Cement, salt and water: From Politecnico di Torino a new material toward green heat

October 08, 2020

Heating the space where we live or work is a common necessity in most of the inhabited areas. The energy requested for this process is responsible for a third of all the energy consumed in Europe; moreover, 75% of this energy is produced with fossil fuels.

The idea of a new material for the thermochemical energy storage comes from a group of researchers of the Applied Science and Technology (DISAT) and Energy (DENERG) departments of the Polytechnic of Turin, and from the Advanced Energy Technology Institute of the Italian National Research Center (CNR-ITAE). The paper was published on the journal Scientific Reports*.

In this study, the researchers demonstrated how it is possible to produce heat by the hydration of salt present inside the pores of cement.

In order to reach to sustainability goals in Europe it is necessary to reduce the use of fossil fuels and to use instead renewable energy-based systems. However, the integration of renewable energy in heating systems entails a time gap between the energy surplus and the daily and annual peaks of demand.

Solar energy, for instance, is widely available in summer months, however the most part of the heating requirement is during the winter, when at our latitudes the day is much shorter. It is evident that the widespread exploitation of renewable energy sources must integrate the development of low cost storage systems, with the goal to balance the time shift between the demand and the offer of energy. One of the possible ways to store energy is the thermochemical approach, that allow to store heat for a virtually infinite time, contrary to the standard approaches.

"Try to dissolve a good amount of salt in a glass of water, what you will notice is that the glass heats up with some salts and cools down with others. A similar phenomenon is at the basis of our materials, with the difference that instead of liquid water we use aqueous vapor, without dissolving the salt. The aqueous vapor interacts with the salt and produces heat. Once completely hydrated, it will be possible to revert the salt to the starting state by a simple drying process, that allows to eliminate the surplus water.

This kind of reaction is well known, and many thermal storage materials have already been developed, however their cost is most often the limiting factor. For instance, a zeolite is one of the best materials from the thermal point of view, but it can cost up to several tens of euros per kilogram. This brings to an unbearable cost when storing the energy needed to heat a room or a whole building. The cement, used as a matrix to host the salt hydrates, is a very interesting materials since it is well known, easily available and cheap." explains Luca Lavagna, post-doc researcher of the Applied Science and Technology Department of Polytechnic of Turin, first author of the paper.

The innovative feature presented by the researchers is indeed the use of cement as a host matrix for the salt. The total cost of the used materials is very low and the energetic behavior is good: the energy cost, measured in stored €/kWh, is lower than most of the current used materials. This new material, moreover, shows an extraordinary stability even after hundreds of heating/cooling cycles. This work can represent the first step toward the creation of a new class, up to now never mentioned in the literature, of composite materials for thermochemical energy storage,
[*] L. Lavagna, D. Burlon, R. Nisticò, V. Brancato, A. Frazzica, M. Pavese, E. Chiavazzo, Cementitious composite materials for thermal energy storage applications: a preliminary characterization and theoretical analysis, Sci Rep. 10 (2020) 12833. https://doi.org/10.1038/s41598-020-69502-0.

Politecnico di Torino

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