Decarbonising district heating is a crucial milestone on the path to achieving climate-neutral heat supply in urban environments. A key technology in this process is the integration of large-scale heat accumulators to temporarily store surplus heat from renewable sources. At present, a consortium led by Wien Energie is investigating the development of a large-scale subsurface heat storage system, planned for midterm construction at the Donaustadt power plant site.
The district heating system plays an important role in Vienna’s heat supply: by 2040, 56 per cent of the city’s heat demand is expected to be met through district heating. A large proportion of the heat is currently still generated by fossil-fuel combined heat and power plants and cogeneration plants. The proportion of these plants is set to decrease substantially over the next few years, with their operations transitioning to green gas. Wien Energie aims to harness deep geothermal energy and large-scale heat pumps as alternative heat sources, with the objective of supplying half of the city’s future heat demand. For the heating transition to succeed, however, large-scale heat accumulators are essential to increase system flexibility by storing surplus local renewable heat produced in summer and making it available during the winter months. Storing heat beneath the earth’s surface is one of several approaches to harness the thermal energy produced in summer for use in winter.
Key technology: earth basin heat storage system
Building on previous research projects and preliminary studies, the ScaleUp1 project is currently developing the foundations for the construction of an earth basin heat storage system in Vienna’s 22nd district. The plan is to construct a storage basin approximately 25 metres deep with a volume of 40,000 m³ at the Donaustadt power plant site in Vienna. Earth basin heat storage systems are designed to integrate seamlessly into the urban environment, with their cover surfaces intended for practical use. The project team, led by Wien Energie, is investigating suitable technologies, materials and construction methods, including questions around integrating an earth basin heat storage system into Vienna’s district heating network. Both water management and geological aspects are taken into account. Currently, various insulation materials are being tested to enable optimal storage of surplus heat at temperatures of up to 95 °C in the underground storage basin. Furthermore, processes are being developed to upscale the pilot plant, paving the way for the future construction of seasonal storage systems with capacities reaching several hundred thousand cubicmetres. The project also includes the simulation and evaluation of the operational, economic and environmental significance of earth basin energy storage systems within the overall portfolio of district heating producers.
Europe´s first pilot plant
Under Wien Energie’s leadership, preparations are underway to pave the way for the pilot plant, scheduled for 2029. The underground large-scale heat storage would be the first of its kind in Europe, potentially establishing it as a global leader in this innovative construction approach. The development of the large-scale heat storage system is further supported at the European level. In 2024, the project was selected as one of four Austrian initiatives to receive funding from the EU Innovation Fund.
„Large-scale heat storage facilities, like those in our ScaleUp and ATES projects, are vital building blocks for Vienna’s heating transition. They enable the intelligent storage of surplus renewable heat generated in summer and its supply in line with demand during the winter months. Such technologies provide the necessary seasonal flexibility needed to sustainably reduce the share of fossil fuels in district heating and help us achieve our objective of climate-neutral heat supply.“
Rusbeh Rezania
Head of alternative thermal assets development at Wien Energie
greenenergylab.at/projects/scaleup/?lang=en
1Project partners: Wien Energie (project management), PORR, GeoSphere Austria, AEE INTEC, ste.p
The ScaleUp project is part of the Green Energy Lab innovation network.
greenenergylab.at
The project’s implementation is funded by the European Union under the EU Innovation Fund.
ec.europa.eu/assets/cinea/project_fiches/innovation_fund/101190982.pdf