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SOCRATCES: Solar integration with Ca-Looping for thermochemical energy storage


Thermodynamic efficiency in CSPs

Use of cheap, abundant and non-toxic materials

Pilot scale demonstration

Energy storage is the greatest challenge for a short-term deeper penetration of renewable energy sources, which are usually characterized by the intermittency of power production.  

SOCRATCES proposed as a solution to this challenge the integration of the “Ca-Looping” (CaL) process to Concentrated Solar Power (CSP) plants. The “Ca-Looping” (CaL) is a process based on the reversibility of the carbonation/calcination of Calcium oxide (CaO). Carbonation is a chemical reaction of carbon dioxide (CO2) to give carbonates of many types, while calcination releases energy. In addition, the great availability of limestone as a source to obtain the necessary raw material and its low price (<10€/ton) are key factors for the feasibility of the process. In this way, the CaL technology is the most promising to form a stable stock of thermochemical energy. 

SOCRATCES aimed to demonstrate the feasibility of this integration by building a pilot-scale plant that uses cheap, abundant and non-toxic materials, as well as technologies already used in the industry. With the development of this prototype, part of the challenges of taking this technology to an industrial level were resolved. It allowed us to understand and optimize much more the operating deficiencies that could appear, and with the long-term objective of increasing the competitiveness and sustainability of Concentrated Solar Power plants. 

 SOCRATCES is built on previous R&D results of the project partners. This results, indicated that the CaL process can be integrated into CSP plants for thermochemical energy storage and power generation. The study was done by means of a simple closed CO2 loop. High global efficiencies (>45%) that were predicted at industrial scale under new CaL conditions implying carbonation under high temperature (>850ºC) at high CO2 partial pressure compatible with high efficiency power blocks. 

SOCRATCES is intended to open a new pathway for next generation of CSP tower plants, technologically feasible, economically viable and sustainable (environmental, social and economic)


The proposed system works as follows:  

Solar irradiation is used to carry out the calcination of CaCO3 (endothermic reaction) in a solar calciner reactor. The product (CO2 and solid CaO) is stored separately. When power is needed the stored products are brought together into the carbonator reactor, where energy is released through the exothermic carbonation reaction. According to the chemical equilibrium and previous kinetics analysis, carbonation can occur fast at temperatures between 650-1000ºC depending on the CO2 partial pressure, which leads to a power cycle thermodynamic efficiency higher than in currently commercial CSP plants. 


  • Prototype demonstration of capacity for energy storage. System tested at TRL5 (maturity levels for technology, at level 5, there is a component validation in a relevant environment). As solids and CO2 storage. 
  • 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 (>850ºC) and Stirling engine which is a heat engine that compresses and expand the gas and the air between different temperatures 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 
  • Improvement on the reliability and CSP plants lifetime while decreasing operation and maintenance costs, hence creating new business opportunities 
  • Development of a new generation of CSP tower with energy storage technology. 
  • To create a pathway to fostering the use of solar energy and reduce the EU energy dependency, thus improving security. 



TTZ (Germany)


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Status: Finished

Contract nº: 72748

CORDIS information: SOCRATCES 

Financing program: H2020

Duration: 1 January 201831 December 2021 (36 months) 

Budget: 4.975.402€ (EC Contribution: 4.975.402 €)

Contact person: Ángela Magno (amagno@bioazul.com)