Long-duration energy storage: get on with it Contents

Chapter 2: The need for long-duration energy storage

The benefits of long-duration energy storage

9.Caroline Still, Senior Associate at Aurora Energy Research, outlined four needs that the grid has that energy storage could meet. The first is firm capacity, “dispatchable capacity that can provide generation during periods of peak demand”. Second, flexible capacity, “the ability to generate capacity to ramp up and ramp down very quickly. As we increase the number of intermittent renewables, we will get rapid changes in generation, as well as rapid changes in demand as we electrify more of the demand.” Third, resolving constraints on the network:

“When the transmission lines are at capacity, they are unable to absorb and transmit any additional renewable energy down south, resulting in renewable turndown or curtailment [deliberate reduction in generation capacity to balance supply and demand] in the north and a turn-up of unabated thermal generation in the south to meet the demand required. Not only is this very costly to the grid—it cost about £1.6 billion in 2022—but it results in additional emissions due to the thermal generation turn-up in the south.”

Fourth, grid stability and security:

“As unabated synchronous generation is decommissioned or operated at lower load factors due to their emissions, we will see a reduction in the stability and operability of the grid. A grid that does not have security in voltage control or frequency control risks blackouts and energy security issues.”10

Box 1: Units of energy and power, and scale of existing energy storage in the UK

For an energy storage system, the amount of energy stored, and the power—energy per unit of time—that the system can deliver at any given time are both important parameters. Together, they determine the typical timescale on which the storage system operates. Power is measured in terms of watts, while in energy the “watt-hour” is the amount of energy delivered by a one-watt power source over one hour. For example, a 40-watt lightbulb running for 25 hours would consume 1,000 watt-hours or 1 kilowatt-hour (kWh) of electricity. (These are standard scientific prefixes: kilo- means a thousand, mega- a million, giga- a billion, and tera- a trillion.) According to Ofgem, the average British household uses 2,700 kWh a year of electricity and 11,500 kWh of gas.

At the national, annual scale, the relevant units of power are gigawatts (GW) and those for energy are terawatt-hours (TWh). For comparison, the Sizewell B power station has a capacity of 1.2 GW and generates around 6.7 TWh in a typical year (as it is not always running at full capacity—the effective percentage of full capacity that is generated on average over a year is called the load or capacity factor.)

Currently, use of dispatchable fossil fuels such as natural gas is increased when demand is high and supply is low and these fuels act as a form of stored energy. The UK stores around 10 TWh of natural gas, compared to 217 TWh in Germany, 122 TWh in France, and 162 TWh in Italy.11

The UK currently has a relatively small amount of low-carbon energy storage deployed, mostly in the form of pumped-storage hydroelectricity (see box 2 for explanations of different forms of energy storage) at 2.8 GW of pumped-hydro, with a storage capacity of 26.7 GWh. In 2022, 2.6 TWh of electricity was used to pump water uphill in these storage facilities, which then generated 2 TWh of electricity in 2022.12 There is also a growing capacity of battery electricity storage at grid-scale, which is discharged more frequently, usually across minutes to hours, and has been estimated at 2.4 GW (2.6 GWh) of capacity across 161 sites.

Comparing power capacity only, and not the length of time the power can be supplied for (which depends on the total energy stored), can be misleading. From these figures, if all the UK’s grid-scale batteries were fully charged and discharged at once, they could provide 2.4 GW for just over an hour; if the UK’s pumped-hydro was fully charged and discharged, it could provide 2.8 GW over nearly ten hours. Balancing the energy system requires matching the instantaneous power demand (GW) and also meeting the energy demand over time (GWh).

Source: Power Technology, ‘Power plant profile: Sizewell B, UK’ (3 February 2024): https://www.power-technology.com/data-insights/power-plant-profile-sizewell-b-uk/?cf-view [accessed 10 January]. British Gas, ‘What is the average energy bill in Great Britain’: https://www.britishgas.co.uk/energy/guides/average-bill.html [accessed 10 January]. Department for Energy Security and Net Zero, Digest of UK Energy Statistics Annual data for UK, 2022 (27 July 2023 ): https://assets.publishing.service.gov.uk/media/64c23a300c8b960013d1b05e/DUKES_2023_Chapter_5.pdf [accessed 10 January]. Royal Society, Large Scale electricity storage (September 2023), para 5.51: https://royalsociety.org/-/media/policy/projects/large-scale-electricity-storage/Large-scale-electricity-storage-report.pdf [accessed 10 January 2024]. Solar Power Portal, ‘Record 800MWh of utility-scale storage added in 2022’ (2 February 2023): https://www.solarpowerportal.co.uk/record_800mwh_of_utility_scale_storage_added_in_2022_according_to_solar_med/ [accessed 10 January] and National statistics, ‘Digest of UK Energy Statistics (DUKES): electricity’ (27 July 2023): https://www.gov.uk/government/statistics/electricity-chapter-5-digest-of-united-kingdom-energy-statistics-dukes [accessed 10 January 2024]

10.Energy storage capacity can allow energy to be bought at times when its availability is high and its price is low and stored until high price periods when it can be used. Martin Scargill, Managing Director at Centrica Storage, referred to an independent study commissioned by Centrica that concluded that “if we had had an extra 35 [TWh] of gas storage on the system, it would have reduced wholesale energy prices by £2.4 billion over the winter of 2021–22”.13 Energy support policies across 2022–23 were estimated to have cost over £50 billion by the Office of Budget Responsibility.14 The Rough gas storage facility, owned by Centrica, stored 41 TWh of natural gas at its peak capacity, representing 70% of UK storage.15 It was closed in 2017 but partially reopened in 2022 in the midst of the gas crisis—the UK has less gas storage than comparator nations in Europe.16 Mr Scargill explained the economic reasons for the period of closure: “There are times when the merchant revenue of trading gas in the open market is sufficient, but it is very volatile … the costs for running or just keeping the facility open would not have been covered by the market.”17

11.Energy storage can provide benefits to the grid. It can reduce curtailment and grid congestion, avoiding wasting energy and reducing the cost of renewable electricity. Energy storage facilities provide power that can be turned on and off at will, enhancing grid flexibility. Long-duration energy storage therefore reduces costs elsewhere in the system and allows a greater proportion of cheap renewables to be built and so reduces electricity prices overall.

12.Domestic energy storage is not just about a resilient decarbonised grid—it is about the security and stability of the whole economy. The global energy crisis that began in 2021 has been an object lesson in the UK’s vulnerability to global wholesale energy price fluctuations, and the consequent effects on inflation. The UK had less storage capacity than comparator nations and came to regret and partially reverse its closure of the Rough gas storage facility.

Box 2: Energy storage technologies

Hydrogen is the leading candidate for longer-duration energy storage over weeks and months. Low-carbon hydrogen can be produced, for example from electrolysis, where electricity is used to split water into hydrogen and oxygen (see box 5). The hydrogen can then be stored under moderate pressure, for example in underground salt caverns or converted depleted gas fields, and later burned to produce electricity or converted into gases that are easier to transport, such as ammonia.

Advantages include the relatively low cost to store large volumes of hydrogen for many months or years. Disadvantages include the low round-trip efficiency (RTE) of 30–40% for electrolysis and conversion back into electricity. (At each stage of the cycle of converting electricity into hydrogen and then burning hydrogen to produce electricity there are energy losses. The round-trip efficiency is the percentage of initial electrical energy put into the storage system that is output from storage and turned into usable electrical energy.) The combination of long storage times but with low efficiency means that hydrogen for electricity is most useful for infrequent cycling and longer-term storage compared to other technologies. A single large cavern could store 200 GWh, and the technology has been deployed at pilot scale, with different components ranging from technology readiness level (TRL) 7–9.18

Batteries can be used to store electricity at grid-scale. Lithium-ion batteries are widely deployed, but typically best for applications over seconds, minutes, or 1–2 hours at most, with the largest single installation globally around 3 GWh and a high round-trip efficiency of up to 90%.19 Alternative chemistries could store energy for longer durations—flow batteries store chemical energy using a liquid electrolyte in separated tanks. The largest existing battery today can store 400 MWh, but GWh-scale is possible. Full-cycle efficiency for these batteries can be 50–80%, with a TRL of 7–8 (i.e. large-scale pilot projects.) They are best suited for storage durations up to 100 hours. Metal anode batteries are at an earlier stage of development but could potentially store energy for up to 200 hours at an RTE of 40–70%.

Compressed air energy storage (CAES) involves storing air at high pressures, where it is stored in tanks or underground caverns and can drive turbines to generate electricity. Advanced CAES (A-CAES) attains higher efficiency by storing and re-using the heat generated during this compression process. Commercial-scale CAES has been developed (TRL8–9), especially in China. Plants can store energy for up to 6–24 hours at a round-trip efficiency of
40–70%, and single caverns could store up to 10 GWh. Liquid-air energy storage involves cooling air to create liquid nitrogen, which expands rapidly when heat is reintroduced to produce electricity. The technology is relatively mature for small systems, with an RTE of around 55% and storage for a few hours on less than GWh scale.

Pumped-hydro storage (PHS) accounts for the majority (~2.8 GW) of low-carbon LDES on the grid today. It requires pumping water uphill into a reservoir for subsequent release through turbines to generate electricity. However, it requires favourable geographical features to be cost-effective, limiting its potential in the UK. It typically stores energy for up to 15 hours at an RTE of 50–80%. Dinorwig, the largest facility in the UK, stores around 9.1 GWh (1.7 GW power capacity.) Some suggestions for novel pumped-hydro storage use fluids that are denser than water to store more energy; they are at a lower technology readiness level.

Other technologies include thermal energy storage technologies, which can store heat, for example in molten salts or phase-change materials—these are discussed in chapter 3. Mechanical forms of energy storage, such as raising and dropping heavy weights on rails or in mine shafts, have also been suggested—these could store energy for several hours at a relatively small scale, but are likely to be expensive. Flywheels, which similarly store energy in rotating wheels, can be used to provide short bursts of backup power and other grid ancillary services.

Finally, synthetic fuels—which could be produced as part of carbon capture, utilisation and storage (CCUS)—could be produced in low-carbon ways and stored in reserve as fossil fuels currently are and converted back into electricity with an RTE of around 30%. Storage on the TWh scale is possible, but these technologies are less ready (TRL 6–7) and are projected to be more expensive than hydrogen.

There is a general trade-off between high-efficiency but high-capital cost technologies that therefore need to cycle energy every few hours or more frequently to recover their cost (e.g. CAES, pumped-hydro storage) and low-efficiency but lower-cost storage which can store large volumes for days and weeks (hydrogen), with some larger flow batteries intermediate between these.

Source: Parliamentary Office of Science and Technology, Longer duration energy storage, POSTnote 688, December 2022. Lond Duration Energy Storage Council, Net-zero power—Long duration energy storage for a renewable grid (November 2021): ldescouncil.com/assets/pdf/LDES-brochure-F3-HighRes.pdf [accessed 27 February 2024] and Royal Society, Large-scale electricity storage (September 2023), table 4: https://royalsociety.org/-/media/policy/projects/large-scale-electricity-storage/Large-scale-electricity-storage-report.pdf [accessed 27 February 2024]

Figure 1: Technology Readiness Levels Source: Technology Readiness Levels, as adapted by the CloudWATCH2

Figure showing levels of technological readiness levels from Idea, Basic Research, Formulation, Validation, Prototype, Demonstration System and Full commercial application

Source: CloudWATCH2, ‘A brief refresher on Technology Readiness Levels (TRL)’: https://web.archive.org/web/20200126083540/https://www.cloudwatchhub.eu/exploitation/brief-refresher-technology-readiness-levels-trl [accessed 19 January 2024]

13.A number of witnesses also told us that there may be an opportunity to export hydrogen and energy storage capacity.20 As Michael Liebreich, Chair and CEO of Liebreich Associates, put it: “Germany has salt caverns … but not everyone does. In a world where everybody needs long-duration storage, perhaps we should be … leaning into it”.21 Officials recognised this potential, with Stef Murphy, Co-Director of Hydrogen and Industrial Carbon Capture at DESNZ, telling us that the Government is “clear that there is the potential for the UK to take advantage of the growth of the hydrogen economy both in the UK and globally, seizing on opportunities presented by the UK’s geology, geography and infrastructure expertise.”22 However, Dr David Joffe, then Head of Net Zero at the Climate Change Committee, sounded a note of caution, telling us that “the industrial benefit of being able to export things is clearly there … but this is quite speculative at this point. It is important to recognise those opportunities, but we cannot be too definitive.”23

14.The UK is currently a net importer of gas for heating and power. With storage, it can develop sufficient offshore renewable generation to be more energy self-sufficient and better insulated from future global shocks. The UK could export its hydrogen and sell its energy storage capacity and expertise internationally if it develops a leading position.

Scale and nature of the need for long-duration energy storage

15.As the UK decarbonises, it will need to electrify its energy system. Electricity demand and supply will increase substantially, with variable renewables like wind and solar playing a dominant role and increasing the weather-dependency of supply.24 Caroline Still said that storage could be relevant across “three different demand profiles: daily, weekly and seasonal”, and that variations in demand would “become more extreme” due to “electrification of things like heating and transport.”25

16.Most energy system modellers see a significant role for a much larger energy storage capacity than exists today. Daniel Murrant, Networks and Energy Storage Practice Manager at the Energy Systems Catapult, said that “we are very much talking about tens of terawatt hours.” He noted that the estimate “depends on the mix of generation technologies” (see box 2), but “whether it is 20 or 100 [TWh] … does not really matter”, as at the moment we have “fractions of a terawatt hour”; a “rapid acceleration in deployment” for long-duration energy storage is required.26

17.Dr Joffe agreed, saying “10 terawatt hours would be pretty low-regrets in terms of what we ultimately need”.27 The Minister from the Department for Energy Security and Net Zero, the Rt Hon Graham Stuart MP, told us that: “the modelling suggests that Great Britain will need more interday and interseasonal storage in the order of terawatt hours to tens of terawatt hours to avoid a reliance on unabated natural gas” and that there was “up to £24 billion in system benefits” from having longer-duration energy storage available.28

18.Asked about the potential for nuclear power, carbon capture and storage, demand-side management or interconnectors to reduce the amount of storage needed, Mr Murrant said “you can reduce it, but I do not think you can move away from that large number … however you cut it, storage is very important.”29 Mr Liebreich described the value of long-duration storage for electricity production in rare events, noting that “what you will not do for that 2% or 3% is carbon capture and storage, because that is a huge amount of infrastructure to build for use just 2% or 3% of the time.”30

19.Ms Still said that “any sort of flexible nuclear is not proven at scale … it does not replace the role that long-duration storage plays”.31 Professor Sir Peter Bruce, Physical Secretary and Vice-President at the Royal Society, explained that “The cost of hydrogen storage would have to be at the very top of our estimates, and the cost of nuclear would have to be at the very lowest of the estimates before the two started to overlap.”32 Mr Liebreich also raised an economic objection to using nuclear to replace storage: “It does not function as back-up for wind and solar—you cannot just turn nuclear on when it is not windy—you must run it as close to 24/7 as you can, because the costs are bad enough anyway.”33

20.Interconnectors to other countries were described as “very important” but Mr Murrant explained that “European weather cycles are broadly similar to ours”, meaning that periods of high demand and low renewable supply will be correlated across Europe. Professor Bruce agreed: “our neighbours will be in a similar position; they will not have that excess generating capacity to supply to us … if we are all suffering from a shortage of electricity, I very much doubt that they will give it to us, no matter what agreements are in place.”34

Figure 2: Change in annual electricity generation under the Committee on Climate Change/AFRY’s central scenario for a fully decarbonised grid.

A graph showing change of electcirity generation sources from Nuclear, Bio-energy, Onshore wind, Low carbon, Net imports, Offshoer wind, Solar and Unabated gas from 2025 to 2035

The graph shows that there is 39 TWh in total of “dispatchable low-carbon” generation needed to balance the system in 2035, much of which will be provided by energy storage.
Source: Climate Change Committee, Delivering a reliable decarbonised power system (9 March 2023): https://www.theccc.org.uk/wp-content/uploads/2023/03/Delivering-a-reliable-decarbonised-power-system.pdf [accessed 10 January 2024].

Box 3: Estimates for the scale of need and costs for long-duration energy storage

Energy system modellers often develop a range of scenarios to cover possible outcomes, in terms of policy decisions about the energy system, technology mixes used and possible trajectories for the economy.

Different modellers will make different assumptions about the forecast mix of supply and demand, including the roles of nuclear power, gas or biomass with carbon capture and storage (CCS), interconnectors and demand-side management, for example. Both supply and demand also increasingly depend on weather conditions, which in turn are subject to climate change. The range of assumptions and constraints that are used in the model lead to a range of different estimates for longer-duration energy storage (LDES) requirements.35 Modellers also typically try to minimise the overall cost of the energy system, subject to constraints such as reaching Net Zero targets and uninterrupted supply. This introduces a dependence on estimates for the future costs of different technologies.

Modellers agree that electricity demand, and supply from renewables, will substantially increase as the economy electrifies to reach Net Zero. For example, the Climate Change Committee forecasts electricity demand to increase by 50% by 2035, and to double by 2050 in its Balanced Pathway scenario. In their modelling, some assumptions on the final mix of electricity generation capacity are taken from the Government’s stated ambitions for wind, solar and nuclear in its 2022 British Energy Security Strategy.36 The CCC calculate the flexibility needs, including storage, needed to balance the grid with this mix of energy generation, assuming a typical year of weather. They find that around 40 TWh of low-carbon, dispatchable back-up generation is used in 2035, of which 30 TWh (14 GW) is hydrogen generation and 10 TWh (2 GW) is gas with carbon capture and storage (CCS). This need for long-duration energy storage is further supported by 41 GWh (11 GW) of medium- and short-term grid storage capacity provided by other technologies.37

The Royal Society adopted a different approach. They argued that the cheapest way to generate electricity will likely be entirely through variable renewables backed up by electricity storage. They also assumed CCS would be unacceptable due to cost and CO2 emissions and would not play a major role in the power sector. They sought to minimise the overall cost of electricity, matching supply and demand in each of 37 years of weather, as opposed to the CCC, whose central modelling used an individual year of “typical” weather, complemented by stress tests of more extreme weather patterns. The choice to model an entirely renewable energy system, and to analyse weather over a longer period of time, which therefore included some years with anomalously low generation due to low wind speeds, partly explains why the Royal Society had a greater estimate of 100 TWh for the amount of LDES required.

The Royal Society estimated that the total cost of providing an electricity system of this kind would require substantial investment from the public and private sector. They estimated that this would entail cumulative investment by 2050 of on the order of £100 billion for energy storage, £100 billion to enlarge and strengthen the transmission grid,38 and £210 billion for the wind and solar capacity needed. For comparison, the UK spent £193 billion on energy in 2022 (8.1% of GDP).39 The UK spent £112 billion on imports of oil-based fuels and gas in 2022 alone.40 The cost of Government support for households and businesses was approximately £78.2 billion across 2022–23 and 2023–24,41 and in the Royal Society’s analysis electricity prices would be £60/MWh in 2050 in their renewables and storage scenario, comparable to the average over the 2010s. During the energy crisis, prices were often over £200/MWh.

The Royal Society’s estimate is an upper limit for how much storage would be required, as they model a grid with no nuclear, biomass, or gas with CCS— for energy systems with less storage, the corresponding cost of storage would be lower. Regardless of how it is delivered, the cost of nationally significant energy infrastructure is substantial—EDF estimates that the cost of Hinkley C, for example, could be as high as £48 billion.42

Neither model explicitly accounts for the effects of climate change on electricity supply and demand, but both include contingencies to account for this and other factors in the storage estimate. Both the CCC and the Royal Society give ranges for their LDES requirements in their reports and make arguments for the validity of their assumptions. For the purposes of this report, we do not rely on any one estimate, but note that the scale is tens of terawatts hours of long-duration storage in both of these recent, sophisticated modelling efforts to answer this question for the UK.

Sources: Climate Change Committee, Delivering a reliable decarbonised power system and Royal Society, Large Scale electricity storage

21.Despite the consensus that at least 10 TWh of storage will ultimately be needed, the Department for Energy Security and Net Zero has not set an explicit target. Emily Bourne, Director of Energy Systems and Networks, DESNZ, said that this is “one of the questions we will consider. But, at the moment, we do not have a … ‘no-regrets’ level.”43 She set out how they were actively consulting on whether a target would be helpful, noting that the Government had not set one at present “because of the level of uncertainty about how the system will evolve and the risk of setting a target that turns out to be inappropriate, either too high or too low.”44

22.When asked about the specific role of long-duration energy storage in responding to a generation shortfall, the Minister said “it is hard for me to give too definitive an answer” because “there are very large terawatt hour variations between the various modelling expectations.”45 The Government set out in its Smart Systems and Flexibility Plan 2021 a target of “30 GW of low-carbon flexible assets (storage, demand-side response and interconnection)” by 2030 (and 60 GW by 2050) to decarbonise the energy system effectively, but does not state how much of this capacity is storage or give an estimate for the volume of energy in TWh that needs to be stored.46

23.A fully decarbonised electricity system will need substantial energy storage across a range of timescales due to increasing variability of supply and demand in an electrified, renewable-powered economy. Estimates of how much long-duration energy storage will be needed differ depending on assumptions about future energy mix, demand, future climate and desired resilience. These assumptions affect, but do not eliminate, the need for long-duration energy storage.

24.However, there is a consensus that tens of terawatt-hours of long-duration electricity storage will be needed to decarbonise the grid, but the Government has not committed to an explicit target. This is several orders of magnitude more low-carbon storage than the UK currently has and will require different technologies from those currently used, such as the 10 TWh of natural gas storage, to be compatible with Net Zero.

25.The Government should, as a matter of urgency, set an explicit minimum target for how much “no-regrets” long-duration energy storage and generating capacity it wants to see operational by 2035. It should set out a credible timescale with interim milestones for achieving this that works backwards from 2035, accounting for decision time, planning and consenting, and construction of facilities. It should also expand on the 30 GW target of short-term storage, interconnection and demand-side response set out in the Smart Systems and Flexibility Plan by outlining the minimum contribution to flexibility that each technology should make.

26.For energy storage systems, energy stored, typical storage duration, final output electrical energy, and the instantaneous power that can be delivered are important parameters. Government policies and targets relating to energy storage—such as the 10 GW hydrogen production target—should make clear both the power (GW) and the energy (TWh) it is intended to produce and store.

27.Energy storage can be used for many different roles on the electricity grid. As well as storage of electricity across different durations, Caroline Still outlined that older generators use the rotation of the generator to help in “voltage control [and] frequency control”. As these generators are decommissioned there would be “a reduction in the stability and operability of the grid” unless the energy system services they provide are replaced. She said that “long-duration storage technologies can provide some, if not many, of those different ancillary services … [such as] inertia, reactive power, frequency control, and black start.”47

28.Daniel Murrant told us that for “lithium-ion [batteries] … you are typically talking about a duration of two to four hours”, and that even adding up millions of car batteries would “only just [get] into the gigawatt range”, so the role for lithium-ion batteries would be “largely on the shorter-duration energy storage side.”48 However, he noted from his work “with SMEs in the storage and flexibility space” that “one of the key barriers is that there is still too much focus on lithium-ion”, with markets “almost subconsciously set-up for lithium-ion”; he argued that “a better definition of storage” which made the distinction between “short, medium, and long-duration” would help to encourage the range of technologies that are needed.49

29.Caroline Still explained that a “mechanism that could benefit long-duration … storage would be one that better incentivises the additional services that long-duration energy storage can provide to the grid … in a longer-term certain price forecast.”50

30.Professor Paul Monks, Chief Scientific Advisor to DESNZ, said “Our modelling agrees with that of the CCC, the National Infrastructure Commission and the Royal Society that we will need more interday and interseasonal storage. It will be in the order of terawatt hours to tens of terawatt hours” and he highlighted the need for a range of technologies to fill different roles: “we will use a wide variety of storage technologies, from shorter-duration technologies such as lithium-ion batteries, flow batteries and the like, through to hydrogen storage, which can provide interannual duration and provide a sustained response when deployed.”51 This distinction between storage durations may not be apparent with a definition of long-duration energy storage as anything over six hours, as proposed by the Government’s consultation.52

31.A range of energy storage technologies will be needed for different energy system services. We are concerned that the excessive policy and investment focus on lithium-ion storage projects has left policymakers, investors and regulators less able to appreciate the need for longer-duration technologies. There is a clear distinction between technologies which perform best across hours and for daily variations (“medium-duration energy storage”), and technologies which can store energy across days, weeks and months (“long-duration energy storage”), which a definition of long-duration energy storage as anything greater than six hours may not capture.

32.The Government, supported by modelling from the Future System Operator, should clarify its definitions for medium- and long-duration energy storage and the roles they are expected to play. It should set or endorse a series of metrics that allow technologies to be compared according to the energy system services that they provide. It should use these to publish an Assessment of Likely Need for long-duration energy storage by the end of 2024; this should include storage timescales, energy stored and power capacity required. It should commit to supporting a range of technologies, beyond just batteries, through financial support mechanisms and research grants for less mature technologies.

Urgency and pace of delivery

33.Daniel Murrant told us that “we are nowhere near what we need for the 2035 [electricity decarbonisation] target.”53 Rachel Hay, the Climate Change Committee’s Head of Energy Supply Decarbonisation and Resilience, said that “the lead times are long … around seven to 10 years for hydrogen storage and seven to 12 years for gas pipelines. The Electricity Networks Commissioner, Nick Winser, talked about “12 to 14 years for electricity transmission”.54 He said that the National Infrastructure Commission “believe that those sorts of facilities—the pipelines that we talk about in the report and the hydrogen storage—can take of the order of 10 years to deliver. We are in 2023; the facilities are needed for 2035, so there is cause for urgency.”55

34.Mr Winser added that “we should not make perfect the enemy of good.” Given how much is missing, “starting to bring out something that is a high-level view … would help an awful lot and could be done quite quickly”.56 This was echoed by Ms Hay, who said “there is definitely a need for pace over perfection … it is not clear at any point in time what the precisely right answer is. The problem is that pursuing that precisely right answer is causing the problem.” As Ms Hay put it: “We just need to make some decisions now, acknowledging that they may not be perfect. The worst decision that we can make is to … not make those decisions.”57 As Dr David Joffe noted, any government guidance would have to be iterative, with initial guidance set out by the Government translated into options by those such as the Future System Operator, with subsequent decisions regarding those options then made by the Government.58

35.There are long lead-in times for delivering energy storage—typically estimated around 7–10 years for most technologies. If the Government waits until there is a clear picture of exactly how supply, demand and the energy system will evolve, it cannot possibly develop storage in time for a decarbonised grid by 2035. The Government should focus on “pace not perfection” in delivering no-regrets projects—it is always possible to iterate on policy as uncertainties are resolved. It should bring forward its support schemes and no-regrets investments as soon as possible.


10 Q 1 (Caroline Still)

11 Energy Monitor, ‘While EU and US act, UK is unprepared for winter energy crisis’: https://www.energymonitor.ai/sectors/opinion-while-eu-and-us-act-uk-is-unprepared-for-winter-energy-crisis/ [accessed 10 January 2024]

12 The 26.7 GWh of pumped-hydro capacity was charged and discharged multiple times over the year, and there are efficiency losses at each stage of the conversion.

13 Q 60 (Martin Scargill)

14 Office for Budget Responsibility, ‘The cost of the Government’s energy support policies’ (October 2023): https://obr.uk/box/the-cost-of-the-governments-energy-support-policies/ [accessed 10 January 2024]

15 Competition and Markets Authority, Rough gas storage undertakings review–Final report (22 April 2016): https://assets.publishing.service.gov.uk/media/571a2323e5274a201400000f/Rough_gas_storage_undertakings_review_final_report.pdf [accessed 10 January 2024]

16 Reuters, ‘Centrica reopens UK’s Rough gas storage site in time for winter’: https://www.reuters.com/business/energy/british-gas-owner-centrica-reopens-rough-gas-storage-site-2022–10-28/ [accessed 10 January 2024] and ‘’Relying on luck’: why does the UK have such limited gas storage?’, The Guardian (24 September 2021): https://www.theguardian.com/business/2021/sep/24/how-uk-energy-policies-have-left-britain-exposed-to-winter-gas-price-hikes [accessed 10 January 2024]

17 Q 63 (Martin Scargill)

18 Technology readiness levels exist on a scale from 1 to 9 which allow technologies to be compared based on how close they are to widespread deployment (see Figure 2).

19 Xoserve, ‘Blog: Energy storage—the missing piece of the net zero puzzle?’ (7 November 2023): https://www.xoserve.com/news/blog-energy-storage-the-missing-piece-of-the-net-zero-puzzle/ [accessed 10 January 2024]

20 Q 11 (Professor Sir Peter Bruce) and Q 27 (Timothy Armitage)

21 Q 72 (Michael Liebreich)

22 Q 89 (Stef Murphy)

23 Q 107 (Dr David Joffe)

24 Climate Change Committee, Delivering a reliable decarbonised power system (9 March 2023): https://www.theccc.org.uk/publication/delivering-a-reliable-decarbonised-power-system/ [accessed 10 January 2024]

25 Q 1 (Caroline Still)

26 Q 2 (Daniel Murrant)

27 Q 107 (Dr David Joffe)

28 Q 109 (Graham Stuart MP)

29 Q 3 (Daniel Murrant)

30 Q 72 (Michael Liebreich)

31 Q 3 (Caroline Still)

32 Q 12 (Professor Sir Peter Bruce)

33 Q 69 (Michael Liebreich)

34 Q 3 (Daniel Murrant) and Q 11 (Professor Sir Peter Bruce)

35 An example can be found in box 2.1 of the CCC’s Report which outlines the modelling assumptions that went into their estimates for the need for flexibility. Climate Change Committee, Delivering a reliable decarbonised power system, p 47

36 HM Government, British Energy Security Strategy (7 April 2022): https://assets.publishing.service.gov.uk/media/626112c0e90e07168e3fdba3/british-energy-security-strategy-web-accessible.pdf [accessed 26 February 2024]

37 See p 54 for these estimates, which also include indicative ranges. Some of this modelling was carried out by AFRY. Climate Change Committee, Delivering a reliable decarbonised power system

38 This estimate is from the National Grid’s calculations for a decarbonised electricity system.

39 CarbonBrief, ‘Analysis: Why UK energy bills are soaring to record highs—and how to cut them’ (12 August 2022): https://www.carbonbrief.org/analysis-why-uk-energy-bills-are-soaring-to-record-highs-and-how-to-cut-them/ [accessed 10 January 2024]

40 OEUK, ‘UK energy import bills more than doubled to £117 billion in 2022 and could hit similar highs this year, a new Offshore Energies UK report will warn’ (22 March 2023): https://oeuk.org.uk/uk-energy-import-bills-more-than-doubled-to-117-billion-in-2022-and-could-hit-similar-highs-this-year-a-new-offshore-energies-uk-report-will-warn/ [accessed 10 January 2024]

41 Office for Budget Responsibility, Economic and fiscal outlook, CP 804, March 2023, box 3.1: https://obr.uk/docs/dlm_uploads/OBR-EFO-March-2023_Web_Accessible.pdf [accessed 10 January 2024]

42 BBC News, ‘Hinkley C: UK nuclear plant price tag could rocket by a third’ (23 January 2024): https://www.bbc.co.uk/news/business-68073279 [accessed 10 January 2024]

43 Q 86 (Emily Bourne)

44 Q110 (Emily Bourne)

45 Q108 (Graham Stuart MP)

46 Department for Business, Energy and Industrial Strategy, Transitioning to a net zero energy system: Smart Systems and Flexibility Plan 2021 (July 2021): https://assets.publishing.service.gov.uk/media/60f575cd8fa8f50c7f08aecd/smart-systems-and-flexibility-plan-2021.pdf [accessed 10 January 2024]

47 1 (Caroline Still) Inertia in power systems is currently provided by rotating turbines in thermal electricity generators. If there is a sudden change in system frequency, such as would be caused by a power plant outage, the turbines keep spinning due to their inertia, which slows down the change in frequency of electricity on the grid while stability is restored, so it is important for controlling the frequency of the alternating electrical current. Renewables do not have the same property of spinning turbines that rotate in sync with the electricity frequency. However, any store of energy that can be accessed sufficiently quickly can help manage system frequency. See ESO, ‘What is inertia’: https://www.nationalgrideso.com/electricity-explained/how-do-we-balance-grid/what-inertia [accessed 10 January 2024]. Reactive power services allow the grid to maintain safe voltages (the voltage determines the amount of power transferred by a given current of electricity), and generators or other electricity system assets that can help maintain voltage control across the network are said to absorb or generate reactive power. See ESO, ‘Reactive power services’: https://www.nationalgrideso.com/industry-information/balancing-services/reactive-power-services [accessed 10 January 2024]. Black start is the process of restarting the grid after a partial or total shutdown, which would require isolated facilities being restarted and gradually connected to each other to form an interconnected electricity system again. This requires individual facilities in strategic locations, which are capable of switching themselves back on in case of a power outage, which the ESO can procure “black start” services from to restart the grid if needed. See National Grid, Black start: https://www.nationalgrideso.com/document/92386/download [accessed 10 January 2024]

48 Q 4 (Daniel Murrant)

49 Q 5 (Daniel Murrant)

50 Q 5 (Caroline Still)

51 Q 83 (Professor Paul Monks)

52 Department for Energy Security and Net Zero, Long duration electricity storage consultation: Designing a policy framework to enable investment in long duration electricity storage (January 2024): https://assets.publishing.service.gov.uk/media/659bde4dd7737c000ef3351a/long-duration-electricity-storage-policy-framework-consultation.pdf [accessed 10 January 2024]

53 Q 5 (Daniel Murrant)

54 101 (Rachel Hay)

55 Q 53 (Nick Winser)

56 Ibid.

57 Q 101 (Rachel Hay)

58 102 (Dr David Joffe)




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