Chitosan/banana peel hydrochar @ paraffin composite beads as a phase change material in packed bed latent heat thermal energy storage unit

Abstract Efficient thermal energy storage (TES) is essential for addressing the mismatch between energy generation and consumption in renewable energy systems. Conventional phase change materials (PCMs) such as paraffin suffer from leakage, low thermal conductivity, and limited structural stability, restricting their practical application. Here, we report the development of a sustainable, high-performance PCM by encapsulating paraffin within a chitosan (CS) and banana peel-derived hydrochar (BPHC) matrix, forming CS/BPHC@Paraffin composite beads via an extrusion–coagulation method. FTIR and microscopic analyses confirmed successful physical encapsulation, preserving chemical integrity and preventing leakage while providing a porous, structurally stable support. Response surface modeling using a Central Composite Design was applied to optimize the CS/Paraffin (0.30–0.40) and BPHC/Paraffin (0.05–0.15) ratios, revealing that increased CS and BPHC content reduces latent heat of fusion and peak melting temperature due to paraffin dilution and crystallization inhibition. The optimized formulation (CS/Paraffin = 0.30; BPHC/Paraffin = 0.05) exhibited an exceptionally high latent heat of fusion of 1,155.74 J/g and a peak melting temperature of 68.92 °C. Packed bed thermal testing demonstrated effective heat absorption, retention, and controlled release, with improved thermal buffering and mechanical stability compared to pure paraffin. This work provides a practical and scalable strategy for valorizing agricultural waste into eco-friendly, structurally robust PCMs, offering significant potential for advanced TES applications in renewable energy systems. Graphical abstract