PURPOSE: To improve the availability by providing a means for classifying cells connected in series into a plurality of cell units then shortcircuiting each cell unit independently and removing the cell unit and a means for compensating AC voltage component corresponding to the removed cell unit.

CONSTITUTION: Upon fault of a solar cell 1B, for example, the solar cell 1B is removed and a shortcircuit switch 11B is closed. Consequently, DC power is fed from remaining solar cells 1A, 1C to an inverter 2 and DC voltage to be fed to the inverter 2 drops to 2/3 of conventional system. When the tap of a tapped matching transformer 10 is switched and the output voltage of the transformer 10 is brought to same level as the conventional system, the number of cell decreases to cause reduction of supply power but parallel operation of the inverter and a commercial power system 4 can be kept continuously.