Could underground heat islands be a new energy source for cities?
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According to a study published in July 2023 by Northwestern University (Illinois, USA), underground urban infrastructure (car parking, tunnels, pipelines, cables) emit residual heat that is stored in subsurface strata and weakens rock and construction materials, especially concrete and clay, but also granite and limestone to some extent. While it rules out any danger to people, the study describes phenomena including cracking, fissuring and settling of foundations, and pollution of underground water, that could affect the quality of some services, including transport. But these subsurface heat islands are also potential sources of geothermal energy. Hence the recommendation from the study’s authors to use geothermal technologies to capture this surplus heat and redistribute it to buildings and energy networks on the surface.