The present work investigates the performance and the energy production of a grid-connected wind farm during six years of operation. The layout and the single line diagram of this, wind farm are shown. A complete record of operational data for five turbines is analysed to study the performance of the wind farm. The study illustrates the variation of the energy and wind speed on annual and monthly basis for the whole examined period. On the other hand, the annual growth in the local consumption of the wind farm is shown. As an important indicator, the capacity factor is analysed for single turbines and for the whole wind farm. Finally, the study attempts to correlate the results to the external and internal factors affecting the performance of these turbines using the available database. (C) 2004 Elsevier Ltd. All rights reserved.