In traditional hybrid concentrating photovoltaic-thermal (PV-T) collectors, suboptimal utilisation of the solar spectrum results in elevated temperatures that adversely affect PV cell efficiency. In this context, solar spectral beam splitting (SBS) designs have emerged as they promise improved solar spectrum utilisation with reduced optical losses. In particular, fluid-based SBS filters, such as novel Ag-ZnO/water hybrid nanofluids, have attracted attention as they 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 PV-T systems. Full-spectrum solar utilisation via SBS enables down conversion in the UV region, transmission of visible and near-infrared light (crucial for Si PV cell optoelectronic efficiency), and absorption of the infrared region. A Ag-ZnO/water nanofluid filter-based PV-T system is investigated and is shown to achieve a thermal efficiency > 65 % with good electrical performance. 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 type of nanofluid filter enhances spectral selectivity, reduces PV cell temperatures, improves heat extraction, and offers dual functionality: cooling and filtration, making it a promising and economically viable candidate for commercial PV-T applications.