In traditional hybrid concentrating photovoltaic-thermal (PV-T) systems, inadequate utilisation of the solar spectrum results in elevated temperatures that adversely affect PV efficiency. Solar spectral beam splitting (SBS) offers an improved design by optimising solar spectrum utilisation with minimal optical losses. Fluid-based SBS filters, such as the novel Ag-ZnO/water hybrid nanofluid, present a significant advantage over conventional filters (e.g., anti-reflective coatings, selective coatings, bandpass filters, long-pass/short-pass filters, dielectric filters). These nanofluid filters serve as both heat transfer and thermal storage mediums, enhancing the overall efficiency of the PV-T system. The full-spectrum utilisation via SBS enables down conversion in the UV region, the transmission of visible and near-infrared light (crucial for Si PV cell optoelectronic efficiency), and absorption of the infrared region. The Ag-ZnO/water nanofluid filter-based PV-T system achieves over 65% thermal efficiency with a stable electrical efficiency, making it an essential spectral splitter. Optimal conditions include an Ag-ZnO concentration of 50 ppm, solar irradiance of 800-1000 W/m2, and optical thickness of 20 mm. The integration of this nanofluid filter enhances spectral selectivity, reduces temperature, improves heat extraction, and offers dual functionality: cooling and filtration, positioning it as a promising and economically viable candidate for commercial PV-T applications.