Underground heat increases as we go deeper into the Earth, offering an almost limitless energy source alongside other renewable alternatives. In some areas of the Earth’s crust, such as Iceland—where geothermal wells are a common energy source—high temperatures are reached at depths of less than one kilometre. This heat generates steam, which can be used for heating systems or to drive turbines.
However, extreme temperatures are not necessary for a domestic geothermal system designed to maintain a comfortable indoor temperature year-round. One company is now exploring the potential of shallow boreholes with a portable tunnelling machine that can be used almost anywhere—from a garage to a backyard.
What are geothermal wells?
A geothermal well is a borehole designed to harness the Earth’s natural heat for power generation or climate control. Typically, these boreholes extend to underground layers where temperatures are higher, capturing geothermal energy to produce electricity, heating, or cooling in a sustainable way.
In terms of depth, geothermal wells can vary greatly—from shallow heat exchange systems with boreholes only a few metres deep to wells that reach several kilometres for high-enthalpy installations, where heat and pressure generate steam to drive a turbine.
Most common types of geothermal wells:
1. Shallow or low-enthalpy wells
- Primarily used for heating and cooling buildings via heat pumps.
- Typically drilled to depths of a few dozen metres.
2. Medium-enthalpy wells
- Ideal for industrial processes and district heating.
- Reach depths of several hundred metres.
3. High enthalpy wells
- Can extend between 1,000 and 3,000 metres (or more).
- Used for large-scale electricity production by extracting steam and high-temperature geothermal fluids.
A mini-tunneling machine in your garden
If you follow our website, you may have come across our discussions on tunnel boring machines (TBMs)—the massive metal worms that carve through the earth to create tunnels for vehicles and passengers, such as the Quito Metro or São Paulo’s Line 6. These machines can weigh up to 5,000 tonnes and require complex operations, typically featuring a cutting head, a propulsion system, and onboard personnel to control them.
Swiss company Borobotics has taken a different approach, developing a miniature tunnel boring machine for geothermal exploration. While its design is similar to conventional TBMs, the differences are substantial. The machine, named Grabowski after the cartoon mole, is less than 14 centimetres in diameter and only 2.8 metres long. Moreover, its “worm” is autonomous and requires less than eight square metres of space to operate. In fact, both the worm and its surface equipment fit into a small van, and a single operator is enough to handle the installation.
Powered by an electric propulsion system, the device features sensors that detect the type of material it is drilling through and automatically stop if it encounters a water or gas deposit, which it can also seal on its own. Additionally, it can adjust its direction as it drills, following the path of least resistance. It is capable of boring through various ground types, from sand to granite.
According to its creators, Grabowski can reach depths of up to 500 metres—still far from conventional geothermal wells but more than sufficient to stabilise a home’s temperature. They note that at a depth of 250 metres, the average temperature is around 14°C. Geothermal heat pumps circulate air to cool buildings in summer and warm them in winter relative to the outdoor temperature.
If you’re interested in other innovative renewable energy solutions beyond geothermal wells and solar power, check out our articles on the triboelectric effect and wave energy.
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