How far are we from cheap multi-day energy storage for renewables?
Storage that can discharge for 10 hours or more is at the pilot stage. In 2024 Great River Energy and Form Energy began construction of an iron-air battery project in Cambridge, Minnesota, rated for up to 100 hours of discharge, and the US Department of Energy announced funding for non-lithium systems of 10 hours or more. The sources reviewed do not show multi-day storage working at grid scale or at a published cost that can be compared with other ways of balancing renewables.
Close. Early pilots are running in the real world.
Pilot stage. A 1.5 MW iron-air system rated for up to 100 hours of discharge was announced in 2024 with construction starting in Cambridge, Minnesota, and is described as the first commercial deployment of Form Energy's iron-air technology (Great River Energy, 2024). No operating record has been published in the sources reviewed, and no source shows multi-day storage deployed across a grid at scale or at a measured cost per kilowatt-hour.
The tech tree
Everything recorded on Vrulum that this future needs, oldest foundations at the top and the goal at the bottom. Lines show what each step requires.
- 2014Flow batteriesPilot and early commercial Unlocked.
- 2016Solid-state batteriesResearch and prototypesRequires: Lithium-ion batteries. Being researched.
- 2017Sodium-ion batteriesPilot and early commercialRequires: Lithium-ion batteries. Unlocked.
- 2023Electrolysers for low-carbon hydrogenPilot and early commercial Unlocked.
- 2023Iron-air batteriesResearch and prototypes Being researched.
- 2024US funding notice for non-lithium systems of 10 hours or moreDone Unlocked.
- 2024Iron-air multi-day storage project broke groundDone Unlocked.
- Date not recordedMulti-day system operating at a utility siteIn progress Being researched.
- Date not recordedPublished multi-year performance studyNot started Locked.
- Date not recordedMeasured efficiency and cost at multi-day durationNot started Locked.
- Date not recordedMulti-day storage in utility plans and market rulesNot started Locked.
- Date not recordedWidespread use on power gridsNot started Locked.
- GoalCheap multi-day energy storage for renewablesGoalRequires: Iron-air batteries, Sodium-ion batteries, Solid-state batteries, Electrolysers for low-carbon hydrogen, Flow batteries, US funding notice for non-lithium systems of 10 hours or more, Iron-air multi-day storage project broke ground, Multi-day system operating at a utility site, Published multi-year performance study, Measured efficiency and cost at multi-day duration, Multi-day storage in utility plans and market rules, Widespread use on power grids. Locked.
The road so far
2 of 7 steps done, 1 in progress.
- Done · 2 Jul 2024US funding notice for non-lithium systems of 10 hours or more
The US Department of Energy's Office of Clean Energy Demonstrations announced up to $100 million for non-lithium pilot projects with at least 10 hours of discharge, with $5 million to $20 million per project and 3 to 15 projects planned. [1]
- Done · 15 Aug 2024Iron-air multi-day storage project broke ground
Great River Energy and Form Energy announced the start of construction on a 1.5 MW iron-air battery project in Cambridge, Minnesota. The battery is rated to store energy for up to 100 hours. [2]
- In progressMulti-day system operating at a utility site
Construction began in 2024 and the project was expected to be operational by late 2025. No published operating or performance data from the site was found in the sources reviewed. [2]
- Not startedPublished multi-year performance study
Great River Energy plans a multi-year study of the system's performance and of its potential for wider use after completion. No results have been published in the sources reviewed.
- Not startedMeasured efficiency and cost at multi-day duration
No published round-trip efficiency or installed cost per unit of energy at 36 hours or more from an operating project was found in the sources reviewed.
- Not startedMulti-day storage in utility plans and market rules
Multi-day storage would need to be valued in utility resource plans and capacity or energy markets to be bought at scale.
- Not startedWidespread use on power grids
No source reviewed shows multi-day storage used across power grids. Reaching this step would need many projects with published costs and performance records.
Why it matters
Wind and solar output varies across days and seasons as well as across each day. Storage that can discharge for several days could reduce the need for backup power plants and oversized generation, but only if its cost per unit of stored energy falls far enough for utilities to buy it in volume.
What stands in the way
- No multi-day system with published operating data was found in the sources reviewed.
- No published round-trip efficiency or installed cost per unit of stored energy at 36 hours or more was found in the sources reviewed.
- The DOE pilot funding announced in 2024 was planned for 3 to 15 projects of $5 million to $20 million each.
Signals to watch
- Published operating data, including round-trip efficiency and availability, from the Cambridge, Minnesota project.
- Named project awards under the US Department of Energy's 10-hour-plus pilot funding, with stated durations and costs.
- Utility procurements or resource plans that include storage rated for 36 hours or more.
- Published installed costs per kilowatt-hour for systems rated 36 hours or more, from operating projects rather than models.
- Results from the multi-year performance study that Great River Energy plans after its system is completed.
Sources
- government report
OCED Issues Notice of Intent for up to $100 Million for Non-Lithium Long-Duration Energy Storage Pilot Projects
US Department of Energy, Office of Clean Energy Demonstrations, 2 Jul 2024. - company announcement
Great River Energy, Form Energy break ground on first-of-its-kind multi-day energy storage project
Great River Energy, 15 Aug 2024.
Last reviewed 21 Oct 2026.