The nanofluids render a potential alternative to ameliorate the performance significantly in heat transfer applications. The influence of Zinc oxide/Ethylene glycol:Deionized water (50:50) on the thermal performance of flat plate solar collector has been evaluated at various volume flow rates, 30 to 150 LPH (litre per hour). The results of dynamic light scattering and UV-vis spectroscopy indicates the instability at higher concentration while 0.2-1 vol% ZnO nanofluid was found stable for longer than 25 days. The particle size analysis determined agglomeration more than the specified limit for 1.4 vol% zinc oxide. The thermal efficiency of the solar collector rises with rising flow rates. However, the outlet temperature was found nearly 318.62 K at 150 LPH flow rate, which is too low for solar applications. The maximum thermal efficiency achieved to be 69.24% (ambient temperature equals to inlet temperature) at 60 LPH for 1 vol% ZnO, which was 19.2% higher than base fluid. At the identical parametric situation, the absorbed energy parameter increased by 18% and removed energy parameter decreased by 62.5% instead of Ethylene glycol:Deionized water. The astounding improvement in the thermal performance of solar collector emboldens the use of ZnO nanofluid instead of the base fluid. (c) 2020 Elsevier Ltd. All rights reserved.