Techno-Economic Assessment of Aquifer and Pit Thermal Energy Storage (ATES and PTES)

Achieving a fully renewable energy system requires the integration of diverse heat sources to meet the thermal demands of residential, commercial, and industrial buildings. Modern district heating and cooling networks (DHNs) are crucial to this transition, as they enable the integration of variable renewable heat sources, including solar thermal, geothermal energy, and industrial waste heat. The seasonality of many renewable heat sources leads to a mismatch between supply and demand that must be addressed on both short-term and long-term timescales. Seasonal thermal energy storage (STES) technologies offer a solution to the challenge of balancing energy supply and demand. STES involves charging storage systems during periods of surplus heat in summer and discharging energy during times of higher demand in winter. Thermal energy can be stored underground using aquifer-, pit-, tank-, and borehole thermal energy storage systems (ATES, PTES, TTES, BTES). A comprehensive technical and economic assessment is therefore essential to identify the optimal solution. This thesis analyzes ATES and PTES at the storage‐system level to determine which technology offers superior thermal efficiency and achieves the lowest levelized cost of storage (LCOS). For the technical assessment of ATES, the results from a Python-based simulation tool are used to quantify storage efficiency over annual charge and discharge cycles. The performance of PTES is evaluated using an in-house Excel model. It computes the geometry of the pit, quantifies the heat losses across the surfaces, and simulates the system's dynamic thermal behavior during charging, discharging, and idle phases. The economic analysis calculates capital expenditures (CAPEX) and operational expenditures (OPEX) for each storage concept, and computes LCOS as the key economic performance indicator. A sensitivity analysis is performed to identify the economic drivers that influence LCOS of ATES and PTES. All technical and economic assessments are conducted for three temperature scenarios to capture the effects on efficiency and cost. Finally, a Pareto‐front diagram synthesizes performance and cost outcomes, highlighting which technology achieves the lowest LCOS and the highest efficiency. The findings furnish decision-makers with a basis that can assist in selecting the most suitable seasonal thermal-storage technology.