In this study, the properties of various types of core-shell nanoparticles (NPs) were evaluated using the finite difference time domain (FDTD) method towards the enhancement of solar absorption performance. Results showed that the resonance wavelength of SiO2@Au NPs lay in the 540-900 nm range, covering the near-infrared and visible regions. The resonance wavelength of SiO2@Ag NPs lay in the 390-830 nm range, covering the entire visible region. SiO2@Au nanofluid with a core-shell ratio of phi = 0.2 exhibited the highest solar absorption efficiency with 64% less Au consumption compared to pure Au NPs. For mixed nanofluids, the mixtures featuring core-shell ratios of 0.1 and 0.6 with mixing ratios of 0.5 for SiO2@Au and 0.6 for SiO2@Ag gave the highest absorption efficiencies. In addition, the peak solar absorption efficiency of a mixed nanofluid of SiO2@Au (phi = 0.1) and SiO2@Ag (phi = 0.4) with a mixing ratio of 0.58 was as high as 94A%. Solar thermal conversion experiments revealed that, under the same conditions, a Au-decorated SiO2 nanofluid showed a comparable efficiency to the calculated solar absorption efficiency of the SiO2@Au core-shell nanofluid (similar to 95.2%); it was as high as 95.9%, higher than those of Au NPs and SiO2 NPs. These results showed that adjusting the core-shell ratios and tuning the mixing ratios of different nanofluids are two efficient methods to enhance the solar absorption efficiencies of SiO2@Au and SiO2@Ag NPs under the optimal conditions.