Periodic Reporting for period 1 - INTERSTORES (International Innovation Network for the Development of Cost- and Environmentally Efficient Seasonal Thermal Energy Storages)
Reporting period: 2024-01-01 to 2025-05-31
Meeting the growing demand for sustainable energy poses a challenge as future systems integrate diverse renewable sources with storage solutions. Seasonal thermal energy storage (sTES) solutions become crucial for peak-shaving and load-shifting, optimising decentralised energy use. In this context, the EU-funded INTERSTORES project brings together 14 partners across 9 countries, aiming to enhance market acceptance and competitiveness by revolutionising sTES technology. By focusing on two innovative sTES variants, Reno-sTES and Giga-CTES, the Project seeks to demonstrate their international market potential. Through full-scale realisation and careful examination of design, costs and environmental impacts, INTERSTORES is set to bridge critical gaps, ensuring reliable, replicable, robust facilities. The Project’s holistic approach promises to reshape the landscape of Europe’s future energy systems.
During this period, two seasonal thermal energy storage (sTES) technologies (Reno-sTES and Giga-CTES) were advanced using a unified methodology adapted to site-specific and technological conditions. Tailored experimental, digital, economic, and environmental approaches were developed, and preparation began at both sites. Monitoring was installed across storage, energy systems, and ambient domains. Integrated planning and execution enabled coordinated data acquisition, while early activities focused on extensive characterisation measures. These included technological, geological, economic, and environmental methods. Thus, comparability supporting assessments of cost, performance, and replicability can be ensured as planned.
At the Reno-sTES site, existing basins are being converted into cost-efficient water-gravel thermal storage, with completion targeted for autumn 2025. Existing materials are reused in line with circular economy principles. Refined monitoring with thermal and moisture sensors is included, and the connection to the energy system is prepared. Real-time data will feed into INTERSTORES’ digital twin framework to support replicable, scalable evaluation. WGTES fillings and insulation materials were assessed for moisture resistance and long-term performance.
At the Giga-CTES site, construction of the world’s largest cavern thermal energy storage system is set to begin in late 2025, with commissioning expected in 2028. In line with a refined design based on techno-economic optimisation, geological and system investigations were conducted. Monitoring equipment was installed around the site, with further installations planned inside the storage. These will support the digital twin during the heat-up phase. Components were studied for durability under extreme conditions using autoclave and electrochemical methods.
A modular framework was established to integrate ground, storage, and energy system models using simplified approaches validated with detailed datasets. These models support optimisation, sensitivity analysis, predictive control, and fault detection. Basin compound and heat exchanger simulations were conducted for Reno-sTES, while a flexible variant was prepared for the digital twin. For the Giga-CTES, simulations refined diffuser designs, and a multiphysics model is being established in alignment with the construction timeline. Energy system models were developed to ensure efficient sTES integration. Regional demand data were used for the Giga-CTES. For the Reno-sTES, potentials were studied through a local model. Digital control and optimisation tools are under development. Subsurface models for both sites capture key processes, including geological features, thermal-hydraulic-mechanical behaviour, and porous media interactions. These are being refined with field data to inform planning and operation.
Environmental performance was addressed through development of a flexible Life Cycle Assessment framework. Site-specific inventories of material, energy, and resource use employed early design data and are updated during construction. A recycling strategy was initiated to align with circular economy objectives, supporting a comprehensive environmental assessment across sTES variants.
A techno-economic evaluation was launched to assess all relevant life cycle costs. Supporting documentation and the planned user guide are in early preparation. Stakeholder mapping, spatial analyses, and geological assessments are in progress to identify potential replication sites. On this basis, market readiness and opportunities for broader sTES deployment across Europe will be explored.
At the Reno-sTES site, existing basins are being converted into cost-efficient water-gravel thermal storage, with completion targeted for autumn 2025. Existing materials are reused in line with circular economy principles. Refined monitoring with thermal and moisture sensors is included, and the connection to the energy system is prepared. Real-time data will feed into INTERSTORES’ digital twin framework to support replicable, scalable evaluation. WGTES fillings and insulation materials were assessed for moisture resistance and long-term performance.
At the Giga-CTES site, construction of the world’s largest cavern thermal energy storage system is set to begin in late 2025, with commissioning expected in 2028. In line with a refined design based on techno-economic optimisation, geological and system investigations were conducted. Monitoring equipment was installed around the site, with further installations planned inside the storage. These will support the digital twin during the heat-up phase. Components were studied for durability under extreme conditions using autoclave and electrochemical methods.
A modular framework was established to integrate ground, storage, and energy system models using simplified approaches validated with detailed datasets. These models support optimisation, sensitivity analysis, predictive control, and fault detection. Basin compound and heat exchanger simulations were conducted for Reno-sTES, while a flexible variant was prepared for the digital twin. For the Giga-CTES, simulations refined diffuser designs, and a multiphysics model is being established in alignment with the construction timeline. Energy system models were developed to ensure efficient sTES integration. Regional demand data were used for the Giga-CTES. For the Reno-sTES, potentials were studied through a local model. Digital control and optimisation tools are under development. Subsurface models for both sites capture key processes, including geological features, thermal-hydraulic-mechanical behaviour, and porous media interactions. These are being refined with field data to inform planning and operation.
Environmental performance was addressed through development of a flexible Life Cycle Assessment framework. Site-specific inventories of material, energy, and resource use employed early design data and are updated during construction. A recycling strategy was initiated to align with circular economy objectives, supporting a comprehensive environmental assessment across sTES variants.
A techno-economic evaluation was launched to assess all relevant life cycle costs. Supporting documentation and the planned user guide are in early preparation. Stakeholder mapping, spatial analyses, and geological assessments are in progress to identify potential replication sites. On this basis, market readiness and opportunities for broader sTES deployment across Europe will be explored.
Already in this reporting period, INTERSTORES advanced its two complementary sTES concepts, demonstrating their potential to support Europe’s transition toward climate-neutral energy systems. On the one hand, the Reno-sTES illustrates how circular construction and low-impact integration can provide flexible storage solutions. On the other hand, the Giga-CTES, though still in its early construction phase, holds its promise as a large-scale, high-temperature storage facility capable of transforming regional energy systems. This dual strategy applies to a wide range of European contexts beyond the state of the art.
Early findings suggest both concepts can significantly reduce emissions and improve grid flexibility as well as sector coupling. Yet, full realisation of this potential requires further project efforts: longer-term operational monitoring will be essential to confirm performance. Transfer sites in diverse settings will strengthen transferability. Hence, continued work is needed to optimise control, material behaviour, and sTES integration.
The foreseen environmental evaluations will confirm the low-impact nature of sTES technologies, based on circularity measures, e.g. reuse of materials and local resource cycles, which have not been implemented before. These benefits must and will be made visible through robust LCA and harmonised sustainability proofs to support broader acceptance and policy alignment.
Market uptake depends on viable business models. High upfront costs, especially for large-scale systems, demand supportive financing and recognition of sTES as critical infrastructure. Tools (e.g. the digital twin) require structured innovation management and IPR support to ensure competitiveness, as foreseen in the activities.
Policy and regulatory frameworks must and will be actively evolved to accelerate uptake. Clearer integration of sTES into climate strategies and streamlined permitting processes are proposed. Standardisation can also help to improve planning certainty. Such frameworks will be vital in building stakeholder confidence; INTERSTORES is committed to further enhancing these key elements.
Efforts to map transfer sites and assess market readiness have laid a foundation for future replication and internationalisation beyond current knowledge. However, real progress will depend on the strategic alliances to be developed in the coming project periods.
In summary, INTERSTORES delivered the proposed, essential groundwork for mainstreaming sTES in Europe. Its combination of technical innovation, digital capability, and environmental responsibility offers a pathway to low-carbon heating. Beyond the project’s scope, realising full impact will require further demonstration, targeted investment, regulatory support, and international momentum.
Early findings suggest both concepts can significantly reduce emissions and improve grid flexibility as well as sector coupling. Yet, full realisation of this potential requires further project efforts: longer-term operational monitoring will be essential to confirm performance. Transfer sites in diverse settings will strengthen transferability. Hence, continued work is needed to optimise control, material behaviour, and sTES integration.
The foreseen environmental evaluations will confirm the low-impact nature of sTES technologies, based on circularity measures, e.g. reuse of materials and local resource cycles, which have not been implemented before. These benefits must and will be made visible through robust LCA and harmonised sustainability proofs to support broader acceptance and policy alignment.
Market uptake depends on viable business models. High upfront costs, especially for large-scale systems, demand supportive financing and recognition of sTES as critical infrastructure. Tools (e.g. the digital twin) require structured innovation management and IPR support to ensure competitiveness, as foreseen in the activities.
Policy and regulatory frameworks must and will be actively evolved to accelerate uptake. Clearer integration of sTES into climate strategies and streamlined permitting processes are proposed. Standardisation can also help to improve planning certainty. Such frameworks will be vital in building stakeholder confidence; INTERSTORES is committed to further enhancing these key elements.
Efforts to map transfer sites and assess market readiness have laid a foundation for future replication and internationalisation beyond current knowledge. However, real progress will depend on the strategic alliances to be developed in the coming project periods.
In summary, INTERSTORES delivered the proposed, essential groundwork for mainstreaming sTES in Europe. Its combination of technical innovation, digital capability, and environmental responsibility offers a pathway to low-carbon heating. Beyond the project’s scope, realising full impact will require further demonstration, targeted investment, regulatory support, and international momentum.