Hmm. If your PV has efficiency > the albedo of the ground it covers, it will be better than SBSP, even if the rectenna is 100% efficient (assuming the emissivity of the PV is at least as good as that of the desert in the far IR). This assumes the rectenna has the same optical properties as the ground it covers.
One could improve the PV by making it highly reflective in the near IR at wavelengths below the bandgap of the cells, while still being highly emissive at the longer wavelengths where it will radiate heat.
One could improve the PV by making it highly reflective in the near IR at wavelengths below the bandgap of the cells, while still being highly emissive at the longer wavelengths where it will radiate heat.