31-08-2026
"The rocks will function as a giant battery beneath our feet," says Ricardo Pereira, NOVA FCT Researcher at GeoBioTec. Photo by João Lima/NOVA FCT
GeoBioTec Researchers, from NOVA FCT, and from the Instituto Dom Luiz, at the School of Sciences of the University of Lisbon, have just published a new study in the journal Geoenergy, which shows how porous rock formations at depth could constitute one of the most promising solutions for large-scale energy storage, helping to overcome one of the main challenges of the energy transition: storing the electricity produced by renewable sources when production exceeds consumption.
This is the first integrated study to combine geological and thermodynamic criteria to assess the potential of Compressed Air Energy Storage in Porous Media (CAES-PM), and the results show that geological reservoirs could reach storage capacities on the order of 1 terawatt-hour (TWh), enough to supply hundreds of thousands of homes. Given the increasing production of electricity from renewable sources, it is essential to have solutions capable of storing energy for days or months.
Unlike conventional batteries, compressed air storage uses the surplus electricity produced by renewable sources to compress atmospheric air, which is then injected into deep geological reservoirs. When there is a need to produce electricity, that air is released and used to drive turbines. Because it uses only atmospheric air, this technology avoids many of the risks associated with the underground storage of combustible or toxic gases, such as hydrogen or carbon dioxide.
"The study analyzes, for the first time and systematically, the influence of depth on the conditions of underground energy storage. As depth increases, pressure and temperature vary simultaneously, factors that directly affect the amount of energy that can be stored. Thus, the rocks will function as a giant battery beneath our feet," says Ricardo Pereira, NOVA FCT Researcher at GeoBioTec.
The study takes on relevance in a context where electrical systems increasingly depend on the integration of intermittent renewable energies. Long-duration storage technologies are considered essential for reducing renewable production waste, for increasing the stability of electrical grids, and for ensuring critical services, such as grid restoration after widespread failures (black start), as occurred in the blackout that affected Portugal and Spain in April 2025.
This work also highlights that the success of this technology depends not only on engineering solutions but fundamentally on rigorous geological characterization. Reservoir size, porosity, permeability, pressure limits, and geothermal conditions are determining factors for the technical and economic viability of these systems.
In addition to demonstrating the technology's high potential, the research suggests a practical methodology to support the identification and evaluation of geological reservoirs with characteristics suitable for future subsurface energy storage projects.
The scientific article, titled "Impact of Depth-Dependent Geological Controls for Assessing Energy Capacity of Subsurface Compressed Air Energy Storage in Porous Media," is authored by Ricardo Pereira, João Silva, and Jorge Maia Alves, and was published in the journal Geoenergy. You can read it here.
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