Nano-engineered organic solid–solid phase change materials for high-efficiency thermal energy storage in renewable systems: a review

Abstract Thermal energy storage (TES) plays a critical role in enhancing the efficiency and sustainability of renewable energy systems. Among TES technologies, phase change materials (PCMs) are widely used due to their high latent heat storage capacity. However, conventional solid–liquid PCMs suffer from leakage, structural instability, and volume expansion, which limit their practical applications. Organic solid–solid PCMs offer a promising alternative by maintaining structural integrity during phase transitions. Recent advances in nanotechnology have further enhanced the thermal properties of organic solid–solid PCMs, improving thermal conductivity, phase transition temperature control, and overall energy storage efficiency. This study explores the nano-engineering of organic solid–solid PCMs through the incorporation of nanomaterials such as metal oxides (TiO2, CuO, Al2O3, ZnO), carbon-based nanomaterials (graphene and carbon nanotubes), and metallic nanoparticles (Cu and Ag). These nano-engineered organic solid–solid PCMs (NEOSS-PCMs) exhibit superior thermal performance, making them suitable for applications in solar energy storage, passive building temperature regulation, and electronic thermal management. Composite formation and nano-encapsulation techniques are investigated to improve stability and prevent material degradation. This work highlights recent advancements, key challenges, and future research directions in the development of high-efficiency nano-engineered organic solid–solid PCMs for TES applications in renewable energy systems.