As thermal energy accounts for more than half of the global final energy demands, thermal energy storage (TES) is unequivocally a key element in today’s energy systems to fulfill climate targets.
Starting from the age-old TES practices in water and ice, TES has progressed today into many energy systems. TES offers benefits in balancing the time and location mismatch between thermal supplies and demands, allowing peak shaving and load shifting while improving energy efficiency and reducing emissions. TES also enables flexible sector coupling via the storage of intermittent renewable electricity with power-to-heat and power-to-cold adaptation. TES is achieved in sensible TES, latent TES (with phase change materials- PCMs) and thermochemical TES (with thermochemical heat storage materials - TCMs), and can be designed for short-term (daily), medium-term (weekly) or long-term (seasonal) storage. There are countless TES systems and applications in commercial use today (led by water and ice, but also with underground TES (with bedrock and/or groundwater), PCM and TCM examples). Regardless, there still is a myriad of aspects requiring research and development (R&D) concerning TES materials, heat exchanger components and systems, to be able to exploit the full potential of TES.
TES research at the Division of Applied Thermodynamics and Refrigeration (ETT) has a long history. The division’s key TES research areas comprise underground (i.e., geothermal) TES (UTES), latent TES with PCMs and also thermochemical TES with TCMs. UTES entails sensible TES in the subsurface, involving borehole TES (BTES), aquifer TES (ATES), and cavern TES (CTES). These systems offer the possibility of seasonally storing large capacities of heat for a relatively low price, and are natural solutions in the Swedish thermal energy systems, with a significant interest in R&D. Modelling the heat transfer of UTES systems, coupled with experimental validation through lab tests and long term full-scale monitoring, is among the ETT division’s core competencies. The division is also dedicated to R&D on latent TES and thermochemical TES, driven by their competitive advantages in e.g. compactness, temperature versatility and temperature regulation capabilities, to elevate their technology readiness levels (TRLs). Here, the design and characterization of new PCMs and TCMs and their property enhancements, as well as the design of heat exchangers, reactors and compact TES system solutions are all embedded in the R&D agenda.
The research conducted in this area cover:
Underground TES (Geothermal TES)
Latent TES (with PCMs)
Thermochemical TES (with TCMs)
Projects
Combined Heat and Power plants in combination with borehole thermal energy storage (completed)
Many combined heat and power plants in Sweden waste large amounts of heat summer time due to low heat demand and permanent generation of electricity. This project will provide design and decision making tools for including seasonal thermal storages in the ground so that summer time waste heat can be use during the winter.
This project aimed to measure advantages and disadvantages of deep borehole heat exchangers as well as to propose design guidelines for multiple borehole fields with coaxial collectors.
District cooling (DC) is an efficient end environmental friendly way of providing cooling particularly for densely populated regions or close-neighborhoods. To lower the installation costs of a DC system yet still to cover the peak cooling demands, cold storage is sought for. Despite experiencing a northern climate, Sweden also has a considerable cooling demand throughout the year, particularly from industrial, service and commercial sectors.
HYSTORE - Hybrid services from advanced thermal energy storage systems
The project HYSTORE (nr. 01096789) is a Horizon project where, KTH Royal Institute of technology is developing one of four thermal energy storage (TES) solutions within the project: PCM HEATING solution. This is a pilot-scale TES using phase change materials (PCMs), designed, constructed and techno-economically optimized in combination with a heat pump.
Integrating Latent Heat Storage into Residential Heating Systems
This project experimentally and numerically investigated the performance of thermal energy storage (TES) tank with phase change material (PCM). The experimental analysis has been conducted on a test rig that is designed and built within this project at the Energy Technology Department at KTH. The test rig’s experimental capacity covers wide range of heating and cooling/refrigeration applications; it can run in the temperature range of - 10 to 90°C with a heating capacity of about 20kW and cooling capacity of about 10 kW. The test rig is fully equipped with highly accurate measurements that facilitate detailed analysis of the PCM-TES tank performance.
Long-term performance measurement of GSHP systems serving commercial, institutional and multi-family buildings
Measured long-term performance data for ground source heat pump systems serving commercial, institutional and multi-family buildings are rarely reported in the literature. Energy use intensity figures are occasionally published, but as they necessarily lump the building loads and the system performance together, they are of limited usefulness in understanding real-world system performance.
Annex 52 will bridge the gap between those who see the heat pump system as a complex environment and the ground source as a black box, and those who see the ground source as a complex environment and the heat pump system as a black box.
The Neutrons for Heat Storage (NHS) project aims to develop a thermochemical heat storage system for low-temperature heat storage (40-80 °C). Thermochemical heat storage is one effective type of thermal energy storage technique, which allows significant TES capacities per weight of materials used. In the NHS project, reversible chemical reactions (absorption and desorption) between metal halides and ammonia (NH3) are used.
Novel tool and guidelines for designing ground source heat pumps (GSHPs) in densely populated areas
Ground source heat pumps (GSHPs) are a widespread technology in Sweden and its spread is forecasted to increase even further. However, designers of such systems lack a dedicated design tool when dealing with independent GSHPs, like in densely populated areas. This results in systems operating with lower efficiency than expected.
Novel tool and guidelines for designing ground source heat pumps (GSHPs) in densely populated areas
Ground source heat pumps (GSHPs) are a widespread technology in Sweden and its spread is forecasted to increase even further. However, designers of such systems lack a dedicated design tool when dealing with independent GSHPs, like in densely populated areas. This results in systems operating with lower efficiency than expected.
PARMENIDES – Plug & plAy EneRgy ManagEmeNt for hybriD Energy Storage
Hybrid energy storage systems (HESS) are responding to the evolving nature of energy systems and have the potential of enabling greater flexibility in energy communities (EC). Understanding and leveraging EC members’ energy-related behaviors, preferences, and constraints can enhance this potential. The PARMENIDES Project aims to develop an interoperable and secure ontology-based Energy Management System for HESS (EMS4HESS) suited for ECs with energy storage technologies, with a focus on the electricity and heating domain, so they can offer flexibility services to the grid, while finding a balance between stakeholders’ individual and collective objectives.
