Exceptional solar harvesting at ultra-low concentration via optimized plasmonic Au@Pt nano-ellipsoids: A multiphysics modeling study

The growing demand for sustainable and low-carbon energy technologies has fueled interest in efficient solar thermal harvesting techniques. Direct absorption solar collectors (DASCs) with plasmonic nanofluids (NFs) have been identified as an attractive replacement for traditional surface-based solar collectors because of their improved volumetric absorption and photothermal conversion ability. Here, we rationally design and optimize bimetallic Ag@Pt and Au@Pt nano-ellipsoids (NEs) as advanced nano-heaters. By tuning the aspect ratio (AR = 1.0 − 4.0), the localized surface plasmon resonance can be continuously shifted from UV to near-infrared, enabling perfect spectral matching with sunlight. The core–shell architecture synergistically combines the strong plasmonic response of Au/Ag with the exceptional chemical stability of Pt. To evaluate NEs, we perform 3-D computational modeling framework using Full-wave field analysis based on finite element method (FEM) to explore optical absorption properties and estimate solar energy efficiencies of plasmonic NFs.The LSPR coupling between Ag core and Pt shell generates hybridized modes spanning 400-1200 nm. The solar-weighted absorption coefficient ( A m , representing the solar spectral absorption efficiency within the nanofluid layer) has been calculated to assess the effective performance of the NFs used in DASCs for specific values of particle aspect ratio, thickness, and concentration. Strikingly, our results demonstrate that Au@Pt NEs achieve an exceptional solar-weighted absorption efficiency ( Am > 99%) at an ultra-low volume fraction of merely 2.0 × 1 0 − 7 . This required nanoparticle concentration is orders of magnitude lower than those typically needed in DASCs based on conventional nanofluids (e.g., metal oxides or carbon-based materials) to attain comparable performance. Moreover, the ellipsoidal geometry yields a superior and more uniform temperature distribution (approximately 15% higher in key metrics) compared to its spherical counterparts, demonstrating their enhanced suitability for solar thermal harvesting applications. Optimized bimetallic NEs demonstrate superior A m factor as compared to conventional NF systems, proving that they may serve as efficient nano-heaters for next-generation solar thermal harvesting in DASCs. • Bimetallic Ag@Pt and Au@Pt nano-ellipsoids are designed and optimized to enhance volumetric solar absorption in DASC at ultra-low particle loadings. • Geometric parameters, particularly aspect ratio and size, are shown to govern plasmonic response, inducing systematic resonance redshifts and broadband absorption enhancement under solar illumination conditions. • The ellipsoidal geometry yields a superior and more uniform temperature distribution (approximately 15% higher in key metrics) compared to its spherical counterparts. • Optimized nanofluids achieve solar-weighted absorption efficiencies exceeding 0.99 at volume fractions (2×10 −7 ), minimizing scattering losses and outperforming several counterparts for next-generation solar thermal harvesting.