Project shows potential for better use of waste heat and renewable energies

Berlin, April 2, 2025 ‒ Berlin must make its heat supply climate-neutral ‒ as stipulated in the Heat Planning Act. Heat storage systems play a central role in this. This is shown by a joint study by the Reiner Lemoine Institute (RLI), the Institute for Ecological Economy Research (IÖW) and the Institute for Climate Protection, Energy and Mobility (IKEM) on behalf of the Berlin Senate Department for Mobility, Transport, Climate Protection and the Environment (SenMVKU). Conclusion: Heat storage systems make it possible to use surplus heat, become less dependent on fossil fuels and reduce the load on the electricity grid. For Berlin, the scientists see a need for action in terms of land availability, legal uncertainties in the approval process and a need for information on the geological conditions.

Seasonal heat storage systems help to shift excess heat from the summer to times of higher heat demand in the winter. There are various types of storage for this purpose. The scientists consider aquifer heat storage systems to be particularly suitable for Berlin. These are open systems for storing and recovering heat in hydraulically sealed groundwater layers.

"Heat storage systems make it possible to use renewable energy more efficiently. They reduce dependence on fossil fuels and ease the burden on the energy system. They are therefore essential for a climate-neutral heat supply in Berlin," says Marie-Claire Gering, research assistant and project manager at RLI, summarizing the results.

Using waste heat and renewable heat more efficiently in Berlin's district heating network
Heat storage systems help to make more extensive use of local waste heat and renewable heat sources, such as from data centers, wastewater heat or solar thermal energy. With rising prices for fossil fuels, for example as a result of emissions trading, and with a higher degree of electrification of the heat supply, heat storage systems are becoming more and more economically attractive.

More capacity for long-term and short-term storage makes sense
With an output of 700 megawatts from renewable energies and waste heat and a storage capacity of up to 440 gigawatt hours, long-term storage could increase the share of renewable heat and waste heat in BEW's Berlin district heating network by around five percent. Short-term storage facilities such as container heat storage could stabilize the electricity grid and cushion peak loads. The study shows that doubling or tripling the existing short-term storage capacity to up to 6.6 gigawatt hours would make sense for Berlin's district heating network.

District storage systems help to make greater use of urban heat sources
In decentralized district networks, aquifer heat storage systems could store up to 33 percent of annual heat. These storage systems are particularly crucial for urban waste heat sources such as data centers or wastewater systems, as they make their energy almost completely usable.

Availability of space as a key obstacle: underground storage as a solution
Berlin has limited space for above-ground heat storage facilities, which can also come up against building law and urban planning hurdles. Underground solutions such as aquifer heat storage are a promising alternative. However, it still needs to be verified whether Berlin's subsoil is geologically suitable for these types of storage facilities. The “Geothermal Energy Roadmap” adopted by the Senate is intended to close existing knowledge gaps.

Legal uncertainties slow down expansion - political decisions needed
In addition to the technical challenges, legal uncertainties in the approval process, particularly in the distinction between mining and water law approval regimes, as well as a lack of transparency in administrative practice, make the implementation of heat storage systems more difficult. A political decision that defines heat storage facilities as part of public services of general interest could accelerate expansion. In addition, general challenges of the energy transition such as high investment costs and other techno-economic obstacles are relevant for the expansion of heat storage.

You can find the final report here (DE). The results of the project will be incorporated into Berlin's heat planning. Further information can be found at berlin.de/waermewende.