Green Therma Selects H&P to Drill Denmark’s Longest Geothermal Well for Aalborg Heat4Ever Demonstration Denmark is moving from geothermal ambition to execution. Green Therma has selected Helmerich & Payne to drill the Heat4Ever demonstration well near Aalborg, a project that could become one of the country’s most technically ambitious geothermal developments and a meaningful test of closed-loop district heating. A milestone for Danish geothermal The Aalborg Heat4Ever project matters because it is designed to prove that geothermal heat can be delivered without relying on a natural hot-water reservoir. Instead of producing groundwater from a conventional geothermal field, the system uses a closed-loop pipe-in-pipe design that circulates the same fluid downhole, heats it in contact with hot rock, and returns it to the surface for district heating use. That distinction is important for Denmark, where district heating is already a major part of the energy system ...
A 400-Year-Old Tudor Mansion Just Chose Next-Gen Geothermal And It Changes Everything
Posted by Robert Buluma | December 11, 2025
Deep in the rolling countryside of Suffolk, England, stands Kentwell Hall ,a moated, red-brick Tudor masterpiece built in 1563, complete with octagonal guard towers, a 16th-century long gallery, and gardens that have hosted queens. For centuries it has been heated (if you can call it that) by a wheezing, century-old oil boiler that gulps thousands of litres of heating oil every winter yet still leaves the 400-year-old rooms chilly and the fuel bills astronomical.
That is about to change , dramatically, invisibly, and permanently.
This week it was announced that Kentwell Hall has selected CeraPhi Energy, a British deep-geothermal pioneer, to carry out a world-first feasibility study and, if successful, install a closed-loop deep geothermal heating system that will make the entire estate net-zero with almost zero visible impact on the Grade I listed building or its priceless interiors.
If this sounds like a small heritage project, think again. This could be the moment geothermal finally breaks out of its “only near volcanoes” stereotype and proves it can decarbonise anything, anywhere , including the most constrained, most beautiful, and most carbon-intensive buildings on earth.
The Impossible Brief
Patrick Phillips, the owner of Kentwell Hall, is blunt: “Historic houses cannot remain so fixed in the past that they become uninhabitable.” The building has 8-foot-thick walls in places, vast Tudor fireplaces that barely throw heat, single-glazed leaded windows that cannot legally be changed, and ceilings so high you could park a double-decker bus inside. The current oil boiler burns through £80,000–£100,000 of fuel a year and still fails to keep the damp at bay.
Air-source or ground-source heat pumps were ruled out early. There simply isn’t enough external space for large collectors without wrecking the moat and historic gardens, and the disruption inside a museum-grade house would be unacceptable. Biomass was dismissed because of lorry deliveries and flue issues. Hydrogen is decades away. Solar thermal on a listed roof? Unthinkable.
That left one option no one had ever tried at this scale on a heritage site: drilling deep coaxial boreholes and running a completely closed-loop system that circulates fluid 1–1.5 km underground to harvest the Earth’s natural heat, then brings it back to the surface with no water extraction, no fracking, and no visible plant except a small energy centre the size of a garden shed.
Enter CeraPhi Energy and its proprietary CeraPhiWell™ technology.
How the “Invisible Power Station” Works
Unlike traditional geothermal that needs hot aquifers or steam reservoirs, CeraPhi’s system is a true closed loop. A single monobore (one borehole, no second return well) is drilled vertically to around 1,500 metres. An inner coaxial pipe sits inside an outer casing. Fluid is pumped down the annulus, absorbs heat from the surrounding rock (even at normal geothermal gradients of 25–35 °C/km that’s 40–60 °C at depth), rises up the insulated inner pipe, and delivers heat via plate heat exchangers to the building’s new underfloor and radiator circuits, and then loops back down forever.
No groundwater is touched. No induced seismicity risk. No open-loop discharge. The surface footprint is smaller than a tennis court, easily hidden behind the existing stable block.
Gary Williams, COO of CeraPhi Energy, calls it “a power station you can’t see, can’t hear, and doesn’t spoil the view.” For Kentwell, the system will supply 100% of space heating and hot water across the main hall, staff quarters, café, events barn, and even the fairy-tale octagonal towers.
From Oil & Gas Playbook to Tudor Palace
CeraPhi was founded by Karl Farrow, a veteran petroleum engineer who spent decades drilling for Exxon and Shell in the North Sea. Like many in the “energy transition from within” movement, he realised that the same tools used to chase hydrocarbons , advanced directional drilling, down-hole heat exchangers, and high-temperature seals , could chase heat instead.
The company has already deployed shallow closed-loop systems, but Kentwell will be the deepest coaxial deployment in Europe and the first on a major heritage asset. If the feasibility study (due early 2026) confirms the geology, drilling could start as early as autumn 2026, with heat flowing by 2028.
The financial model is equally groundbreaking: CeraPhi is proposing a Heat-as-a-Service (HaaS) contract. They fund, build, own, and operate the system. Kentwell pays only for the heat delivered at an agreed pence-per-kWh – expected to be 30–50% cheaper than the current oil bill and completely index-proof against fossil fuel volatility. The estate’s carbon footprint plummets overnight, and the 460-year-old house gains a 100-year heating solution.
Why This Tiny Suffolk Project Could Reshape Global Geothermal
1. It proves closed-loop systems can work in “normal” geology
Britain has no Iceland-style volcanoes, yet the temperature gradient under Suffolk is perfectly adequate. If it works here, it can work under London, Paris, Tokyo, or Chicago.
2. It destroys the heritage roadblock
Thousands of castles, cathedrals, palaces, and stately homes across Europe are terrified of net-zero targets because retrofits seem impossible. Kentwell is about to give them a blueprint.
3. It showcases the Heat-as-a-Service escape hatch
Capital cost has always been geothermal’s biggest barrier. By shifting to an off-balance-sheet service model, suddenly schools, hospitals, universities, and housing associations can go geothermal without upfront CapEx.
4. It accelerates the talent crossover
Every metre drilled at Kentwell will be executed by ex-oilfield crews using rigs, mud systems, and logging tools straight out of Aberdeen or Houston. The energy transition needs hundreds of thousands of these skilled workers , this project is a live advertisement.
The Bigger Picture: 2025 Is Becoming the Year of Anywhere-Geothermal
Kentwell Hall is not alone. Just in the last six months:
Google and NV Energy announced a 24/7 geothermal-powered data centre deal with Fervo Energy in Nevada
The International Energy Agency now says next-generation geothermal could supply 10–15% of global electricity and an even larger share of heat by 2050 , if we can crack the “anywhere” problem. Kentwell Hall is about to provide the most elegant proof point yet.
A Tudor House Looks to the Deep Future
Patrick Phillips sums it up: “We have a duty to hand Kentwell on in better condition than we found it. That means keeping it warm, keeping it authentic, and keeping it here for another 400 years.”
When the system switches on (projected 2028), visitors walking the Long Gallery will feel radiant warmth underfoot but see no radiators, no trenches, no solar panels cluttering the roofline. The moat stays pristine, the Tudor brickwork untouched, the oil tank removed forever.
Below their feet, a silent river of heat will flow from 1.5 km down, harvested by technology born in the oilfields, financed by a 21st-century service contract, and delivered into one of England’s finest 16th-century houses.
If that isn’t the perfect metaphor for the energy transition , old and new, invisible yet transformative, pragmatic yet visionary , then nothing is.
Keep your eyes on a quiet corner of Suffolk. The geothermal revolution may have just found its most unlikely and most beautiful flagship.
Source:CeraPhi Energy
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