Solar energy storage has become more attractive recently. Especially latent thermal energy storage (LTES) with large energy storage density and isothermal heat storage/retrieval characteristics is a hot research topic. In this paper, sodium nitrate, potassium nitrate and their mixture were used as the base materials, and expanded graphite (EG) with high thermal conductivity and chemical stability was used as an additive to enhance the thermal conductivity. EG with the mass fraction of 10% was added to the base materials to form mixed phase change materials (PCMs), and the thermal characterizations of the mixture were studied extensively. Transient hot-wire tests showed that the addition of EG influenced the apparent thermal conductivity significantly. The test results showed good agreement with theoretical predictions of porous models. Tests with differential scanning calorimeter (DSC) revealed that the melting/freezing points of mixed PCMs shifted slightly, compared with pure nitrates.
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