Optimization of wind farm (WF) layout has been studied in the literature with the objective of maximizing the wind energy capture. Based on the power spectrum density (PSD) theorem, this paper shows that the WF layout affects not only the total harvested energy but also the level of power fluctuation, which in turn influences required capacity of battery energy storage system (BESS) needed to mitigate the inherent power fluctuation of the wind farms. Since both harvested energy level and BESS capacity directly influence the profit of WF owner, the effect of WF layout on these quantities are taken into account simultaneously and WF layout optimization problem is redefined. Genetic algorithm (GA) is then employed in order to optimize the resulting objective function. The proposed method and optimization process are performed on the layout of an actual offshore WF using real wind data. A new index is introduced to quantify the power fluctuations, and energy curtailment is assessed. The comparative analysis between the actual layout performance and the optimal layout in different scenarios is conducted, showing the reduction of power fluctuations and improvement of energy curtailment. In addition, different BESS technologies have been analyzed to study the impact of their parameters on the optimization results.