Investigations of stable surface-modified gold nanofluids optical filters based on optical optimization for photovoltaic/thermal systems

Nanofluid filters have become increasingly popular for solar photovoltaic/thermal (PV/T) systems due to their tunable optical and thermal properties, especially for some plasmonic nanofluids. However, towards optimizing the characteristics of the plasmonic nanofluids filters, by identifying the best nanofluid parameters and improving their long-term dispersion stability, more researches need to be conducted. In this work, the effects of nanoparticles concentration, optical thickness and nanoparticle size on performance of Au nanofluids filtered PV/T systems are investigated theoretically. The PV/T systems can obtain optimal merit function (MF) of 1.367 and 1.357 for Au/water nanofluid and Au/ethylene glycol (EG) nanofluid, respectively. Then, surface-modified Au nanoparticles capped with polyethylene glycol (PEG) or polyvinylpyrrolidone (PVP) polymers are prepared and dispersed in water and EG, respectively. The stability of the stabilizer coated Au nanofluids upon long-term ambient storage, continuous heating, cyclic flowing and solar radiation is discussed. Au + PVP/EG nanofluids exhibit more excellent thermal stability than that of Au + PVP/water. To study the effectiveness of the optimal Au + PVP/EG nanofluids filtered PV/T system, indoor flowing experiments are conducted. The optimal MF of 1.95 and exergy efficiency of 13.98% is achieved filtered by Au + PVP/EG nanofluid with concentration of 29.2 ppm when mass flow rate is 2 mL/min.