Novel solid–solid phase-change cascade systems for high-temperature thermal energy storage. (1st January 2019)

• Record Type: Journal Article
• Authors: Bayon, Alicia; Liu, Ming; Sergeev, Dmitry; Grigore, Mihaela; Bruno, Frank; Müller, Michael
• Is Part Of: Solar energy. Volume 177(2019)
• Page Start: 274
• Page End: 283
• Publication Date: 2019-01-01
• Subjects: Thermal energy storage -- Cascaded PCM -- Concentrated solar energy -- Li and Na sulfates; Solar energy -- Periodicals; Solar engines -- Periodicals; 621.47
• DOI: 10.1016/j.solener.2018.10.085
• Languages: English
• ISSNs: 0038-092X

Abstract

Highlights: Na and Li sulfates solid-solid PCM mixtures are proposed for cascade systems. The thermal stability, specific heat capacity and latent heat are obtained. NaLiSO4 is the most stable material with lower cost. NaSO4 shows irreversible phase transition. A selected mixture of LiSO4 and NaLiSO4 shows $50.2 kWhth −1 . Abstract: In this work, we investigate novel solid–solid phase-change cascade systems based on mixtures of lithium and sodium sulfates. Solid–solid phase-change materials (PCMs) can be coupled with concentrated solar power technologies. They present several advantages over solid–liquid PCMs including lower thermal expansion, lower or no corrosiveness, and no need for encapsulation. In solid–solid PCMs, the energy is stored during crystal structure transitions. Specifically, lithium sulfate undergoes a crystal structure transition (monoclinic to cubic) at 576 °C, which is a suitable temperature for concentrated solar thermal technologies. Due to the high cost of lithium sulfate, we evaluated the potential of mixing lithium with sodium sulfate to create solid–solid cascaded PCM systems to provide higher thermal storage densities. We used differential scanning calorimetry, high-temperature in situ X-ray diffraction and thermogravimetric analysis to evaluate the phase-transition temperature, phase-change enthalpy, specific heat capacity, crystalline phase composition and thermal expansion. The obtained values for heat capacity and enthalpies of phase transitions showed good agreement with available thermodynamic databases. Therefore, further calculations of thermodynamic properties of each mixture in the system were performed for designing cascaded latent thermal energy storage system. From the PCM mixtures studied, NaLiSO4 shows the greatest stability under ambient conditions. A mixture of 59.17% NaLiSO4 and 40.83% Li2 SO4 allows an optimum charge of both PCMs for power cycles such as supercritical CO2 . Economic assessment revealed that this cascade system has an estimated cost of $50.2 kWhth −1 .