Over last decade, performance of direct absorption solar collector (DASC) system has displayed better prospects than conventional surface absorption solar collector. More recently, nano-sized metallic particles have been introduced to enhance the optical signature of the working fluids and hence the overall thermal performance of DASC systems. However, one of the significant issue of these metallic nanoparticles is narrow absorption wavelength range in solar spectrum. Blended nanofluids have shown an excellent approach for absorbing a broadband range of solar radiation. In the present study, a photothermal performance analysis is carried out based on a prototype concentrating DASC system (asymmetric compound parabolic collector) using blended plasmonic nanofluids under real-time outdoor testing conditions. A blended plasmonic nanofluid is prepared by mono-spherical Silver (Ag) and Gold (Au) nanoparticles of sizes around 5–10 nm and 20–30 nm, respectively. The study presented the optical properties, stability of prepared nanofluids and photothermal conversion performance of concentrating DASC system and compared it to a flat DASC system with the same absorber area. The experimental results showed that the temperature rise in the concentrating DASC system was significantly higher than that in the flat DASC system under the same working conditions. The study shows that using plasmonic nanostructures in concentrating DASC systems can be advantageous over base fluids for high thermal efficiency.