Comparative Analysis of Al 2 O 3 /Water–TiO 2 /Chlorophyll Hybrid Nanofluids in a Photovoltaic–Thermal Solar Water Heating System

ABSTRACT Photovoltaic–thermal (PVT) solar water‐heating systems simultaneously generate thermal and electrical energy; however, their performance is limited by the low thermal conductivity of conventional working fluids, resulting in inadequate heat removal and elevated photovoltaic cell temperatures. Although nanofluids have been widely investigated to overcome this limitation, studies have focused primarily on inorganic nanoparticles, while bio‐hybrid nanofluids remain unexplored in PVT applications. This study presents the first comparative experimental and numerical investigation of Al 2 O 3 /water and TiO 2 /chlorophyll bio‐hybrid nanofluids against water in a flat‐plate PVT collector. Both nanofluids were prepared at 0.5 wt.% using the two‐step method and evaluated experimentally under outdoor conditions, while a three‐dimensional CFD model developed in ANSYS Fluent was validated against experimental measurements ( R 2 > 0.999; RMSE < 0.062°C). Thermal, electrical, overall, and energy‐saving efficiencies, together with entropy generation and thermal performance factor, were analyzed. The TiO 2 /chlorophyll nanofluid exhibited the highest thermal efficiency (38.74%), outperforming Al 2 O 3 /water (35.96%) and water (27.77%), while achieving electrical, overall, and energy‐saving efficiencies of 12.61%, 51.35%, and 71.89%, respectively. The superior performance is attributed to enhanced thermal conductivity, improved surface wettability, and additional solar absorption by chlorophyll. The validated CFD model identified an optimum nanofluid concentration of 3 vol.% that minimized entropy generation and maximized thermal performance. These findings establish TiO 2 /chlorophyll as a promising sustainable working fluid for high‐efficiency PVT systems and provide validated design guidance for future PVT solar energy applications.