Techno-economic planning and construction of cost-effective large-scale hot water thermal energy storage for Renewable District heating systems

Seasonal thermal energy storage (TES) is envisioned as a major player in the future district heating (DH) systems where large shares of renewables are being integrated. Therefore, in order to fulfill the seasonal tasks, such storage systems are characterized with large volumes. Yet, the integration of such large-scale storage technologies is not easily planned and realized. There exist numerous challenges e.g. TES type, volume and ground conditions, need to be tackled in order to obtain an optimal planning solution for TES integration. Given their promising applications, the scope of this work is limited to tank and pit thermal energy storage. Accordingly, this contribution firstly discusses the modeling of seasonal TES in finite element tools. Then, it examines the influence of a list of parameters i.e. TES construction type, geometry, volume and DH characteristics, on TES performance. Later, the work develops a methodology for construction techno-economic analysis of such technologies. It is revealed that the tank TES has always better performance than pit, but on the other hand it is always characterized with higher capital cost. As TES volume increases, the performance difference between tank and pit starts to vanish. Further, the DH characteristics play a major role in TES performance. It is depicted that lowering DH temperatures will ultimately lead to lower thermal losses from TES. Another important finding is the applicability of the suggested performance indicator for techno-economic analysis as it relates the technology capital cost to the effective volume of TES. The contribution also investigates the influence of insulation level on TES performance and it is found that for volumes larger than 500,000 m(3), there is no major performance difference between the tank or the pit in case of insulation enclosing TES envelope. However, it is also revealed that insulation is needed only and solely to preserve the ground quality when large volumes are realized. (C) 2019 Elsevier Ltd. All rights reserved.