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Long-Duration Storage

Long-duration storage is a small, competitive set of non-lithium-ion technologies. The confirmed participants are ESS Tech, Eos Energy Enterprises and Energy Vault, with TETRA Technologies supplying electrolyte to Eos. The recent evidence is mixed. Eos has drawn $87 million under a U.S. Department of Energy loan to fund a second production line, and Energy Vault has received development approval for a 125 MW / 1 GWh project in New South Wales. Against that, the filings show heavy dependence on financing, tariff and sourcing exposure, and policy uncertainty. Customer concentration cannot be quantified because no major customers are on record, and ESS Tech and TETRA have no activity data for the last 90 days.

Active institutional funds added a net $384.4 million in Q2 2026, versus $279.3 million in Q1 2026. 100% of companies in this sub-theme saw increased active positions in Q2 2026.

Overview

Long-duration storage covers systems built to discharge over multiple hours to multiple days, including flow batteries, compressed air, thermal and gravity designs. Conventional short-duration lithium-ion projects are excluded. Within the confirmed set, ESS Tech develops iron flow batteries, and Honeywell is a joint development partner that also licenses patents to ESS Tech through its affiliate UOP LLC, which is itself a customer. SoftBank, through its affiliate SBE, is a related-party investor and joint development partner of ESS Tech. Eos Energy sells a long-duration storage cube, the Z3, whose electrolyte is supplied by TETRA Technologies as preferred strategic supplier under an agreement signed in January 2024. Energy Vault sells battery energy storage systems, including B-VAULT products. The three system makers name one another as competitors in the non-lithium-ion and longer-duration segments. Lockheed Martin also competes through its GridStar Flow product. At the boundary with short-duration storage, the group faces lithium-ion incumbents including Tesla, Samsung, BYD and Fluence. ESS Tech also names Fluence and Stem as competitors in dispatch and optimization software. The sub-theme is capital-intensive and manufacturing-led, and its economics depend on tax incentives, trade policy and government-linked financing.

Investment Thesis

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Bottleneck Tracker

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Key Companies

Related Events

SectorForm Energy and Antora Raise $1.3B for Long-Duration StorageAug 12, 2026

Long-duration energy storage has historically been the missing link between renewable generation and reliable baseload power; this scale of capital injection signals the sector is moving from demonstration to commercial deployment. Iron-air and thermal storage directly threaten the incumbent role of natural gas peaker plants, which are dispatched precisely during the multi-hour gaps these batteries target. Grid operators and utilities planning capacity additions will face a new cost-competitive alternative to gas peakers, reshaping procurement decisions for years. Renewable energy developers gain a credible storage partner that extends the economic window of solar and wind assets, improving project IRRs. Incumbent battery chemistries like lithium-ion face competition in the long-duration segment where they are cost-disadvantaged at multi-day timescales.