Welcome back to this week’s Battery Business Insights article on Redox One and its plan to build long-duration storage from its parent company’s chrome. Redox One has secured the raw material; the batteries are still at demonstration stage. According to Redox One, the mining group Tharisa spun it off in 2022, and it makes the liquid that stores the energy in its iron-chromium flow batteries next to Tharisa’s mine in South Africa.
A flow battery keeps its energy in liquid electrolyte held in tanks and turns it into power in a stack, so energy and power can be sized separately. BetterE Expedition published an interview and a factory tour at Redox One on 9 September 2026. In May, Tharisa reported that the first MWh-class iron-chromium system had passed factory acceptance testing, with deployment to customers planned for mid-year (Tharisa). For a buyer, the question is when that system reaches a customer.
By the Numbers: Raw Material Secured, Batteries Still in Demonstration
- 10 MWh a year — Electrolyte the South African pilot plant can make today, with a ramp-up to about 200 MWh under way, according to Redox One (BetterE Podcast, 2026)
- 75 GWh — Electrolyte the group’s annual raw-material availability could make, an estimate according to Redox One (BetterE Podcast, 2026)
- MWh-class — Size of the first iron-chromium system to pass factory acceptance testing, according to Tharisa (Tharisa, May 2026)
- 8 to 16 hours — The chemistry’s sweet spot for storage duration, according to Redox One (BetterE Podcast, 2026)
- Seven to eight times — How much cheaper iron-chromium electrolyte is than vanadium electrolyte, according to Redox One (BetterE Podcast, 2026)
- About 70 staff — Headcount, 25 of them in Dortmund, according to Redox One (BetterE Podcast, 2026)
- About 45% — South Africa’s share of world chromite ore mining in 2025. (USGS, 2026)
- 1973 — The year NASA began the project that selected iron and chromium for flow batteries. (NASA)
Tharisa Is Owner, Supplier and First Customer at Once
Redox One is controlled by Tharisa, a platinum-group-metals and chrome producer whose mine lies on the southwestern limb of the Bushveld Complex in South Africa, the largest source of PGMs and chrome globally, according to the company. Their own descriptions of the tie differ: Tharisa’s site calls Redox One a wholly owned subsidiary, while Redox One’s site names Tharisa its majority shareholder. Either way, the battery maker’s supply and strategy run through its parent.
Cheap Electrolyte Comes at the Cost of More Space
For the BetterE Podcast, Simon Voß of BetterE Expedition visited Redox One in Dortmund. After a tour of the test hall and the lab, he talked with Gebauer and Jake Iverson, Vice President of Business Development, about why the company bets on iron and chromium, who buys first and what Europe would have to change.
The case for iron-chromium rests on price. Gebauer puts its electrolyte at roughly seven to eight times cheaper than vanadium electrolyte, an estimate for the liquid alone rather than a finished system. He concedes that the electrolyte stores less energy, so a system needs more of it for the same kilowatt-hours. The chemistry trades floor space for a cheaper electrolyte.
Duration is where the fit lies, the company says: 8 to 12, perhaps 16 hours of storage, while an off-grid mine needs roughly 8 to 10 hours to run through the night on solar power. Iverson describes the first customers as users behind the meter, starting with Tharisa and its mining affiliates on weak grids or off-grid. That parent already runs a 40 MW on-site solar plant at its mine, and only 9% of its power came from the state utility Eskom in the quarter to 30 September 2025. Redox One also wants to sell capacity or power as a service and run the batteries itself. Its first market is the parent’s own mines.
Iverson also says that 70% of the world’s chromium reserves lie in South Africa; US Geological Survey figures, set out below, give a lower share. The supply argument stands without it.
The Dortmund Lab Works on the Chemistry’s Known Weakness
Dortmund develops and tests; it does not manufacture. The city is familiar ground for Gebauer, who co-founded the vanadium flow battery company Volterion there, according to Redox One; the Boysen Group took a majority of it in 2019. In the test hall, according to the company, small batteries run around the clock beside a 20-foot container system with two tanks and four stacks, a scale-up by a factor of 10. Next to it stands electrolyte from the South African pilot plant, made from the mined ore; the company calls the 20,000 litres a rather small batch, the amount used in normal testing. That liquid is the product the group can already make.
Gebauer openly names hydrogen generation and capacity fade as major issues of iron-chromium flow batteries, and the lab tests ways to rebalance the electrolyte to slow the fade. Results then move, the company says, to larger batteries in the field, mainly in South Africa and in China; those were not shown. What remains open is not supply but how long the capacity lasts.
An Old NASA Chemistry Returns Because Vanadium Stayed Expensive
Iron-chromium is not new. NASA’s Redox project began in 1973, not in the 1960s as Redox One’s website says, and ended with a 1 kW, 13 kWh system storing solar power (NASA, 1984). A 2015 laboratory study found that iron-chromium cells lose capacity faster than all-vanadium cells but hold cost advantages at large capacities. Dortmund is working on a weakness that is decades old.
Vanadium remains the most deployed flow chemistry, yet the high cost of its electrolyte has held back wider adoption, and about 90% of vanadium goes to steel. China’s State Power Investment Corp put a megawatt-level iron-chromium plant into trial operation in February 2023, storing 6,000 kWh over six hours. The opening is real, but so is the competition.
On the survey’s own numbers, the raw-material case still holds. South Africa produced about 45% of the world’s chromite ore in 2025 but holds under 30% of reserves, 350,000 of more than 1,200,000 thousand tonnes. Kazakhstan and southern Africa together hold 95% of known resources (USGS, 2026). Concentrated supply favours whoever owns a mine.
Germany’s Ten-Hour Rule Opens a Door, but Gas Gets There First
The proof still due is a customer installation. Its production report of 14 July 2026 reported no deployment of the MWh-class system, and an August trade article still described the battery as in development. Until a system runs at a customer, the cost advantage stays on paper.
Europe’s opening is regulatory. Germany’s parliament adopted a capacity framework, the StromVKG, on 10 July 2026, with EU state-aid approval outstanding. It asks for at least ten consecutive hours at 80% of installed capacity, a duration inside iron-chromium’s range. Its first auction, on 8 September 2026, favours gas plants; battery storage may enter the more technology-neutral rounds from December 2027. Certain projects must also use main components made in the EU or a partner country. That rule makes a European electrolyte plant a commercial question.
Such a plant is the company’s most pressing need, at a site where a chemicals permit does not take three or four years and energy prices are low. Redox One also says it is about to work on a larger project with one of Germany’s or Europe’s largest power producers, which it did not name. Both are plans, not contracts.
Bottom Line
Redox One owns what most flow battery makers buy: the raw material and a working electrolyte process, at pilot scale of about 10 MWh a year. What it has not yet shown is a MWh-class battery running for a customer, or a fix for the chemistry’s capacity fade. For a storage buyer, this is a technology to pilot, not to buy at scale. For Europe, its case rests on duration rules such as Germany’s ten hours, not on daily trading. The chrome is in the ground; the megawatts are still in the test hall.
Battery Business Insights is an independent industry publication. Figures reflect the most recent data available at the publication date. Company statements, targets and estimates are stated as such and are not confirmed outcomes.
References: BetterE Expedition — From Mine to MEGAWATT @ Redox One; Redox One — About Redox One; BetterE Expedition — From Mine to MEGAWATT, Factory Tour @ Redox One; Tharisa plc — H1 FY2026 interim results presentation; Tharisa plc — Production report Q3 FY2026; Tharisa — Redox One; Tharisa plc — Redox One, a mine-to-megawatt solution officially launched (SENS); Mining Weekly — PGMs mine ramps up renewable-energy use; USGS — Mineral Commodity Summaries 2026, Chromium; NASA — Redox Storage System Development Project, Final Report (Hagedorn, 1984); Zeng et al., Journal of Power Sources 300 (2015); China Daily via gov.cn — New energy-storing tech at forefront of nation’s transition; IDTechEx — Flow Battery Technologies Beyond Vanadium; Herbert Smith Freehills Kramer — Germany adopts new capacity framework for 11 GW; International Flow Battery Forum — Volterion sponsor profile.
