Smart Grid Battery: Redox Flow Battery

Redox Flow Battery

In the redox flow battery, two electrolytes are pumped through a flow reactor

This article is about the Redox Flow Battery

In the Redox Flow Battery, two electrolytes are pumped through a flow reactor. The redox-active ions are oxidized in the reactor or reduced in the vicinity of the electrodes.

The membrane allows the non-redox-active ions (such as H+ and NA+) to go to the other side of the membrane in order to maintain the electrolyte balance, and electrical neutrality.

Redox Flow Battery

The most well known electrolyte combinations are Zn / Br (1,85V) and full vanadium (1,26V).

The advantage of a vanadium redox flow with two electrolytes is that the crossing of vanadium ions through the membrane is less harmful to the life span.


Despite their higher efficiency of 65-75%, vanadium batteries are still more expensive than Zn / Br batteries achieving a 60% efficiency: based on a 250MWh / 50MW system vanadium cost $ 620-740 / kWh and Zn / Br $ 290-350 / kWh (Montoya, et al., 2014).

Increasing capacity

Another advantage of redox flow batteries is that power and capacity are disconnected. By replacing the electrolyte tank, the capacity can be easily increased, and by changing the reactor design (more cells, bipolar electrode), the power can be increased.

The disadvantage is that the system pumps, sensors, reservoirs and need management and that redox flow batteries have low energy densities. Recent research, however, claims to have increased its capacity by 70% thus can be greatly reduced (Pacific Northwest National Laboratory, 2014)


Redox Flow Battery

The system at ‘Yokohama Works’ – is using the world’s largest vanadium redox flow battery and Japan’s largest concentrated photovoltaic (CPV) units

1. Japan

The Pacific Northwest National Laboratory expects a reduction of the price of vanadium redox flow batteries from $ 0.15 / kWh in 2015 to $ 0.10 / kWh in 2020.

The calculations are based on a lifetime of the battery (> 5000 cycles)

Redox Flow Battery

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2. Germany

At Gildemeister Energy Solutions the Cellcube FB10-40 (10kW / 40Kwh) is described in a brochure which concludes € 2,400 / kWh, excluding maintenance.

(This price is calculated subtracting the costs of the PV system, starting from $ 600 / kWp PV panels)

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Redox Flow Battery

Value of a Vanadium Redox Flow Battery for Frequency Regulation in Texas

3. Prices drop

April, 2014, Clean Technica has calculated $ 750-1000 / kWh for 1-4 MWh and $ 500-750 / kWh for more than 5MWh.

(The costs of electrolyte and the electrolyte tanks are 30% of the total costs. So prices can drop significantly with a larger capacity)

Value of a Vanadium Redox Flow Battery for Frequency Regulation in Texas


4. Redflow -/- 50% costs

Redflow, the Australian provider of energy storage flow batteries, has announced that it has decreased its zinc-bromide battery (ZBM) cost by 50% through technology improvements and a stronger manufacturing relationship with Flextronics. The company is now able to offer its naked ZBM product at a cost of US$20c per kWh throughput, down from US$48c just 6 months ago.  With this dramatic reduction, energy from Redflow’s ZBM product drops below grid price.


Redox Flow Battery

Vish Viswanathan calculated the costs of redox flow batteries in which the demand for vanadium will be 6 times the current price

5. Vish Viswanathan

Vishwanathan et al have been contacted producers and have got estimations for a scenario in which the demand for vanadium will be six times the current demand, up to 600MWh.

They calculated a current price of $ 500 / kWh and an estimated price of $ 300 / kWh for a 1MW / 4MWh system with 15000 cycles.

Organic Redox Flow battery may revolutionize energy storage. Until now, flow batteries have relied on chemicals that are expensive or difficult to maintain, driving up the energy storage costs.


Redox Flow Battery

Trent M. Molter, President and CEO of Sustainable Innovations, LLC, provides expertise on implementing the Harvard team’s technology into commercial electrochemical systems.

6. Harvard USA develops metal free flow battery

Under the OPEN 2012 program, the Harvard team received funding to develop this innovative grid-scale battery.

This organic battery is metal free and relies on the electrochemistry of naturally abundant:

  • inexpensive
  • small organic (carbon-based) molecules called quinones
  • which are similar to molecules that store energy in plants and animals.

The active components of electrolytes in most flow batteries have been metals. Vanadium is used in the most commercially advanced flow battery technology now in development, but its cost sets a rather high floor on the cost per kilowatt-hour at any scale. Other flow batteries contain precious metal electrocatalysts such as the platinum used in fuel cells.

The new flow battery developed by the Harvard team already performs as well as vanadium flow batteries, with chemicals that are significantly less expensive, and with no precious metal electrocatalyst.

Quinones are abundant in crude oil as well as in green plants. The molecule that the Harvard team used in its first quinone-based flow battery is almost identical to one found in rhubarb. The quinones are dissolved in water, which prevents them from catching fire.

Trent M. Molter, President and CEO of Sustainable Innovations, LLC, provides expertise on implementing the Harvard team’s technology into commercial electrochemical systems.

Overview Redox-Flow Companies and StartUps


One of a few companies on this list producing redox-flow batteries, EnerVault’s long-duration batteries are based around iron-chromium redox-flow batteries. Naturally, being redox-flow technology, it is targeted at grid and commercial/industrial applications, not electric vehicles.

Imery Power Systems

Imergy Power Systems is another vanadium redox flow battery company. Its offering is for stationary storage applications all the way down to the residential level. It has landed a few notable deals lately, including with the US Navy.


Redflow, the Australian provider of energy storage flow batteries, provides a range of batteries. From the small Zinc Bromide 8 kWH to a container battery – the LSB (Large Scale Battery). This LSB is suitable for commercial and utility applicationsof 600–800Vdc.

Why? Because it provides high energy density up to 660kWh for a single LSB, multiple containers can be interfaced for larger projects and it is a plug and play DC solution

Primus Power

Primus is installing zinc-bromine flow batteries with a single tank and no flimsy membrane separator for a system that provides “duration without degradation.”

Backed by DBL, the same VCs behind SolarCity and Tesla, Primus Power has signed up a couple utilities, Puget Sound Energy and Modesto Irrigation District, and a Department of Defense microgrid in San Diego. For utility-scale or commercial/industrial behind-the-meter storage, its modular systems claim a cycle life beyond 20,000 cycles, have been tested by Sandia National Labs, and will soon be testing with PG&E.


Younicos combines lithium-ion batteries with sodium-sulfur batteries and vanadium redox flow batteries in order to create something akin to a super battery.

But its biggest competitive advantage is reportedly the software that optimizes these batteries for the best performance and greatly extended lifespan in grid storage applications.

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