Energy storage is one of the the greatest challenges for a short-term deeper penetration of Concentrating Solar Power (CSP) plants, which are usually characterized by the intermittency of power production. The Ca-Looping (CaL) process based upon the reversible carbonation/calcination of CaO is one of the most promising technologies for thermochemical energy storage (TCES). The wide availability of natural limestone (almost pure CaCO3) and its low price (<10€/ton) are key factors for the feasibility of the CaL process.

SOCRATCES is aimed at demonstrating the feasibility of the CSP-CaL integration by erecting a pilot-scale plant that uses cheap, abundant and non-toxic materials as well as mature technologies used in the industry, such as fluidized bed reactor, cyclones or gas-solid heat exchangers.

SOCRATCES global objective is to develop a prototype that will reduce the core risks of scaling up the technology and solve challenges; further understanding and optimise the operating efficiencies that could be obtained; with the longer-term goal of enabling highly competitive and sustainable CSP plants.



Prototype demonstration of capacity for energy storage. System tested at TRL5. 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 and power block.


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.

Main benefits of SOCRATCES concept (CSP-Calcium-Looping integration)

SOCRATCES concept approach to the challenges

Energy storage - High density thermal storage
- Low heat loss
- Affordable and sustainable solutions
- Cheap, efficient and non-toxic. Price objective for commercial application <12€/kWh.
- High CaO conversion stability, reaching residual values up to 0.5.
- Seasonal storage capacity system.
- Integration and uses of calcination by-products.
- Validation of the concept at small prototype level. Identification and solution of challenges for scaling up the technology.
Receiver/ Heat transfer fluid - Reduce cost of receiver.
- Effective heat transfer.
- Effective calcination demonstrated at laboratory level at reduced temperatures.
- Use of already available solar receiver technology.
- Integration of receiver and calciner. Synergies between CSP tower and Flash Calcination technologies.
- Flash Calcination technology available from CALIX (partner of consortium).
- Validation of the concept at small prototype level. Identification and solution of challenges (solid transport, attrition, etc) to scale up technology.
Power cycle Increase maximum temperatures of power cycle. - High temperature carbonator allows higher efficiencies in power cycle.
- Capacity of direct and indirect integrations between carbonator and power cycle.
- Direct integration reaches efficiencies ≥45% using commercial turbine technology with pressure ratios below 8 and carbonator pressure below 10bar.
- Indirect integration allows the combination with external heat cycles (Stirling, SCO2, Rankine).
- Validation of the energy storage concept at small prototype level with technologies adapted at the scale.
- Identification and solution of challenges for control and integration, load changes, fast response, effects on carbonator, and steps to scale up the technology.
- Study of scale up step for gas turbines (SCO2, CO2) and steam turbines technologies.

SOCRATCES approach

CO2 closed loop/ Power block Direct Integration

CO2 closed loop/ Power Block Indirect Integration

Project management, coordination and assessment of the project results