Dear Reader,

For the 55th issue of our heatbeat Research Newsletter, we take a look at geothermal usage in district heating networks.

The first paper "Medium-deep geothermal resources in the Molasse Basin: A geological, techno-economic, and ecological study of large-scale heat pump integration" from Jeßberger et al. covers the usage of a medium-depth geothermal source in combination with a heat pump for district heating application.The second paper this month gives an overview of German research sites in the field of aquifer thermal energy storage with the title "Current research on aquifer thermal energy storage (ATES) in Germany" from Stemmle et al.

The first paper titled "Medium-deep geothermal resources in the Molasse Basin: A geological, techno-economic, and ecological study of large-scale heat pump integration" presents a comprehensive assessment of the potential for integrating medium-deep geothermal systems with large-scale high-temperature heat pumps (HTHPs) in the northern South German Molasse Basin (SGMB). The goal is to identify a sustainable and cost-effective path to decarbonize district heating networks (DHNs), especially where traditional high-temperature geothermal sources are unavailable.

Unlike deep geothermal projects that require high drilling costs and reach temperatures above 80°C, medium-deep systems (at depths ≤ 2500m and temperatures ≤ 80°C) offer lower exploration costs but necessitate heat pumps to raise water temperatures for compatibility with existing DHNs. This study combines geological modeling, techno-economic analysis, and a detailed life-cycle assessment (LCA) to evaluate this hybrid approach's feasibility.

A base scenario at 1000 m depth with 45.6 °C water and 100 kg/s flow was analyzed, yielding a levelized cost of heat (LCOH) of 113€/MWh and a payback period of 5 years. Sensitivity analyses showed that LCOH could range from 77 to 151€/MWh depending on geological conditions, electricity prices, and system configurations. Deeper wells and higher brine flow rates reduce LCOH and improve performance. Environmentally, the system achieved a greenhouse gas emission intensity of 103g CO₂/kWh - close to the EU's taxonomy threshold of 100g CO₂/kWh, with electricity consumption being the dominant factor.

The study's novelty lies in its holistic regional approach, moving beyond isolated case studies. It provides actionable insights for municipal planners and policy makers as they transition to low-carbon heating solutions. Future research should explore dynamic electricity pricing, CO₂ taxation, and broader scalability under varying grid decarbonization scenarios.

The second paper ("Current research on aquifer thermal energy storage (ATES) in Germany") provides a comprehensive review of the current state of aquifer thermal energy storage (ATES) and mine thermal energy storage (MTES) research in Germany. These underground thermal energy storage (UTES) technologies are seen as critical tools to support the decarbonization of the heating and cooling sector, which represents nearly 50% of Germany's final energy consumption. ATES systems use groundwater-bearing aquifers to store thermal energy seasonally - either at low temperatures (LT-ATES) using waste heat or high temperatures (HT-ATES) from sources such as industrial waste heat or solar thermal energy.

The review covers 3 LT-ATES, 8 HT-ATES, and 2 MTES research sites across Germany. Although these studies span diverse locations and methods, most are still in early-stage development with low technology readiness levels (TRL 2-4). Notably, HT-ATES projects are more prevalent, indicating growing interest in high-temperature storage integration with district heating networks. However, few initiatives aim for real-world implementation. Key barriers include complex regulatory frameworks, permitting challenges, and site-specific constraints, especially in urban areas.

Pilot projects in Berlin, Freiburg, Mannheim, and Munich demonstrate the technical potential and innovative applications of ATES and MTES, including integration with high-temperature heat pumps and the reuse of abandoned mines. Despite positive simulation and test results, wider adoption is limited by uncertainties in economic viability, system performance, and environmental impacts.

The paper concludes by calling for more demonstration projects, streamlined regulation, and targeted R&D funding to raise TRLs. Emphasis is placed on integrating ATES into existing urban energy systems and performing comprehensive techno-economic and ecological assessments. The study positions ATES and MTES as promising yet underutilized solutions in Germany's energy transition.

Further Information

As always, we recommend reading the article in full. In addition to this research newsletter and various blog posts, we have added a monthly feature update to our blog, summarizing important developments and new features in our heatbeat Digital Twin. You can find the first entry at "https://heatbeat.de/en/blog/64/"

The next issue of our newsletter will be published on June 4, 2025.