During the last 4 years, a substantial wind energy penetration was encountered mainly in the Greek mainland. At the same time, limited size new wind-parks were built in the numerous Greek islands, although their wind potential is clearly higher than the one for the mainland and their wind energy generation could be used to replace electricity produced by diesel engines and gas turbines at moderate and high cost, respectively. This negative conclusion for the Greek island communities underlines the inability of the local weak autonomous electrical networks to entirely absorb the gradually increased wind-energy production. Thus, in the present work, special attention is paid to correctly estimate the annual income loss of existing wind-parks, due to the wind energy rejection by the autonomous island electrical grids. For this purpose a complete and reliable method is developed, able to realistically calculate the instantaneous wind-power production rejected by the local electricity-generation system, according to the information provided by the system operator and the wind-park owners. The present analysis is based on extensive time series of real data and measurements. Applying the proposed method to the Crete-island network situation, a remarkable amount of wind produced electric-energy rejection is predicted for the last 3 years, which is definitely rising in the course of time. Calculation results are well in agreement with the official monthly data provided by the local power-utility, in view of the existing power-purchase agreement between the private wind-power investors and the local network management. (C) 2004 Elsevier Ltd. All rights reserved.