Long Duration Energy Storage: the key to a 100% renewable energy grid

Introduction

The UK Government’s Clean Power 2030 Action Plan sets out to meet 95% of electricity requirements with renewables and nuclear power by 2030.¹ Plans include 43-50GW of offshore wind, (up from 14.7GW currently) 27-29GW of onshore wind (up from 15.7GW currently), and 45-47GW of solar power (up from 21.5GW). In 2024 renewable sources provided 50% of Great Britain’s electricity.² But as we become increasingly reliant on variable renewable sources, we also need to develop flexibility to accommodate and store these variable outputs. We need the ability to shift demand to times of plentiful supply and to shift supply to times of high demand. The 2030 Action Plan sets out to compliment renewable sources with 23-27 GW of battery capacity, and 4-6GW of long‑duration energy storage (LDES). Iberdrola, owner of Scottish Power, points out that LDES is “the key enabler for a 100% renewable electricity grid.”³ Energy storage systems can work in concert with other flexibility technologies to balance the grid, maximise use of low-cost renewable electricity, and provide resilience during periods of low generation.⁴ Looking beyond 2030 to a fully decarbonised energy system – not just electricity, but including heat and transport – these technologies offer us the opportunity to achieve our decarbonisation aims for 2050.

Lithium-Ion Batteries

Lithium-ion batteries currently supply around 90% of global energy storage capacity, mainly in short-duration, two- to four-hour applications.⁵ Longer duration energy storage – eight-hours or more – is in relatively low demand because renewables dominate in only a handful of locations. But it will be increasingly required for grids as renewable generation increases. It used to be thought that scaling lithium-ion batteries up to a storage duration of more than eight hours would not be cost effective, but fierce competition between lithium-ion suppliers is driving down costs, so longer duration storage is now economically feasible. The New South Wales government, for example, has awarded contracts to six new big lithium-ion battery projects⁶ which can deliver much longer duration storage than most experts had imagined possible – all longer than eight hours. Low-cost solar generated in the middle of the day can now be stored rather than curtailed and fed into the grid when demand peaks in the evening.⁷

But lithium-ion batteries aren’t the only way to store energy, and they are being challenged by a group of novel technologies aimed at storing energy for very long periods. BloombergNEF’s latest research⁸ suggests that other LDES technologies are poised to rival them for certain applications, with some already offering cheaper storage over eight hours.⁹ Most of these technologies are still at an early stage and costly, but some already achieve lower costs than lithium-ion for longer durations. Thermal energy storage and compressed air storage, for example, are the least expensive LDES technologies.¹⁰

The Cap and Floor Scheme

In January 2024, the Department for Energy Security and Net-Zero (DESNZ) launched a consultation on a new scheme for unlocking investment in LDES technologies to help with energy security and keep power system operating costs down as more variable renewable generation comes online. Research conducted by the energy research and consultancy firm LCP Delta for the government modelled potential electricity system operating cost savings if up to 20GW of LDES capacity is deployed this decade. It revealed potential savings of £24bn, equivalent to more than 3% of total costs by reducing both the cost of payments to renewables to turn off and the cost of gas generation.¹¹

In October 2024, the government decided to introduce a LDES cap and floor scheme that will be delivered by Ofgem. This scheme is intended to ensure investors receive a minimum amount of revenue to enable investment in LDES assets. Alongside this, the cap on revenue provides returns to consumers for their support, where LDES assets operate above the cap.¹²

The cap and floor scheme builds on the approach already used to successfully deliver more electricity interconnection. In March 2025, following a consultation, Ofgem and DESNZ published a joint Technical Decision Document detailing the regime specifics.¹³ This confirms key final details of the scheme: it sets out how the scheme will operate, when the first application window will open, how much initial capacity will be sought, and which projects will be eligible to apply, amongst other details.

On 8 April 2025, Ofgem opened the first application window,¹⁴ and published a Guidance for Applicants.¹⁵ Then, on 23^rd September 2025, Ofgem announced it had completed the eligibility assessment for the Cap and Floor scheme. Projects that met the eligibility criteria then proceeded to the Project Assessment stage. 77 projects entered the final assessment stage, 48 were lithium-ion batteries; five were pumped hydro storage; 16 were vanadium-flow/ zinc batteries; five were vanadium-flow batteries; one was compressed air storage and two were liquid air and battery hybrids.¹⁶ These projects are mostly expected to be available in 2030 with a few available by 2033.

Most of the 77 projects are lithium-ion batteries, so some concerns have been expressed that these will be direct competitors to short duration, unsubsidised lithium-ion batteries.¹⁷

“Lithium-ion batteries aren’t the only way to store energy, and they are being challenged by a group of novel technologies aimed at storing energy for very long periods”

Vanadium Flow Batteries

21 of the 77 projects use vanadium flow batteries.¹⁸ These can store power for up to 12 hours compared with about four to eight hours for lithium-ion batteries. They also have the ability to charge and discharge continuously without degrading. Vanadium flow batteries are non-flammable and can operate effectively without the need for additional fire suppression systems. They do not contain conflict minerals (such as cobalt) and are almost completely recyclable at end of life. The key working element inside a vanadium flow battery – vanadium – is sustainably sourced and more abundant than lithium or copper, with deposits in regions across the world. Vanadium supply is dominated by China, Russia, South Africa, and Brazil, with about 70% produced as a co-product of steel slag. Supply is increasingly supported by recycling of industrial biproducts.

The taxpayer-owned UK Infrastructure Bank has invested £25 million in a company called Invinity Energy Systems, which manufactures vanadium flow batteries in Bathgate and Motherwell in Scotland.^{19, 20} The Company has also attracted several private investors.²¹

Of the 21 projects, 16 were a mixture of vanadium-flow and zinc batteries and five were vanadium flow batteries alone. Frontier Power, based in Warwickshire has announced a landmark partnership with Invinity aimed at deploying vanadium flow batteries at an unprecedented scale as part of Ofgem’s LDES procurement process. The collaboration aims to position the UK as a global leader in advanced energy storage technologies.²² The 16 vanadium and zinc projects accepted by Ofgem were all submitted by Frontier.

Zinc Batteries

Frontier Power Ltd is also collaborating with Eos Energy Storage which produces aqueous zinc batteries in the US. Eos Energy says their batteries offer a significant reduction in the levelized cost of storage – as much as a 25% reduction when compared to lithium-ion batteries.²³ Aqueous zinc batteries overcome the limitations of conventional lithium-ion technology. They are non-flammable, non-corrosive, and fully recyclable at the end of their useful life. They provide utility, industrial, and commercial customers with a proven, reliable energy storage alternative for three to 12-hour applications. The Frontier-Eos partnership opens the door to developing local manufacturing in the UK. Should significant LDES project volumes materialize using Eos technology, it could incentivize the establishment of manufacturing operations in the UK, supporting domestic supply chains and job creation.

Pumped Hydro Energy Storage

Great Britain already has 2.8GW of LDES across four Pumped Hydro Energy Storage (PHES) facilities in Scotland and Wales. These operate like natural batteries and are already crucial to the electricity system. Each facility uses two water reservoirs at different elevations and power is generated when water moves down from one to the other passing through a turbine. When demand for electricity is low, water is pumped back up to the upper reservoir where it is stored for future use.

Five Pumped Hydro Energy Storage projects, all in Scotland, have entered Ofgem’s final assessment stage: Coire Glas, Earba, Glenmuckloch, Loch Kemp, Loch na Cathrach. Between them, they have a capacity of 4.6GW.

A sixth project – to expand the existing Cruachan Pumped Hydro Storage scheme did not apply for funding because the costs of the project have increased so the owners,Drax, have put the project on hold for now.²⁴

Coire Glas, located at Loch Lochy in the Great Glen, received planning consent back in 2020.²⁵ At 1.3GW with up to 30GWh of storage capacity, it could power three million homes for up to 24 hours. SSE has completed a 1.2km exploratory tunnel, marking a significant milestone for the project.²⁶

The Earba project, being promoted by Gilkes Energy, was granted planning consent in March 2025. At 1.8GW and up to 40GWh of capacity would be even larger. The proposal is to use Loch Leamhain as the upper reservoir and Loch Earba as the lower reservoir – both in the Highlands. A tunnel approximately 3km long will connect the two water bodies.²⁷

The Glenmuckloch proposal would use an old coal mine near the village of Kirkconnel in Dumfries and Galloway. At 200MW and 1.6GWh of capacity the power station would be capable of powering about 210,000 homes for eight hours with one full discharge of the upper reservoir and could start dispatching electricity by 2029, the earliest of any of the pumped storage projects being planned. Unlike some pumped storage power stations, Glenmuckloch will be a closed-loop system. It was granted planning consent in November 2016. This was varied again in 2022 to increase the operational life of the scheme.²⁸

The Loch Kemp pumped storage scheme would have a capacity of 660MW and 9GWh of energy. The project will use two existing bodies of water, Loch Kemp and Loch Ness. It would supply over one million homes with instantaneous clean electricity for up to 15 hours. A planning application was submitted in November 2023.²⁹ The project is being promoted by Statera – a UK-based energy company that develops, owns and operates flexible generation, battery storage, pumped storage hydro and green hydrogen projects.

Loch na Cathrach Pumped Storage is a 500MW hydro scheme, first conceived in 2015 and granted consent by Scottish Government ministers in June 2021. It would be located on a site around 14km south-west of Inverness and will harness the waters of Loch Ness. This facility is expected to have a storage capacity of approximately 2.8GWh– in other words it could generate at full capacity for over six hours. The project is owned by the Norwegian State-owned company Statkraft.³⁰.

Liquid Air Energy Storage

Highview Power has two 3.2GWh power plants, planned for development in the UK by 2030, which entered Ofgem’s final assessment stage and would be based at Hunterston in Ayrshire and Killingholme in Lincolnshire.³¹

Highview’s Liquid Air Energy Storage technology captures excess renewable energy when demand is low, and stores it as liquid air for hours, days or even weeks. It works by compressing air into a liquid and then cooling it to temperatures of almost minus 200^oC. The air is stored in insulated tanks at low pressure. When power is needed it will be drawn from the tanks and heated up so it expands, resulting in a high-pressure gas that powers a turbine.

On 21^st November 2025 Greater Manchester Mayor, Andy Burnham, officially broke ground for Highview’s prototype liquid air energy storage plant near Carrington which will deliver 300MWh of storage and an output of 50MW for six hours, enough to serve 480,000 homes.³²

£300m of funding is being provided by the UK Infrastructure Bank, Centrica, and a syndicate of investors including mining multinational Rio Tinto, financial giant Goldman Sachs, Danish investor Kirkbi, and US-based Mosaic Capital Partners. Centrica has put £70m into the project.³³

Compressed Air Energy Storage

There is one Compressed Air Energy Storage project on the list of projects deemed eligible to enter Ofgem’s final assessment stage. Located in Teesside, it is expected to have a discharge capacity of 50MW.

Compressed Air Energy Storage is considered to be a mature form of storage. When there is surplus electricity on the grid, the Storelectric compressed air energy storage system can use it to compress air to around 70 bar pressure, also storing the heat. Then, when electricity is required, air and heat are released through turbines. Compressed Air Energy Storage is well known, having been built in Huntorf, Germany in 1978 and McIntosh, Alabama, US in 1991. Both plants continue to operate successfully and safely, providing vital grid balancing services. Both store air in subterranean salt caverns. However, they have relatively low efficiency rates (42-54%), because they use gas to re-heat decompressing air. The Storelectric system can eliminate the need for gas re-heating, thus improving efficiency.

Storelectric Teesside Ltd is in the process of acquiring around 550 acres of industrial land on Teesside which includes underground caverns.³⁴

Sodium-Ion Batteries

There are many energy storage alternatives to using expensive lithium-ion batteries which either didn’t apply or didn’t make it onto Ofgem’s list of ‘projects eligible’ to receive support under the ‘cap and floor’ scheme.

One such alternative, which is gaining a lot of attention, is the sodium-ion battery. The costs of sodium-ion batteries  are fast declining.³⁵ It is still uncertain whether they will become a disruptive alternative to lithium-ion technology, but they could offer significant cost-savings due to the abundance and accessibility of sodium, which is considerably cheaper and more abundant than lithium.³⁶ Although sodium-ion batteries have yet to achieve widespread market adoption, they are already approaching cost parity with lithium-ion batteries. Sodium-ion batteries could be manufactured on existing lithium-ion battery production lines with only minor modifications.³⁷

Unlike lithium-ion batteries, sodium-ion batteries are not susceptible to bursting into flames when dropped or charged in the wrong way. Sodium-ion batteries could be a game-changer – enabling our grids to run on 100% renewables.³⁸

The Chinese company, CATL, is the largest battery producer in the world. It has been making sodium-ion batteries for some time, but it has now announced plans to increase production, with integration into production of electric vehicles by July. CATL says that up to half the market could switch to sodium.³⁹

In Europe, the European Economic and Social Committee will place sodium-ion batteries at the centre of its work on the EU’s industrial strategy. A list of manufacturers developing this technology in Europe includes Faradion (UK), which describes itself a market leader in non-aqueous sodium-ion batteries. It says sodium-ion batteries are recognised as an emergent technology and a key part of the solution for cheaper, cleaner energy. They are cheaper and safer than lithium-ion, with a higher energy density and a wider operating temperature range than other batteries^.40

In Austria, a company called Salzstrom has unveiled a sodium-ion battery system for use in commercial applications, having previously launched a residential photovoltaic storage system based on its sodium-ion technology. The market response to that system significantly exceeded Salzstrom’s expectations. Company co-founder, Jürgen Ellensohn, says: “Many companies are specifically looking for alternatives to lithium – whether for sustainability reasons or due to safety considerations.”⁴¹

Iron Air Batteries

Yet another new type of battery, called an iron-air battery, is based on the oxidisation (rusting) of iron. The battery is designed, by Form Energy, to cost-effectively store and discharge energy over multiple days. The first-ever project is being built with electricity supplier Great River Energy in Cambridge, Minnesota.⁴²

Great River Energy, a non-profit cooperative, will evaluate the iron-air battery system’s operation over ‘several years’. New Scientist explains how it works: “when charging, a current electrochemically converts iron oxide – rust to you and me – into iron and releases oxygen as a gas. When discharging, the battery sucks oxygen back from the air and turns the iron back to rust, generating a flow of electricity.” Each of Form Energy’s batteries is about the size of a washing machine – not suitable for an EV, but fine for grid-scale storage. The company has started building its first factory in West Virginia.⁴³ Form Energy’s batteries are capable of storing electricity for 100 hours.⁴⁴

One of the projects planning to use Form Energy’s batteries is in Ireland’s County Donegal. FuturEnergy Ireland, a joint venture between Coillte and ESB, has been granted planning permission to build Europe’s first iron-air battery facility. Known as the Ballynahone Energy Storage project, it will look modest – a collection of weatherproof containers on a three-hectare site beside an electrical substation – but what it represents could be transformative.⁴⁵

One alternative to lithium-ion is the sodium-ion battery. The costs of sodium-ion batteries are fast declining. They could offer significant cost-savings due to the abundance and accessibility of sodium, which is considerably cheaper and more abundant than lithium. They could be a game-changer – enabling our grids to run on 100% renewables.

Gravity Storage

Gravitational energy storage is another technology being developed for long-duration energy storage. Gravity energy storage systems have inherent advantages in that they typically have a long operating life with a minimal maintenance burden. They are also relatively simple and do not require hazardous or scarce materials.⁴⁶

Sadly, Edinburgh-based Gravitricity went into liquidation in 2025. Gravitricity developed a below-ground gravity energy storage system that worked by raising weights in a deep shaft and releasing them when energy is required. In 2021, Gravitricity successfully built and operated a grid-connected demonstrator at the Port of Leith in Edinburgh, validating key aspects of the technology and providing a tangible proof-of-concept for the underlying engineering approach. Little information, beyond the company’s poor financials, is available as to what went wrong.

Meanwhile, on the other side of the Atlantic, Energy Vault’s groundbreaking EVx™ is the world’s first commercial-scale Gravity Energy Storage System (GESS), providing industry leading round-trip efficiency and a 35-year operating life. It has two gravity storage projects in China.⁴⁷

Flywheels

Flywheel energy storage works by spinning a rotor (flywheel) and maintaining the energy in the system as rotational energy. When energy is extracted from the system, the flywheel’s rotational speed is reduced; adding energy to the system correspondingly results in an increase in the speed of the flywheel. Because energy is stored kinetically flywheels avoids many of the limitations of chemical batteries. They can charge and discharge ten times faster and only use widely available materials.

A Utah-headquartered company called Torus produces flywheel-based energy storage systems for both residential and commercial applications. The company claims its flywheel-based technology is differentiated from chemical batteries by being 95% recyclable, unaffected by temperature fluctuations and has a 25-year service life.⁴⁸ In September 2025 Torus secured a $200 million investment to accelerate the deployment of its modular hybrid power plant solutions, which combines the strengths of mechanical flywheels with advanced battery storage.⁴⁹

Another US-based Flywheel developer, Qnetic, has just raised $5 million to launch domestic manufacturing in California and deploy the first units of its flywheel energy storage system.⁵⁰

In the UK a company called Levistor is working with National Highways on a trial of its flywheel-based energy storage system (FESS) to provide a short-term power boost for fast EV chargers when the grid is unable to meet the high demand. It allows an EV driver to add 100 miles of range with just five minutes of charging.⁵¹

Heat Batteries

Heat storage is rising up the agenda. Heat provides more than half the total energy demanded by industry, but according to the Institution of Mechanical Engineers (IMechE) electric batteries and hydrogen have hogged the limelight to the neglect of simple systems storing heat.⁵²

There are various types of heat-based batteries available such as those made of rocks, bricks or sand and heated with an electric coil. They can deliver high temperatures — anything from 100 to 1,500 degrees — to make food, beverages, paper, chemicals and a host of other materials which account for about a quarter of current fossil fuel consumption globally. Using electricity directly can be expensive, but by using heat batteries in conjunction with heat pumps, and using off-peak electricity, it can be cheap enough to provide high temperature heat for industry.

Finland inaugurated the world’s largest sand battery in 2025. The 1MW/100MWh thermal storage system developed by Polar Night Energy is an industrial-scale unit in Pornainen which began operating in 2025 where the district heating company, Loviisan Lämpö, uses the sand battery as the main production facility in its district heating network.⁵³

Another Finnish company, TheStorage, says that its thermal storage technology could reduce industrial energy costs by up to 70% and cut carbon emissions by as much as 90%. The system converts renewable electricity into heat, stores it in sand, and delivers it on-demand for industrial heating. In January 2026, TheStorage installed its first industrial-scale pilot at a brewery, putting the technology to the test in a real-world setting producing steam for the brewery’s production lines.⁵⁴

In East Lothian, a company called Sunamp has received £9.25m in government funding to trial an advanced system in 100 homes across the UK. Its technology relies on storing heat and cold in a phase-change material similar to the gel used in pocket hand-warmers. Its heat batteries are four times more efficient at storing heat than tanks of water, allowing it to use a much smaller tank – smaller than a washing machine. These can be used, for instance, in conjunction with heat pumps. The heat pumps can be run overnight on off-peak electricity to charge up the heat battery. The battery is then discharged to heat water for the central heating systems during the day.⁵⁵

“Using electricity directly can be expensive, but by using heat batteries in conjunction with heat pumps, and using off-peak electricity, it can be cheap enough to provide high temperature heat for industry.”

Hydrogen

Hydrogen is a much talked about way of storing renewable energy. The technology for producing it, by electrolysing water with renewable energy and then using the hydrogen that is released to power gas turbines, is straightforward. The less straightforward aspect is storing hydrogen for any length of time because its escapes from even thick metal tanks quite easily.

But it can be stored in large underground facilities similar to storage facilities used for natural gas. For instance, the ‘Rough’ gas storage facility off the Yorkshire coast could be used for hydrogen storage. This facility alone would store around 10TWh of hydrogen energy, enough, on its own to power all of (at current levels) UK electricity supply four to five days even if there was not a single kWh of anything else available.

A disadvantage of hydrogen burned in conventional gas turbines is that NOx emissions are much higher compared to methane – unless that is, the hydrogen is used in fuel cells (where there are no NOx emissions). The cost of fuel cells is coming down quickly, although they are still a lot more expensive than gas turbines. On the other hand, RWE in Germany is planning an 800MW gas turbine designed specifically to burn 100% hydrogen with much reduced NOx emissions.⁵⁶

One way of avoiding hydrogen leaking out of storage is by converting it to methane or ammonia. Ammonia can be produced by mixing hydrogen generated through using renewable energy to hydrolyse water and mixing with nitrogen at the same time. Lots of ammonia is currently stored for use in the fertiliser industry. Ammonia is unique as a fuel because it does not contain carbon, which means its combustion does not produce CO₂ emissions.

100% Renewables

As we move on from decarbonising the electricity system in 2030 to decarbonising the whole energy system by 2050, energy storage will become even more crucial whilst also offering a cheaper more secure path to net zero. A study by renowned energy modellers at Finland’s LUT University demonstrates that a 100% renewable energy system for the UK is not only technically feasible but also offers a much cheaper path towards achieving net zero in 2050 compared to the UK Government’s pathway for net zero. The UK could provide all the energy it needs from renewable sources in conjunction with short and long duration energy storage without the need for new nuclear stations or fossil gas peaker plant.⁵⁷

The 100% renewable energy scenario including inter-annual storage is calculated to be €129bn cheaper in total cost compared with the UK Government’s present pathway to achieving net zero by 2050. In addition, the 100% renewable energy scenarios reduce the quantity of CO₂ emitted in the period up to 2050 by over a fifth compared the Government scenario (Current Policy Scenario). The main trend across all 100% renewable energy scenarios is the electrification of all sectors, leading to high system efficiency and reduced primary energy demand. The scenario is dominated by offshore wind but also includes large amounts of inter-annual energy storage to cope with fluctuations in wind power outputs within and between years. The study found that storing renewable energy as renewable electricity-based methane in conventional natural gas storage facilities is the most cost-effective means of inter-annual storage. The methane is converted from air captured CO₂ and green hydrogen using renewable electricity.

Given the nuclear industry’s history of delays and cost overruns, the Government should urgently examine 100% renewable energy scenarios with inter-annual energy storage as a contingency if nothing else. In the meantime, it should plan for a further LDES Cap and Floor Assessment round with a particular focus on promising technologies which failed to make it on to Ofgem’s Assessment List in this round, particularly sodium-ion and iron-air batteries as well as gravity storage.

1. Clean Power 2030 Action Plan, DESNZ 15^th April 2025 https://www.gov.uk/government/publications/clean-power-2030-action-plan/clean-power-2030-action-plan-a-new-era-of-clean-electricity-main-report#shortduration-flexibility

2. Renewable UK 27^th Mar 2025 https://www.renewableuk.com/news-and-resources/press-releases/official-stats-show-renewables-generated-over-half-uk-s-electricity-for-the-first-time-in-2024/

3. See Long-duration energy storage: the key to power decarbonisation, Iberdrola (accessed) 16^th March 2026  https://www.iberdrola.com/about-us/what-we-do/energy-storage/long-duration-energy-storage

4. Clean Flexibility Roadmap, DESNZ, 23^rd July 2025 https://www.gov.uk/government/publications/clean-flexibility-roadmap/clean-flexibility-roadmap

5. PV Magazine 30^th March 2024, https://www.pv-magazine-australia.com/2024/03/30/weekend-read-can-anything-topple-lithium-ion/

6. Renew Economy 5^th Feb 2026 https://reneweconomy.com.au/nsw-awards-contracts-to-six-huge-8-hour-battery-projects-including-the-biggest-in-australia/

7. Renew Economy 6^th Feb 2026 https://reneweconomy.com.au/first-solar-battery-hybrid-sends-power-into-evening-peak-heralding-radical-changes-for-australias-main-grid/

8. Long duration energy storage to challenge lithium-ion batteries, Energy Live News 3^rd June 2024 https://www.energylivenews.com/2024/06/03/long-duration-energy-storage-to-challenge-lithium-ion-batteries/ and https://about.bnef.com/insights/clean-energy/lithium-ion-batteries-are-set-to-face-competition-from-novel-tech-for-long-duration-storage-bloombergnef-research/

9. Energy Live News 3^rd June 2024 https://www.energylivenews.com/2024/06/03/long-duration-energy-storage-to-challenge-lithium-ion-batteries/

10. BloombergNEF 4^th June 2024 https://about.bnef.com/insights/clean-energy/lithium-ions-grip-on-storage-faces-wave-of-novel-technologies/

11. Edie 10^th Jan 2024 https://www.edie.net/long-duration-energy-storage-could-cut-24bn-from-uk-power-system-costs/

12. Long Duration Electricity Storage: Proposals to Enable Investiment, DESNZ, 10^th October 2024 https://www.gov.uk/government/consultations/long-duration-electricity-storage-proposals-to-enable-investment#full-publication-update-history

13. Long Duration Electricity Storage: Technical Decision Document, Ofgem & DESNZ 11^th March 2025 https://www.ofgem.gov.uk/sites/default/files/2025-03/Long%20Duration%20Electricity%20Storage%20Technical%20Decision%20Document.pdf

14. Ofgem letter 8^th April 2025, https://www.ofgem.gov.uk/sites/default/files/2025-04/Decision%20to%20open%20application%20window%201%20for%20Long%20Duration%20Electricity%20Storage.pdf

15. Guidance for the cap and floor scheme application: Long Duration Electricity Storage (window one), Ofgem 8^th April 2025 https://www.ofgem.gov.uk/sites/default/files/2025-04/Application%20guidance%20LDES%20window%201.pdf

16. LDES Eligibility Assessment Outcome, Ofgem 23^rd September 2026 https://www.ofgem.gov.uk/sites/default/files/2025-09/LDES%20Eligibility%20Assessment%20Outcome.pdf

17. Solar Power Portal 10th Feb 2026 https://www.solarpowerportal.co.uk/battery-storage/ldes-over-procurement-will-absolutely-impact-merchant-bess-buildout-successful-first-window-bidder-says

18. See https://invinity.com/vanadium-flow-battery-safety/

19. This is Money 12^th May 2024 https://www.thisismoney.co.uk/money/markets/article-13407621/Britains-nascent-battery-industry-receives-shot-arm-Government-foreign-investors.html

20. Linkedin Feb 2026 https://www.linkedin.com/posts/invinity-energy-systems_energystorage-ldes-vfb-activity-7429602010712219648-5uRU/

21. Solar Power Portal 10^th Sept 2025 https://www.solarpowerportal.co.uk/energy-storage/invinity-energy-systems-lands-25-million-investment-and-new-partners

22. Frontier Power & Invinity Joint Press Release 18^th Feb 2025 https://www.frontierpower.biz/https/wwwfrontierpowerbiz/newsandinsights/frontier-power-announces-collaboration-with-invinity-to-deploy-flow-batteries-in-the-uk

23. Eos Energy https://www.eose.com/solutions/

24. BBC 7^th May 2025 https://www.bbc.co.uk/news/articles/c5yly4x3gedo

25. See https://www.coireglas.com/project

26. International Water Power 12^th Aug 2024 https://www.waterpowermagazine.com/uncategorized/sse-completes-exploratory-tunnel-for-coire-glas-project/

27. Earba Storage 28^th March 2025 https://earbastorage.co.uk/earba-psh-project-secures-major-planning-consent/

28. Times 12^th Aug 2024 https://www.thetimes.com/business/economics/article/disused-scottish-coalmine-ready-to-enter-the-green-power-era-j5jcb9lsh

29. See https://lochkempstorage.co.uk/plans-and-progress

30. See https://projects.statkraft.co.uk/loch-na-cathrach/

31 Highview Power 23^rd Sept 2025 https://highviewpower.com/news-announcements/highview-power-announces-two-long-duration-energy-storage-projects-eligible-for-support-under-uk-governments-cap-and-floor-scheme/

32. Highview Power 21^st Nov 2025 https://highviewpower.com/news-announcements/mayor-of-greater-manchester-andy-burnham-officially-breaks-ground-on-highviews-pioneering-liquid-air-energy-storage-facility-in-carrington-manchester/

33. Telegraph 13^th June 2024 https://www.telegraph.co.uk/business/2024/06/13/british-gas-owner-backs-300m-liquid-air-energy-project/

34. Storelectric 16^th Feb 2026 https://storelectric.com/storelectric-exchanges-contracts-to-purchase-industrial-land-in-teesside/

35. Power Technology 1^st July 2024 https://www.power-technology.com/features/exclusive-sodium-batteries-to-disrupt-energy-storage-market/

36. PV Magazine 28^th Nov 2025 vhttps://www.pv-magazine.com/2025/11/28/sodium-ion-battery-cells-could-drop-to-40-kwh-says-irena/

37. PV Magazine 9^th Jan 2026 https://www.ess-news.com/2026/01/09/sodium-ion-battery-cells-already-near-lithium-ion-cost-parity-set-to-get-cheaper/

38. The Conversation 21^st July 2024 https://theconversation.com/sodium-ion-batteries-are-set-to-spark-a-renewable-energy-revolution-and-australia-must-be-ready-234560

39. Undecided Tech 8^th April 2025 https://undecided.tech/why-the-biggest-battery-company-is-betting-against-lithium/

40. See https://faradion.co.uk/about-us/

41. PV Magazine 26^th Feb 2026 https://www.pv-magazine.com/2026/02/26/austrias-salzstrom-unveils-sodium-ion-storage-system-for-commercial-applications/

42. Energy Storage News 19^th Aug 2024 https://www.energy-storage.news/iron-air-multi-day-energy-storage-form-energy-first-pilot/

43. New Scientist 16^th July 2026 https://www.newscientist.com/article/mg26335002-500-how-incredibly-simple-tech-can-supercharge-the-race-to-net-zero/

44. Latitude Media 29^th Oct 2025 https://www.latitudemedia.com/news/forms-first-100-hour-batteries-are-hitting-the-grid/

45. Irish Times 5^th June 2025 https://www.irishtimes.com/environment/climate-crisis/2025/06/05/new-batteries-based-on-rusting-will-help-make-irelands-energy-secure-and-clean/

46. Energy Storage News 11^th Jan 2024 https://www.energy-storage.news/patents-for-gravity-energy-storage-who-is-filing-them-and-whats-being-protected/

47. Energy Vault https://www.energyvault.com/solutions/long-duration

48. Energy Storage News 8^th April 2024 https://www.energy-storage.news/non-lithium-energy-storage-tech-firms-torus-and-alsym-raise-combined-us145-million/

49. Mercom 16^th Sept 2025 https://mercomcapital.com/torus-secures-200m-from-magnetar-to-scale-hybrid-energy-storage/

50. Renewables Now 6^th March 2026 https://renewablesnow.com/news/flywheel-storage-start-up-qnetic-raises-usd-5m-to-launch-us-production-1290907/

51. Electrive 29^th Nov 2024 https://www.electrive.com/2024/11/29/uk-to-test-kinetic-energy-storage-system-on-motorways/

52. Guardian 1^st April 2024 https://www.theguardian.com/environment/2024/apr/01/thermal-energy-storage-industry

53. PV Magazine 28^th August 2025 https://www.pv-magazine.com/2025/08/28/worlds-largest-sand-battery-inaugurated/

54. PV Magazine 30^th Jan 2026 https://www.pv-magazine.com/2026/01/30/thestorage-launches-its-first-industrial-scale-sand-based-heat-storage-system/

55. See https://sunamp.com/

56. RWE 29^th May 2024 https://www.rwe.com/en/press/rwe-generation/2024-05-29-rwe-plans-hydrogen-ready-combined-cycle-gas-turbine-at-gersteinwerk-in-werne/

57. Breyer, C et al 100% Renewable Energy for the United Kingdom, LUT University January 2023 https://100percentrenewableuk.org/wp-content/uploads/100-RE-23-Dec-.pdf