The Challenge of Planning and Constructing Large-Scale Hot Water TES for District Heating System: A Techno-Economic Analysis

-In an international context (e.g. Germany, Denmark), the integration of long-term thermal energy storage (TES) into block heating systems already exists. Yet, the so-called pit TES cannot be easily applied to central European district heating (DH) systems because of the varying heat demand, temperature level, TES size and geometry a ground conditions (e.g. presence of groundwater), etc. Thus, within the framework of the Austrian Flagship project Giga_TES (FFG), very large-scale underground TES are developed and optimized by means of simulations. The aim is to provide solutions that enable a significant reduction of fossil fuels that traditionally are needed in DH systems. This can be achieved through an optimized design of a multifunctional TES allowing short-term as well as long-term heat storage with appropriate dimensioning and optimal planning of solar thermal, waste heat use and heat pumps for a specific location and system. The envisioned size of new giga-scale storage technologies and the construction in the subsurface require new construction methods. Experiences show that improvements are needed on material performance and durability and on materials and component development. Cost effectiveness and system integration call for higher storage density and thus, higher temperatures, imposing even higher demands on the materials used. This together with the requirements of vapour tightness, serviceability and durability of innovative solutions for cover, wall and bottom with respect to liners and insulation call for novel materials and construction methods. Hence, numerical models are developed to optimize the thermal, structural, system integration and economic performance of materials, components and system. This contribution highlights the challenges of constructing cost efficient giga-scale TES. Different construction methods for tank and pit TES are compared with respect to their investment costs. The thermal performance of the different TES is compared by means of numerical simulations for a set of boundary conditions.