Integration of a Thermochemical Storage process in a Rankine cycle, driven by concentrated solar energy – In-STORES

The concentrated solar power (CSP) will take a significant part in the diverse scenarios for reduction of greenhouse gas emissions. The CSP sector presents the considerable advantage, in comparison with the other intermittent energies, to be able to integrate a storage function, which allows to shift the electricity production to periods of strong environmental or economic interest. For it, a high-temperature thermal storage has to be integrated between the solar receiver and the power block.
Compared to existing systems (sensible or latent heat), the thermochemical storage processes constitute innovative and promising solutions, still in the state of research. The thermochemical processes based on reversible solid /gas reactions are particularly relevant by their high effective energy density (until 400 kWh /m3) and operating temperatures (until 1000°C) depending on the reactants.

The aim of this project is to investigate the integration of such a thermochemical process in a CSP installation by an approach which aims at the global optimization of the performances of the power plant integrating this storage. For that purpose, the project focuses on the following key points :

1) The concepts of coupling the thermal storage and the power plant: the objective is to enhanced transfers between the themochemical reactor and the Rankine cycle. The coupling modes will be analyzed in an exhaustive way, then simulated. The most pushed integration of the storage to the Rankine cycle will be looked for. We shall analyze the impact on the sizing, the functioning and the performances of every component, but also globally of the solar plant.

2) The thermochemical reactor: it will achieve a thermal storage adapted to the CSP sector according to several criteria: operating temperature, energy density, stored energy, restored power... A strongly compact reactor (a fixed bed) will be chosen. By means of a local model, we shall
model and optimize the gas and heat diffusion network, as well as the kinetics and transfer characteristics of the composite (combining the reactive salt with a binder), according to the above criteria.

3) An experimentation on a pilot: the pilot will couple a reactor of optimized configuration and a complete Rankine cycle, according to the high performance concept selected at point 1. We shall analyze the functioning and the performances of components, and the global performances of the whole system. A particular attention will be paid to the dynamic aspects depending on several causes: variability of the solar source, the intermediate phases of the thermochemical reactor functioning, the variation of the reaction kinetics.

4) The scenarios of storage/production for CSP: they cover from the peak production (a few hours a day) to the base production (over 24 hours) and strongly influence sizing, investments, saling price of the produced electricity, environmental criteria … A global model of solar installation integrating a thermochemical storage will allow to realize an economic optimization by a global approach coupling sizing of the system and choice of the scenarios of storage/production. Several applications are in scope: large-sized power plant, solar installation coupled with a smart-grid, isolated installation.

5) The impact of the thermochemical storage on the CSP sector: in parallel with the scenarios, we shall study the extrapolation to a large-scale reactor, by investigating the size of modules and an adequate manufacturing process optimizing the cost of the reactor. Simulations of these configurations will be done thanks to the tool developed in point 2. Furthermore, a life cycle analysis will allow to direct the choice of the configuration in order to reduce the environmental impacts.