We model the performance of mm-scale optical power transmission to enable power electronics applications such as compact, high-efficiency optically-isolated gate drivers. We develop a model integrating the efficiency of the optical emitter and photovoltaic (PV) cell as well as the geometry of their optical coupling. A detailed analysis of the wavelength and intensity-dependent efficiency of light emitted diodes (LEDs), lasers, and PV cells from among Si, GaAs, and InGaP technologies provides benchmark data to understand the scaling limits of this system. Based on these models, we present a regime of sizes and power densities over which optical power transmission could outperform traditional magnetics in applications requiring high-voltage isolation. We show that despite moderate efficiency in the range of 15% - 40%, optical power transfer has significantly better scaling to smaller size and higher isolation voltages while affording a number of system-level advantages