Cyclic properties of thermal storage/discharge for Al-Si alloy in vacuum for solar thermochemical fuel production

Thermal energy storage using phase-change materials (PCM) can be utilized for load shaving or peak load shifting when coupled to a solar thermochemical reactor, reformer, or gasifier for the production of solar fuel. The PCM is embedded in packages or used in bulk in these storage systems, and therefore the compatibility of the encapsulation materials and the selection of the PCM are key factors for ensuring the long operational life of the system. Various kinds of molten fluoride, chloride and carbonate salts, and mixed molten salt, which function at high temperatures of over 500 degrees C, are known to cause corrosion or thermal degradation. It is therefore worth studying new high-temperature PCM thermal storage alternatives to these molten salts for use in solar thermochemical processes. In this study, the focus was on aluminum-silicon alloy (Al-Si alloy) as a high-temperature PCM thermal storage medium, and the compatibility of this alloy with graphite-carbon encapsulation material was experimentally examined. The cyclic properties of thermal storage/discharge for Al-Si alloy as a latent-heat energy storage material was studied with respect to various thermal cycles. A thermal stability test was performed for the Al-20wt% Si, Al-25wt% Si, Al-30wt% Si, and Al-35wt% Si alloys placed in the graphite container in vacuum. The temperature increasing and cooling performances of the Al-Si alloy were measured during the thermal storage (heat-charge) mode and during the cooling (heat-discharge) mode. The oxidation level of the Al-Si alloy after the cyclic reaction (20 cycles) was evaluated using an electron probe microanalyzer (EPMA). (C) 2015 The Authors. Published by Elsevier Ltd.