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Geothermal energy

Harnessing the Earth's heat

Reading time: 7 min

What is geothermal energy?

Geothermal energy is a renewable, clean, and inexhaustible energy obtained by harnessing the heat of the Earth’s interior stored in rocks, soils, and groundwater.

This energy resource is present everywhere, but it can only be harnessed in locations with specific physical conditions. In the most favorable locations, it can be found naturally in hot springs, geysers, or volcanoes.

This renewable source is a key element in the path towards decarbonization as it can cover an important part of the demand for air conditioning and electricity in our buildings and industries. To give us an idea, a geothermal plant of about 10 MW is capable of producing annually enough energy to power more than 23,000 homes, and its use would avoid emitting about 57,000 tonnes of CO₂ each year.

How is geothermal energy obtained and how does it work?

The earth is made up of different strata or rock layers from the center to the outside. Its core is a solid, incandescent mass composed of minerals, gases, and molten rocks. When rainwater seeps through the Rarth’s crust, it forms mantles, deep-water streams, and confined aquifers. When they come into contact with high subsurface temperatures, they create a geothermal reservoir formed by water and steam at elevated temperatures.

Now, let’s take a look at how this precious natural resource is obtained:

Drilling

To access this source of hot water from underground, you must locate and drill in the appropriate area. These boreholes are usually between 10 and 15 centimeters in diameter and their depth depends on the physical and geological conditions of the area.

Extraction

Geothermal probes in the form of pipes are then inserted. These contain water or antifreeze liquid that when descending to the deepest zones is heated and rises again driving a pump where the heat exchange takes place.

Production

To transform the heat energy into electricity, a geothermal plant must be installed on the reservoir to collect the natural fluid (water and steam) and transform it into mechanical energy using a turbine. Generally, water and steam are separated.

The steam generated in this process is conducted through a network of pipes to produce thermal or electrical energy. In turn, the water can be used directly as domestic water or to heat homes. Once used, it is channeled back into the subsoil. Thanks to the latest technology, the fluid circulates at all times in a closed circuit without any emission of gases into the atmosphere, and when it cools, it's returned to the subsoil as water, where it once again captures the heat.

Advantages of geothermal energy

Geothermal energy is a renewable source of continuous production, 24 hours a day, 365 days a year.

It is a stable energy, as it doen't depend on wind or sun fluctuations.

Geothermal installations have a low visual impact and don't generate emissions. In addition, they take up a small amount of land and are compatible with other uses.

It is an indigenous resource that avoids dependence on foreign energy.

Uses and applications of geothermal energy

The possibilities of using and developing geothermal energy depend mainly on two factors: temperature and thermal fluid flow.

At low temperature (less than 100 degrees Celsius)

It's used for thermal utilization in industrial and agricultural processes.
It's also used in district heating and cooling systems.
Finally, in spas or to generate domestic hot water.

Medium temperature (between 100 and 150 degrees Celsius):

It is mainly intended for thermal use in various sectors such as the industrial, residential, or service sector.
Secondarily, it is used to generate electricity.

High temperature (over 150 degrees Celsius):

It can directly transform water vapor into electricity.
It is also used, eventually, in heating systems.

Some of the uses of geothermal energy in the home include geothermal heating, underfloor heating, domestic hot water, and geothermal heat pumps for heating or cooling buildings.

Repsol adds geothermal energy to its multi-energy supply

At Repsol, the first company in its sector to set itself the goal of zero net emissions by 2050, we have developed a unique and differential value proposition for our customers. Therefore, we have the most complete offer of sustainable energy solutions for the home, mobility, and the industrial sector.

To complete this multi-energy offer, our Company is studying the feasibility of developing geothermal energy in the Canary Islands. The geothermal potential of some of the islands could be sufficient to install plants that would supply electricity to a significant proportion of the population, providing the archipelago with an emission-free energy source, as well as greater energy independence than it currently has. For the time being, we'll carry out evaluations of this geothermal potential in Gran Canaria, for which it has requested geothermal exploration permits from the island government authorities.