Michael Barnard’s “Sit Down with a Geothermal Expert”

Michael Barnard has compiled and updated his geothermal research and articles in Clean Technica into a single, freely available report, called Beyond the Hype: Geothermal in Context, Separating viable heat solutions from speculative drilling dreams.

He’s dedicated a short chapter in the report to summarise the podcast discussion Michael had with Simon Todd in April 2025.

With many thanks to Michael here is that summary.

When I sat down with Simon Todd, founder of Causeway Energies, I expected a wide-ranging discussion about the current and future prospectsfor geothermal. What I got was both a masterclass in geology and an inside view of how a veteran of oil and gas thinks about repurposing those same skills and technologies for the energy transition. Todd has a habit of pulling apart assumptions, diving into technical detail, and then looping back to the strategic question: how do we actually make heat clean, affordable, and secure?

For those interested in the discussion, here are transcripts with embedded podcast links of part one and part two of the conversation. Todd’s story begins in Belfast, then across the water to Bristol and on to a PhD in geology in Kerry. That set him on a 25-year career with BP, where he rose through technical and managerial ranks, running projects in the North Sea, the Gulf of Mexico, Trinidad, and the onshore United States. He saw innovation, scale, and black swans up close. After leaving BP in 2014, he dabbled in consultancy, but when University College Dublin nudged him toward geothermal in 2019, the “sliding doors moment,” as he calls it, was complete. He co-founded Causeway Energies with colleagues, intentionally straddling Northern Ireland and the Republic to keep one foot in the EU and another in the UK. That strategic positioning is as important as the rocks they drill into.

When Todd explains geothermal, he starts with the basics. The Earth’s core sits at about 6,000 °C, with surface temperatures a mere fraction of that. Heat leaks out slowly, because rocks are poor conductors. In most places, temperature rises around 25 °C per kilometer below 15 meters depth. At tectonic boundaries or hotspots, gradients are much higher. That’s where conventional geothermal lives—steam and flash turbines in volcanic zones like Iceland, Indonesia, or Nevada. The economics of conventional plants look good because the heat is shallow and accessible. But that’s a tiny portion of the Earth’s surface. For most of the world, geothermal means something different.

One alternative is ground source heat pumps, what Todd prefers to call shallow geothermal. Closed-loop systems circulate a glycol mixture through polyethylene tubes in boreholes 150 to 200 meters deep, exchanging heat with the surrounding rock. These systems perform best with seasonal balancing: pulling heat in winter, storing it back in summer. He points out that thermal energy storage underground can reach round-trip efficiencies of 80 to 90%, making them ideal for cities with both heating and cooling demand. Toronto or Chicago, with their opposite seasonal loads, could use shallow geothermal like a giant underground battery. The coefficient of performance is key: the closer the source and sink temperatures, the higher the efficiency. A well-designed ground source system can reach a COP of four or five, sometimes over ten for cooling.

Open-loop systems use aquifers instead of closed tubes. In Belgium and the Netherlands, thousands of aquifer thermal storage systems already serve commercial buildings, but Ireland and the UK have virtually none. Todd shakes his head at that missed opportunity. The geology is straightforward: aquifers are permeable rock sponges, not underground lakes. With hundreds of millidarcys of permeability, they can deliver useful flows. The physics is simpler than oil and gas, because it is single-phase water flow, not messy mixtures. He likes to point out that airports in the Netherlands use aquifers to store summer heat for de-icing runways in winter, a model that Dublin Airport could copy.

From there, Todd moves into deeper systems. Directional drilling, perfected in the oil patch, allows geothermal developers to reach sideways into aquifers or fractured zones. Advances in drill bits, mud motors, and sensors have cut drilling times dramatically. Companies like Fervo are applying shale’s playbook to granite, using horizontal drilling and hydraulic stimulation to create enhanced geothermal systems. Todd is cautiously optimistic about Fervo. Their early projects show stable flow and temperature after several years, avoiding the steep declines seen in shale wells.

They’ve cracked multi-well pads and stage stimulations. But the economics remain unproven. Shale wells deliver energy quickly, albeit inefficiently. Geothermal wells might last longer but deliver less energy per dollar invested. Todd’s back-of-the-envelope math suggests geothermal’s value proposition is still weaker than oil or solar. To work, enhanced geothermal has to be flexible and dispatchable, competing not with baseload coal but with wind and solar plus batteries. That is a high bar.

He is even more skeptical of deep closed-loop systems like Eavor. Their kilometer-scale U-tubes suffer from the same problem as shallow loops: conduction is slow. Initial heat drops rapidly, then stabilizes at a lower level. To get meaningful output, you need enormous borehole lengths and very high formation temperatures. The economics deteriorate quickly as depth increases. He prefers to stay in the “Goldilocks zone” of 500 to 1,500 meters, where drilling costs are manageable and aquifer temperatures are high enough to give industrial heat pumps an edge. In one Liverpool study, Causeway found that a 500- to 700-meter aquifer at 18 to 20 °C beat both air source and river water systems, delivering a three-year payback. That extra 6 °C made all the difference to COP and operating costs.

Todd dismisses the science fiction visions of ultra-deep drilling for supercritical steam. If it were feasible, oil and gas would already have done it. Beyond the depth and temperature challenges, there are unanswered questions about how to extract and manage the heat once you get there. He calls himself an interested spectator, but Causeway Energies is not betting on lasers and microwaves.

Instead, Causeway’s focus is squarely on industrial heat. About half of global emissions come from heat, and half of that demand sits in the sweet spot for heat pumps: under 200 °C. Most industrial processes—brewing, food processing, pasteurization—can run on 120 °C steam or hot water. Today’s industrial heat pumps, using natural refrigerants like ammonia or CO₂, are already capable of delivering that. The trick is to pair them with moderate geothermal resources. With a COP of five, one megawatt of electricity can deliver five megawatts of heat. That multiplier is what makes the economics compelling. At 500 to 1,500 meters, aquifers tend to be brackish or saline, avoiding drinking water conflicts. Regulations still require modeling thermal plumes and reinjection, but the technical hurdles are manageable. In some cases, hybrid standing column wells—half open, half closed loop—can deliver three to five times the thermal power of pure closed loops, at lower capital cost.

Causeway is building business models around thermal purchase agreements, project finance, and off-balance-sheet solutions for clients. They have tested brewery projects in Nigeria and feasibility studies in the UK, with hospitals and distilleries next in line. Their first commercial pilots will be proof points for policymakers and investors. Todd is pragmatic: first-of-a-kind projects in Ireland are still needed, even if the technology is proven elsewhere. People only believe what they see in their own backyard.

At the end of our conversation, Todd returned to his “why.” Half of energy emissions are heat, and fossil fuel dependence is an acute vulnerability for Ireland and the UK. Affordable, indigenous, secure heat is not just a climate issue but a resilience issue. For him, this is legacy work, not fortune-seeking. After BP, he and his wife are comfortable. Now he wants to make a difference, applying extraction skills to a different kind of resource. His focus is not on futuristic lasers or speculative closed loops, but on the practical sweet spot: moderate depth aquifers, industrial heat pumps, and thermal storage. It may not be glamorous, but it is exactly the kind of pragmatic solution the energy transition needs.