An Ag@TiO₂/ethylene glycol/water solution as a nanofluid-based beam splitter for photovoltaic/thermal applications in cold regions

Traditional heat transfer media such as water or air were used to cool the solar arrays with elaborate infrastructure and auxiliary facilities, resulting in an extra operating cost. Nowadays, new thermal management technologies, such as dichroic thin-film splitters and nanofluid beam splitters, have been developed to ensure normal cell operation at ambient temperatures. In this work, Ag@TiO₂ nanoparticles were used for the ability of selectively absorbing incident sunlight. The ethylene glycol/water solution (3:2, v/v) was selected as the base fluid because of its low freezing point which can be used in cold regions. The nanoparticles that were suspended in the base fluid formed a beam splitter for photovoltaic/thermal applications. As well, the beam splitter maintained the optical concentration as low as possible, which held the solar cell at low temperature without heat sink. The results showed the effect of nanofluid concentration on beam splitter temperature changes, photovoltaic conversion performance, and power conversion efficiency under 1 kW m⁻² of solar illumination. An overall solar energy utilization efficiency of up to 83.7% at 1 kW m⁻² was achieved when the nanoparticle concentration was as low as 200 ppm. This high performance was attributable principally to broadband light absorption, which produces a large amount of thermal energy. We also found that the adjustability of the nanofluid concentration was adequate to cope with the relative (cost-driven) changes in the electric and thermal energies of the photovoltaic/thermal system. This indicated that the Ag@TiO₂/glycol/water (3:2, v/v) nanofluid may potentially find photovoltaic/thermal applications in beam splitters operating in cold regions, given its low freezing point and high solar energy utilization efficiency.