Chemical and sorptive thermal storage methods

Thermal storage systems

Different thermal storage methods
Classification of different thermal storage methods.

Chemical and sorptive heat storage systems which are counted as thermochemical storage systems, are relatively new, promising technology approaches with considerable benefits compared to both the sensible and the latent-heat storage systems. Here storage densities can theoretically be up to 10 times above those of the medium water; i.e. these systems can store much more energy without requiring a bigger construction volume. This energy is bound by means of physicochemical processes thus almost eliminating thermal loss. The combination of both advantages facilitates the efficient time-based storage of thermal energy and its transport. Due to similarities with heat pumps with regard to thermodynamic processes, sorptive systems can be applied to cooling processes at the same time.

Functionality of sorptive thermal storage sytems

Schematic diagram
Schematic diagram of sorptive thermal energy storage.
Zeolithschüttung im Versuchsreaktor
Zeolite balls in pilot plant reactor.

The Fraunhofer IGB is currently working with sorption systems utilizing a physico-sorptive bond between the reaction pair adsorbent (A) – adsorptive (B) with a preferably high energy turnover. This principle is reversible: A + B ↔ AB + heat (see Fig. with schematic diagram). When charging the storage medium, heat is added to substance AB which then dissociates into A and B components. To recover the heat the A and B components have to react with each other again. As long as a reaction between A and B is prevented, the heat which is stored by way of chemical energy cannot be released. The preferred adsorptive is water. It possesses a high phase transition enthalpy, is economic and harmless at the same time. The adsorbent (e.g. zeolite) has to bind the highest amount of water possible by adsorption.