Nanofluids (NFs) are promising materials for solar-energy harvesting. The main drawback of NFs is their instability and longtime preparation methods that the purpose of this work relies on overcoming these problems. The Cr, Mo, and W NFs in polyethylene glycol (PEG) were synthesized by laser ablation in liquid (LAL). The capability of the prepared NFs in photo-thermal conversion was investigated under 60 min solar simulator irradiation at 1 Sun and thermo-physical properties of them (SER, Etotal, E%, and B) were calculated, indicating Cr NF has the highest photo-thermal conversion efficiency (E% ≅ 85% at its near-to-surface). The comparison of nanoparticles radius obtained with transmission electron microscopy (TEM) and the hydrodynamic radius obtained with dynamic light scattering (DLS) methods, reveals that nanoparticles were surrounded by a thick layer of PEG molecules, leading to the super-stable and long-life NFs. The effect of the nanoparticle concentration, light intensity, and consecutive heating–cooling cycles on the performance of NFs was investigated. Under 1 h sunlight illumination (~850–960 W/m2 intensity), the surface temperature of Cr NF reaches ≅ 65 ℃, indicating the Cr NF is highly eligible for photo-thermal conversion in the real outdoor condition. The low cost and simplicity of the synthesis method, no need to use stabilizer, super durability, high-thermal stability, low rate constant of heat dissipation, and high photo-thermal conversion efficiency confirms that Cr/PEG NF can be used as potential working fluid for direct absorption solar collectors (DASCs).
