To provide a method for flattening a power load factor at a power demand place or its neighborhood by solving the problem that a pumped storage power plant is generally located far from a power demand place, has restrictions on the location and power transmission loss is caused in the pumped storage power generation system used for flattening a power load factor.

In the method of flattening a power load factor, a rotating battery power storage device is installed at a power demand place or its neighborhood, power is supplied to the power storage device and energy is stored at midnight in which power demand is small and the stored energy is used as necessary as power.