Nanofluid can be used as an effective spectral beam splitter to enhance the performance of hybrid PV/T system. In this work, we innovatively developed CoSO4-based Ag nanofluid which might be utilized as fluid optical filter for hybrid PV/T system with silicon concentrator (CPV) solar cell. Firstly, highly dispersed Ag/CoSO4 nanofluids with various concentrations were prepared. The results from the measured optical transmittance of the prepared nanofluids show that Ag/CoSO4 nanofluid has a strong absorption over a broader spectrum than that of water-based one. Subsequently, the effect of Ag nanofluids filters on the electrical performance of the silicon CPV cell was discussed. Ag/CoSO4 nanofluids produce lower short circuit current and thus lower electrical output than Ag/water nanofluids at the same mass fraction of Ag nanoparticles, whereas they yield higher stagnation temperature than Ag/water nanofluids. A theoretical model for optimizing the optical properties of the nanofluids filters and determining merit function (MF) was introduced to evaluate the filtering performance of Ag/CoSO4 nanofluids in PV/T systems. The results show that the MF value of PV/T system with Ag/CoSO4-2 nanofluid filter is greater than both that with a typical Ag-SiO2 (core-shell)/water nanofluid filter and with a Ag/water nanofluid filter. And the calculated MF values for PV/T systems with Ag/CoSO4 nanofluid filters reach a nearly constant value higher than 1.371 when the mass fraction of Ag nanoparticles contained in the Ag/CoSO4 nanofluid ranging from 24 ppm to 57 ppm. Peak MF value is achieved when the mass fraction of Ag nanoparticles is 37 ppm.