This paper provides an insight into power flows in a system with included variable energy sources, in this case wind farms. In the first chapter, the basic facts about wind, how it is created, how much wind energy is and how it is calculated, are presented, then the wind distribution density functions are given. Basic things about wind turbines, their types and parts of individual wind turbines are explained. It is shown how the wind affects the production of wind turbines and how wind farms affect EES. In the second chapter, the importance of power flows in the EES is presented and the main principles of calculating power flows using deterministic and probabilistic methods (point estimate method, method of cumulants, Monte Carlo method) are explained. In the third chapter, an insight into the probabilistic Monte Carlo method is given. The methods of generating the input variables of the method are given and the method of calculation is explained. Chapter number four is the practical part of this work, where the calculation of power flows using the Monte Carlo method for the case without wind farms in the system, as well as cases with connected wind farms for different levels of correlation, was made on the 24-IEE bus model.