Geothermal Energy – the heat is on

An Irish proverb advises that a good start is half the work (Tús maith, leath na hoibre). With geothermal, some elementary geology pays dividends.

‘Geothermal’ means ‘heat from the earth’, an energy flow driven by temperature differences within our planet’s interior. The energy is trickling slowly through our planet’s geological structures, from a 6,000°C  core (similar to that on the sun’s surface) to the cooler earth’s surface (on average 5–30°C). 

Looking more closely, the earth’s internal heat map is complex. In essence, below an initial thin layer of 20 meters, the earth’s temperature increases with depth, on average around 25°C per kilometre, until we reach the inferno at the core. 

But averages can deceive. At tectonic plate boundaries and volcanoes, hotter-than-mean temperatures are observed near the earth’s surface. Here, high-temperature steam can drive conventional turbines to produce electrical power. The canonical case is the Hellisheiði electric power station near Reykjavik in Iceland, providing valuable diversification for the country’s hydropower system. Moreover, the available heat simultaneously supplies hot water to the city.

This combined heat and power (CHP) solution does not depend on fossil fuels. Nor is it a mainstream solar technology (photovoltaic) or one of its derivatives (wind, wave, and hydro). 

Instead, it is distinctive and well-diversified. And diversification benefits are an essential source of value in any energy system – as we are painfully aware today. 

Of course, Iceland-style opportunities are restricted because suitable volcanic hot spots across the globe are relatively sparse, and often far from population centres. 

Does that confine sourcing geothermal energy to the gushing geysers, of only marginal relevance to Britain and Ireland? 

At a recent Investec seminar, addressed by a founder of Causeway Energies, Dr Simon Todd* the answer was a resounding ‘no’.

To understand why, think holistically, and think heat rather than electricity per se.

We have significant demand for space heating in our homes, offices and factories, as well as for industrial and agricultural processes. Demand for heat as part of final energy consumption in the UK amounts to around 45% of total final energy consumption. 

Geothermal resources could contribute to meeting a proportion of heat demand, most of which does not require the very high temperatures for electricity generation or heavy-industry activities. For many heating purposes, geothermal energy may offer an alternative to gas, oil, and even direct electrification. 

Shifting available geothermal heat to where it is needed (using a ground-source electric pump, for example) may use much less energy than converting electricity directly to heat. The ratio of useful heat moved to work input, known as the coefficient of performance (COP), can reach 4x for a well-designed community ground-sourced heating system. 

Thousands of shallow geothermal systems (operating to depths of several hundred metres) are already used by our geographical neighbours, Belgium and the Netherlands – many provide heat to public buildings. The basic technology is ‘open loop’, with groundwater pumped directly from aquifers (rock sponges) or flooded mines to the property.

How many are in the UK and Ireland? 

Practically none. 

Of course, environmental scrutiny is always justified. But our Benelux cousins are particularly good at that. In the UK, with many former mines now closed, are we missing a trick?

More sophisticated technologies can also operate at shallow depths. IKEA has operated a ‘closed loop’ geothermal system in Dublin since 2009. A suitable fluid circulates constantly between the earth and underground, able to provide heat in winter and cooling in summer. This turns the ground into a type of energy battery, with heat pulled from the earth in winter and returned in summer.

The approach also helps to minimise overall energy system costs in Ireland**, in a similar way to other storage solutions. 

Overall, the deeper one dives into the subject, the more it is evident that the geothermal ecosystem is evolving. We have only scratched the surface. As one example, ‘deep geothermal’ moved forward in early 2026 with Geothermal Engineering Ltd’s new, first-of-a-kind power station and lithium-extraction facility in Cornwall, a project with the deepest onshore well in the UK (5 kilometres underground).

However, the message from the Investec energy seminar was that we don’t need to go into the murkier world of deep geothermal exploration and research to find available geothermal answers to our current energy challenges. Instead, it boils down to creating a viable regulatory/policy framework to encourage project development, and to the capital markets to create a virtuous investment cycle. Public and private sectors working in tandem can make this a win-win for all.

To conclude, deep geothermal is often included in the ‘science fiction’ part of energy discussions. 

But geothermal need not be rocket science.

For UK energy policy right now, geothermal energy  can form part of a broader set of energy solutions – a lot closer to home than the Strait of Hormuz, and potentially more reliable to boot. 

Further Listening and Reading: 

* Redefining Energy Tech Podcast (Michael Barnard with guest Simon Todd). Geothermal – drilling for Decarbonisation (2 episodes). 

**An Assessment of Geothermal Energy for District Heating in Ireland, Geological Survey Ireland

Detail on Simon’s work can be found at causewaygt.com