Flat-plate solar collectors (FPSCs) offer a cost-effective solution for reducing carbon emissions from building heating. However, their effectiveness is hindered by low thermal efficiency. Utilisation of favorable nanofluids with enhanced thermophysical properties holds promise for improving FPSC performance. Nanofluid represents an advanced heat transfer medium that markedly enhances traditional fluids' heat transfer capabilities. Key areas of focus for enhancing the overall efficiency of FPSC include optimising design parameters and enhancing the convective heat transfer coefficient between the absorber tubes and fluid. Thus, this study evaluates the effectiveness of FPSC employing Al₂O₃-MWCNT (50:50%)/radiator coolant hybrid nanofluid on thermal performance. The study explores various operating parameters such as collector inlet temperature (ranging from 298 to 333 K), mass flow rate (ranging from 0.03 to 1.2 L/mins), and nanoparticles’ volume fraction (ranging from 0.1 to 0.5%). Numerical results indicate that increasing the volume fraction up to 0.5% enhances energy and exergy efficiency by 2.21% and 5.78%, respectively. However, it leads to 5.31% increase in the friction factor and 3.23% increase in pressure drop. The results show that using a hybrid Al₂O₃-MWCNT/radiator coolant increases efficiency by 24% at 0.5 vol%. Ultimately, the heat transfer properties of the device showed improvement.