High-temperature aquifer thermal energy storage for low-carbon energy districts in Southern Europe

Seasonal thermal energy storage combined with district heating networks represents a promising pathway for reducing greenhouse gas emissions from urban heat supply. This study investigates the energy and environmental impacts of integrating a high-temperature aquifer thermal energy storage (HT-ATES) system into the district heating network of Tirano, northern Italy. The objective is to evaluate the contribution of HT-ATES to district heating decarbonization under hydrogeological conditions that are relatively unfavourable for thermal energy storage. The proposed system combines long-term thermal energy storage with renewable-based heat-supply technologies, including biomass boilers and a cogeneration plant, while retaining a diesel boiler solely as backup. System performance is simulated dynamically in TRNSYS 18 using real heating-demand data, whereas aquifer thermal behaviour is modelled in FeFlow to represent groundwater flow and heat transport. Despite the challenging storage conditions, the HT-ATES system achieves a thermal recovery efficiency of 25.2 % and enables the district heating network to operate with minimal reliance on fossil fuels. Under the assumption of climate-neutral renewable energy sources, the proposed configuration achieves carbon neutrality. These results demonstrate that meaningful decarbonization can be achieved even in non-ideal hydrogeological settings, highlighting the potential of HT-ATES to integrate surplus renewable thermal energy into district heating systems.