The Development of a Suitable Host Matrix Material for Salt-Hydrate Thermochemical Energy Storage

Seasonal storage of solar thermal energy has great potential for heating applications in both the developed world and in emerging markets. TCES (thermochemical energy storage) using salt-hydrate reactions is promising, due to its relative low cost, low temperature requirements, and reversibility, but issues with poor conductivity, conglomeration, and the formation of brines limit its usefulness. This research focuses on the development of a suitable matrix material to host various salt hydrates, especially in systems using liquid water for hydration. The material studied was a novel combination of expanded graphite and carbonized flour, impregnated with calcium chloride hexahydrate. The matrix was evaluated on absorptivity, material strength, and salt retention over a number of hydration-dehydration cycles. These properties were also examined under varying material compositions. A functional baseline composition is the pre-carbonization weight ratio of 1:4:5 expanded graphite:flour:water. Generally, as relative flour content increased, material strength increased and absorptivity decreased. Initial water content seemed to have little influence on the final product. The theoretical energy density of the salt-matrix complex is 325 kJ/kg or 1.35*105 kJ/m³. The matrix material has performed well in a prototype solar-powered desorption reactor and in preliminary air and water heating application tests.