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The Life Cycle Assessment (LCA) approach provides a conceptual framework for a detailed and comprehensive comparative evaluation of the environmental impacts as important sustainability indicators.
Recently, several LCAs have been conducted to evaluate the environmental impact of wind energy. Different studies may use different assumptions and methodologies and this fact could produce important discrepancies in the results among them. However, the comparison with other sources of energy generation can provide a clear picture about the environmental comparative performance of wind energy.
An LCA considers not only the direct emissions from wind farm construction, operation and dismantling, but also the environmental burdens and resources requirement associated with the entire lifetime of all relevant upstream and downstream processes within the energy chain. Furthermore, an LCA permits quantifying the contribution of the different life stages of a wind farm over the priority environmental problems.
The wind energy LCAs are usually divided into five phases:
VESTAS Wind Systems (Vestas, 2004 and 2005) conducted several LCAs of onshore and offshore wind farms based on both 2MW and 3MW turbines. The purpose of the projects was to carry out a life cycle assessment of an offshore wind farm and an onshore wind farm, respectively, as a basis for assessment of environmental improvement possibilities for wind farms through their life cycles.
Within the framework of the EC project ECLIPSE several LCAs of different wind farm configurations were performed. The technologies studied in ECLIPSE were chosen in order to be representative of the most widely used wind turbines. Nevertheless, a wide range of the existing technological choices were studied:
Within the EC project NEEDS, life cycle inventories of off-shore wind technology were developed along with several other electricity generating technologies. The wind LCA focused on the present and long-term technological evolution of off-shore wind power plants. The reference technology for the present wind energy technology was 2MW turbines with three-blade upwind pitch-regulation, horizontal axis and monopile foundations. An 80-wind-turbine wind farm located 14 km off the coast was chosen as being representative of the contemporary European offshore wind farm.
In the framework of the EC project CASES, an estimation of the quantity of pollutants emitted at each production stage per unit of electricity for several electricity generation technologies is performed. Among them, onshore and offshore wind farms are analysed.
Finally, the Ecoinvent v 2.0 database, includes LCA data of several electricity generation technologies including an onshore wind farm using 800kw turbines and an offshore wind farm using 2MW turbines.
Results extracted from the above mentioned LCA studies for onshore wind farms regarding several of the most important emissions are shown in Figure 1.2. Bars show the variability of the results when several wind farm configurations are considered in a study.
Carbon dioxide emissions vary from 5.6 to 9.6 g/kWh in the consulted references. Methane emissions range from 11.6 to 15.4 mg/kWh. Nitrogen oxides emissions range from 20 to 38.6 mg/kWh. Non-methane volatile organic compounds are emitted in quantities that range from 2.2 to 8.5 mg/kWh, particulates range from 10.3 to 32.3 mg/kWh and, finally, sulphur dioxide emissions range from 22.5 to 41.4 mg/kWh. All of these quantities, with the only exception being particulates, are far below the emissions of conventional technologies such as natural gas (see Figure 1.3).
Figure 1.2. Emissions from the production of 1kWh in onshore wind farms throughout the whole life cycle
Another main outcome of all the reviewed studies is that the construction phase is the main contributor to the emissions and hence the environmental impacts. As can be observed in Figure 1.3, the construction phase causes about 80% of the emissions. The operational stage, including the maintenance and replacement of materials, is responsible for 7% to 12% of the emissions, and the end-of-the-life of the wind farm is responsible for between 3% to 14% of them.
Figure 1.3. Contribution of the different life cycle phases to the relevant emissions. Source: own elaboration using ECLIPSE results
Regarding the construction stage, Figure 1.4 shows the contribution of the different components. Important pieces in the environmental impacts of the construction phase of an onshore wind farm are the tower and the nacelle but not the rotor blades. Foundations are also an important source of emissions. Connection to the grid contributes to an important part of all the studied emissions. Emissions from transport activities during the construction phase are only relevant in the case of NOx and NMVOCs emissions.
Figure 1.4. Contribution of the components of the construction phase to the different emissions. Source: own elaboration based on ECLIPSE results
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