| Abstract |
In thermal geoengineering applications, the storage of thermal energy offers a large potential for increasing and optimizing the efficiency of renewable energies. During the past decades, research programs in Europe have particularly focused on buried, technically closed thermal energy storage systems (TES). During low demand phases, these systems allow energy to be stored on a seasonal basis to contribute cost-effectively to energy supply during periods of high demand. As preferred technical variants, three concepts have emerged: Pit Thermal Energy Storages (PTES), Tank Thermal Energy Storages (TTES) and Water-Gravel Thermal Energy Storages (WGTES). Placed in-ground, they have different (geo-)thermal properties, which vary from system to system and represent individual advantages or disadvantages. Based on a comprehensive database, our presentation reviews the state-of-technology in TES, whereby most systems and those with the highest storage volumes are located in Denmark, Germany and Sweden. Through innovations in the field of thermal geoengineering, materials, and construction techniques, a consistent trend towards further improved efficiency can be observed, both energetically and economically. However, we identify the remaining key challenges in technical, environmental and socio-economic terms, which impede global market availability and require further research. Critical issues are the optimization of thermal insulations to minimize energy losses, the improvement of long-term stabilities of used materials, and the mitigation of substantial construction and maintenance costs. Furthermore, our presentation uncovers unexploited potentials in the field of performance optimization. Some of these arise with the advanced integration in heating and cooling networks. Linkages to excess energy from industry, data centers, or geothermal systems offer further possibilities for an enhanced use of TES. Finally, we point out concepts for further increasing the prospective potential of this geothermal technology, for example by dynamically linking differently configured storage systems. |