Comprehensive life cycle assessment of a large tank thermal energy storage in a district heating system

: Decarbonization of urban energy systems is critical for achieving climate neutrality, with district heating systems (DHS) representing an opportunity to integrate sustainable heat sources. Tank thermal energy storages (TTES) enable temporal decoupling of heat generation and demand, while enhancing flexibility and efficiency in DHS. This study presents a life cycle assessment (LCA) of a TTES in Linz, Austria, following ISO 14040/44 standards and employing the ReCiPe 2016 midpoint method. The assessment covers construction, operation, and end-of-life phases, with heat supplied by different generation units. Multifunctionality of combined heat and power units was addressed using exergy-based, Finnish, and substitution methods across multiple scenarios, with a functional unit of 1 MWh thermal energy delivered to the DHS over a 30-year TTES lifetime. Results demonstrate that the operational phase dominates environmental impacts, contributing over 99.25 % of climate change emissions, whereas construction burdens remain below 1 %, which is also due to the high energy throughput of the daily to weekly storage. Scenario analysis demonstrates that allocation method choice critically influences LCA outcomes, ranging from -115.2 to 808.3 kg CO 2 -eq/MWh for TTES. Findings highlight the importance of modeling operational dynamics and multifunctionality in TTES-LCA studies.