A controller supplies power generated by a solar cell to a device, charges a storage cell with surplus power obtained by subtracting the power used by the device from the power generated by the solar cell, supplies stored power from the storage cell together with the power generated by the solar cell to the device when there is no surplus electrical power, and switchably executes: a local-production-for-local-consumption algorithm in which a power deficiency, which is obtained by subtracting the power generated by the solar cell and the power supplied from storage cell from the power used by the device, is supplied from a commercial power system; and a peak assistance algorithm having a surplus power selling mode that allows surplus power to flow upstream to the commercial power system and a peak assistance mode that allows all the generated power from the solar cell to flow upstream to the commercial power system and supply stored power from the storage cell to the device.