How do batteries and pumped storage hydro compare as electricity storage technologies for renewable-intensive systems like the UK's?

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Summary

Batteries (primarily lithium-ion) and pumped storage hydropower (PSH) are the two dominant grid-scale electricity storage technologies relevant to the UK's transition to a renewable-intensive power system. They are not straightforwardly competitive: they excel at different timescales, serve partially different grid functions, and face different cost trajectories, geographic constraints, and planning horizons. A research programme on this question must address technical performance, economics, UK-specific deployment context, grid system needs, and the complementarity or substitutability of the two technologies in a net-zero electricity system.

This page sets out the research strategy. Sub-pages will be created for each major research area and linked below as they are completed.

Research tree

Research strategy

Framing the question

The question is not "which is better?" but rather: given the UK's specific grid characteristics, geography, and net-zero trajectory, how do the two technologies compare in terms of the functions they can perform, at what cost, and at what scale?

Key framing decisions:

  1. Duration is the organising variable. Batteries and PSH are not head-to-head competitors across all use cases. Lithium-ion batteries are currently cost-competitive for short-duration storage (roughly 1–4 hours). PSH is the established technology for longer-duration storage (4–12+ hours). As the grid becomes more renewable-intensive, longer-duration storage needs grow. This is where the two technologies most directly interact.
  2. The UK has specific geographic constraints. PSH requires suitable topography (large elevation differences, available water, proximity to grid). The UK's existing PSH fleet (Dinorwig 1.7 GW, Ffestiniog 360 MW, Cruachan 440 MW, Foyers 300 MW) is concentrated in Wales and Scotland. New sites are limited. Battery storage has no such geographic constraint and can be deployed anywhere with grid connection.
  3. Costs are moving in opposite directions. Lithium-ion battery costs have fallen ~90% since 2010 and are projected to continue falling. PSH is capital-intensive with costs that have not fallen significantly. The crossover point for different duration brackets is a key research question.
  4. The two technologies provide partially different grid services. PSH with large rotating machinery provides synchronous inertia and black-start capability that batteries (as inverter-based resources) do not inherently provide. This is increasingly relevant as fossil generators retire.

Sub-question 1: Technical characteristics

Goal: Establish the basic technical envelope of each technology — what it can and cannot do — before attempting economic or policy comparison.

Key parameters to establish for each technology:

  • Round-trip efficiency (AC-to-AC)
  • Typical discharge duration range
  • Response time (ms to minutes)
  • Cycle life and degradation
  • Power-to-energy ratio flexibility
  • Parasitic losses (self-discharge)
  • Scalability (minimum and maximum practical size)
  • Black-start and inertia provision

Primary sources:

  • IEA, Electricity Storage and Renewables: Costs and Markets to 2030 (2017, with updates)
  • IRENA, Electricity Storage Valuation Framework (2020)
  • Lazard, Levelised Cost of Storage (annual, most recent version)
  • NESO (formerly ESO), Electricity Ten Year Statement (ETYS) — technical parameters
  • BEIS/DESNZ, Electricity Generation Cost Report
  • Staffell et al., "The role of hydrogen and fuel cells in the global energy system," Energy & Environmental Science (2019) — for context on storage comparisons

Completed page: Batteries vs PSH: Technical comparison

Sub-question 2: Economics and cost trajectories

Goal: Establish current costs (capital, operational, levelised) and projected cost trajectories for each technology, across relevant discharge durations.

Key parameters:

  • Capital cost: £/kW (power capacity) and £/kWh (energy capacity), separately — important because PSH is often cheap per kWh but expensive per kW
  • Levelised Cost of Storage (LCOS) — accounts for efficiency losses, cycle life, discount rate
  • Operation and maintenance costs
  • Cost of grid connection and grid reinforcement
  • Projected cost in 2030, 2035, 2050

Key comparison point: at what discharge duration does PSH become cost-competitive with or cheaper than batteries? At what battery cost does it make sense to add short duration batteries and use them "in series" to simulate longer duration storage? What is the optionality value of being able to use short duration batteries either in parallel to cover peaks, or in series to cover longer durations?

Primary sources:

  • Lazard LCOS (annual) — widely cited industry benchmark
  • BloombergNEF, Energy Storage Outlook (annual)
  • Aurora Energy Research, UK storage market reports
  • AFRY/Pöyry (now AFRY), UK storage valuations for BEIS
  • NESO Future Energy Scenarios — storage cost assumptions
  • Schmidt et al., "Projecting the future levelized cost of electricity storage technologies," Joule (2019)
  • Cole & Frazier, Cost Projections for Utility-Scale Battery Storage: 2023 Update, NREL

Completed page: Batteries vs PSH: Economics and costs

Sub-question 3: What storage durations does the UK grid need?

Goal: Establish what the UK's renewable-intensive grid actually requires in terms of storage duration and capacity — this determines which technology (or mix) is fit for purpose.

The UK's grid is moving towards high shares of wind (offshore and onshore) and solar. Key storage needs arise from:

  • Diurnal cycling (day/night solar): met by 2–4 hour batteries
  • Weather-driven variability (multi-day wind droughts, "dunkelflaute"): requires days-to-weeks of storage — beyond current battery economics
  • Seasonal balancing: requires very long-duration storage (weeks to months) — neither batteries nor PSH currently cover this economically
  • Frequency/inertia services (sub-second to seconds): batteries excel here
  • Capacity adequacy (peak demand periods): both technologies contribute

The duration question is the central one for the batteries-vs-PSH comparison. Research should identify:

  • How many hours of storage does NESO's modelling suggest the UK needs in a 2035 clean grid / 2050 net-zero grid?
  • What share of this is short-duration (batteries' territory) vs medium-duration (PSH's territory)?
  • What does NESO's Holistic Transition Pathways or Future Energy Scenarios say?

Primary sources:

  • NESO, Future Energy Scenarios (2024, 2025)
  • NESO, Electricity Ten Year Statement
  • NESO, Constraint Management Roadmap / Path to 2035
  • Element Energy / Imperial College, The Value of Flexibility (BEIS-commissioned studies)
  • Sepulveda et al., "The role of firm low-carbon electricity resources in deep decarbonization of power generation," Joule (2018) — on the value of long-duration storage
  • Dowling et al., "Role of long-duration energy storage in variable renewable electricity systems," Joule (2020)

Planned page: Batteries vs PSH: Storage duration and UK grid needs

Sub-question 4: UK deployment — PSH

Goal: Establish what PSH capacity exists in the UK, what is planned, and what the realistic constraints on new development are.

Existing UK PSH capacity:

  • Dinorwig (1,728 MW, 9 GWh): Snowdonia; the UK's largest; operational since 1984; owned by First Hydro
  • Ffestiniog (360 MW, ~1.3 GWh): Snowdonia; operational since 1963
  • Cruachan (440 MW, 7.1 GWh): Scottish Highlands; currently being expanded to 600 MW by Drax
  • Foyers (300 MW): Loch Ness; owned by SSE

Pipeline projects:

  • Coire Glas (SSE Renewables, 1,500 MW / 30 GWh): Upper Loch Ness; consented 2024; would be the UK's largest; £1.5bn estimated cost; not yet under construction
  • Red John (Statera Energy, 450 MW): Loch Ness; consented
  • Glyn Rhonwy (Snowdonia Pumped Hydro, 99 MW): Wales; consented; slower progress
  • Balmellie and other proposed sites in Scotland

Key constraints on new PSH in the UK:

  • Topographic suitability: limited sites outside Scotland and Wales
  • Planning: long lead times, environmental impact on landscapes and water
  • Capital intensity: PSH requires large upfront investment with uncertain revenue streams
  • Revenue uncertainty: UK capacity market and ancillary services revenues do not currently provide clear long-term investment signals for 8–12 hour storage

Primary sources:

  • SSE Renewables Coire Glas project documentation
  • Drax Cruachan expansion updates
  • British Hydropower Association submissions to BEIS/DESNZ consultations
  • Regen / Energy Networks Association, UK long-duration storage reports
  • DESNZ, Review of Electricity Market Arrangements (REMA) consultations — relevance to PSH revenue stacking

Planned page: UK pumped storage hydro: current and planned capacity

Sub-question 5: UK deployment — batteries

Goal: Establish current UK battery storage capacity, the project pipeline, and the economics of deployment.

Key facts to establish:

  • Current installed GB battery capacity (MW / MWh) — around 5 GW as of early 2026, growing rapidly
  • Breakdown by duration (1-hour, 2-hour, 4-hour systems)
  • Revenue streams: Balancing Mechanism, Dynamic Containment, STOR, capacity market, wholesale arbitrage
  • Co-location economics (batteries co-located with solar or wind farms)
  • Key projects: Minety (800 MW, Wiltshire), Cottingham, Gore Street, etc.
  • Forward pipeline: planning consents, grid connection queue

Primary sources:

  • NESO Balancing Mechanism reports
  • Ofgem capacity market quarterly reports
  • Cornwall Insight UK battery storage market tracker
  • Solar Media / Energy Monitor battery pipeline data
  • BEIS Energy Trends (storage chapter)
  • Modo Energy, UK Battery Storage Market Reports (monthly)

Planned page: UK battery storage: current and planned capacity

Sub-question 6: Grid services comparison

Goal: Compare the two technologies across the full range of grid services they can provide, with particular attention to services that only one technology can provide.

Key services to compare:

  • Frequency response (Dynamic Containment, Dynamic Moderation, Dynamic Regulation): batteries excel — sub-second response
  • Synchronous inertia: PSH's rotating machinery provides this natively; batteries do not (they can provide synthetic inertia but this is not equivalent)
  • Black-start capability: PSH can provide this; batteries are less established
  • Capacity adequacy (T-1, T-4 capacity market): both qualify
  • Longer-duration shifting (overnight wind charge, evening peak discharge): PSH advantage at longer durations
  • Reactive power / voltage support: both can provide

The inertia question is increasingly important as coal and gas retire. The UK grid is running at historically low inertia levels. PSH provides a grid stabilisation service that batteries cannot fully replicate.

Primary sources:

  • NESO, System Operability Framework (annual)
  • NESO, Inertia and Rate of Change of Frequency (RoCoF) requirements (technical papers)
  • National Grid ESO, Stability Pathfinder procurement — shows what grid services are valued and at what price
  • Ofgem, Review of GB Energy System Operation
  • Miller et al., "Invited Review Article: Flywheels in hybrid energy storage systems," and related inertia literature

Planned page: Batteries vs PSH: Grid services comparison

Sub-question 7: Environmental comparison

Goal: Compare the environmental footprint of each technology across the full lifecycle.

Key dimensions:

  • Materials: lithium-ion batteries require lithium, cobalt, nickel, manganese; PSH requires civil engineering materials (concrete, steel) but no rare materials
  • Carbon footprint per kWh stored (lifecycle)
  • Land use
  • Water use and impacts on local hydrology (PSH reservoir construction)
  • End-of-life: battery recycling challenge vs PSH longevity (50–100 year asset life)
  • Supply chain risks: battery materials are subject to geopolitical concentration (DRC cobalt, Chinese lithium processing)

Primary sources:

  • IEA, The Role of Critical Minerals in Clean Energy Transitions (2021, updated)
  • Peters et al., "The environmental impact of Li-ion batteries and the role of key parameters," Renewable and Sustainable Energy Reviews (2021)
  • European Commission JRC, lifecycle assessment studies on storage technologies
  • Benchmark Mineral Intelligence on battery materials supply chains

Planned page: Batteries vs PSH: Environmental and land-use comparison

Sub-question 8: Policy and investment framework

Goal: Establish how UK policy and regulation currently treats storage, and what reforms are under discussion that could affect the relative economics of each technology.

Key policy questions:

  • Does the UK capacity market currently provide adequate revenue certainty for long-duration storage (PSH)? (The answer is broadly: no — the T-1 auction horizon is too short for PSH investment decisions.)
  • Is there a dedicated long-duration storage support mechanism? (DESNZ has consulted on LDES — Long Duration Energy Storage — policy.)
  • What is the status of REMA (Review of Electricity Market Arrangements) and its implications for storage?
  • Planning reform: the 2023 NSIP threshold change (50 MW to 350 MW for battery storage) and its effect on the pipeline.
  • Network charging: how do storage assets pay for grid use?

Primary sources:

  • DESNZ, Long Duration Energy Storage Consultation (2021 and subsequent)
  • DESNZ, Review of Electricity Market Arrangements (REMA) consultation documents
  • Ofgem, Access and Forward-Looking Charges Review
  • House of Lords Environment and Climate Change Committee, In our hands: behaviour change for climate and nature — storage policy recommendations
  • British Hydropower Association, Pumped Storage Policy Asks
  • Regen, Powering Up Britain: Storage and Flexibility submissions

Planned page: Batteries vs PSH: Policy and regulatory framework

Recommended research sequence

  1. Technical comparison (Sub-question 1) ✓ — establish the basic factual framework before economics or policy
  2. Storage duration and UK grid needs (Sub-question 3) — this determines what the relevant comparison space is
  3. Economics (Sub-question 2) ✓ — with duration context now established, cost comparison is more meaningful
  4. UK PSH deployment (Sub-question 4) — concrete UK context for PSH
  5. UK battery deployment (Sub-question 5) — concrete UK context for batteries
  6. Grid services (Sub-question 6) — the nuanced services comparison, especially inertia
  7. Environmental (Sub-question 7) — often overlooked but increasingly salient
  8. Policy framework (Sub-question 8) — what explains current deployment patterns and what could change them

The key sources page (Batteries vs PSH: Key studies and sources) should be built up continuously throughout the research process rather than left to the end.

Key sources (initial list)

To be expanded into Batteries vs PSH: Key studies and sources.

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