Thermal storage as a heat source for sCO₂ processes

The EU's long-term climate strategy and the European Green Deal highlight the pivotal role of renewable energies towards a clean energy system and decarbonisation. Despite technological progress and cost reductions, the stochastic nature and lack of dispatchability of wind and solar energy sources require fast development of large-scale energy storage to provide increased security of supply to the whole electrical system. The main challenge in integrating 100 % renewable energy sources (RES) into the energy system is the lack of large-scale energy storage to make intermittent renewable energy manageable. CO₂ based electrothermal energy and geological storage system is a “high-risk/high-reward” concept aiming to bring a high-efficient, cost-effective and scalable energy storage technology by making feasible the integration of transcritical CO₂ cycles with underground energy storage achieved through the simultaneous CO₂ storage and geothermal heat extraction.

CEEGS has exceptional characteristics regarding:

• RES integration
• scalable and up to large-scale energy storage
• combined CO₂ geological sequestration
• capacity for integration with large CO₂ producers
• heating and cooling integration
• low environmental impact and costs

The concept is based on a hybrid system for energy storage and underground carbon utilisation in a closed-loop as heat transfer fluid. If successful, it would allow high energy storage capacity due to underground repository and partial CO₂ sequestration in the terrain. It utilises the synergies of transcritical systems and underground storage with high energy capacities compared to only surface tanks and additional contributions of thermosiphon and geothermal heat. It implies low costs and environmental impact. It is a trigeneration system that can provide electricity, heat and cold. The key challenges for advancing this concept are related to the interface between the transcritical cycle and the subsurface storage.

Further information: CEEGS project

References

• Unger, S.; Fogel, S.; Schütz, P.; Ramirez, R. C.; Carro, A.; Carneiro, J.; Hampel, U.
  The sCO₂ facility CARBOSOLA: Design, purpose and use for investigating geological energy storage cycles
  Proceedings of the ASME Turbo Expo 2024, DOI: 10.1115/GT2024-122133
• Patent: Unger, Hampel (2024)
  Wärmespeicher
  DE10 2023 123 958.9

Funding

Novel CO₂-based Electrothermal Energy and Geological Storage system – CEEGS (HORIZON, Grant number 101084376). The authors are responsible for the presented content.