Geospatial analysis for identifying suitable sites for subsurface seasonal thermal energy storage : a case study of city of Zurich

With the ongoing expansion of district heating networks in Switzerland and many other European countries, there is a growing need for energy storage, both short-term and long-term to decarbonize the heating sector. Seasonal Thermal Energy Storage (STES) systems provide a sustainable and low-cost means for balancing energy demand and supply throughout the year, particularly in regions with fluctuating seasonal heating and cooling requirements. While in the cities, available space for large storage facilities is highly limited there is a large, untapped potential for energy storage in the subsurface. Many underground thermal energy storage (UTES) options are available to decarbonize the heating sector and are well explored internationally, including aquifer thermal energy storage (ATES), borehole thermal energy storage (BTES), pit thermal energy storage (PTES) or cavern thermal energy storage (CTES). The exploitation of the available UTES potential is key for the security of supply and the decarbonization of the heating sector. The consideration of potential STES sites and technologies is currently not part of the strategic energy planning on the level of cantons and municipalities such that many opportunity windows will close as the expansion of the district heating networks progresses. To address this challenge, this study introduces a geospatial analysis methodology developed to systematically identify suitable sites for STES systems by integrating multiple critical factors. Key factors include proximity to demand centers, existing infrastructure, and waste or excess energy sources; availability of local renewable energy sources; and site properties such as slope, land ownership, and size. Further datasets such as groundwater maps or other geological features can be integrated. The approach employs publicly available Geographic Information System (GIS) data to map and evaluate these criteria spatially. The proposed multi-criteria analysis, tested in the city of Zurich, produces a ranked long list of potential sites for STES deployment. In a further step, various short-lists can be created by selective weighting of individual criteria, giving stronger weights e.g. to STES technology-specific aspects or spatial planning aspects. This paper outlines the geospatial methodology, incorporating the role of renewable and waste energy sources in guiding site selection. The preliminary findings from the Zurich case study demonstrate the effectiveness of the approach and its potential to help identify suitable sites for Seasonal Thermal Energy Storage (STES) systems in other urban areas.