Transpired solar collectors (TSC) are an efficient means of building heating but due to the demand / use mismatch their capabilities are maximised when paired with a suitable storage technology. The hydration and / dehydration of inorganic salts provides an appropriate energy storage medium which is compatible with the air temperature provided by a conventional TSC (<70 C). The study reports on the technical appraisal of materials which are compatible with building scale energy storage installations. Two salts (CaCl 2 , and LiNO 3) were impregnated into porous vermiculite to form a salt in matrix (SIM). Their performance during the discharge portion of the cycle at high packing density was examined using a laboratory scale reactor. Reactor and exit temperature increases were considerably lower than those predicted from first principles. Peak reactor temperature rises of only 14 C were observed with a reduction in temperature output from this initial peak over 60 hours. Poor salt utilization resulting from deliquescence near the reactor inlet was identified as being the source of the reduced performance. Changes in reactor size, orientation and cycling between input periods of moist and dry air did not improve reactor performance. The investigation has identified that moist air transit through the packed SIM reactor column is limited to approximately 100 mm from the air inlet. This has implications for reactor design and the operation of any practical building scale installation. Predictions of building scale energy storage capabilities based on simple scaling of laboratory tests under estimate considerably the volume and complexity of equipment required.

A novel study is undertaken on low cost thermochemical storage which utilizes temperatures which are compatible with low grade renewable energy capture. The discharge performance of thermochemical storage matrix materials is assessed using a custom developed experimental apparatus which provides a means of comparing materials under scaled reactor conditions. The basic performance of three salts (CaCl 2 , LiNO 3 and MgSO 4 ) was investigated and their subsequent performance using layering and blending techniques established that the performance could be increased by up to 24% through the correct choice of mixing technique. Layering the CaCl 2 on the LiNO 3 provided the most efficient thermal release strategy and yielded a thermal storage density of 0.2 GJ/m 3 . The research also uniquely highlights the important finding that incorrect mixing of the materials can lead to a significant reduction in efficiency with freely mixed CaCl 2 and LiNO 3 possessing a storage capacity of less than 0.01 GJ/m 3 as a result of chemical interactions between the deliquesced materials in close proximity. The paper has impact for the design and control of thermochemical storage systems as it clearly identifies how performance can be improved or degraded by the choice and the structuring of the materials.