US Patent 9520623 Grid-connected power supply system

A grid-connected power supply system includes a power generation apparatus configured to generate power by using natural energy and connected in parallel to a commercial power grid; a electricity storage device; and a control device configured. The control device predicts an amount of power to be generated on a subsequent day by the power generation apparatus and a power demand of the loads and charges the electricity storage device with power in a time zone in which an electricity rate of the commercial power grid is relatively low if a predicted value of the amount of power to be generated is lower than a predicted value of the power demand, or does not charge the electricity storage device with power during the time zone if the predicted value of the amount of power to be generated is not lower than the predicted value of the power demand.