Flow batteries

Also known as Redox flow batteries, Vanadium redox flow batteries, VRFB, Organic flow batteries

Flow batteries store energy in liquid electrolytes kept in tanks and pumped past electrochemical cells to charge and discharge. The vanadium version has reached utility scale in China, where a 100 MW / 400 MWh installation was reported as connected to the grid in 2022, but system cost, efficiency and long-term durability are still being established.

Pilot and early commercialDemonstratedReviewed 21 Oct 2026
AI illustration · Illustrative scene, not a photograph of the specific device or experiment.

In plain language

A normal battery keeps its energy inside the electrodes, so the power and the energy are tied together. A flow battery keeps its energy in two liquids stored in separate tanks. Pumps move the liquids through a stack of cells, where a chemical reaction either takes energy in (charging) or gives it back (discharging).

Because the tanks and the cell stack are separate, the size of the stack sets how much power the battery can deliver, and the size of the tanks sets how long it can run. Operators can therefore add storage time by adding more liquid, without buying more cells. Flow batteries are being considered for grid storage, where the aim is to hold surplus solar or wind power for hours and release it at peak demand.

Technical explanation

In a redox flow battery, two electrolytes contain dissolved metal ions or organic molecules that change oxidation state during charge and discharge. The electrolytes flow through an electrochemical cell in which a membrane separates the two sides. Vanadium systems use the same vanadium element in both tanks, which limits cross-contamination through the membrane. Power is set by electrode area and the number of cells in the stack; energy is set by electrolyte concentration and volume.

Laboratory work has broadened the chemistry beyond vanadium. Huskinson and colleagues (2014) reported a metal-free aqueous flow battery that paired an anthraquinone molecule with a bromine couple, reaching a peak power density above 0.6 W per square centimetre and retaining over 99% of its storage capacity per cycle. Lin and colleagues (2016) reported a redox flow battery with an alloxazine-based organic electrolyte; only the title and bibliographic record were checked for this profile, so no performance figures are given. These are laboratory results, and the published work does not show how such chemistries perform at grid scale over many years.

At utility scale, the best-documented installation in the sources reviewed is the Dalian vanadium system in China. Its first phase is rated 100 MW / 400 MWh and was reported by pv magazine as connected to the grid in September 2022. Modelling work, such as the 2024 University of Padua assessment, projects future capital cost and lifetime; these are projections, not measured results. Full-system round-trip efficiency, which includes pumping and power electronics, was not stated in the sources opened for this profile, so no efficiency figure is given here.

What the evidence says

Each statement is typed by the strength of its evidence and linked to the source that supports it.

Demonstrated Shown in a published experiment, test or shipping product.

A metal-free aqueous flow battery using an anthraquinone molecule and a bromine couple reached a peak power density above 0.6 W per square centimetre and retained over 99% of its storage capacity per cycle in laboratory tests.

Sources: [1] · Abstract

Reported, unverified Stated by a company or team but not independently confirmed.

Lin and colleagues report a redox flow battery with an alloxazine-based organic electrolyte. Performance figures from this paper were not checked for this profile.

Sources: [2] · Title and bibliographic record (Crossref) · low confidence

The first phase of the Dalian vanadium flow battery station, rated 100 MW / 400 MWh, was reported in September 2022 as connected to the grid, providing peak shaving and valley filling for local solar and wind output.

Sources: [3] · Article body · medium confidence

The first phase of the Dalian station cost about 1.9 billion yuan, and the second phase would take the total rating to 200 MW / 800 MWh.

Sources: [3] · Article body · medium confidence

Vanadium flow batteries have lower energy density than lithium-ion batteries, and high upfront cost holds back their uptake.

Sources: [6] · Article body · medium confidence

Proposed A design or plan that has not yet been built or tested.

As reported by ESS News, a 2024 University of Padua techno-economic model estimates that vanadium flow battery capital costs could fall to 260 euros per kWh for a 10-hour system, assuming a 20-year life with one cycle per day.

Sources: [6], [4] · ESS News article body; Applied Energy paper not opened · medium confidence

The US Department of Energy's long-duration storage analysis expects the 2030 levelised cost of eleven storage technologies to exceed the 0.05 dollars per kWh target, but says the most cost-effective innovations could bring pumped hydro, compressed air and flow batteries below that level by 2030, with an average potential cost reduction of 66% for flow batteries.

Sources: [5] · Article body · medium confidence

Limitations and open problems

  • Energy density is lower than that of lithium-ion batteries (ESS News, 2024, summarising the Padua study).
  • Upfront capital cost is high, and sources note it as a main reason for slow uptake; the sources reviewed do not give a verified current installed cost in dollars per kilowatt-hour.
  • The Padua cost figure of 260 euros per kWh is a breakeven projection, not a current price. It assumes a 20-year life with one cycle per day, as reported by ESS News (2024); the paper itself was not opened.
  • Published lab results for the metal-free and alloxazine chemistries come from laboratory cells, and the sources reviewed do not show multi-year operation at grid scale.
  • Full-system round-trip efficiency is not verified in the sources reviewed here, so any figure quoted elsewhere should be checked against a stated system definition.
  • The US Department of Energy analysis of long-duration storage cost assumes no marginal increase in industry investment beyond currently planned levels (Utility Dive, 2024). The DOE report itself could not be read for this profile.

Possible future uses

Speculative

Ideas, not predictions. None of these has been demonstrated.

  • Multi-day storage paired with solar or wind farms in regions that have long periods with little renewable output.
  • Organic flow batteries built from abundant carbon-based materials, if stability and cost are shown in long-term tests.
  • Storage at industrial sites or remote grids where the tanks can be sited on land that is not used for other purposes.

Timeline

  1. 2014Huskinson and colleagues report a metal-free aqueous flow battery using an anthraquinone molecule and a bromine couple in Nature. Sources: [1]
  2. 18 Jul 2016Lin and colleagues publish a redox flow battery using an alloxazine-based organic electrolyte in Nature Energy. Sources: [2]
  3. Sept 2021The US Department of Energy's Long Duration Storage Shot sets a goal of cutting the cost of 10-hour-plus storage by 90% from the 2020 lithium-ion baseline. Sources: [5]
  4. 29 Sept 2022pv magazine reports the first phase of the Dalian vanadium flow battery station (100 MW / 400 MWh) as connected to the grid, for peak shaving and valley filling. Sources: [3]
  5. 2024Poli and colleagues publish a techno-economic assessment of future vanadium flow batteries in Applied Energy. ESS News reports a projected breakeven capital cost of 260 euros per kWh at 10 hours. Sources: [4], [6]
  6. 13 Aug 2024A US Department of Energy report on long-duration storage costs, as covered by Utility Dive, states that the most cost-effective innovations could bring flow battery levelised cost below the 0.05 dollars per kWh target by 2030. Sources: [5]

Futures this could help bring about

AI illustration
How far away?

Cheap multi-day energy storage for renewables

Pilots · 2 of 7 steps done

Glossary

Redox flow battery
A battery in which energy is stored in liquid electrolytes held in external tanks and converted to electricity in a separate cell stack.
Electrolyte
The liquid that carries electric charge between the electrodes; in a flow battery it also stores the energy.
Round-trip efficiency
The share of electricity put into storage that can be recovered later, after losses from conversion, pumping and storage.
Levelised cost of storage
The cost of each kilowatt-hour delivered over a storage asset's life, including capital, operating and charging costs, divided by the energy it delivers.

Sources

  1. peer reviewed paper
    A metal-free organic-inorganic aqueous flow battery
    Brian Huskinson, Michael P. Marshak, Changwon Suh et al.. Nature, 2014. DOI: 10.1038/nature12909. Accessed 21 Oct 2026.
  2. peer reviewed paper
    A redox-flow battery with an alloxazine-based organic electrolyte
    Kaixiang Lin, Rafael Gómez-Bombarelli, Eugene S. Beh et al.. Nature Energy, 18 Jul 2016. DOI: 10.1038/nenergy.2016.102. Accessed 21 Oct 2026.
  3. news
    China connects world's largest redox flow battery system to grid
    Beatriz Santos. pv magazine, 29 Sept 2022. Accessed 21 Oct 2026.
  4. peer reviewed paper
    Techno-economic assessment of future vanadium flow batteries based on real device/market parameters
    Nicola Poli, Cinzia Bonaldo, Michele Moretto et al.. Applied Energy, 2024. DOI: 10.1016/j.apenergy.2024.122954. Accessed 21 Oct 2026.
  5. news
    Further innovation required to achieve $0.05/kWh target for long-duration storage: DOE
    Brian Martucci. Utility Dive, 13 Aug 2024. Accessed 21 Oct 2026.
  6. news
    Evaluating the profitability of vanadium flow batteries
    Marija Maisch. ESS News, 1 May 2024. Accessed 21 Oct 2026.

Revision history

3 changes since this profile was created.

Changes on 21 Oct 2026
Published on owner instruction (content loop iteration 59)0949756
Sources and claims re-checked against originalsfbb434c
Initial profile drafted from primary sources7e66249