Comprehensive life cycle assessment of selected seasonal thermal energy storage systems

The utilization of seasonal thermal energy storage (sTES) systems is essential for balancing fluctuations between demand and surplus of heating/cooling in modern energy systems and to reduce overall greenhouse gas emissions from space heating. However, large storage volumes are required to store the heat over extended periods leading to a high demand for construction materials and processes. Yet, no comprehensive environmental evaluation compares sTES technologies across their life cycle phases. This study employs life cycle assessment to quantify the environmental impacts of three different type of sTES: a tank thermal energy storage (TTES), a water-gravel thermal energy storage (WGTES), and a pit thermal energy storage (PTES). Aquifer thermal energy storage (ATES) systems are also included as reference for evaluating the results. Greenhouse gas emissions from the construction phase vary between 1.4 (PTES) and 29.4 g CO2-eq/kWhth (WGTES), depending on the type of installation, storage size, and construction materials. Utilizing water as a filling material and large storage volumes with reduced surface-to-volume ratios enhance environmental performance. Controversely, materials such as concrete, steel, foam glass gravel, and related transport processes contribute significantly to the environmental impact. These should be replaced wherever possible by sustainable alternatives without compromising storage capacity and efficiency.