Research Project: Heat Storage for a Climate-Neutral Berlin

Berlin is on a journey towards climate neutrality, and one essential part of this transition is the city's heating supply. To help the city achieve its goal, the Reiner Lemoine Institute (RLI), the Institute for Ecological Economic Research (IÖW), and the Institute for Climate Protection, Energy and Mobility (IKEM) conducted a joint study. Their findings showed a need for large, seasonal heat storage systems in Berlin.

Why are these heat storage systems so important? They can store extra heat during the summer months and use it in winter when demand is higher. With the right type of storage, specifically aquifer heat storage, Berlin can become less dependent on fossil fuels and ease pressure on the power grid. Aquifer heat storage stores and recovers heat in isolated groundwater layers.

"Heat storage allows us to use renewable energy more efficiently," explains RLI's Marie-Claire Gering. "It reduces dependency on fossil fuels and relieves the energy system, making it essential for a carbon-neutral heating supply in Berlin." However, the researchers see a need for action concerning the availability of space, uncertainty in the approval process, and information on geological conditions.

Heat storage systems can effectively utilize local waste heat and renewable heat sources such as data centers, wastewater heat, or solar thermal. As fossil fuel prices rise (due to emissions trading and a growing degree of electrification in heating supply), heat storage becomes an increasingly attractive option economically.

Regarding large-scale and short-term heat storage, Berlin could substantially increase the share of renewable heat in its entire heat supply. Long-term storage could boost the share of renewable heat and waste heat by about five percentage points, given storage capacity up to 440-gigawatt hours. Meanwhile, short-term storage like hot water tanks could stabilize the power grid and buffer peak loads, making a two- to three-fold increase in existing short-term storage capacity beneficial.

In decentralized district networks, aquifer heat storage could store up to 33% of the annual heat. Particularly beneficial for urban waste heat sources like data centers or sewer systems, this type of storage is crucial because it fully harnesses their energy.

One significant challenge is limited space for above-ground thermal stores, which also face planning and legal obstacles. Underground solutions like aquifer heat storage are a promising alternative, but Berlin's subsurface geological suitability for this type of storage still needs investigation. A senate-approved Geothermal Roadmap aims to fill this knowledge gap.

In addition to these technical challenges, uncertainties in approval procedures and a lack of transparency in administrative practices may hinder heat storage implementation. The expansion of heat storage could be accelerated with a political push that defines it as public welfare. Other challenges include high investment costs and techno-economic hurdles prevalent in the clean energy transition.

The project's results provide invaluable insights for Berlin's heat planning in its pursuit of climate neutrality.