[#6.4.3.1|Section 6.4.3.1]] ). The process of using electricity to generate a gaseous fuel, such as hydrogen or ammonia, is termed power-to-gas (PtG/P2G) ( [[#IEA--2020h|IEA 2020h]] ). When injected into the existing gas infrastructure ( [[#6.4.5|Section 6.4.5]] ), it has the added benefit of decarbonising gas ( [[#Brandon--2015|Brandon et al. 2015]] ). Electricity can be used to generate hydrogen, which is then converted back into electricity using combined-cycle gas turbines that have been converted to run on hydrogen. For greater compatibility with existing gas systems and appliances, the hydrogen can be combined with captured carbon dioxide to form methane and other synthetic fuels ( [[#Thema--2019|Thema et al. 2019]] ), however, methane has high global warming potential and its supply chain emissions have been found to be significant ( [[#Balcombe--2013|Balcombe et al. 2013]] ).

PtX can provide all required grid services, depending on how it is integrated. However, a significant amount of PtX is required for storage to produce electricity again ( [[#Bogdanov--2019|Bogdanov et al. 2019]] ) due to the low roundtrip efficiency of converting electricity to fuel and back again. However, portable fuels (hydrogen, methane, ammonia, synthetic hydrocarbons) are useful in certain applications, for example, in energy systems lacking the potential for renewables. The high energy density of chemical storage is essential for more demanding applications, such as transporting heavy goods and heating or cooling buildings ( [[#IEA--2020h|IEA 2020h]] ). Research is needed into more efficient and flexible electrolysers which last longer and cost less ( [[#Brandon--2015|Brandon et al. 2015]] ).

'''Hydrogen and reversible hydrogen fuel cells (H/RHFC).''' Hydrogen is a flexible fuel with diverse uses, capable of providing electricity, heat, and long-term energy storage for grids, industry, and transport, and has been widely used industrially for decades ( [[#6.4.5.1|Section 6.4.5.1]] ). Hydrogen can be produced in various ways and stored in significant quantities in geological formations at moderate pressures, often for long periods, providing seasonal storage ( [[#Gabrielli--2020|Gabrielli et al. 2020]] ). A core and emerging implementation of PtX is hydrogen production through electrolysers. Hydrogen is a carbon-free fuel holding three times the energy of an equivalent mass of gasoline but occupying a larger volume. An electrolyser uses excess electricity to split water into hydrogen and oxygen through the process of electrolysis. A fuel cell performs the reverse process of recombining hydrogen and oxygen back into water, converting chemical energy into electricity (Elzinga et al. 2014). Reversible hydrogen fuel cells (RHFCs) can perform both functions in a single device, however, they are still in the pre-commercial stage, due to prohibitive production costs.

Hydrogen can play an important role in reducing emissions and has been shown to be the most cost-effective option in some cases, as it builds on existing systems (Staffell et al. 2018). Fuel cell costs need to be reduced and the harmonies between hydrogen and complementary technologies, such as batteries, for specific applications need to be explored further. Hydrogen can provide long-duration storage to deal with prolonged extreme events, such as very low output of wind generation, to support resilience of future low-carbon energy systems. Research in this technology focuses on improving roundtrip efficiencies, which can be as high as 80% with recycled waste heat and in high-pressure electrolysers, incorporating more efficient compression ( [[#Matos--2019|Matos et al. 2019]] ). Photo-electrolysis uses solar energy to directly generate hydrogen from water ( [[#Amirante--2017|Amirante et al. 2017]] ).

'''Table 6.6 | Technical characteristics of a selected range of battery chemistries, categorised as those which precede LIBs (white background), LIBs (yellow background) and post LIBs (blue background).'''

{| class="wikitable"
|-
| Battery type

| Technology maturity

| Lifespan (cycles)

| Energy density (Wh L –1 )

| Specific energy (Wh kg –1 )

| Price (USD kWh –1 ) in 2017

|-
| Lead acid

| High

| 300–800 e

| 102–106 e

| 38–60 e

| 70–160 e

|-
| Ni MH

| High

| 600–1200 e

| 220–250 e

| 42–110 e

| 210–365 e

|-
| Ni Cd

| High

| 1350 b

| 100 b

| 60 b

| 700

|-
| High-temperature Na batteries

| High

| 1000 e

| 150–280 h

| 80–120 a

| 315–490 h

|-
| LIB state of the art

| High

| 1000–6000 e

| 200–680 c

| 110–250 c

| 176 f

|-
| LIB energy-optimised

| Under development

|
| 600–850 c

| 300–440 c

|
|-
| Classic Li Metal (CLIM)

| Under development

|
| 800–1050 c

| 420–530 c

|
|-
| Metal Sulphur (Li S)

| Near commercialisation

| 100–500 e

| 350–680 c, h

| 360–560 c, h

| 36–130 e

|-
| Metal Sulphur (Na S)

| Under development

| 5000–10,000 h

|
|-
| Metal Air (Li/air)

| Under development

| 20–100 e

|
| 470–900 d

| 70–200 e

|-
| Metal Air (Zn/air)

| Under development

| 150–450 e

|
| 200–410 d

| 70–160 e

|-
| Na ion

| Under development

| 500 g

|
| 600 g

|
|-
| All-solid-state

| Under development

|
| 278–479 c

|
|-
| Redox

| Under development

| &gt;12,000–14,000 j

| 15–25 j

| 10–20 j

| 66 j

|}

Note: With the exception of the All-solid-state batteries, all use liquid electrolytes. Source: a Mahmoudzadeh et al. 2017; b [[#Manzetti--2015|Manzetti and Mariasiu 2015]] ; c [[#Placke--2017|Placke et al. 2017]] ; d [[#Nykvist--2015|Nykvist and Nilsson 2015]] ; e [[#Cano--2018|Cano et al. 2018]] ; f [[#Bloomberg%20Energy%20Finance--2019|Bloomberg Energy Finance, 2019]] ; g You and Manthiram 2017; h [[#Fotouhi--2017|Fotouhi et al. 2017]] ; i [[#IRENA--2017b|IRENA 2017b]] ; j [[#Yang--2020|Yang et al. 2020]] .

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==== 6.4.4.2 Societal Dimensions of Energy Storage ====

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Public awareness and knowledge about electricity storage technologies, their current state, and their potential role in future energy systems is limited ( [[#Jones--2018|Jones et al. 2018]] ). For instance, people do not perceive energy system flexibility and storage as a significant issue, or assume storage is already taking place. Public perceptions differ across storage technologies. Hydrogen is considered a modern and clean technology, but people also have safety concerns. Moreover, the public is uncertain about hydrogen storage size and the possibility of storing hydrogen in or near residential areas ( [[#Eitan--2021|Eitan and Fischhendler 2021]] ). Battery storage both on the household and community level was perceived as slightly positive in one study in the UK ( [[#Ambrosio-Albala--2020|Ambrosio-Albala et al. 2020]] ). However, financial costs are seen as a main barrier. The potential of EV batteries to function as flexible storage is limited by the current numbers of EV owners and concerns that one’s car battery might not be fully loaded when needed.

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