Pomegra
The Imperial College spinout formerly known as RFC Power has secured £10 million to commercialise manganese flow batteries - technology designed to hold surplus renewable power for hours or days, not minutes.
Key Takeaways:
- British Business Bank led the £10M Series A, joined by Centrica, Ceres Power, and Temasek Trust's climate fund.
- Certain Energy's manganese flow batteries claim round-trip efficiency above 75%, within range of lithium-ion for multi-hour storage.
- Proceeds fund a MWh-scale demonstration in India and an expanded UK research facility.
Lead
Certain Energy, rebranded from RFC Power, closed a £10 million Series A on 26 August 2026, with the British Business Bank contributing approximately £3.5 million as lead investor. Centrica, Ceres Power Holdings, and Temasek Trust's Catalytic Capital for Climate and Health (C3H) fund also participated. The company frames its addressable market around an estimated £8 billion annual cost of curtailed renewable generation on the British grid. Valuation was not disclosed.
What Does Certain Energy's Technology Actually Do?
The core product is a flow battery using manganese as its electrolyte - a departure from the vanadium chemistry used in most commercial flow systems and from the lithium compounds that dominate short-duration storage. Manganese is substantially cheaper and more widely available than vanadium. Because energy capacity in a flow design scales with tank volume rather than cell count, a single installation can extend discharge duration from hours to days by adding electrolyte storage, not additional electrochemistry.
The company claims round-trip efficiency above 75%. That figure matters because it places manganese flow batteries within commercial range of lithium-ion for applications beyond two hours. Below that threshold, lithium-ion retains a cost edge. Beyond it, the economics shift toward flow architectures.
Why Does Multi-Hour Storage Matter Now?
Britain's grid has been accumulating a structural imbalance. Renewable capacity has grown faster than storage infrastructure, creating repeated episodes where wind and solar output must be curtailed because no viable sink exists for the excess generation. Grid operators pay producers to switch off. The cumulative bill, spread across recent years, accounts for the £8 billion figure Certain Energy cites.
Lithium-ion batteries, which currently dominate the storage market, are optimised for two to four hours of discharge. Grid operators increasingly need systems capable of carrying surplus midday solar through evening demand peaks, or buffering multi-day wind droughts. No technology currently fills that gap at proven commercial scale and bankable cost. That gap is where long-duration energy storage (LDES) companies are competing.
Who Backed the Round - and Why It Matters
The British Business Bank's lead signals active government interest in cultivating domestic LDES champions as the UK builds toward its clean energy infrastructure targets. Centrica's participation introduces strategic logic beyond pure financial return: the energy supplier operates grid services businesses that would benefit directly from access to cheap, dispatchable multi-hour capacity. Ceres Power Holdings, which previously held RFC Power on its balance sheet before the spinout and rebrand, retains a financial stake in the business. Temasek Trust's C3H fund adds an international dimension, reflecting continued appetite from sovereign and philanthropic capital for climate infrastructure at early commercial stage.
The mix of government development finance, a strategic utility, a technology parent, and an international climate fund is characteristic of LDES rounds at this stage - each investor has a different exit horizon and a different reason to want the technology proven.
What Comes Next?
Certain Energy plans to deploy a grid-connected MWh-class demonstration in India, a market where peak demand management and renewable curtailment pressure make the technology commercially relevant at smaller scale than the UK grid typically requires. A parallel expansion of its UK research facility is intended to develop a supply chain capable of delivering replicable projects rather than one-off installations.
The India project serves two purposes at once. It allows the company to demonstrate the system at commercial scale while sidestepping the UK's well-documented grid connection queues and planning timelines. The operational data generated will be what European and North American project finance desks ask for before committing capital.
What Are the Remaining Hurdles?
The company faces the familiar challenge for pre-commercial storage startups: moving from credible laboratory results to bankable project economics without the cost reductions that only come with volume. Flow batteries have a long track record of performing well in pilots and struggling to close the gap with lithium-ion at scale. Manganese chemistry is less proven than vanadium in deployed systems, which means counterparties will demand more performance evidence before signing long-term contracts.
The £10 million buys time and data. It does not, on its own, buy market position.
Outlook
Certain Energy enters the commercial phase at a moment when grid operators and utilities are actively seeking LDES alternatives to lithium-ion for multi-hour applications. The manganese electrolyte addresses cost and availability constraints that have limited vanadium flow adoption. The India demonstration is the critical near-term milestone - if the efficiency numbers hold outside controlled conditions and the system proves bankable, the company will be positioned to attract the project-level capital needed to move beyond single installations and into grid-scale deployment.
