99.3%. Above that line, lithium carbonate stops being a chemistry demonstration and becomes a battery input. In early September, Geothermal Engineering Ltd (GEL) reported that carbonate drawn from the deep brine beneath its United Downs plant in Cornwall had cleared that threshold, making it the first producer in Europe to turn geothermal brine into technical-grade lithium carbonate.
The company has generated electricity at the same site since February, when its binary power plant came online. The lithium is a second product from the same well.
That detail is the whole story.
Its carbonate clears the 99.3% technical-grade bar, so it can be sold to battery producers without further refining.
The hard part is no longer chemistry. It is scale, brine variability, and financing across dozens of new wells.
United Downs carbonate purity
Independent analysis of the plant's lithium carbonate from deep geothermal brine, reported September 2026 as a European first. · GEL, 2026
A well that sells twice
Deep geothermal has always been a capital problem wearing a geology costume. A well costs millions before it produces a single megawatt-hour, and the heat it taps sells into a power market that rewards cheap gas on calm days.
Its answer is to sell the same brine twice. First as electricity, generated by an organic Rankine cycle binary plant. Then as lithium, pulled from the fluid before it is reinjected. As we wrote in September, Fervo's 396 MW Google deal turned enhanced geothermal into a baseload business. The difference at United Downs is the second revenue line.
ThinkGeoEnergy, which has followed the Cornwall project since its first steam test in 2021, makes the case directly: lithium extraction provides additional revenue generation that can significantly improve the economics of deep geothermal projects.
Producing lithium carbonate that exceeds the purity specification for Technical Grade material is a major milestone for GEL and an important validation of our technology. We are demonstrating that it is possible to produce a high-quality, saleable lithium product in the UK with the highest environmental standards.— Dr Ryan Law, CEO, Geothermal Engineering Ltd
At United Downs the electricity came first. The power station is the UK's first operational geothermal plant, and the lithium facility beside it is the country's first commercial-scale geothermal lithium plant. Both came online this year, within weeks of each other.
The numbers behind the claim
Technical grade is a market boundary, not a laboratory trophy. It means the carbonate meets the purity specification battery producers require without further refining, so it can move straight into a supply chain.
The company says independent analysis put its material above 99.3%, the same threshold the company now sells against. Technical-grade lithium carbonate trades internationally, including on the Shanghai Metals Market. The reference price was about $22,000 per tonne on 20 August 2026, according to market data cited by ThinkGeoEnergy.
Reference carbonate price
Shanghai Metals Market reference price for technical-grade lithium carbonate on 20 August 2026. · ThinkGeoEnergy, 2026
At that price, volume decides everything. United Downs is targeting around 2,000 tonnes a year by 2029, up from an initial 100-tonne production line. The wider ambition is roughly 30,000 tonnes a year across multiple UK sites by 2033, according to the Institute of Materials, Minerals and Mining.
United Downs output target
Its planned United Downs output; the company targets about 30,000 tonnes a year across its UK portfolio by 2033. · IOM3, 2026
The UK government wants 10% of national critical-mineral demand met from domestic production by 2035, including at least 50,000 tonnes of lithium carbonate. It is one of a small group of projects positioned against that number.
Brine is not a uniform feedstock
Every geothermal lithium project stands or falls on one engineering choice: how to pull lithium from a fluid that also carries far more sodium, calcium, and magnesium. The industry calls it direct lithium extraction (DLE). The method is the differentiator.
Adsorbents, ion-exchange resins, and membranes compete on selectivity, water use, and how well they tolerate a specific aquifer's chemistry. A process tuned to one brine can fail in the next valley.
Why the adsorbent, not the well, decides the outcome
That variability is why no single process has won, and why the pilot phase matters more than the announcement that follows it.
The Salton Sea is the largest test bed. TerraLithium, a subsidiary of Occidental Petroleum, and BHE Renewables, a Berkshire Hathaway Energy company, reported in June that they had produced lithium chloride from geothermal brine at the Calipatria facility, converted it into battery-grade lithium carbonate, and separately turned lithium chloride into lithium hydroxide using commercial-scale electrolysis. BHE runs ten geothermal plants in the Imperial Valley that process 50,000 gallons of lithium-rich brine a minute and generate 345 megawatts.
Those figures sit an order of magnitude above Cornwall's. They also rest on a basin with a documented, decades-old lithium resource and a $15 million Department of Energy grant behind the extraction work.
What the milestone does not prove
Purity is necessary. It is not sufficient.
The company has produced technical-grade carbonate at a plant that started near 100 tonnes a year. The distance from there to 2,000 tonnes is a scale-up problem: more wells, more brine throughput, more adsorbent, and a reagent supply chain that does not yet exist at volume. The distance from 2,000 tonnes to 30,000 is a different problem again, because it requires several aquifers to behave the way Cornwall does.
Capital is the second constraint. It secured £10 million in financing from ABN AMRO in May 2026 to expand lithium production, and a £1.8 million grant through the UK's DRIVE35 automotive programme before that. Both are small next to the wells the company's targets imply. The bank debt shows lenders now treat geothermal lithium as financeable. It does not show the funding is solved.
Price is the third. Lithium carbonate at $22,000 a tonne is far below the 2022 peak that pulled a wave of speculative projects into the market. A dual-revenue asset tolerates a soft price better than a lithium-only mine, which is the strategic argument for geothermal. It does not make the price irrelevant.
Demand is the fourth. Grid storage is the fastest-growing lithium use, and as we wrote in September, sodium-ion cells are already taking the first bite out of lithium's share of that market. Geothermal lithium is a supply-side story arriving as one of its demand anchors softens.
Whether United Downs steps from 100 to 2,000 tonnes a year, and whether the 2029 target holds.
Purity consistency across batches, not just the first independent analysis.
Which project reaches commercial output first: Altmark in Germany, Cross Lanes in Cornwall, or the Salton Sea.
UK progress against the 2035 target of 50,000 tonnes of domestic lithium carbonate, and the US Department of Energy's $69 million geothermal critical-materials funding round opened in April 2026.
What happens next
Does geothermal lithium become a real supply source this decade?
Probability: 65%. Its own targets imply roughly 2,000 tonnes at United Downs by 2029, and its German and UK peers are a step behind.
✅ Arguments for
DLE skips the evaporation ponds that made conventional brine projects slow and water-intensive.
Lenders and governments are now underwriting pilots rather than concepts.
Confirmation criteria: at least two European projects at commercial scale and a second independent purity certification.
❌ Arguments against
Scale-up capital is large relative to revenue at $22,000 a tonne.
Lithium demand forecasts have overshot before, and sodium-ion storage is now competing for the same grid-storage demand.
Disconfirmation criteria: GEL slipping its 2029 target, or a major DLE project shelving expansion.
Development scenarios
🟢 Optimistic scenario (30%)
Implications: European geothermal lithium passes 10,000 tonnes a year before 2030 and becomes a routine second revenue line for new geothermal plants.
🟡 Base-case scenario (50%)
Implications: Geothermal lithium is proven but niche, and the UK's 2035 target leans on other sources.
🔴 Pessimistic scenario (20%)
Implications: Several projects stall at pilot scale, and geothermal development reverts to power-only economics.