TY - JOUR A1 - Bott, Christoph A1 - Ehrenwirth, Mathias A1 - Trinkl, Christoph A1 - Bayer, Peter T1 - Component-based modeling of ground-coupled seasonal thermal energy storages JF - Applied Thermal Engineering N2 - Seasonal thermal energy storages are considered a central element of modern, innovative energy systems and help to harmonize fluctuating energy sources. Furthermore, they allow for an improved coupling between the electricity and heating sectors. Despite recent improvements of planning processes and enhanced models, significant discrepancies between projected and measured heat losses were revealed. Additional shortcomings of available tools relate to limitations in specifying geometry, internal design, or physical processes. Addressing these drawbacks, this study employs a revised, alternative approach by using a flexible, component-based, model (“STORE”). It allows variable flexible parameterizations to study diverse design scenarios. After introducing relevant seasonal thermal energy storage components, processes and mechanisms, datasets, and evaluation techniques, a plausibility test is presented that applies a common thermal energy storage model for benchmarking. In a test study, the re-use of a circa 1,000 m3 large swimming pool is simulated. STORE is used to investigate performance trends caused by different designs (e.g., insulation thicknesses, materials at individual interfaces). For the plausibility test, the results show a high degree of coverage and good applicability. Further, the results of the test study show a storage efficiency of 12.4% for an uninsulated base case, which can be improved to 69.5% in case of the most complex, highly insulated configuration. Critical trends are revealed, covering reduced peak capacity levels (26.5 to 23.5 MWh) and raised average filling temperatures (39.1 to 45.2 °C). Improved long-term behavior involves reduced environmental impacts due to reduced heating of the ambient soil (+7.9 K compared to +14.1 K after 2 years). General conclusions reveal that an optimal design should initially focus on an external cover of soil and top insulation. However, evaluations should base on multiple parameters depending on the target criteria. This is where the present model is highly useful. The capability of STORE to rapidly analyze a plethora of scenarios proves its high applicability for optimizing the planning processes of seasonal thermal energy storage projects. UR - https://doi.org/10.1016/j.applthermaleng.2022.118810 KW - Seasonal Storage KW - Thermal Energy Storage KW - Component-based Modeling KW - Matlab / Simulink KW - Large-scale TES KW - Planning and Design Y1 - 2022 UR - https://doi.org/10.1016/j.applthermaleng.2022.118810 UR - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:bvb:573-34926 SN - 1873-5606 VL - 2022 IS - 214 PB - Elsevier CY - Amsterdam ER - TY - JOUR A1 - Bott, Christoph A1 - Dressel, Ingo A1 - Bayer, Peter T1 - Paraffin wax as self-sealing insulation material of seasonal sensible heat storage systems BT - A laboratory study JF - PLOS ONE N2 - Seasonal heat storage is considered as one of the key elements on the path to a low-emission economy. Embedded in local district heating networks, they raise the share of renewable energies and balance out highly fluctuating supplies of e.g. solar systems or windmills. The technology of seasonal heat storage can be described as almost technically mature, with well-established concepts and some systems being in operation for a considerable time. Nevertheless, the operating experience gained to date also revealed two critical problems. On the one hand, even smallest leakages in sealing foils led to irreparable breakdowns. On the other hand, heat loss in the marginal areas was revealed as a key deficiency, preventing the technology from advancing towards global marketability. This study presents an experimental approach to address these two key issues in the field of seasonal energy storage. Two small-scale laboratory tests were carried out to test paraffin wax as a completely novel component in the marginal area of seasonal storages. This is based on two material properties: As hydrophobic and mobile medium, the warmed and molten paraffin should actively seal the fissures and holes in the event of leakage. Additionally, the latent heat storage properties of the paraffin wax should increase the systems’ total storage capacity and reduce lateral heat losses via its low thermal conductivity. With retardation periods from 2.5 to 4 hours, the results show an effective phase change effect of the paraffin wax, which reduces energy losses and allows to buffer short-term, intensive loading and unloading processes. By storing up to 138 kJ/kg energy in the paraffin wax, increased capacities of application-scale pit storages by up to 40.70 MWh are to be expected. Additionally, the self-healing features could be successfully demonstrated: With only small losses of between 1.5 and 17%, the paraffin wax effectively sealed artificially incised leaks. Thereby, the mechanism was most effective for local defects. Following these positive demonstrations of feasibility, technical design questions still remain, which concern prevention of deformation of the paraffin wax. Once solved, this new component can then provide a path for further optimization of seasonal heat storage technologies. UR - https://doi.org/10.1371/journal.pone.0236056 Y1 - 2020 UR - https://doi.org/10.1371/journal.pone.0236056 UR - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:bvb:573-34535 SN - 1932-6203 VL - 15 IS - 7 PB - PLOS CY - San Francisco ER -