Geothermal energy
Geothermal energy: harnessing the Earth's heat to support the energy transition
Decarbonisation Renewable energy
Geothermal energy makes it possible to use heat from inside the earth for electricity, hot water and heating, offering an alternative to fossil fuels. Although it is a type of renewable energy with many years of history, it is still largely unknown. Find out what geothermal energy is, how it works and its advantages.
The thermal energy harboured by nature has been known since ancient times, when the feared volcanic eruptions threatened the survival of crops and populations. However, the ability to harness this heat from within the earth's interior and transform it into geothermal energy began in the 19th century.
In 1818, the French engineer and entrepreneur François Jacques de Larderel developed a technique for collecting steam emitted by cracks in the ground through which boiling water and underground fumes flow near Montecerboli (Italy). He used it to heat the boilers in a chemical factory producing boric acid and succeeded in increasing both productivity and energy savings. Larderel's ingenuity was the starting signal for the development of geothermal production in the 20th century.
Despite its long history and the growing importance of renewable energies, geothermal energy is still little known. We will tell you what this type of energy is, what it is used for, how it works and what its advantages are.
What is geothermal energy?
The Greek etymology of the name gives us many clues as to what geothermal energy involves: geō (earth) and thermós (heat). That is, energy that comes from the heat of the earth. The European Geothermal Energy Council (EGEC) defines it as "energy stored in the form of heat below the earth's surface". This definition refers to heat stored in rocks, soils and groundwater, whatever their temperature, depth or source.
It is considered a renewable and clean energy. The heat it provides is unlimited and the temperature of the subsoil is very stable, which allows high energy yields to be obtained.
There are different types of geothermal energy depending on the type of natural resource from which it is extracted (hot water, dry wells, geysers, dry steam), the depth of drilling (shallow, from a few metres to great depths above 10 km) or the temperature of the water (from high to low temperature), among others.
Types of geothermal energy and their uses
Geothermal energy can be used to generate electricity or for thermal applications. The potential of this type of energy depends primarily on the temperature of the geothermal resources:
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Low temperature (less than 100°C)
The energy obtained is used for thermal applications in industrial and agricultural processes, in urban heating and cooling systems and to produce domestic hot water.
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At medium temperatures (100°C to 150°C)
Its applications are mainly thermal (heating, domestic hot water) in the industrial, residential and service sectors. To a lesser extent, it is used to generate electricity.
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At high temperatures (over 150°C)
It is used to generate electricity. It is also occasionally used in geothermal heating systems.
How do geothermal power plants extract energy?
The earth is made up of several rocky strata or layers that run from the centre to the outermost zone. The planet's core is a solid, glowing mass of minerals, molten rocks and gases, predominantly iron and nickel. Above the core is the mantle, also quite fluid and hot, and finally the Earth's crust, the shallowest layer, which is still about 20 km thick.
When water from precipitation seeps through the earth's crust, it forms masses of water (deep streams and aquifers) which, when in contact with the heat of the subsoil, give rise to a geothermal reservoir consisting of water and steam at high temperatures. Sometimes the heat exists, but not the aquifer, so in order to exploit geothermal energy it is necessary to inject a fluid that allows it to be extracted (usually water).
Geothermal power plants extract thermal energy in the form of hot water and steam. At the surface, this energy is harnessed either directly by separating the steam from the mixture with a cyclone separator or indirectly using a heat exchanger. The excess water is re-injected back underground to restart the cycle and the resulting steam is sent to a turbine to generate electricity.
Advantages of geothermal energy
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Alternative to fossil fuels
As it is a renewable source of continuous energy, it offers a great alternative to fossil fuels.
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Energy stability
It is a stable energy source because it does not depend on fluctuations in weather conditions such as wind or sunshine.
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Virtually inexhaustible
Geothermal resources are practically inexhaustible on a human scale.
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Efficient
It can deliver significant savings in both energy consumption and operating costs. Although the initial investment is substantial, it is highly durable and requires very little maintenance.
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Unobtrusive
Geothermal facilities have a low visual impact and do not generate external noise. Furthermore, they produce minimal waste.
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Boosts the economy
The renewable energy sector employed more than 16 million people worldwide in 2023, according to the International Renewable Energy Agency (IRENA) and the International Labour Organisation (ILO).
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Drives innovation in the sector
Technologies are under development, such as millimetre-wave drilling by Quaise Energy, which have progressed from the laboratory to field trials and aim to access the Earth's depths at a reasonable cost.
Disadvantages of geothermal energy
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High initial cost
Developing geothermal projects requires significant upfront investment. Even in the exploratory phase, a substantial initial investment is required to assess the project's viability.
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Geographical limitations
Not all areas are suitable, as this depends on the temperature of the subsoil and the available resource. Some countries, such as Iceland and the Philippines, have large geothermal reserves that enable them to meet almost a third of their electricity demand with this energy.
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Environmental and technical risks
Extracting this energy can lead to leaks of harmful gases, potential impacts on groundwater and in some cases induced microseismicity. However, these risks depend on the type of installation, the geology of the site and the quality of technical management.
Geothermal energy and the energy transition
Geothermal energy can play a significant role in the energy transition because it is a manageable renewable source, capable of providing a continuous supply of electricity and heat without being directly dependent on the sun or the wind. According to the International Energy Agency (IEA), geothermal energy could meet up to 15% of the growth in global electricity demand by 2050.
Furthermore, geothermal power stations can operate flexibly, which contributes to the stability of electricity networks, making it possible to meet demand at all times. Consequently, with technological improvements and investment incentives for projects, the potential for growth is greater than is commonly believed.
Geothermal energy: innovation and the future
Although geothermal energy currently accounts for less than 1% of global energy demand, it is a sector with great potential. Innovation in geothermal energy is currently focused on making access to deeper and hotter resources viable, using technologies such as enhanced geothermal systems, closed-loop systems and advanced millimetre-wave drilling. The International Energy Agency (IEA) estimates that these technologies could significantly expand the use of geothermal energy, enabling up to 800 gigawatts of global capacity by 2050 and meeting up to 15% of electricity demand by 2050. In other words, the technical potential exists to meet several times the global demand for electricity and heat.
However, the future of this energy source depends not only on technology but also on funding, regulation and risk mitigation during the initial phase of projects. The IEA notes that growth in geothermal energy could mobilise substantial investment, but political support and financial schemes are key to the expansion of this sector.