The photothermal conversion performance (PCP) of a nanofluid-based solar energy system is investigated numerically and experimentally. The impacts of particle size, volume concentration, nanoparticle type, base fluid type and collector inclination angle on the PCP are investigated. It is observed that using nanoparticles improves the ability to absorb solar energy. Temperature gain is 2.2, 3.2, 3.8, 4.2, and 9 times better than pure water for water-based Al, Al2O3, Au, Cu, and Graphite mono nanofluids, respectively. Interestingly, blended nanofluids containing the same nanoparticles significantly argument the optical properties, with useful heat enhancement ranging from 62.8 (mono) to 194 kJ/kg (hybrid). However, the collector's inclination angle, which ranges from 0 to 60°, has a negative impact on the PCP by reducing the solar radiation absorption of the nanofluids due to a decrease in the radiation penetrating the collector. Furthermore, as nanoparticle size increases, so does the thermal performance of the nanofluid. An experimental investigation is carried out for pure water and nanofluid at various wind speeds and solar irradiation levels ranging from 1 to 4 m/s and 200–1000 W/m2, respectively, to validate the numerical results. •Photothermal performance of a nanoparticle based solar collector is experimentally and numerically investigated.•Attenuation of pure working fluid is augmented by nanoparticles.•Improving nanoparticle diameter enhances temperature gain.•Blended nanoparticles further enhance useful heat capacity.•Tilt angle diminishes thermal capacity of the collector.