The paper investigates the influence of the period covering wind data on the technical and economic analysis of wind power generation. This study is applied to two sites located in the south of Algeria. Using 12 years of wind data collected by the Algerian Meteorological Office, the annual evolutions of mean wind speed and direction are examined. Then two data periods are considered for the evaluation of (i) the wind resource, (ii) the expected annual energy production and (iii) the electricity generated cost. The influence of the data period on the predicted results is highlighted.