A solar power supply system includes a load device, a solar panel that converts light energy into electrical energy, an energy storage device storing the electrical energy from the solar panel, a charge/discharge control device, and a transformer device. The charge/discharge control device selects one of the energy storage device and the solar panel as an operation power supply to the charge/discharge control device and generates an output voltage. The transformer device transforms the output voltage of the charge/discharge control device into a driving voltage to drive the load device. A feedback circuit generates a feedback signal according to an actual power consumption of the load device. A power detector detects an instant output power of the charge/discharge control device. A power regulator minimizes the output power of the charge/discharge control device according to the instant output power of the charge/discharge control device and the actual power consumption of the load device.