Data centres (DCs) are the backbone of the digital economy, but they are also major energy consumers, accounting for 1–2% of global electricity use. In Europe, their electricity demand is projected to reach 98.5 TWh/year by 2030, corresponding to 3.2% of total electricity demand. Most of this energy ultimately becomes waste heat, which is typically released into the environment via cooling systems. Even with energy-efficient practices, the amount of waste heat generated is substantial—estimated at 50 TWh/year, enough to meet the heating needs of about 2.5% of the European building stock. Despite this potential, waste heat recovery (WHR) from data centres is underutilized due to the relatively low temperature of the waste heat, the mismatch between when heat is produced (often in summer) and when it is needed (mainly in winter), and technical, economic, and regulatory hurdles to integrating DC waste heat into district heating networks (DHNs). However, the political and strategic context is rapidly evolving, with the European Commission pushing for greater energy efficiency and sustainability in data centres, through new regulations and funding initiatives. Moreover, updates to the Energy Efficiency Directive (EED) and Renewable Energy Directive (RED) are making heat recovery mandatory above certain thresholds and the EU Taxonomy Regulation is setting sustainability criteria for investments, including waste heat recovery. There is thus growing pressure and opportunity for data centres to become active contributors to sustainable urban energy systems.
In this context, the THUNDER Project aims to unlock the untapped potential of data centre waste heat by developing and demonstrating innovative, efficient, and cost-effective seasonal thermal storage solutions based on thermochemical materials (TCMs), which offer high energy density, near-zero thermal losses, and modularity for urban environments. These storage systems will be integrated with high-temperature heat pumps to upgrade low-grade waste heat to useful temperatures for district heating. The full system will be validated in a real-world demo site in Varna, Bulgaria, including both fixed and mobile (“Heat on Wheels”) storage solutions, to overcome the challenge of direct DC-to-DHN connection. Replicability and scalability will be assessed by conducting pre-feasibility studies in 10 additional sites across Europe and novel business and financial models for DC heat recovery will be developed, including “energy as a service” concepts, and address regulatory and policy barriers. Co-design and training workshops will involve stakeholders and raise social awareness, supporting market uptake and replication. A holistic sustainability assessment (environmental, economic, social) will be delivered, ensuring alignment with EU Taxonomy and Sustainable Development Goals (SDGs).
Demonstration activities will provide operational proof of concept, with the goal of achieving:
• At least 70% storage efficiency
• Energy density of 120 kWh/m³ (double current commercial TCMs)
• Halved capital costs for TCM storage
• Significant energy and CO2 savings (e.g. 90 kWh/m³ and 24 kgCO2/m³ of TCM storage, compared to methane heating)
