Recent developments in nano-enhanced phase change materials for solar thermal storage

The effective utilization of solar energy is feasible by matching the energy supply to demand with selective solar collectors and energy storage. Solar thermal systems with thermal storage using phase change material (PCM) are beneficial in storing heat for later use. Although PCM has a high energy density due to latent heat, improving its low thermal conductivity is essential for adequate heat storage. Simultaneous improvement of thermal conductivity and maintaining the energy storage density of PCM using additives is a real challenge. The present review discusses the effects of different additives on improving the performance of nano-enhanced PCM. The additives are carbon, graphene, graphite, metals and their oxides, silicon, nanotube/fiber, graphene nanoplatelets, foam, carbon soots, zeolite, MXene, and carbonized kapok fiber. This review examines the preparation, characterization, mechanisms, factors affecting thermal conductivity, and applications of PCMs. Practical and compact energy systems with a selective combination of thermal conductivity enhancements are essential for the thermal energy needs of the domestic and industrial sectors. Few additives exhibit exceptional thermal conductivity by maintaining latent heat due to porous structure. This comprehensive review could help researchers select suitable enhancement additives to the PCM used for solar thermal applications.