There is great potential in the subsoil of cities to generate energy through renewable sourcesThese energies take advantage of existing infrastructures, such as subway tunnels, underground pipelines or even the footsteps of pedestrians. A key aspect is the ability to take advantage of air currents or residual heat from these underground spaces. This approach makes it possible to reduce dependence on fossil fuels and contribute to greater sustainability in urban areas.
Wind energy underground
One of the first applications that has begun to be explored is the generation of Wind power in subway tunnelsIn cities, trains running on these infrastructures create air currents that can be used by tunnel energy for the installation of small wind turbines.
The passage of trains generates an air movement known as the “piston effect”, with an average speed of up to 6 kilometres per hour. Wind turbines designed for these confined spaces can produce wind energy, generating up to 1 watt for each wind turbine installed.
Francisco Bugarín, CEO of Tunel Energy, highlights that the versatility of the project allows the wind turbines to be installed on different surfaces, such as factories or even schools.
These currents are not only used to generate electricity in subway tunnels, but also in factory or school corridors, where constant air currents are produced. The wind turbines are modular and can be adjusted to the energy needs of each site. For example, just three of these small wind turbines could power a three-watt LED light bulb.
In addition to the low installation cost, estimated at around three hours, one of the main advantages of this system is its easy maintenance. The modular system allows the infrastructure to be scaled according to the energy demands of each environment.
Underground thermal energy generation
Another renewable source being studied is the utilization of residual heat generated in tunnels, stations and underground water pipes. In places like the Metro de MadridThe heat generated by stations and trains can be reused to heat nearby spaces.
At stations such as Puerta del Sol, researchers from the Polytechnic University of Madrid (UPM) They have estimated that the residual heat can generate enough thermal energy to supply several homes or even public buildings. This heat is stored and can be used for heating sanitary water or reduce heating costs in other adjacent infrastructures.
The city of London is another innovative example. In the Islington district, waste heat generated in the underground is reused to produce thermal energy, enough to power more than 600 homes and a state school. This approach has shown that large cities have great potential to harness underground renewable energy effectively.
In addition to London, other cities such as Vienna y Helsinki They have implemented similar systems to take advantage of the heat generated by their metro networks, significantly reducing CO2 emissions.
Applications of geothermal energy in the urban environment
La geothermal is another renewable technology that can be used in cities. This energy comes from the heat stored underground, and in urban environments it is mainly used for pool heating through heat pumps.
In Madrid, the Madrid Subterra Association is working on innovative projects that seek to take advantage of geothermal heat not only in private homes, but also in large infrastructures, such as the Comprehensive Transportation Center Madrid. This geothermal system, located next to Plaza de Castilla, will allow large spaces to be heated with considerable energy savings, as well as reducing CO70 emissions by up to 2%.
La Polytechnic University of Valencia has also demonstrated the potential of geothermal energy for air conditioning large buildings. In this sense, the Feria de Madrid (IFEMA) has implemented geothermal systems that allow significant savings in its energy costs.
Another example can be found in the city of Paris, where entire neighbourhoods are heated thanks to geothermal networks. This technology is not only applied to individual homes, but covers up to 60% of the energy demands of several districts in the south of the city.
Urban innovations: harnessing waste energy
Waste heat has also become an emerging source of energy in urban environments. This heat, which
Generally lost in sewage systems, subway stations or traffic tunnels, it can be reused for thermal purposes in nearby buildings and offices.
En Madrid, the Community is betting on taking advantage of these underground infrastructures to promote the decarbonization and improve energy efficiency. According to its Energy, Climate and Air Strategy 2023-2030, the use of these residual energies will be key to fighting against the heat island affecting large cities.
One of the most notable initiatives is the regenerative braking system in the Madrid Metro, which converts kinetic energy into electricity, allowing it to be reused in the underground facilities. This technology could be integrated with energy storage systems for use during peak hours.
The Moratalaz sports centre takes advantage of underground water wells to generate thermal energy, achieving a 39% saving on the energy bill of sports facilities.
In increasingly sustainable cities, such as Helsinki or New York, waste heat is used not only to heat homes, but also to reduce significant amounts of carbon emissions. These pioneering cities demonstrate that waste energy from underground is a key element in the energy transition.
The great potential of urban subsoil is becoming increasingly important in the transition towards clean energy. Harnessing renewable and non-conventional energy in underground infrastructure is not only an innovative solution, but an urgent need to mitigate climate change and improve sustainability in cities.