Sustainable ZnO-biochar/paraffin phase change composites for photovoltaic thermal management: Characterization and mathematical modeling

In this study, a sustainable hybrid phase-change composite consisting of paraffin wax (PW), wood-derived biochar (BC), and ZnO nanoparticles was developed for photovoltaic thermal management. PW–BC composites with 2.5–12.5 wt% BC were first prepared to determine the optimal biochar loading, and the selected formulation was then modified with ZnO-loaded biochar fillers containing 10, 20, and 30 wt% ZnO. The prepared composites were characterized using XRD, FTIR, SEM, TEM-EDX, BET, XPS, TGA, DSC, and thermal conductivity measurements. Among the investigated samples, PW–ZnO20@BC10 showed the most balanced thermophysical performance, achieving a thermal conductivity of 1.32 W · m −1 ·K −1 , corresponding to increases of 340% and 200% compared with neat PW and PW–BC10, respectively. The optimized composite also retained a high latent heat storage capacity of 163.2 J g −1 and showed a specific heat capacity of 3.87 kJ·kg −1 ·K −1 . The experimentally measured properties of PW–ZnO20@BC10 were incorporated into a mathematical model of an integrated PV/PCM cooling system. The simulation results predicted that the optimized composite would reduce the PV peak cell temperature by up to 24.6% under near-daily operating conditions and 25.3% under typical transient conditions. These results demonstrate that ZnO-functionalized biochar can substantially enhance the heat-transfer performance of paraffin-based PCMs while preserving their latent heat storage capacity, offering a sustainable and cost-effective strategy for photovoltaic thermal regulation.