Abstract: A solar cell power system includes a device which determines the occurrence of solar array bus lockup by detecting the voltage of the power bus, the discharge current of the storage battery, and the solar array current (or the load current) and performing a calculation using these items of data in addition to the regulated bus voltage to emit a lockup signal, by which the magnitude of the load is reduced, thereby cancelling the lockup state. Alternatively, a solar cell system may include a lockup cancelling drive device, which accumulates in a coil cancelling-drive, energy supplied from the storage battery and then discharges this energy to the power bus, thereby cancelling the lockup stage without reducing the magnitude of the load.