Solar calcium-looping integration for thermo-chemical energy storage

      Dispatch of Concentrating Solar Power (CSP) plants has a peak around noon as well as significant variations over minutes or hours due to cloud coverage. To manage this electricity production, thermochemical energy storage (TCES) use materials that perform a reversible chemical reaction (endothermic in one direction and exothermic in the other) to store/release energy through a cyclic process.

      As TCES works at very high temperatures (450–1300 ºC), it is the most promising candidate for thermal energy storage in new generation CSP plants working above 800 ºC. Moreover, TCES provides seasonal storage with no heat losses (the energy is stored in the chemical bound of the compounds) with high energy densities (about 240-1090 kWh/t).

      Among many materials for TCES (hydrides, metal oxides and carbonate salts), the calcium looping process (CaO3 ↔ CaO + CO2) stands out because the raw material is cheap (<10€/t) and earth-abundant, products are non-toxic (also, there are no byproducts), and energy storage density reaches 390 kWh/t. SOCRATCES project aims at demonstrating the feasibility of calcium looping as energy storage technology by erecting a pilot-scale plant that stores solar energy in a concentrated solar power plant.

Energy storing process

Energy discharging process

  • Prototype demonstration of capacity for energy storage. System tested at TRL5.

  • Successful calcination at prototype scale by means of flash calcination technology.

  • Successful carbonator design with possibility for the scale-up. Integration of high temperature carbonator (>700ºC) and Stirling engine for power production.

  • Particles attrition, agglomeration and fouling analysis. Successful solids conveying and control system management.

  • Study of CaO precursor and process conditions to allow high and stable multicycle activity.
Completed 100%

Project info

1 January 2018 – 31 December 2021

Total budget: 4,975,402.50 €

  •  University of Seville
  •  CSIC
  •  University of Zaragoza
  •  Virtualmechanics S.L.
  •  Bioazul
  •  Vertech Group
  United Kingdom
  •  Calix Europe Ltd.
  •  Politecnico di Torino
  •  National Research Council
  •  Sociedade Portuguesa de Inovação
  •  CERTH
  •  Aristotle University of Thessaloniki
  •  TTZ Bremerhaven
  •  ISITEC GmbH

General coordinator
R. Chacartegui (
University of Seville
Further information:

[1] Calcium looping as chemical energy storage in concentrated solar power plants: Carbonator modelling and configuration assessment. M Bailera, P Lisbona, LM Romeo, LI Díez. Applied Thermal Engineering, Volume 172, 25 May 2020, Pages 115186.
[2] Energy consumption minimization for a solar lime calciner operating in a concentrated solar power plant for thermal energy storage. P Lisbona, M Bailera, T Hills, M Sceats, LI Díez, LM Romeo. Renewable Energy, Volume 156, August 2020, Pages 1019-1027.
[3] Design and operational performance maps of calcium looping thermochemical energy storage for concentrating solar power plants. S Pascual, P Lisbona, M Bailera, LM Romeo. Energy, Volume 220, 1 April 2021, Pages 119715.
[4] Modelling calcium looping at industrial scale for energy storage in concentrating solar power plants. M Bailera, S Pascual, P Lisbona, LM Romeo. Energy, 2021, Pages 120306.

This project received funding from the European Commission by means of Horizon 2020 (LCE-07-2016-2017), the EU Framework Programme for Research and Innovation, under Grant Agreement no. 727348.