Thermochemical heat storage

An important contribution to sustainable energy is an efficient use of solar heat and industrial waste heat. Storage of energy is an important issue in this context. Traditional sensible heat storage techniques offer a number of disadvantages. Substantial heat loss and relatively low energy density are the most serious drawbacks. An alternative to heat storage in water tanks is the thermochemical heat storage utilizing reversible physical chemical processes offering the advantage of high energy density and very low energy losses. The sorption-desorption equilibrium of water vapor in microporous materials such as zeolithes is one such example. More recently, research has been conducted in the use of chemical reactions such as hydration-dehydration reactions of metal salts for the thermochemical storage of energy.

The use of salt hydrates in a thermochemical system is based on the release of the heat of hydration. Hence, a salt hydrate storage system is charged by the endothermic thermal dehydration of the respective higher hydrated salt. Many salts can be dehydrated at temperatures that can well be achieved using solar thermal collectors. In this state, the energy can be stored over long periods of time implying its application for seasonal storage. The exothermic back reaction may be initiated by simply increasing the water vapor partial pressure.

The performance of a salt hydrate storage system largely depends on the kinetics of the hydration and dehydration reactions. The objectives of our research are as follows: (1) Selection of appropriate metal salts based on their thermodynamic properties and the kinetics of the respective hydration and dehydration reactions. (2) Testing of different porous substrates including mesoporous materials for the salt hydrate.

This research is a collaboration with the group of Prof. Christian Kaps at Bauhaus-Universtät Weimar.