The Annual Energy Production (AEP) estimated over the lifecycle of the project is one of the most important factors to determine the profitability of wind power project. The methods used to estimate the AEP in a wind farm requires an assessment of the uncertainties associated at all steps. To finance a wind power project, banks requires that the developer submit the uncertainties related to the estimation of AEP’s wind farm, to mitigate errors and increase the project reliability. The appropriate assessment of uncertainties is critical to determine the feasibility and risk in developing a wind energy project. This study presents the main sources of uncertainty in the energy estimate process in wind farms. This information is important for the correct analysis of the economic viability of the project.