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Subproject 9

Hybrid and latent TES

Novelty of the solution of the subproject 

SP9 introduces compact hybrid solutions that seamlessly combine latent and sensible TES
technologies, bringing significant advancements to the field. Novelty and unique aspects include:

  • Tailored PCMs: The storage utilizes PCMs with customizable melting temperatures to meet specific requirements. This flexibility allows for optimized energy storage and release, as well as increased COP of heat pumps.

  • Space-Constrained Integration: Addresses the challenge of space constraints in STES by utilizing underground locations and exploiting the combined use of decentralized storage units at building level.

  • Enhanced Energy Transfer Stations: The hybrid swarm TES can be seamlessly incorporated into conventional energy transfer stations, increasing their storage capacity by up to a factor of five compared to water-based systems.

  • Decentralized Heat Supply: The storage solution empowers buildings to partially meet their own heat demand by utilizing the storage capacity available at the substation.

  • Environmentally Friendly Storage Media: The envisioned PCMs are environmentally friendly, posing no risk to the environment or building occupants.

  • Suited for Ultra-Low-Temperature Grids: The hybrid swarm TES is particularly suitable for ultra-low-temperature grids, where the temperature spread is limited to ~5 K.

  • Versatile PCM Integration: The PCM can be incorporated in the storage unit either in the form of capsules or within a heat exchanger where the heat transfer surfaces separate the PCM from the circulating water.

  • Advanced Control Strategies: SP9 develops novel control strategies for swarm storages in thermal grids, optimizing smart operations. System performance is maximized by means of load optimization and predictive models.

Objectives of the subproject 


  • Advance understanding of hybrid TES and the effect of encapsulated PCM on thermal
    stratification of water-based TES.

  • Bring together knowledge in the fields of TES, data science, an AI to enable smart operation
    of swarm storage systems. 

  • Advance the field of swarm thermal energy storage by improving the understanding


  • Specific investment costs of the STES of <10 CHF/kWh based on installed storage capacity.

  • Enhance economic profitability of PV/HP-systems by boosting PV self-consumption to 100%. 

  • Enhance economic profitability of thermal grids by allowing an increased heat density through reduction of the aggregated peak power of the grid.


  • Contribute to the use of smart buildings for the integration of renewables in the energy system.


  • Demonstrate successful aggregation of multiple energy storage systems, enabling the
    provision of both STES to the thermal grid and flexibility services to the electric grid.

  • Demonstrate seamless interoperability of the swarm storages and ensure efficient and reliable operation of the TES systems.

Research partners

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