Enhanced thermal regulation in photovoltaic panels using milled carbon fiber-reinforced multi-layer bio-based phase change materials

• Multi-layer PCMs enhance PV cooling and electrical efficiency. • Milled carbon fibers boost PCM thermal conductivity. • Bio-based PCMs reduce PV temperature by up to 4.78 °C. • RSM model optimizes PCM thickness and nanoparticle content. • Achieved peak PV efficiency of 12.22% with optimized PCMs. The performance of photovoltaic (PV) panels is highly sensitive to temperature rise, which leads to reduced electrical efficiency and long-term degradation. Passive thermal regulation using phase change materials (PCMs) has emerged as a promising solution, particularly for building-integrated photovoltaic systems. To address these limitations, this study develops a multi-layer, bio-based PCM system enhanced with milled carbon fiber (MCF) nanoparticles to improve both thermal and electrical performance of PV panels. Three novel PCMs are synthesized by blending beeswax and coconut oil in different volume ratios, arranged in a descending melting point order to optimize heat regulation. To enhance thermal conductivity, MCF nanoparticles (0–10 wt%) were uniformly dispersed within the PCM layers. A Response Surface Methodology (RSM) was employed to optimize the PCM layer thicknesses and MCF concentration for maximum electrical efficiency and minimal PV surface temperature. Experimental validation is conducted under realistic operating conditions. Results indicate that PCM 1 (75 % beeswax, 25 % coconut oil) and PCM 2 (50 % beeswax, 50 % coconut oil) reduce PV panel temperature by 2.70 °C and 4.78 °C, respectively, while PCM 3 (25 % beeswax, 75 % coconut oil) exhibits an inverse effect. In the multi-layer configuration, PCM 1 thickness up to 7.5 mm improves electrical efficiency, while PCM 2 and PCM 3 show benefits between 5–15 mm. Optimal MCF nanoparticle incorporation (8.63 wt%) enhanced thermal conductivity, achieving a PV efficiency of 12.22 % and a panel temperature of 38.43 °C.