Page 213 - Materials Chemistry, Second Edition

Life-Cycle Assessment of Wind Energy 201

The standards usually applied in wind turbine design require turbines to be
equipped with two independent braking systems, so both aerodynamic and
mechanical brakes are usually fitted: the aerodynamic system is located at the tip
of the blades or over the whole rotor blades to change the pitch angle. On most
turbines, the second system is usually a mechanical disk brake, which is intended
mainly to be used should the aerodynamic system fail, and when the turbine is
stopped for repair or maintenance work.

3 Wind Turbine LCA

3.1 State of the Art

The relevant scientific literature contains various life-cycle analyses of wind power
and wind turbines (Ardente et al. 2008; Ben et al. 2008; Góralczyk 2003;
Tryfonidou and Wagner 2004; Wiese and Kaltschmitt 1996; Gürzenich et al. 1999;
Uchiyama 1995; Nadal 1998; Haack 1981; Krohn 1997; Uchiyama 1996;
Schleisner 2000; Lenzen and Munksgaard 2002; Lenzen and Wachsmann 2004;
Crawford 2009; Weinzettel et al. 2009; Martínez et al. 2009). Most of them focus
on energy analysis and CO 2 emissions, and their results vary considerably. This
should come as no surprise in view of the significant developments in the field of
wind energy in recent years: in a very short time, wind turbines have been
developed with widely differing electricity generating capacities, ranging from
rated power outputs of just a few kW to the latest large multimegawatt turbines
(7.5 MW). Moreover, issues such as estimated useful lifetime and equivalent hours
of annual production significantly affect the final results of any study conducted. In
spite of the variability observed, a clear tendency is found in which CO 2 emissions
per kWh produced decrease as the rated power of the turbine increases. The results
also show levels of emissions and environmental impact that are far lower than
those of other conventional sources of electricity generation.
With this in mind, the present study focuses on current, multimegawatt wind
turbines, seeking to obtain LCA data for wind power at the present time.

3.2 LCA of a 2 MW Wind Turbine

This wind power LCA focuses on the type of wind turbine most widely used all
over the world at this time: the multimegawatt double-fed induction generator
(DFIG).