Peritectic compounds for compact thermal energy storage at high temperature – Pc2TES

Pc2TES aims at developing a new kind of materials with high potential for cost-effective compact thermal energy storage (TES) at high temperature. The proposal is based on a ground-breaking idea which consists in using chemical compounds formed during peritectic transitions. The term peritectic refers to reactions in which a liquid phase (L) reacts with at least one solid phase (a) to form a new solid phase (ß). The reaction is reversible and takes place at constant temperature. The formed phase (a) is either a solid solution of one of the components, an allotropic phase of one of the components, or a new stoichiometric compound. In such materials, the thermal energy will be stored by two consecutive processes: a melting/solidification process and a liquid-solid chemical reaction. On cooling (discharge process), the pro-peritectic phase ß(s) starts to nucleate once the liquid phase reaches the liquidus temperature, and then it grows until the peritectic temperature is reached. At this point, the liquid phase reacts with ß(s) to form a(s). On heating (charging process), the solid a(s) decomposes at the peritectic temperature into a liquid phase and the solid ß (s). Then, the solid ß(s) melts.

As far as we know, this idea has never been proposed before and no team in the world is exploring it. It follows the recent preliminary research conducted by partner 1 (I2M) and might lead to a TES technology with higher performances and lower cost than those currently used or investigated. The proposal will focused on the 300-600°C temperature range, which allows covering a wide spectrum of significant and challenging applications. Compared to the state-of-the-art in TES at high temperature, the main expected advantages of using peritectic compounds are as follows:

Compact TES. The effective energy density provided by the liquid-solid reaction leading to the peritectic compound lies within the interval 200-400 kWh/m3 in many cases, whereas it can be as high as 400-650 kWh/m3 when the energy associated to the melting/solidification of the pro-peritectic solid is added. These values are comparable (even higher) to those of gas-solid reactions under investigation in the world and make peritectics attractive for large-scale TES applications.

Simple TES technology. Contrary to gas-solid reactions in which chemical reactants have to be separated, the liquid phase and the solid phases involved in peritectic formation separate and recombine by themselves. Moreover, the storage material works at atmospheric pressure both in charge and in discharge. As a result, simple storage concepts, like one-single tank with storage material in bulk and embedded heat exchanger, will apply.

Cost-effective TES solutions. The investment cost (as well as those of operation and maintenance) will be therefore much lower than that of the technologies based on solid/gas reactions. Moreover, as the expected volumetric energy density is much higher than that of currently used phase-change materials, the investment cost should be lower than that of latent heat storage technologies and probably close to that of the cheapest sensible heat storage systems.

To summarize, the perictectic compounds could lead to TES solutions gathering the advantages of the technologies currently used or investigated while avoiding their respective drawbacks.