Seasonal storages increasing the share of renewables in urban districts

District heating systems fully based on renewable energies require very large storages that allow seasonal storage of large amounts of renewable heat or waste heat respectively. Additionally these large storages are able to raise flexibility of the district heating networks.

Compared to currently installed heat storages the storage volume has to be increased tenfold and at the same time it is necessary to place the required huge volume subsurface. This is quite challenging in respect of materials and construction of these giga-scale storages.

The Austrian lead project giga_TES aims at developing giga-scale storage concepts for urban districts with integrating large shares of renewables focusing on Austrian implementations.

Photo Credit: Arcon-Sunmark

Challenges

Three Austrian sites will be investigated in respect of the main challenges like construction, geology and geophysics, materials, district heating system and its operating characteristics, economic aspects, public acceptance etc.. The three sites will be used as demonstration systems throughout the project.

Types of seasonal heat storages
Types of seasonal heat storages
Photo Credit: Solites
Geology

Geologie

Hydrogeology

Hydrogeologie

Photo Credit: Christoph Muser et al., Machbarkeits-Vorstudie eines saisonalen Groß-Wärmespeichers für Linz, Abschlussbericht der Sondierung, Mai 2015 (e!mission.at Forschungsprojekt Nr. 843937 des Klima- und Energiefonds)
Goals
1
Comprehensive overview of requirements and challenges for application and installation of giga-scale heat storages
and development of a scientific decision tool for representative future application scenarios internationally and for Austria
2

Development of innovative and optimal construction methods for giga-scale heat storages

with particular regard to ground conditions. Based on five typical ground and rock profiles various ground-mechanical approaches addressing deep pit excavations are going to be assessed and the respective potentials outlined.
3

Elaboration of economically viable solutions for critical storage components such as base plate, liner and cover.

4

Development of novel polymeric and anorganic materials for the construction of large-scale heat storages

as well as development of tests and methods for lifetime assessment to make accelerated and more realistic pre-selection of such materials.
5

Development of simulation models considering different modelling depths, validation and application of the models for optimising the construction in respect to relevant boundary conditions

Additionally a methodology predicting the ground and ground water temperature increase depending on specific geologic and hydrogeologic conditions and the storage construction is going to be developed. Furthermore a co-simulation platform for optimising the system configuration and control strategy is going to be established.
6

Assessment of the additional benefit and importance of large-scale storages in respect to existing and future district heating networks,

analysing sensitivities and correlation of system parameters regarding relevant boundary conditions and with special focus on Austrian boundary conditions.
Exemplary demonstration systems
Photo Credits: Solites
Components of large-scale heat storage (liner and cover)
Photo Credits: Marstal Fjernvarme

Research areas

01

Development of components and technologies

02

Materials development and testing

03

Computer aided storage optimisation

04

System integration and storage management

To reach 100% renewable energy supply in the long term large-scale thermal storages like pit storages or large tank storages are necessary for district heating systems. As the systems are going to be installed in urban areas the required surface should be minimized because of relatively high land costs in cities. Through installing the storages subsurface it is possible to use the surface for recreation or installation of solar collector fields and therefore minimizing of costs is reached. District heating systems require thermal energy storage volumes from 50 000 m³ to 1 M m3 corresponding to 1 bn. litres. Currently large thermal energy storages are run in Germany and mainly in Denmark, storage volumes installed lately reaching nearly 200 000 m³.

Because of the low number and the few years existing large-scale thermal storages have been in operation so far experiences with these storages for district heating systems are still limited. Improvements especially in respect to performance and durability are necessary. Cost efficiency and system integration require higher storage densities and therefore higher temperatures leading to even higher requirements in respect to the applied materials. Vapour tightness, serviceability and durability of innovative solutions for cover, walls and liners require novel materials and components as well as improved test methods. Additionally innovative construction methods are needed because of the targeted storage size and its subsurface construction. Therefore the project is structured according to the following R&D areas: Development of Components and Technologies, Materials Development and Testing, Computer Aided Storage Optimisation, System Integration and Storage Management

 

Materials development and testing
Photo Credits: Johannes Kepler Universität Linz (JKU) / Gernot Wallner
Computer aided storage optimisation
Photo Credit: AEE INTEC
System integration and storage management
Photo Credit: AEE INTEC

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