Elevated operating temperatures significantly reduce the efficiency and lifetime of Si photovoltaic (PV) modules, motivating the development of spectrally selective passive radiative cooling (PRC) coatings that dissipate heat without compromising solar energy harvesting. Here, we propose and numerically investigate a multilayer metal–dielectric metasurface composed of a staircase-shaped silica (SiO2) grating integrated onto a Si/Al platform, where the Al layer acts as a reflective back mirror and the Si layer represents the PV absorber. The design addresses the limited emissivity and impedance mismatch of conventional planar dielectric coatings in the 8−13𝑢⁢𝑚 atmospheric transparency window. The structure is engineered by systematically optimizing the grating step heights, lateral widths, and periodicity to promote synergistic excitation of surface phonon-polariton resonances (SPhPs) and guided-mode resonances. Electromagnetic (EM) simulations under TM polarization, using experimentally measured complex refractive indices for SiO2, Si, and Al, were performed to evaluate spectral emissivity, angular response, and solar absorptance. The optimized SiO2/Si/Al metasurface achieves an average emissivity of 0.92 within the 8−13𝑢⁢𝑚 window while maintaining low solar absorptance across 0.3−0.9μ⁢m and preserving absorption near the Si bandgap (∼1.1um). Thermal performance was assessed using a coupled radiative–convective energy balance model under AM1.5G solar irradiation. The proposed structure reduces the equilibrium temperature of the structure by more than 21K relative to bare Si, corresponding to a projected PV efficiency improvement approaching 10%. Although sub-ambient daytime cooling is not achieved due to residual solar absorption inherent to PV integration, the metasurface functions effectively as a radiative heat-rejection coating compatible with real-world Si solar modules. These results demonstrate that engineered dielectric micro-gratings can overcome the emissivity limitations of planar films and provide scalable, all-inorganic solutions for PV thermal management.