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Geothermal potential identified in the subsoil of Tarragona places six Catalan municipalities at the center of studies on renewable air conditioning, shared thermal networks, energy efficiency, and reduction of fossil fuel use, while technical analyses measure costs, feasibility, and necessary conditions for implementation.
Included in preliminary projects of heating and cooling networks, six municipalities in the province of Tarragona are evaluating the use of shallow geothermal energy, a technology that takes advantage of the thermal stability of the subsoil through heat pumps powered by electricity.
Although the work was recorded in 2025, it does not correspond to the discovery of an unprecedented or literally infinite reserve, but to the study of a known renewable resource, available in the first 100 to 200 meters of depth in Catalan areas.
Promoted by the Cartographic and Geological Institute of Catalonia, the ICGC, the studies included the participation of the energy engineering cooperative SUNO, responsible for the six preliminary projects and the simulations related to the consumption of the considered buildings.
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At this stage, Ascó, Flix, Montbrió del Camp, Mont-roig del Camp, El Perelló, and Ulldemolins received evaluations on possible collective networks aimed at the air conditioning of properties and the production of sanitary hot water.
Shallow geothermal energy takes advantage of the stability of the terrain
Known as very low temperature geothermal energy, the energy considered in the projects is present in the first hundreds of meters of the subsoil and, according to the classification adopted by the ICGC, remains in ranges below 30 degrees Celsius.
Instead of extracting a fuel stored underground, the system promotes thermal exchanges with the terrain, using its relatively stable temperature to heat environments in winter, remove heat in summer, and assist in the supply of hot water.
For this reason, the technology cannot be described as a newly located deposit exactly at 200 meters, as the potential for exploitation varies according to geology, property demand, and the planned sizing for each capture field.
At the same time, the maps developed by the institute function as preliminary estimates and do not replace detailed studies, executive projects, or three-dimensional analyses of the subsoil, required before the construction of a geothermal facility at a given address.
Fifth-generation networks would connect different buildings
In the preliminary designs, vertical geothermal capture fields would be connected to water circulation networks, distributing thermal energy among the served buildings without transporting extremely hot or cold liquids over long distances.
Installed in each property or set of buildings, decentralized heat pumps would raise or lower the received temperature to the necessary level for heating, cooling, and sanitary hot water production at consumption points.
The preliminary designs predominantly feature a single-pipe configuration and unidirectional flow, associated with the concept of fifth-generation district networks, also known as 5GDHC, developed to work with more moderate temperatures and improve energy balance.
In parallel, technicians evaluate the integration of photovoltaic solar panels, whose electricity could support part of the water pumping and equipment operation, reducing dependence on energy acquired from the conventional grid.
Reduction of emissions depends on the electricity used
Without direct combustion at the consumption point, shallow geothermal can reduce the use of gas, oil, and other fuels in boilers, transferring heat between the ground and buildings to meet local climate needs.
With this substitution, emissions produced in the buildings themselves decrease, while the amount of carbon dioxide associated with heating and cooling can also fall when the system is correctly designed for the available geological conditions.
Still, heat pumps, electronic controls, and circulation equipment require electricity, which prevents automatically classifying the operation as entirely free of energy expenditure or carbon emissions throughout its useful life.
Depending on the efficiency of the equipment, the origin of the electricity, and the possible combination with renewable sources, the environmental footprint of the networks can only be determined after the technical definition of each project and its operational model.
Implementation requires technical and financial studies
Before any construction, the work needs to combine thermodynamic simulations of the buildings’ demand, possible routes for the pipelines, and financial, environmental, operational, and commercial evaluations adapted to the conditions found in each of the six municipalities.
Among the factors capable of altering viability are the number of connected properties, consumption profile, distance between buildings, terrain characteristics, and the cost of the necessary drilling to install geothermal probes.
As they remain in the planning phase, the preliminary projects do not mean that the six networks are built, contracted, or accompanied by a definitive schedule, as they still precede executive development, licenses, and the execution of the works.
Furthermore, the transformation of studies into infrastructure will depend on municipal decisions, funding sources, and technical results capable of demonstrating that the service can operate safely, efficiently, and in line with local demand.
Savings with air conditioning have not yet been calculated
According to the ICGC, shallow geothermal energy can generate savings in electricity or fossil fuel consumption, as well as reduce emissions, but the effective result varies depending on the installed system and the thermal needs of each building served.
In the case of the municipalities of Tarragona, confirmed percentages of bill reductions, investment values, financial return periods, or public amounts allocated to the implementation of heating and cooling networks have not yet been disclosed.
As these numbers do not exist, the claim that costs will drastically fall remains unproven, although the anticipated economic evaluations may indicate which locations have favorable technical and financial conditions to move the projects forward.
The Catalan experience demonstrates how small cities can study collective solutions for renewable air conditioning, but the concrete impact will depend on the executive projects, available funding, required authorizations, and the effective implementation of the planned infrastructure.
With the networks still under evaluation and no officially disclosed savings, will the six municipalities be able to transform the thermal potential of the subsoil into a lasting, accessible service capable of reducing dependence on conventional air conditioning systems?
