No abstract

More than 30% of Germany’s final energy consumption currently results from thermal energy for heating and cooling in the building sector. One possibility to achieve significant greenhouse gas emission savings in space heating and cooling is the application of aquifer thermal energy storage (ATES) systems. Hence, this study maps the spatial technical potential of shallow low-temperature ATES systems in Germany. Important criteria for efficient ATES operation considered in this assessment encompass suitable hydrogeological conditions, such as aquifer productivity and groundwater flow velocity, and balanced space heating and cooling demands. The latter is approximated by the ratio of heating and cooling degree days, which is incorporated as a time-dependent criterion to also evaluate the impact of climate change on the ATES potential. The hydrogeological and climatic criteria are combined within a spatial analysis revealing that, regarding the upcoming decades, about 54% of the investigated German area are very well or well suitable for ATES applications, largely concentrating on three regions: the North German Basin, the Upper Rhine Graben and the South German Molasse Basin. Considering time-dependent climatic conditions, the very well or well suitable areas will increase by 13% for the time period 2071–2100. This is mostly caused by a large relative area increase of the very well suitable regions due to an increasing cooling demand in the future. The sensitivity of the very well and well suitable regions to the criteria weightings is relatively low. Accounting for existing water protection zones shows a reduction of the country-wide share of very well or well suitable areas by around 11%. Nevertheless, the newly created potential map reveals a huge potential for shallow low-temperature ATES systems in Germany.

ZusammenfassungDer saisonale Versatz von Angebot und Nachfrage im Wärmesektor kann über Speicherlösungen ausgeglichen werden. Für die jahreszeitliche Speicherung von Wärme und Kälte sind Aquiferspeicher (ATES) als vielversprechende Lösung vermehrt in den Fokus gerückt. Mit derzeit jeweils nur einem betriebenen Niedrigtemperatur- (NT) und Hochtemperaturspeicher (HT) fristet die Technologie in Deutschland allerdings noch immer ein Nischendasein. Diese Studie liefert einen Überblick über die aktuelle Entwicklung der Aquiferspeicherung in Deutschland und diskutiert Stärken und Schwächen sowie Chancen und Risiken. Trotz eines großen Nutzungspotenzials wird der Markteinstieg in Deutschland durch fehlende Anreizprogramme, mangelnde Kenntnisse sowie nicht vorhandene Pilotanlagen erschwert. Die Speichertemperaturen von HT-ATES (> 50 °C) erhöhen dessen Nutzungsmöglichkeiten, haben aber verstärkte technische und legislative Risiken zur Folge. Eine kommerzielle ATES-Nutzung in Deutschland ist daher nur möglich durch die Anpassung genehmigungsrechtlicher Anforderungen, die Schaffung von Fördermaßnahmen, die Umsetzung von Demonstrationsanlagen und die Darlegung von deren wirtschaftlichen und ökologischen Vorteilen.

Wicked problems occur when decision-makers face constant change or unprecedented challenges and when uncertainty, complexity, and stakeholder divergence are high. We shed light on wicked problems in the German energy transition. Our methods consist of a multiple-case study and comparative multi-criteria analysis, utilising the wicked problems theoretical framework introduced by Horst Rittel and Melvin Webber (1973). Based on four exemplary cases, our research covers four core energy transition sectors: energy supply (developing onshore wind power), heating/cooling (using shallow geothermal energy systems), transport (decarbonising the transport sector), and industry (decarbonising the chemical industry sector). Cross-case results illustrate where and how the 10-point frame of wicked problems manifests in the German energy transition. We do not argue that the German energy transition is inherently wicked, yet we stress the need to consider potentially wicked facets of energy transition challenges. Our results show that the four cases exhibit more wicked tendencies in the governance domain than in the technical dimension. All cases exhibit wicked facets in the governance dimension, given strong normative assumptions, value divergence, and complex governance structures with a plurality of actors. From a technical perspective, the four cases still exhibit some wicked tendencies, e.g. raw material provision, skilled workforce, and waste management. The cases differ in technology maturity, state of knowledge, and degree of policy output and regulations. In applying the wickedness lens, we acknowledge that energy transition problems cannot be solved merely by technical measures but need to be tamed. Our work reflects which challenges and main barriers pertain to the four cases of the German energy transition. Understanding the elements of wickedness in a specific problem in the first step offers insights for addressing and managing these challenges in the next step.

Tunnel geothermal systems hold the potential to promote decarbonization of the building heating and cooling sector. They can be integrated into existing infrastructure, resulting in low additional costs. In addition, these systems have large contact areas with the ground leading to larger heat fluxes. However, tunnel geothermics is relatively unknown and rarely used. Thus, the objective of this study is to provide an overview of the two primary tunnel geothermal system types as well as their application and potential. Open hydrothermal systems use the tunnel drainage water as a heat source, whereas closed absorber systems harness the heat flux from the subsoil and the warm tunnel interior via heat exchangers. The evaluation of the global application of existing and planned tunnel geothermal systems shows that all open systems are currently located in mountainous regions with a thick rock overburden. In contrast, closed absorber systems are mostly installed in urban tunnel infrastructures. The spatial distribution of geothermal tunnel systems has a focus in central Europe with Switzerland, Germany and Austria being the countries with the highest number of installed systems. Finally, this study also presents a brief summary of existing methods to determine the geothermal potential of tunnels.