Long-duration energy storage: get on with it Contents

Chapter 1: Introduction

1.To reach the UK’s Net Zero targets, the energy system must be transformed. This involves substantial electrification—where fossil fuel use in transportation, heating and industry is replaced by electricity—in parallel with expansion and decarbonisation of the electricity supply—replacing fossil-fuelled electricity generation with low-carbon alternatives. Renewable energy, predominantly from wind and solar, is expected to play the main role in the UK.

2.Renewable energy from wind and solar will deliver a variable supply of electricity due to changes in the weather. Electrification of heating and transport means that demand for electricity will be larger and also more variable over time. Climate change and its effects on weather will also impact both renewable supply and energy demand. The electricity system will need to be substantially expanded and made more resilient to ensure that it can deliver a secure power supply whatever the load demands or weather systems it is experiencing.

3.Energy storage technologies allow energy generated by renewables to be stored over time and used when it is required and therefore are increasingly viewed as essential for Net Zero. Energy storage facilities across different durations can be used to fulfil different roles on the grid, from minute-to-minute control of the frequency and voltage of the electricity supply, through to helping to balance variations in supply and demand over hours, days, weeks or even years.

4.The Climate Change Committee (CCC) concluded that storage will play a key role in decarbonising the electricity system cheaply and effectively by the Government’s 2035 target.4 The Royal Society estimated that a substantial volume of long-duration storage, enough to supply approximately a third of current annual UK electricity generation, could ultimately be needed.5 They found that long-duration storage is particularly important to address supply shortfalls from renewables due to infrequent but extended periods of low wind and little sunlight in winter.

5.The Government is responding to these requirements with changes to some of the key institutions responsible for planning, operating and regulating the energy system. The Department for Business, Energy and Industrial Strategy was split into new departments, including the Department for Energy Security and Net Zero (DESNZ), in February 2023.6 The National Grid was previously split into the National Grid Electricity Transmission owners, who own the cables and substations, and the Electricity System Operator (ESO), which takes responsibility for balancing supply and demand on the grid.7 With the introduction of the Energy Act 2023, the Electricity System Operator will become an independent body, the Future System Operator (FSO), which will take responsibility for planning the future electricity and energy systems, as well as operating them day to day.8 The FSO is expected to be fully set up in 2024. In addition to this, Ofgem, the energy regulator, now has a specific mandate to support the Government reaching Net Zero by 2050.9

6.Definitions of long-duration energy storage vary—in this report we use “medium-duration energy storage” to refer to technologies best suited to storing energy between 4 and 24 hours, up to a few days at most, while “long-duration energy storage” applies to technologies that store energy across periods of multiple days, to weeks, months or even years. This report will discuss the need for medium- and long-duration energy storage and the technologies that could provide it. It will discuss existing and proposed Government policies in support of long-duration energy storage in the UK and the wider changes in the energy system required to facilitate its deployment.

7.Chapter 2 sets out the scale of long-duration energy storage needed and the benefits it can provide to the grid. Chapter 3 discusses different technologies that can provide long-duration energy storage and makes policy recommendations to support their development. Chapter 4 sets out the broader context for deploying storage in the UK energy system and makes recommendations for how it should be reformed to allow long-duration energy storage to scale up.

8.We are grateful to all who provided their views in oral or written evidence and to Professor Keith Bell, who acted as Specialist Adviser to the committee.

4 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]

5 There is a range of different estimates for the amount of long-duration energy storage needed. See box 3 for a discussion of this. The Royal Society estimated 100 terawatt-hours (TWh) of storage would be needed. See Royal Society, Large Scale electricity storage (September 2023), box 1: https://royalsociety.org/-/media/policy/projects/large-scale-electricity-storage/Large-scale-electricity-storage-report.pdf [accessed 10 January 2024] and Department for Business, Energy and Industrial Strategy, ‘Plans unveiled to decarbonise UK power system by 2035’ (7 October 2021): https://www.gov.uk/government/news/plans-unveiled-to-decarbonise-uk-power-system-by-2035 [accessed 10 January 2024]

6 House of Lords Library, King’s Speech 2023: Energy security and net zero (1 November 2023): https://lordslibrary.parliament.uk/kings-speech-2023-energy-security-and-net-zero/ [accessed 10 January 2024]

7 ESO, ‘What we do’: https://www.nationalgrideso.com/what-we-do [accessed 10 January 2024] The electricity transmission network’s wires and substations are owned and maintained by SSEN Transmission in the North of Scotland, SP Transmission in the South of Scotland and National Grid Electricity Transmission (NGET) in England and Wales. The electricity system in Great Britain is operated by the Electricity System Operator, which was split away from NGET in 2020.

8 In January 2024, it was announced that the Future System Operator will be called the National Energy System Operator (NESO). For the purposes of this report, we will refer to it as the Future System Operator as this was the name in use when our evidence was gathered. Department for Business, Energy and Industrial Strategy and Department for Energy Security and Net Zero, ‘Energy Security Bill factsheet: Future System Operator’ (1 September 2023): https://www.gov.uk/government/publications/energy-security-bill-factsheets/energy-security-bill-factsheet-future-system-operator [accessed 10 January 2024] and ESO, ‘ESO announces the name of the forthcoming Future System Operator’ (22 January 2024): https://www.nationalgrideso.com/news/eso-announces-name-forthcoming-future-system-operator [accessed 10 January 2024]

9 Ofgem: ‘Ofgem welcomes Energy Act getting Royal Assent’ (26 October 2023): https://www.ofgem.gov.uk/publications/ofgem-welcomes-energy-act-getting-royal-assent [accessed 10 January 2024]

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