Plasmonic supraballs for full-spectrum photothermal conversion in DASCs: a comparative spectral, thermal, and exergetic analysis

Plasmonic supraballs exhibit broadband optical behavior that may benefit direct absorption solar collectors (DASCs); however, their performance as dispersed working media in DASCs has not been established. This study presents a numerical prediction of the optical, thermal, and exergetic performance of a DASC containing gold supraballs, using literature-derived effective optical data and comparing the results with conventional gold-nanoparticle nanofluids under identical conditions. The supraball architecture combines the localized plasmonic response of its constituent nanospheres with collective, nonlocalized multipolar modes, producing broadband absorption across 0.4-2.5 μm. At a solid-gold volume fraction of f V = 0.05% and a collector height of 1 mm, the supraball suspension achieves an absorption efficiency of ∼97%, compared with ∼70% for the conventional gold-nanoparticle suspension. At f V = 0.025%, the supraball and nanoparticle collectors achieve thermal efficiencies of approximately 75% and 48% and exergetic efficiencies of approximately 2.23% and 0.94%, respectively, corresponding to relative enhancements of approximately 55% and 137%. At the same solid-gold concentration of 0.05%, the supraball suspension reduces the channel height required to exceed 95% absorption from 8 mm to 1 mm, representing an 87.5% reduction. At a fixed height of 8 mm, it achieves ∼96% absorption using only 0.005% solid gold, compared with 0.05% for conventional nanoparticles, corresponding to a tenfold reduction in noble-metal mass. These results demonstrate the predicted system-level potential of gold supraballs for compact and materially efficient DASCs, subject to three-dimensional optical and experimental collector-level validation.