Nanofluids have garnered a lot of attention for their potential to modify thermal properties, particularly the thermal conductivity. While these modifications have been heavily investigated within the heat transfer and materials community, nanofluids additionally offer the potential for major modification to the radiative properties of the host fluid. Of particular interest here is how the modification of the radiative properties of fluids through nanoparticle dispersions can lead to enhanced energy conversion in systems dependent on radiative transport. By adjusting the size, shape, material, volume fraction and particle structure drastic modification can be achieved leading to enhanced efficiency within systems such as solar collectors, and night sky radiators. A summary review of the mechanisms that lead to enhanced efficiency are presented as well as new topics such as dynamic radiative property control with core-shell multifunctional nanoparticles.