Underground Thermal Energy Storage in dense urban areas

TOPIC ID: HORIZON-CL5-2026-02-D3-22

Type of grant: Call for proposals

General information

Programme:

Call: Cluster 5 Call 02-2026 (WP 2025) (HORIZON-CL5-2026-02)

Type of action: HORIZON-IA HORIZON Innovation Actions

Type of MGA: HORIZON Lump Sum Grant [HORIZON-AG-LS]

Status: Forthcoming

Deadline model: single-stage

Planned Opening Date: 16 September 2025

Deadline dates: 17 February 2026 17:00 (Brussels time)

Topic description

Project results are expected to contribute to all of the following expected outcomes:

• Advanced European innovative knowledge basis and increased technology competitiveness in the area thermal storage;
• Improved security of the future European renewable-based energy system;
• Contribution to the decarbonisation of cities and densely populated urban areas with high safety solutions;
• Significant reduction of LCOHS (Levelised Cost of Heat Storage);
• Local communities are engaged and their expectations are responded to.
• Technology developers practice inclusive societal engagement which is early, continuous, and sensitive to the technical specificities (e.g. local resource, subsurface uncertainties) and social challenges (e.g. low public awareness) of underground thermal energy storage technologies in the context of densely populated urban areas.

In scope are novel technologies, interfaces, design methods and organisational concepts that result in the most effective and sustainable use of subsurface space in dense urban areas by Underground Thermal Energy Storage (UTES) systems such as ATES, CTES and BTES.

Proposals should consider the integration in the existing energy grids and interaction with other urban uses of the subsurface (e.g., subways, underground utilities, buildings), including energy geostructures of buildings, tunnels, slabs, energy sheet pile walls, etc., with potential geothermal heating, cooling, and sinks or storage opportunities.

Proposals should address the uncertainties in the seasonal energy demand to increase the predictability of the required subsurface space, the interactions among systems for the sake of optimal use of subsurface and thermal efficiency.

Projects are expected to deploy one or more demonstrators and can address, for example, one or more of the following exemplary areas:

• Optimal utilisation of geothermal resources and thermal energy storage in urban settings, addressing high (above 70 degrees Celsius), medium (30-70 degrees Celsius) and/or low temperatures (10-30 degrees Celsius) and possible requirements for retrofitting of the building stock;
• Subsurface models for a sustainable underground thermal storage and geothermal use in cities;
• The integration of heat pumps, advanced thermal storage, and interface with district heating infrastructures to contribute to the thermal and power grid flexibility;
• Studying the impact of subsurface urban heat islands (SUHI) on the potential of shallow geothermal energy use in cities, using, for instance, long-term subsurface monitoring networks, satellite monitoring and models;
• Best practices strategies for subsurface land-use plans in European cities; well/borehole placement strategies;
• Mutual interaction of existing and future neighbouring UTES systems from geotechnical, energy, and regulatory point of view;
• Management of energy grids on an urban scale and system optimisation thorough digital twins predicting operational, environmental and economic response, as well as the interaction between the storage system and the local grids, under different scenarios;
• Creation of large (time and scale-wise) open multisensory datasets to foster heat energy storage at the European scale which should adhere to the FAIR data principles, adopt data quality standards, data integration operating procedures and GDPR-compliant data sharing/access good practices developed by the European research infrastructures, where relevant.
• Use of advanced monitoring systems such as fibre optic sensors, satellite imagery, etc. for monitoring and early detection of adverse impact of UTES at a district scale level and providing measures to mitigate such effects.

Consideration should be given to de-risking solutions, and dedicated support schemes that guide innovative energy storage technologies through to the commercialisation stage. The consortium should assess the current regulatory context and provide recommendations linked to the proposed solutions for shaping future needs (e.g., regulatory, standardisation, permitting). In addition, appropriate local community engagement initiatives as well as expectations and experiences of underground thermal storage infrastructures (and to what extent it varies in dense urban areas) should be explored.

This topic requires citizens engagement and dialogue and the effective contribution of SSH disciplines and the involvement of SSH experts, institutions as well as the inclusion of relevant SSH expertise, in order to produce meaningful and significant effects enhancing the societal impact of the related research activities and ensure the translation of innovation into real-life outputs.

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The submission system is planned to be opened on the date stated on the topic header.

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