Direct absorption solar collector (DASC) is a promising technology for solar energy harvesting. Recently, nanofluids have shown great potential for DASC applications due to their tunable optical absorption properties. An advanced composite combining plasmonic gold nanoparticles (Au NPs) and hedgehog-like hierarchically structured ZnO particles (HPs) was prepared and used in DASCs. The nanofluid prepared with 1.0 mg mL(-1) Hp-Au exhibited excellent stability and broadband optical absorption properties, and reached an equilibrium temperature of similar to 125 degrees C within 1 h of solar heating at an irradiation power of 10 kW m(-2). A new photothermal conversion efficiency model was established to evaluate the solar harvesting performance of the HP-Au/oil nanofluid by simultaneously considering the effect of the working fluid temperature on the heating and cooling efficiencies. Compared to the base fluid, the HP-Au/oil nanofluid exhibits a 240% enhancement in photothermal conversion efficiency. The HP-Au/oil nanofluid shows great potential as a working fluid in direct absorption solar collectors.