Energy storage plays a crucial role in decarbonizing the global energy system, particularly in the heating sector, which accounts for nearly 50 % of global energy demand. However, a significant challenge remains in balancing supply and demand from renewable energy sources. High-Temperature Aquifer Thermal Energy Storage (HT-ATES) presents a promising solution by enabling seasonal energy storage and shifting thermal loads efficiently. The successful implementation of HT-ATES requires a comprehensive understanding of both subsurface geological conditions and surface constraints to identify optimal storage sites. This study introduces a favorability assessment framework for HT-ATES systems across the Swiss Molasse Plateau (SMP), utilizing spatial multi-criteria play-based analysis (SMCPBA). Two key geological targets—the Cenozoic Molasse and Upper Mesozoic formations—are assessed alongside energy system criteria to pinpoint high-potential areas for future development. The findings highlight major urban centers such as Geneva, Lausanne, and Zurich as prime candidates due to their significant heat demand. However, broad-scale estimations necessitate higher-resolution data and site-specific feasibility studies for accurate assessment and implementation. The scalability of this methodology makes it applicable to various geographic contexts, supporting targeted pilot projects and feasibility assessments. Advancing HT-ATES technologies through refined methodologies and practical applications will contribute to Switzerland’s sustainable energy transition and long-term energy resilience.

High-Temperature – Aquifer Thermal Energy Storage (HT-ATES) can significantly increase Renewable Energy Sources (RES) capacity and storage temperature levels compared to traditional ATES, while improving efficiency. Combined assessment of subsurface performance and surface District Heating Networks (DHN) is key, but poses challenges for dimensioning, energy flow matching, and techno-economic performance of the joint system. We present a novel methodology for dimensioning and techno-economic assessment of an HT-ATES system combining subsurface, DHN, operational CO ₂ emissions, and economics. Subsurface thermo-hydraulic simulations consider aquifer properties (thickness, permeability, porosity, depth, dip, artesian conditions and groundwater hydraulic gradient) and operational parameters (well pattern and cut-off temperature). Subject to subsurface constraints, aquifer permeability and thickness are major control variables. Transmissivity ≥2.5 × 10 ⁻¹² m³ is required to keep the Levelised Cost Of Heat (LCOH) below 200 CHF/MWh and capacity ≥25 MW is needed for the HT-ATES system to compete with other large-scale DHN heat sources. Addition of Heat Pumps (HP) increases the LCOH, but also the nominal capacity of the system and yields higher cumulative avoided CO ₂ emissions. The methodology presented exemplifies HT-ATES dimensioning and connection to DHN for planning purposes and opens-up the possibility for their fully-coupled assessment in site-specific assessments.

The storage of heat in aquifers, also referred to as Aquifer Thermal Energy Storage (ATES), bears a high potential to bridge the seasonal gap between periods of highest thermal energy demand and supply. With storage temperatures higher than 50 °C, High-Temperature (HT) ATES is capable to facilitate the integration of (non-)renewable heat sources into complex energy systems. While the complexity of ATES technology is positively correlated to the required storage temperature, HT-ATES faces multidisciplinary challenges and risks impeding a rapid market uptake worldwide. Therefore, the aim of this study is to provide an overview and analysis of these risks of HT-ATES to facilitate global technology adoption. Risk are identified considering experiences of past HT-ATES projects and analyzed by ATES and geothermal energy experts. An online survey among 38 international experts revealed that technical risks are expected to be less critical than legal, social and organizational risks. This is confirmed by the lessons learned from past HT-ATES projects, where high heat recovery values were achieved, and technical feasibility was demonstrated. Although HT-ATES is less flexible than competing technologies such as pits or buffer tanks, the main problems encountered are attributed to a loss of the heat source and fluctuating or decreasing heating demands. Considering that a HT-ATES system has a lifetime of more than 30 years, it is crucial to develop energy concepts which take into account the conditions both for heat sources and heat sinks. Finally, a site-specific risk analysis for HT-ATES in the city of Hamburg revealed that some risks strongly depend on local boundary conditions. A project-specific risk management is therefore indispensable and should be addressed in future research and project developments.