Solar energy, being it free and endless, is an attractive source of energy that can be converted into electricity by means of a Concentrating Solar Power (CSP) plant. However, the biggest limit of such technology is the intermittency and the diurnal nature of the solar light. For their future development, CSP plants need to be coupled with a storage system. Finding an inexpensive, efficient mean of storing energy produced by CSP plants would be a milestone for the fast growing of the renewable energy sector. At this purpose, Thermochemical Storage (TCS) systems can directly store solar energy produced by the CSP plant during on-sun operation mode as heat and reuse it on demand during off-sun operation mode. The SESPer project aims to the identification of promising candidate storage materials for TCS system to bring the development of this technology to a level closer to the commercial scale and to favor the transference of these systems to the CSP plants installation.
Perovskite oxides (ABO3) have drawn interest as potential candidates for TCS systems. They exhibit a continuous oxygen release/uptake within a very wide temperature range, through the creation/destruction of oxygen vacancies in the crystal lattice. The working principle of a TCS system based on perovskite consists in the following reaction:
ABO3 (s) ↔ ABO3-δ (s) + δ/2 O2 (g)
The reduction, being endothermic, is the heat storage step, while oxidation releases heat when it is required.
The amount of reversibly exchangeable oxygen, δ, is a function of temperature and oxygen partial pressure. One of the most interesting characteristic of such materials is that the cations can be easily replaced by similar elements, without undergoing any phase change. This means that the material can present a wide array of possible behaviors, with the extent of reduction (δ) varying broadly. Many of the perovskite types until now studied contain rare earth elements, which makes them costly and unavailable for large-scale amounts. The overall objective of this project is to study perovskites with more earth abundant elements (i.e. Ca, Fe, Mn-based) for identifying the most promising candidate storage medium on which it is carried out a comprehensive thermodynamic study that enables the evaluation of the heat storage capacity. Additional specific objectives are scaling-up the synthesis and testing the perovskites under realistic operating conditions.