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The eutectic Na 2 CO 3 -Li 2 CO 3 salt is widely used as an electrolyte in the Molten Carbonate Fuel Cell because of its high both ionic conductivity and operating temperature. The major objective of this study was to investigate the thermal stability of the binary salt as a phase change material for thermal energy storage through thermal decomposition analysis in different environments and thermal cycling. The composition of the binary salt was determined using FactSage software 6.4 and its thermophysical properties were experimentally investigated using a Simultaneous Thermal Analyzer and X-Ray Diffraction. The results show that the eutectic Na 2 CO 3 -Li 2 CO 3 salt has a melting/solidification point of 498.3 ± 0.1 °C/483.9 ± 0.1 °C, with a heat of fusion of 330.8 ± 0.6 J/g and heat of solidification of 329.2 ± 0.3 J/g. The thermal decomposition analysis indicates that the eutectic molten salt has good thermal stability in a CO 2 environment without weight loss at temperatures up to 600 °C. However, 0.8% weight loss is observed at 500 °C in a N 2 atmosphere, which is associated with the thermal decomposition of the eutectic salt to produce corresponding metal oxides and CO 2 . The CO 2 environment could inhibit the thermal decomposition, thus resulting in higher thermal stability of the binary salt in CO 2 than when in N 2 . Hence, an operating environment has a large effect on the thermal stability of the eutectic Na 2 CO 3 -Li 2 CO 3 salt. The eutectic salt exhibits high thermal stability in CO 2 after 500 thermal cycles with little change in its thermal properties compared with the initial sample. [ABSTRACT FROM AUTHOR]

Abstract In the current study the feasibility of using solar-based renewables coupled with thermal energy storage (TES) to displace gas for heating was explored. To assess the feasibility, a numerical model of an air-based encapsulated phase change (EPCM) storage system was developed, validated, optimised, and economically costed. The optimised air-based EPCM system utilised a high and low melting temperature phase change material (PCM) with a sensible storage filler. It was found that a capsule radius of 10 mm and PCM volume of 13% resulted in the lowest cost of discharged thermal energy of $25.55/kWh when storage effectiveness and pumping power was considered. This system was then coupled to solar data for Adelaide, South Australia, to simulate the performance of a 1 MWt heat load over a year. By solving an hourly system generation and demand profile, it was found that a concentrated solar thermal (CST) and photovoltaic (PV) system coupled with TES was able to economically reduce gas consumption by 45–65% when the price of gas was $30/GJ. By employing near-term cost estimates for CST and PV systems coupled with TES, it was found that gas consumption could be reduced by similar amounts with a gas price of $20/GJ. Highlights • Solar-based renewables coupled with TES is explored to reduce commercial/industrial reliance on gas as a heat source. • A numerical model of an air-based EPCM system is developed, validated, optimised, and economically costed. • A 2-PCM hybrid system was found to produce the desired performance at the lowest cost ($25.55/kWh t). • Both PV and CST systems are able to currently compete with gas as a heat source when the gas price is more than $25/GJ. • Predicted cost reductions coupled with low cost grid electricity show these systems capable of being economic at $15/GJ. [ABSTRACT FROM AUTHOR]

In this work, the eutectic Na 2 CO 3 –NaCl molten salt was investigated as a new high temperature phase change material for solar thermal energy storage. The composition of the eutectic binary salt was determined with the aid of FactSage software and its thermophysical properties were investigated using a Simultaneous Thermal Analyzer (STA) and X-Ray Diffraction (XRD). Inductively coupled plasma analysis has shown that the composition of the as-prepared sample is consistent with the nominal one. The STA results exhibit that the melting point of the eutectic salt is 637.0 °C and its heat of fusion is 283.3 J/g whereas its specific heat is a function of temperature, which all are in agreement with the theoretical values determined by the FactSage software. The thermal stability analysis indicates that the eutectic molten salt has good thermal stability without weight loss in a CO 2 environment at temperatures below 700 °C, compared with 0.51% weight loss in a N 2 atmosphere. The weight loss observed in the latter, is most likely to be due to the salt׳s decomposition at high temperature. The thermophysical properties of the salt such as melting temperature, latent heat of fusion and solidification, varied marginally after 50 and 100 thermal cycle tests. This demonstrates that the eutectic Na 2 CO 3 –NaCl salt is a promising high temperature phase change material when used in a CO 2 environment or encapsulation. [ABSTRACT FROM AUTHOR]