Experimental Characterization and Statistical Analysis of Water-Based Gold Nanofluids for Solar Applications: Optical Properties and Photothermal Conversion Efficiency

Optimizing optical and photothermal properties of the solar nanofluids (NFs) to be used in direct absorption solar collectors is a key issue to maximize efficiencies in these collector types. This work both experimentally and statistically analyzes the influence of the size (5 and 20 nm) and concentration (5.1, 28.2, and 51.3 ppm) of gold nanoparticles (NPs) on several important variables for collector performance: NF stability, extinction coefficient, photothermal efficiency, etc. The research work shows that the addition of small amounts of gold NPs, whose surface plasmon resonance has wavelengths close to 520 nm, greatly improves the light absorption capacity of the base fluid (water). The statistical analysis confirms the influence of NP size and concentration on photothermal conversion efficiency (PTE), which lead to an increase of up to 121% for the smallest-sized NF with the highest concentration.