Enhanced Solar Photothermal Conversion by Hollow Nanopillars

The final chapter explores the enhancement of solar photothermal conversion using plasmonic nanoparticles in direct absorption solar collectors (nanofluids). It addresses the limitations of complex multi-component mixtures by proposing a single-component hollow nano-cylindrical structure that is more stable and easier to process. The chapter performs a detailed comparative analysis of four plasmonic materials: silver (Ag), gold (Au), copper (Cu), and titanium nitride (TiN). For gold nanocolumns, the hollow structure is shown to significantly boost photothermal conversion efficiency by exciting resonances on both inner and outer surfaces, enhancing the localized electric field and absorption. While hollow silver nanocolumns exhibit more absorption peaks, the concurrent increase in scattering limits their overall efficiency gain. In contrast, materials like Cu and TiN, which possess inherently broad absorption spectra, show minimal efficiency improvement with structural modifications. The chapter uses electromagnetic field and resonance mode analysis to reveal how Localized Surface Plasmon Resonance and Propagating Surface Plasmon Resonance effects are manipulated by the hollow geometry. The findings provide a strategy for selecting materials and structural parameters to optimize solar harvesting in nanofluids, contributing to the development of efficient, cost-effective, and stable solar thermal conversion systems.