A British startup spun out of Imperial College has closed a £10 million Series A to push a manganese-based flow battery toward commercial deployment, betting that cheap, earth-abundant chemistry can solve the grid's hardest storage problem: holding clean power for days, not just hours.
Certain Energy, which operated as RFC Power until this week, said the round was led by the British Business Bank with backing from Centrica, Ceres Power, and Temasek Trust's Catalytic Capital for Climate and Health. The company plans to use the cash to build a grid-connected system rated in the megawatt-hours in India, expand its UK research site, and stand up a supply chain for repeatable projects.
The funding lands at a moment when grid operators across Europe are paying wind and solar farms to switch off because the network cannot absorb their output. UK Energy Security Minister Michael Shanks called long-duration storage "the missing piece" needed to bank clean power "for days, not hours."
Why manganese, and why a flow design
Most grid storage today relies on lithium-ion cells borrowed from electric vehicles. Those work well for short shifts of a few hours, but they get expensive fast when the sun has set and the wind has dropped and the grid still needs power the next morning. Flow batteries take a different route: energy is stored in liquid electrolyte held in tanks, and electricity is made when that liquid passes through a cell stack.
Certain Energy's chemistry is built around manganese, the twelfth most abundant element in the Earth's crust. Because the active material sits in fluid, the company can stretch discharge time simply by making the tanks bigger. That turns a four-hour system into an eight- or twelve-hour one without redesigning the core. The firm says its round-trip efficiency sits above 75 percent, enough to compete with lithium-ion on the grid services operators actually buy, while also covering the longer reserve periods a renewables-heavy network demands.
Its patented electrolyte is designed for a 20-year working life with little capacity fade. Materials and design, the company argues, could pull marginal storage costs down to roughly one-tenth of comparable vanadium flow systems and well below lithium-ion on a delivered-energy basis. Vanadium has long been the commercial benchmark for flow storage, so a cheaper earth-abundant alternative would remove a real cost ceiling.
The curtailment bill it is built to cut
The pitch rests on a specific, growing pain. Last year the UK government paid about £1.5 billion to renewable generators to curb output during peak production, when supply outran the wires. Left unchecked, the grid operator expects that bill to climb toward £8 billion a year by 2030. Every pound spent switching off clean power is a pound of wasted generation that a storage tank could have captured instead.
Executive chair Mark Selby framed the maths directly. "The renewable power market is held back by its vulnerability to external factors," he said, pointing to the gap between when clean energy is made and when it is needed. Chief executive Tim von Werne called long-duration storage "the missing piece of the clean energy system," and said manganese flow is the chemistry he expects to win it.
For utilities, the value is resilience as much as savings. As wind and solar take a larger share of supply, the grid leans on gas peaker plants to fill the gaps. A multi-day store lets operators ride through calm, cloudy stretches without reaching for fossil generation, and it reduces the curtailment that erodes the economics of every new renewable project.
What the money actually buys
The round was led by the British Business Bank, which put in £3.5 million of public capital. Centrica, the integrated energy group, Ceres, the clean-energy technology licensor that acquired RFC Power in September 2025, and C3H all joined. Ceres's involvement matters: the flow-battery maker now sits inside a portfolio that includes fuel cells and electrolysers, giving it a licensing-style route to manufacturing rather than building gigafactories from scratch.
The headline deployment is a grid-connected MWh-class unit in India, a market where solar output is huge by day and demand peaks in the evening. A second use of the funds is expanding the UK research facility and lining up component suppliers so future units can be reproduced rather than hand-built. Stuart Paynter, finance lead at Ceres, noted the rare combination of a low-cost abundant chemistry and "a credible, capital-efficient route to manufacturing."
Where it sits in the long-duration race
Certain Energy is not alone in chasing storage that lasts beyond the evening peak. The field now spans iron-air systems from Form Energy, gravity and compressed-air schemes, and sodium-ion packs from CATL aimed at shorter grid shifts. Manganese flow sits in a narrower lane: a liquid chemistry that scales with tank size and avoids both lithium and vanadium supply risk.
That positioning helps explain the investor mix. Centrica brings a customer that owns generation and retail load; Ceres brings manufacturing partnerships; the British Business Bank brings patient public capital willing to back a physics bet with a long commercial horizon; and Temasek Trust's climate vehicle brings global reach, including the India project. The rebrand from RFC Power to Certain Energy signals a move from research label to product name.
The technology still has to prove it can be built at volume and earn money on real grids. Flow batteries have promised cheap long-duration storage for years, and vanadium systems have shipped but stayed niche on cost. Certain Energy's bet is that swapping an expensive metal for abundant manganese, paired with a 20-year electrolyte, tips the economics enough to scale. The India system will be the first public test of that claim.
For readers tracking the chemistry race, the CATL sodium-ion buildout CATL sodium-ion BESS shows how a major cellmaker is approaching the same duration gap from the solid-electrode side, while more background on the category lives at Battery Tech.
The bottom line
A £10 million round will not by itself reshape how grids store energy. But it backs a specific wager: that the world's grids need hours-to-days storage built from materials that are cheap and widely available, not just denser. If Certain Energy's manganese electrolyte holds up for 20 years in the field, the curtailment bill it targets — heading toward £8 billion a year in the UK alone — becomes a market worth chasing. The money is in; the tanks are next.
Sources: Certain Energy / Temasek Trust announcement, ESG Today, Ceres Power.
