This paper presents a simplified methodology to estimate the impact of wind power over operating reserves in isolated power systems. The methodology is based on a convolution approach that merges the fluctuations of wind speed with the natural variations of demand, and formulates the probability distribution function of variables as a non-Gaussian behavior. The estimation renders a histogram containing the probability distribution of operating reserves required in different time spans. The methodology also estimates the LOLP indicator to assess the operative reserve of the system. An application on the expansion plan of a Chilean isolated power system is presented and results indicate that the methodology is able to estimate operating reserve needs in a time span ranging from 1 to 30 minutes, which adequately satisfy the future needs of this isolated power system. © 2013 IEEE.