Large-scale heat storage systems will play a central role in increasing the necessary flexibility of district heating networks and enable the further expansion of renewable energies or the integration of waste heat in these systems. To overcome challenges in design, realization and operation of this technology and to enable its application in as many countries as possible, it was decided to initiate Task 39 "Large Water Heat Storage for District Heating Systems".

The main objective of Task 39 was to determine the aspects that are important in planning, decision-making and implementing large thermal energy storages for integration into district heating systems and for industrial processes, given the boundary conditions for different locations and different system configurations.

This will include the definition of representative application scenarios and the definition of dedicated storage concepts as well as the techno- economic evaluation of best practice examples. Furthermore, the development, improvement and implementation of new material testing methods were targeted. This is because currently available liner materials are not optimized for the use in large thermal energy storages. In addition, the number of available simulation models for large thermal storages are rare and limited or they are not publicly available as they have been developed for specific tasks in research projects. Therefore, Task 39 aimed to inventory and compare numerical simulation models of large thermal energy storages.

Due to existing synergies, four types of large-scale heat storage types are considered in the Annex:

• Pit Thermal Energy Storages (PTES)
• Tank Thermal Energy Storage (TTES)
• Aquifer Thermal Energy Storages (ATES)
• Borehole Thermal Energy Storages (BTES)

The Austrian partners contributed different work to this collaborative project. In addition to leading Task 39 as Operating Agent (AEE INTEC), the Austrian institutes were active in material issues relating to polymer liners (JKU Linz), the development of storage concepts and their evaluation (AIT, SOLID, AEE INTEC) as well as issues relating to the simulation of earth basin heat storage (UIBK, AEE INTEC; AIT).

The results of Task 39 are:

• Fact sheets on storage concepts and examples of applications.
• A description of the most important steps in the preparation, planning, design and construction of large heat storage facilities, with key performance indicators and best practice examples.
• A description of new material testing procedures, guidelines/recommendations for water quality and a draft database of materials suitable for use in large heat storage facilities.
• Inventory and comparison of numerical models, validation data sets and recommendations for the simulation of large heat storage facilities.
• A list of large-scale thermal storage facilities built worldwide.

The results of Task 39 are available on the task website.

Austria (Operating Agent), Canada, Denmark, France, Germany, Italy, Netherlands, Sweden, Switzerland, Turkey, United Kingdom, United States

Project leader

Dr. Wim van Helden
AEE - Institut für Nachhaltige Technologien
Feldgasse 19, 8200 Gleisdorf
E-Mail: w.vanhelden@aee.at

Project partners

Dr.-Ing. Fabian Ochs
Technikerstraße 13, 5. Stock, Raum 515
E-Mail: fabian.ochs@uibk.ac.at

ao. Univ.-Prof. DI Dr.mont. Gernot M. WALLNER
Science Park 2 - 1st Floor - Room S2 122
E-Mail: gernot.wallner@jku.at

Dr. Abdulrahman Dahash
AIT – Austrian Institute of Technology GmbH
Center for Energy, Giefinggasse 4, 1210 Wien
E-Mail: abdulrahman.dahash@uibk.ac.at

Maria Moser, MSc
SOLID SOLAR ENERGY SYSTEMS GMBH
Am Pfangberg 117, 8045 Graz
E-Mail: m.moser@solid.at