Boosting PV/T system performance with hybrid ZnO–water nanofluid cooling and passive airflow: a practical insight into the role of nanoparticle concentration

This study numerically investigates the performance enhancement of a hybrid photovoltaic-thermal (PV/T) system using ZnO-water nanofluid (0.1-0.5 % volume concentration) circulated at a constant flow rate of 0.0025 kg/s, combined with natural air convection. A comprehensive 3D steady-state model was developed employing the finite volume method, incorporating the standard k-ε turbulence model and Boussinesq approximation for buoyancy effects. The system features an innovative design with 16 triangular-profile cooling tubes beneath the PV panel to maximize heat transfer efficiency. Numerical simulations solved the governing equations for mass, momentum, and energy conservation under realistic Algerian climatic conditions, with validation against experimental data showing excellent agreement. Results demonstrate that increasing nanoparticle concentration significantly improves system performance, with the 0.5 % nanofluid achieving maximum electrical (15.56 %) and total thermal (75.60 %) efficiencies, representing improvements of 4.2 and 42.3 % respectively over conventional water cooling. The constant-flow nanofluid circulation maintained stable cooling performance while enhancing thermal energy recovery, with outlet temperatures increasing by 3.77 K at peak irradiance. This study provides critical insights into optimizing bi-fluid PV/T systems through nanofluid concentration control at fixed flow conditions, offering a practical solution for simultaneous electricity generation and thermal energy harvesting in solar applications.