Development of a sodium acetate trihydrate-based phase change material for efficient solar/electric-to-thermal energy conversion

The need to heat buildings during peak periods increases energy consumption. Solar/electric-to-thermal energy conversion heat storage systems can effectively address the heating mismatch issue due to variable solar light intensity. Sodium acetate trihydrate (SAT), borax, and sodium carboxymethyl cellulose (CMC) were used as the solar/electric energy storage medium, nucleating agent, and thickening agent, respectively. A carbon material, expanded graphite (EG), was used as the thermal conductor and solar/electric energy conversion enhancer. EG also acts as a nucleating agent synergistically with borax. The results show that adding 4 wt% EG, 1 wt% borax, and 2 wt% CMC decreased the supercooling of SAT to 1 °C without phase separation, and the composite exhibited excellent thermal cycling stability and a high latent heat storage capacity of 261.5 J/g. The thermal conductivity of the composite increased by 287.7% compared to pure SAT, and its solar-to-thermal energy conversion and electric-to-thermal energy conversion efficiencies reached 90.3% and 87.1%, respectively. This study offers a method for developing thermal storage systems with multiple energy conversion capabilities for prospective applications in solar energy utilization, electrical energy recovery, and building heating.