Life-cycle energy analysis of wind turbines - an assessment of the effect of size on energy yield

Wind turbines, used to generate non-fossil fuel based electrical power, are typically considered to take only a number of months to produce as much energy as is required in their manufacture and operation. With a life-expectancy of upwards of 20 years, the renewable energy produced by wind turbines over their life can be many times greater than that embodied in their production. Many previous studies of the life-cycle energy requirements of wind turbines are based on methods of assessment now known to be incomplete. These studies may underestimate the energy embodied in wind turbines by more than 50%, potentially overestimating the energy yield of those systems and possibly affecting the comparison of energy generation options. With the increasing trend towards larger scale wind turbines comes a respective increase in the energy required for their manufacture. It is important to consider whether or not these increases in wind turbine size, and thus embodied energy, can be adequately justified by equivalent increases in the lifetime energy yield of such systems. This paper presents the results of an assessment of the effect of wind turbine size on their life-cycle energy yield and addresses the issue of incompleteness associated with many past life-cycle energy studies. Energy yield ratios of 21 and 23 were found for a small and large scale wind turbine, respectively. This represents an 11% increase in the energy yield ratio of the larger turbine over that of the smaller turbine. The embodied energy component was found to be more significant than in previous studies, emphasised here due to the innovative use of a hybrid embodied energy analysis method. The life-cycle energy requirements were shown to be offset by the energy produced within the first 12 months of operation.