In a majority of the populated regions, a general requirement is to heat the space where humans live or work. The energy needed for this process makes up one-third of all the energy consumed in Europe. Furthermore, 75% of this energy is produced using fossil fuels.
A research group at the Applied Science and Technology (DISAT) and Energy (DENERG) departments of the Polytechnic of Turin, as well as from the Advanced Energy Technology Institute of the Italian National Research Center (CNR-ITAE) has now proposed the concept of a new material to store thermochemical energy.
In the study, which was published in the Scientific Reports journal, the team showed how it is possible to generate heat by the hydration of salt present within the pores of cement.
To achieve sustainability targets in Europe, it is essential to decrease the usage of fossil fuels and to alternatively use renewable energy-based systems. But the addition of renewable energy in heating systems involves a time gap between the energy excess and the everyday and yearly peaks of request.
For example, solar energy is broadly available in summer months, but the major part of the heating is needed in winter, while at the latitudes the day is much shorter. It is obvious that the extensive exploitation of renewable energy sources should incorporate the creation of low-cost storage systems, with the aim of balancing the time shift between the demand and supply of energy.
One possible way to store energy is the thermochemical method, which enables heat to be stored for a virtually endless time, in contrast to the normal 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.
Luca Lavagna, Study First Author and Post-Doc Researcher, Department of Applied Science and Technology, Polytechnic of Turin
Lavagna continued, “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,” added Lavagna.
The novel feature proposed by the team is certainly the use of cement as a host matrix for the salt. The entire cost of the materials used is very low, and the energetic activity is optimal—the energy cost, quantified as stored €/kWh, is lower compared to a majority of the materials used at present.
Furthermore, this new material exhibits remarkable stability even after hundreds of cooling or heating cycles. This study can represent the initial step toward the development of a new class of composite materials for the storage of thermochemical energy, a class that has never been mentioned in the literature to date.
Lavagna, L., et al. (2020) Cementitious composite materials for thermal energy storage applications: a preliminary characterization and theoretical analysis. Scientific Reports. doi.org/10.1038/s41598-020-69502-0.