Although wind technology produces no emissions during operation, there is an environmental impact associated with the wind turbine during the entire life cycle of the plant, from production to dismantling. A life cycle assessment is carried out to quantify the environmental impact of two existing wind turbines, a 1.8 MW-gearless turbine and a 2.0 MW turbine with gearbox. Both technologies will be compared by means of material usage, carbon dioxide emissions and energy payback time based on the cumulative energy requirements for a 20 year life period. For a quantitative analysis of the material and energy balances over the entire life cycle, the simulation software GEMIS (R) (Global Emission Model of Integrated System) is used. The results show, as expected, that the largest energy requirement contribution is derived mainly from the manufacturing phase, representing 84.4% of the total life cycle, and particularly from the tower construction which accounts for 55% of the total turbine production. The average energy payback time for both turbines is found to be 7 months and the emissions 9 gCO(2)/kWh. Different scenarios regarding operation performance, recycling of materials and different manufacturing countries such as Germany. Denmark and China are analysed and the energy payback time and carbon dioxide values obtained. Finally, the wind energy plant is compared with other renewable and non-renewable sources of energy to conclude that wind energy is among the cleanest sources of energy available nowadays. (C) 2011 Elsevier Ltd. All rights reserved.