This paper describes the connection analysis between a wind farm with 21 MW capacity and an energy storage system with the electrical grid. The core of the study is focused on the voltage drop test in a wind farm according to IEC 61400-21 standard which is explained and analyzed. Moreover, the battery sizing and model is explained step by step; likewise, the converters model and control to correctly charge and discharge the battery. Finally, there is a power quality analysis between the connection of the designed battery and the grid.