What is geothermal energy
The energy originated from the Earth's heat
The Greek etymology of the name says it all: geo, Earth, and thermós, heat. Geothermal energy is in fact a form of renewable energy that originates from natural heat from underground.
This heat is used to produce electricity or to heat buildings: geothermal plants extract it through deep wells, turning it into thermal or electrical energy.
Given that it is a clean and constant source, geothermal energy offers significant environmental benefits, with very low emissions compared to fossil fuels.
Geothermal heat
Geothermal heat is generated mainly from the heat stored in the Earth's core and mantle and from the decay of radioactive materials in the Earth's mantle.
This heat, depending on depth, is evident at different temperatures and can be captured by different techniques:
- low enthalpy systems (up to 100 °C),
- medium enthalpy systems (between 100 °C and 150 °C)
- high enthalpy systems (above 150 °C).
Low-enthalpy applications use heat near the surface, normally a few tens of meters deep, for the direct heating of buildings and water systems through heat pumps (low-enthalpy geothermal systems).
In medium and high enthalpy, heat is extracted from deeper reserves and is used for driving turbines for electricity generation.
In addition to electricity generation, medium- and high-enthalpy heat can also be used for the direct heating of buildings (space heating), providing heat to greenhouses, or for industrial applications.
Geothermal plants, especially high-enthalpy plants, are located in areas rich in geothermal activity such as geological faults or volcanic areas.
The history of geothermal energy
Literature, medicine and technology
How geothermal energy works
Journey to the center of the Earth
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Geothermal plants are designed to harness the Earth's heat and convert it into electricity or heating.
For electricity generation, wells up to 3,000 meters deep are drilled in areas with significant geothermal resources.
Underground heat, in the form of high-pressure steam, rises from underground and is piped to a turbine.
There are several cycles for heat utilization:
- In dry steam cycles, natural steam coming directly from the ground drives the turbine;
- In the flash cycle, subsurface heat is used to vaporize water at high pressure, with some of it passing into a gaseous state and powering the turbine.
- In the binary cycle, on the other hand, heat is transferred to a low-boiling point fluid that evaporates and drives the turbine, enabling geothermal resources to be used at lower temperatures. The steam is then condensed and converted to water, often through a heat exchanger or condenser. The water can be fed back into the ground to complete a closed loop, thereby sustaining the entire process.
In addition to electricity generation, geothermal heat can also be used for direct heating. This is done in two ways:
- For high-energy-content resources (medium- to high-enthalpy geothermal energy): Heat from hot water or steam extracted from geothermal wells can be directed to heat exchange systems for domestic or industrial uses.
- For low-enthalpy systems: Geothermal heat pumps are installed at relatively shallow depths to transfer heat from the ground to buildings or homes, keeping them warm in winter and cool in summer. The system operates on a closed loop where a fluid circulates, absorbing heat underground and releasing it inside buildings.
The benefits of green heat
An incredible potential
A 2006 report by MIT (the Massachusetts Institute of Technology) highlights how Earth's potential for geothermal energy could provide green energy for roughly 4,000 years.
Uninterrupted and constant
Day, night, sun, rain: none of these conditions has any impact on geothermal energy. Hence, the Earth’s heat is always fully and readily available.
Low management costs
Once a geothermal plant goes online, its management costs are significantly lower compared to other technologies.
Frequently asked questions about geothermal energy
There is an enormous amount of energy underground, thanks to untapped potential. It is a power source that optimizes resources: the heat that cannot be used immediately is put back into the system, thereby enhancing energy saving. Here are all the answers to any questions you might have about this renewable energy source.
Did you know?
Geothermal power, culture, food, and wine: a challenge for Tuscany
How could a handful of villages perched on Tuscany’s hillsides attract over 60 thousand visitors each year (a number that’s set to grow)? With a diverse and enticing cultural offer for both kids and grown-ups, excellent food and wine products, but with geothermal vents being the main attraction. Larderello houses the intriguing Museum of Geothermal Power, and with 30 thousand tickets sold each year, it’s undoubtedly the highlight, while inside the Larderello 3 power plant, a concert arena was set up in 2017 to house musical and theatrical performances. The wide and varied sustainable tourism offer is completed with nature treks in the Biancane di Monterotondo Marittimo and the Fumarole di Sasso Pisano natural parks.
Tuscany served tourists another tasty encore in 2009 with the world’s first Renewable-power Food community: a food farming association uniting several businesses and entrepreneurs. What do they have in common? A varied, world-class range of foodstuffs like cheese, olive oil, vegetables, beers and wines, all produced with geothermal energy.
Geothermal energy in the world
In 2021, according to the most recent International Renewable Energy Agency (IRENA) report, global installed geothermal capacity was 16 Gigawatts, or 0.5% of total renewables, with more than 30 countries producing geothermal electricity.
The United States, a global leader in the sector, has an installed capacity of more than 3.7 GW.
The Philippines, with about 1.9 GW, covers nearly one-fifth of its electricity demand with geothermal.
Indonesia has installed about 2.2 GW, and is aiming for significant expansion.
In Asia, Japan has 576 MW.
Mexico is also a significant player, with nearly 1 GW of installed capacity, mostly in the Cerro Prieto region.
New Zealand has 1,042 MW.
Iceland has less installed capacity (about 0.7 GW) but uses geothermal mainly for heat production, with which it covers almost 90% of the country's domestic heating needs.
Turkey, on the other hand, with 1.7 GW of capacity, is seeing rapid growth through new geothermal projects.
Africa, particularly Kenya, is significantly advancing geothermal production, which currently amounts to 985 MW of installed capacity.
In the ranking of the top 10 geothermal electricity-producing nations, Italy is also included, with an installed capacity of 916 MWe.
Innovation and the future
Technological innovation in geothermal energy is making the field increasingly efficient and versatile. One of the main examples is the introduction of advanced drilling techniques, such as laser or plasma drilling, which enable greater depths to be reached while reducing exploration costs.
Furthermore, Enhanced Geothermal Systems (EGS) use fluid injections to increase the permeability of hot but dry rocks, expanding the possibilities for use even in areas not naturally rich in resources.
Another important type of innovation involves improved binary cycles, which enable heat sources to be enhanced at lower temperatures through the use of low-boiling point fluids. In addition, the integration with Grids of district heating and energy storage systems is optimizing the use of geothermal heat for thermal purposes and for balancing electrical generation from nonprogrammable renewable sources, such as solar and wind.
In some countries – such as Canada, Colombia, and Hungary – several pilot projects are being implemented to use or re-purpose existing wells in oil and gas fields in order to recover geothermal energy, at significantly reduced costs.
Research on mineral recovery from geothermal springs has intensified in recent years. Successful demonstration projects in France, Germany, Iceland, New Zealand, the United Kingdom, and the United States have shown that the production of lithium and silicon dioxide is technically feasible. Large-scale commercial projects still depend on further development to make the process economically and environmentally sustainable.
