Sizing optimization of district heating components with High-Temperature Aquifer Thermal Energy Storage: Techno-economic analysis for different renewable energy levels

District heating systems must decarbonize by replacing fossil fuel-based heat sources with sustainable alternatives. To fully utilize the capacity of renewable sources, seasonal thermal energy storage is necessary due to seasonal supply–demand mismatches. High-Temperature Aquifer Thermal Energy Storage (HT-ATES) offers a promising solution, but its cost-effective deployment requires coordinated sizing with the sustainable heat source, which has received limited attention in literature. This study presents a techno-economic and renewable share analysis of district heating systems incorporating deep geothermal heat, solar thermal collectors, HT-ATES, and gas boilers. We identified representative heat demand profiles for different climates by clustering to ensure broader applicability of the findings. We show that the demand profile is important for the cost-effectiveness of district heating. The results show that HT-ATES is cost-effective in most scenarios compared to natural gas boilers, particularly when paired with a geothermal source. Geothermal energy was generally more economically favorable than solar thermal collectors. Achieving 100% renewable heat supply is cost-inefficient because it requires large additional capacity for limited additional load, increasing costs by 15% compared to 99% renewable share. However, 90% renewable share can be reached with only 5% cost increase compared to the optimum, using geothermal energy. These insights provide guidance for district heating designers, operators and policymakers on optimal component sizing and promote the informed use of HT-ATES to support cost-effective decarbonization of district heating. Representative demand profiles are expected to be used often in research, as they proved influential on the levelized cost of heat.