A system for power management electrically connected to a solar cell is provided. The system for power management includes a photo-sensor, a controller electrically connected to the photo-sensor, and a power manager. The photo-sensor detects an illumination (illuminance or irradiance) of an environment where the solar cell is located. A look-up table of illumination vs. maximum output power is built in the controller, wherein a corresponding maximum output power is determined by the controller according to the illumination detected by the photo-sensor. The power manager is electrically connected to the controller and the solar cell. The power manager controls the output current of the solar cell so as to equalize an output power of solar cell and the corresponding maximum output power. A method for power management is also provided.