Long Duration Energy Storage (LDES) Market

The global long duration energy storage (LDES) market size was USD 3.42 Billion in 2025 and is expected to register a revenue CAGR of 24.6% during the forecast period. Market revenue growth is supported by grid operators moving from pilot-scale long duration storage demonstrations to gigawatt-scale procurement backed by revenue-certain support mechanisms, most notably the UK energy regulator Ofgem's Window 1 minded-to decision of 26 June 2026, which provisionally selected 16 projects totalling approximately 7.65 gigawatts of power capacity and 136.9 gigawatt-hours of storage capacity for its long duration electricity storage cap and floor scheme, spanning pumped storage hydro, compressed air, lithium-ion, zinc battery, and flow battery technologies with discharge durations of eight to 22 hours. In the United States, the Section 48E technology-neutral investment tax credit extends standalone energy storage eligibility through at least 2032, though prohibited foreign entity of concern restrictions applying to projects beginning construction after 31 December 2025, and a material assistance cost ratio requirement starting at 55% for storage technology in 2026, are reshaping which long duration storage supply chains qualify for credit value. These regulatory demand signals are converting a project pipeline that has historically depended on venture capital and government grant funding into one increasingly backed by contracted revenue, utility procurement, and hyperscale data center offtake commitments. These are some of the key factors driving revenue growth of the market.

Flow batteries, iron-air batteries, thermal energy storage systems, advanced compressed air energy storage, and CO2 battery technology are the principal commercial technology categories constituting the long duration energy storage market, with vanadium flow batteries currently holding the largest base of grid-connected operating capacity due to China's concentrated manufacturing and deployment base. For instance, in December 2025, Rongke Power, China, completed and connected the Jimusaer Vanadium Flow Battery Energy Storage Project in Xinjiang, a 200 megawatt, 1 gigawatt-hour system paired with a 1 gigawatt photovoltaic plant, becoming the first vanadium flow battery installation to reach gigawatt-hour scale and extending Rongke Power's global operating fleet to more than 3.5 gigawatt-hours. Iron-air and thermal battery technologies remain earlier in commercial deployment, with most disclosed projects still in the tens-of-megawatt range, while utilities and hyperscale data center operators are increasingly the counterparties driving new contracted long duration storage capacity.

However, long duration energy storage technologies outside lithium-ion and pumped hydro remain commercially unproven at the scale grid operators are now procuring, creating financing and insurance underwriting challenges that slow project conversion from signed agreement to financial close. Publicly disclosed financial results illustrate the gap between procurement enthusiasm and commercial maturity: one NYSE-listed iron flow battery manufacturer reported full-year 2025 revenue of just USD 1.6 million against a net loss of USD 63.4 million and disclosed substantial doubt about its ability to continue as a going concern. Installed cost per kilowatt-hour for iron-air, thermal, and advanced compressed air systems remains two to three times higher than mature lithium-ion benchmarks, and supply chain constraints in vanadium electrolyte and specialty alloy inputs add further cost and lead-time uncertainty. These factors substantially limit long duration energy storage market growth over the forecast period.

Based on technology, the global long duration energy storage market is segmented into flow batteries, iron-air batteries, thermal energy storage, advanced compressed air energy storage, and CO2 battery systems. The flow batteries segment commands the largest revenue share because vanadium and iron flow chemistries have the longest commercial operating track record among non-lithium long duration technologies, with China's Rongke Power alone operating more than 3.5 gigawatt-hours of grid-connected vanadium flow capacity and UK-listed Invinity Energy Systems reporting a 256% year-on-year increase in 2025 revenue, other income and project grant contributions to £17.8 million as its Endurium platform scales toward utility and commercial and industrial customers across Europe, North America, and Asia.

The iron-air batteries segment is expected to register a rapid revenue growth rate in the global long duration energy storage market over the forecast period. Iron-air battery technology is designed to deliver 100 or more hours of continuous discharge at a manufacturer-disclosed target cost below USD 20 per kilowatt-hour, positioning it as the technology category best suited to multi-day and seasonal storage duration that flow batteries and lithium-ion systems cannot economically address. Utility offtake commitments, including agreements to deploy iron-air systems at multi-megawatt scale with major regulated utilities, are converting a technology that entered commercial demonstration only in the past several years into one of the fastest-scaling segments of the market, supported by continued US Department of Energy Long Duration Storage Shot cost-reduction targets for 10-plus-hour storage technologies.

• 01What is the global long duration energy storage (LDES) market size in 2025 and what CAGR is expected during 2026-2035?
• 02What UK Ofgem Window 1 minded-to decision was published in June 2026 and how much long duration storage capacity did it provisionally select for cap and floor revenue support?
• 03What gigawatt-hour-scale vanadium flow battery milestone did Rongke Power achieve with its Jimusaer project in China and what does the project's bid price imply for flow battery cost trends?
• 04What full-year 2025 financial results did NYSE-listed ESS Inc report and what going-concern risk did the company disclose?
• 05What revenue growth did UK-listed Invinity Energy Systems report for 2025 and what new sales agreements did the company sign with Ideona in Hungary?
• 06What USD 230 million financing did Hydrostor secure in August 2026 and which flagship project does it advance toward financial close?
• 07What manufacturer-disclosed target cost has Form Energy set for its 100-hour iron-air battery technology and how does this compare with current vanadium flow battery pricing?
• 08How do prohibited foreign entity of concern restrictions and the Section 48E material assistance cost ratio affect long duration storage supply chain eligibility for US tax credits from 2026?
• 09What eligibility threshold does Ofgem apply to determine which technologies qualify for the UK's long duration electricity storage cap and floor scheme, and why did most standard lithium-ion battery projects fail to qualify for Window 1?
• 10Why does the gap between disclosed commercial revenue and announced project pipeline scale matter more than headline gigawatt figures for assessing long duration energy storage market maturity in 2026?

This report covers the global long duration energy storage (LDES) market across all major segments and geographic regions. Primary research combines panel conversations with industry experts and is cross-referenced against company annual reports and government agency data. All market size figures use 2025 as the base year with a 2026-2035 forecast period.