This article presents a modelling study of external magnetic field effect on a bifacial silicon solar cell's electric power and conversion efficiency. After the resolution of the magnetotransport equation and continuity equation of excess minority carriers, we calculate the photocurrent density and the photovoltage and then we deduce the solar cell's electric power before discussing the influence of the magnetic field on those electrical parameters. Using the electric power curves versus junction dynamic velocity we determine the maximum electric power, the operating point of the solar cell, and the conversion efficiency according to magnetic field intensity. The numerical data show that the solar cell's maximum electric power and conversion efficiency decrease with magnetic field intensity.