The application of solar-to-thermal conversion phase change material in novel solar water heating system

Solar energy has been widely used in water heating systems. Latent thermal storage technology using phase change material (PCM) has also attracted great attention in energy storage field. In this study, two kinds of composite PCM- sodium acetate trihydrate/expanded graphite (SAT/EG) and sodium acetate trihydrate/graphene oxide/expanded graphite (SAT/GO/EG) were prepared using a physical hybrid method. The melting temperature and latent heat of SAT/EG were 57.9 degrees C and 218.1 J/g, respectively. GO showed a negligible influence on the thermal thermophysical characteristics of composite PCM. Exposed in solar radiation, two PCMs can experience phase change almost at same rate. The leakage tests were conducted on these PCMs with the purpose of confirming the density of PCMs. The highest densities at which the PCMs can keep good shape stabilities were 0.8 g/cm 3 for SAT/EG and 1.0 g/cm(3) for SAT/GO/EG, which indicates that traces of GO (less than 0.1 wt%) can improve the shape stability of compressed PCMs. A solar water heating system equipped with a new type of collector was constructed by employing SAT/GO/EG (1.0 g/cm(3), 1628 g) as the solar-absorbing substance and thermal storage medium simultaneously. Under real solar radiation, the SAT/GO/EG can finish phase change and reach the temperature above 70 degrees C from 9:00 AM to 2:00 PM on a typical day in Zhuhai, China. The solar-to-thermal conversion efficiency of the system was calculated to be 54.5%. These results illustrate that SAT/GO/EG possesses excellent solar-absorbing performance and shows great promise in designing novel solar water heating system.