The deficient utilisation of the solar spectrum in conventional hybrid concentrating photovoltaic-thermal (CPVT) technologies leads to a detrimental decrease in PV efficiency due to elevated temperatures. Solar spectral
beam splitting (SBS) is an advancement in PV-T system design, which aims to use the full solar spectrum with
minimal optical losses. The implementation of fluid-based SBS designs is economically feasible, with optical
features that can be tuned by selecting suitable nanofluids with a desired concentration. Fluid-based SBS
filters are advantageous over other filters for PV-T systems due to their ability to operate simultaneously as
thermal storage as well as heat transfer media in these systems. In the present study, we report on the optical
and thermophysical properties of a novel water-based Ag-ZnO hybrid nanofluid. The filter is synthesised by
adding Ag to ZnO nanoparticles by a wet chemical method for improved stability. Silver (Ag) allows visible light
harvesting (down conversion of UV to the visible region of the solar spectrum) and good optical properties in
the visible and near-IR regions. An Ag shell can be embedded into the core of zinc oxide (ZnO) nanoparticles
for improved stability. The presence of ZnO enables excellent optical properties, including high visible
transmittance and high UV absorption. The presence of structural defects in ZnO induces colour centres which
are deep traps emitting in the visible. Ag-ZnO nanofluids with different nanoparticle concentrations were tested
to measure absorbance and transmittance using UV spectroscopy. These nanofluid filters can be used for full
spectrum utilisation (by SBS) which helps in achieving: (i) down conversion in the UV region, (ii) transmit visible
and near IR (NIR) region (desired wavelength of Si PV cell optoelectronic efficiency) ,and (iii) absorb (filter)
the IR region of the solar spectrum (for downstream thermal use/applications).