Study of peritectic compound Li4(OH)3Br for high temperature thermal energy storage in solar power applications

This paper focus on the study of peritectic compound Li4(OH)3Br for thermal energy storage in solar power applications. A thoroughly characterization of Li4(OH)3Br as storage material has been performed by measuring transition temperatures (280–289 °C), enthalpies of transition (247 J/g), specific heats (c.a. 1.68 J/g/K in solid, 2.52 J/g/K in liquid) and thermal conductivity (0.47 W/m/K at room temperature). The effect of the synthesis conditions on the storage properties has been investigated as well. It is concluded that neither the cooling rate applied during the synthesis stage nor the type of atmosphere used (ambient air and protective argon atmosphere) has an influence on the material's performance. The stability of the material to thermal cycling has also been analysed, showing good cycling stability. Moreover, particular attention is paid to the elucidation of mechanisms of formation of Li4(OH)3Br. It is shown that Li4(OH)3Br needs neither the presence nor contact with the pro-peritectic phase to form. It nucleates and grows directly from the melt so as pure-phase Li4(OH)3Br final microstructure is achieved. An attempt to enhance the storage capacity of the material by addition of different types of carbon nanoparticles has been carried out. Assets of Li4(OH)3Br as storage materials for high-pressure DSG solar power plants have been assessed through comparison with reference material NaNO3. Main advantages of Li4(OH)3Br are higher volumetric latent heat storage capacity (+54%) and lower volume changes during phase transitions (3% vs. 11%), which would translate into smaller storage tanks (−33%), lower size heat exchangers and longer lifetime