Abstract: A solar power system uses a solar panel to convert light energy to electricity for charging a battery through a photo sensor. The photo sensor uses a switching unit to control whether the battery can be charged or discharged. The battery further connects to a sensing and protecting circuit and an over-discharge protecting circuit. The sensing and protecting circuit protects the battery from being over-charged. The over-discharge protecting circuit stops the discharging of the battery when the output voltage of the battery is lower than a low threshold.