Smart grid is a brand new power system that allows the installation of a high percentage of powers from renewable energy sources. Our previous work proposed a new operation method for smart grid which assures both the power quality and the economy of the operation. Concretely, we have derived a criterion which is very useful for judging whether the frequency maintenance is completely assured or not. Then, the uncertainty bound of distributed renewable energy in wide areas was determined by evaluating the smoothing effect based on its statistical property. Further, a peak-cut operation method was proposed which can improve the frequency performance with an increase in the generation cost. However, this method excludes the installation capacity of renewable energy sources from consideration and cut the peak power of each PV plant by the same proportion. This paper makes an improvement on this issue and formulate a new peak-cut operation method.