Geothermal Energy is heating up
Why geothermal finally starts to get more attention
Abstract
Some people see Geothermal in the same league as fusion and the hydrogen econmy, always just around the corner to break through and then it will solve all our energy problems. But in difference to the other two technologies there are now some companies that are so far in their development of advanced geothermal energy systems that they actually signed contracts to deliver heat and electricity at scale, namely Sage Geosystems, Eavor, and Quaise.
There is more to geothermal than the mindboggling new tech and ideas these three are working on. People tend to only think of electricity production from geothermal, but the much more important contribution to decarbonisation will come from extracting heat from the ground. Most people have seen already such “shallow” geothermal applications, namely ground source heat pumps.
Table of contents
What is Geothermal and why do we care?
Geothermal energy is essentially energy extracted from underground. The core of the earth is essentially very similar to the sun constantly generating energy in the form of heat. This heat is warming up the crust and ensures that already a relative short distance underground there are pretty stable temperatures, and this heat energy can be extracted using pipes, where a medium is pumped through. These pipes are either run through boreholes, but the most shallow systems are just buried a few meters underground.
Where the earths crust is thin, i.e. in regions with volcanos like on Iceland, the ground is so hot that steam >150ºC can be produced, and used to produce electricity and run low energy processes with. These systems are already in use for over a hundred years, but as these are rather special areas in the world, it seemed only be of interest to very few people.
This is where all the recent developments and particularly the above mentioned companies come into play. Making use of the energy in the ground promises a renewable heat source based on well tested technology from the oil and gas industry. (Pun intended!) So we do care, because geothermal does open up a clear path to decarbonising heat and eventually also electricity. But not just that it makes use of the enormous knowledge base and skills build in oil and gas, giving geologists and well engineers and all the other professions around exploration and production an important role in the energy transition.
The "Workhorse" of Geothermal: Heat
As the energy underground is available as heat and converting heat into other forms of energy is generally not very efficient, the first uses are in decarbonising heat. As example, to heat a building with a ground source heat pump and a required temperature of 60-70ºC, you would need to drill to about 160m depth. But for a low temperature central heating system with 35-40ºC just 10-15m would be more than sufficient.
But where ground source heat pumps come really into their own is in low industrial heat applications asking for 80-120ºC heat, as this would require bore holes at about 500m depths, which is for drillings standards still relatively close to the surface. As this is a very typical temperature range for food production, for cleaning and drying, and also in pharmaceutical production, a pretty big part of industrial heat can be covered with this range. Higher temperatures can be achieved by either drilling deeper, or using another heatpump to lift the temperature further.
One important side condition is that although the heat energy in the ground gets constantly replenished, in the upper layers of the earth crust constantly extracting heat will cool down the ground faster than the heat is conducted from the lower layers. For winter heating this is of no problem, but for industrial heat required whole year round this is something that needs to be considered. The other variable that engineers are considering in their designs is the surface area available for heat exchange. One particularly fascinating method is based on the development of directional drilling, which allows bends in a well, so that the hole is even horizontal in the end. This technique allows to add also several “legs” to a central hole, increasing the surface, but also allowing to switch off some holes for the regeneration of the heat in the area.
Current state of the art technology for geothermal heat production at large scale is the use of underground “aquifers” kind of underground lakes that are drilled into like an oil reservoir, but producing hot water not oil. Most of the system are “open loop”, i.e. there are to wells, water is produced from the one and pumped back through the other at a different location in the aquifer. Recently, companies realised an interesting potential of these installations: the water coming from these deep rocks contains many minerals, and particualrly lithium. So in combination with modern membrane based mineral extraction systems, both heat and minerals can be extracted in a more sustainable fashion.
Obviously, drilling deeper will allow even higher temperatures, but of course there is an economical trade-off between the much higher drilling costs and risks and the costs and capabilities of electric boilers and industrial heatpumps. But of course again it also depends on the geology at a given location, what is really required.
Advanced Geothermal: producing electricity everywhere?!?
Advanced Geothermal systems are technologies that try to overcome the geological limitations in form of the heat gradient available in a certain location. The three companies, Eavor, Quaise, and Sage Geosystems, are exemplary for different approaches in this area. All of them are aiming to actually produce electricity from Geothermal systems. The massively differing approaches mean that efficiency measured in electricity generation is very different.
Eavor is using the before mentioned directional drilling to create underground loops at a depth of several kilometers. The loops themselves are again several kilometres long. This ensures both sufficient heat and electricity production to make the system economically viable. In 2023 a study in the Netherlands showed that by improving the drilling technology a cost saving of 20% and a footprint suitable even in urban surroundings is achievable. The cost saving would also eliminate the need for a CAPEX subsidy. The first European project of Eavor is under construction in Geretsried, Bavaria, and is planned to deliver the first electricityin Q3/2025. A connection to the district heating network is planned for 2026. So soon we will learn, if their innovative case-less system actually works as intended at scale!
Sage Geosystems are intending to make use of another newer technique from the oil and gas industry: fracking. But in difference to the dreaded technique to release shale oil and gas trapped in stone, they will not use loads of harmful chemicals and are looking for much more stable rock formations, without methane or other gasses trapped in them. They intend to press “heavy” water underground creating cracks in the stone, expanding the surface area for the heat exchange. The heat extraction uses two wells, like is typical also in gas production, where one well is the injector, the other is the collector well. Obviously, if the temperatures are high enough, the heat will be sufficient to generate steam and can be used to generate electricity. For the energy generation Sage developed a special turbine, run with supercritical CO2. They did not stop there innovating: they realised that their system can also be used as energy storage. By using only one well into which they inject water under high pressure, using renewable electricity, the kinetic energy is stored as pressure, and back transformed to electricity using a Pelton turbine, as also pumped hydro does. The storage does not necessarily provide a heat application, but as the water will warm up underground the temperature can be scavenged using a heat pump.
Quaise are the most innovative company of the three, and does link to nuclear fusion of all things! The inventor, Prof. Paul Woskov of MIT, came up with the idea to use gyrotrons used in fusion to heat up plasma, to evaporate rock instead of drilling by mechanical means. This allows quaise to drill much deeper than other drilling equipment can go for three reasons: the drillbit needs constant cooling, and if the surroundings heat up to several hundred ºC this will get difficult, or at least very expensive. Then there is the so-called drilling mud that transports the drilled material back to the surface would also need to withstand the temperatures, and the pumps would need to be able to create enough pressure. Finally, normally boreholes need so-called casings, so no unwanted water, oil, gas,… enters the well. These casings can only be of a certain length, and need to be placed before continuing the drilling, so the hole is decreasing in size, as the drillbit has to fit through the casing. By essentially evaporating the stone the system melts the material and glaslike surfaces form, creating a casing stable enough to seal and securely stabilise the hole. The enormous heat then transports the rock particles out of the hole. So at the end of the day, Quaise is expecting to be cheaper in drilling cost, thanks to no casing, and being able to drill constantly 24/7, because no drill bit changes are required either. But the most important point is of course that they believe they can with their technique drill well beyond the depths achieved by conventional equipment and therefore are able to get to rock hot enough to generate supercritical steam at 375ºC, essentially anywhere on earth. They are scaling to the final 1MW gyrotron soon, and intend to deliver the first well by the end of 2026 and the first electricity between 2028 and 2030.
Is the Geothermal Heat already on?
Here we just collected a number of stories around geothermal energy and its various forms. While all the heat applications are more or less rock solid known and tested solutions, the three example of advanced geothermal are all still under development and will require to proof they can deliver what they promise! Even in ground source heatpumps there is still a lot to gain. In the Netherlands a pilot project looked into combining the typical foundation poles for buildings with piping for ground source heatpumps saving the costs of separate ground works. This is particularly interesting for building in urban areas, where there is no option to realise separate installation next to a new building.
What do you think? Will geothermal energy finally hit the steep part of the s-curve and fulfill its promise of cheap and controllable electricity and heat nearly everywhere on earth?
