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Energy Balance analysis

The energy balance is an assessment of the relation between the energy consumption of the product and the energy production throughout the lifetime. The energy balance analysis in Vestas V90 3.0 MW shows that, for an offshore wind turbine 0.57 years (6.8 months) of expected average energy production are necessary to recover all the energy consumed for manufacturing, operation, transport, dismantling and disposal.

As far as an onshore wind turbine is concerned, the energy balance is similar but shorter than the offshore one, with only 0.55 years (6.6 months) needed to recover the energy spent in all the phases of entire lifecycle. This difference is due to a larger grid transmission and larger steel consumption for the foundations in an offshore scheme.

The V 80 2 MW turbines installed in Horns Rev only needed 0.26 years (3.1 months) to recover the energy spent in the offshore installation. The same turbines installed in the Tjaereborg onshore wind farm had an energy payback period of about 0.27 years (3.2 months).

Comparative benefits with conventional and renewable technologies systems

Several studies have been conducted from different institutions and enterprises in order to quantify the environmental impacts of energy systems.

The Vestas study also analysed the environmental impacts produced by average European electricity in 1990 (data from EDIP database) compared with the electricity generated by an offshore wind power plant and an onshore wind power plant. The comparison shows that wind electricity has a much better environmental profile than the average Danish electricity for the year of the project. The impacts are considerably lower in case of wind energy than European electricity in all the analysed impacts categories. However, the comparison is not quite fair, as the system limits of the two systems differ from each other. The comparison was made to see the order of magnitude (See Figure 1.14).

Figure 1.14. Onshore, offshore and electricity system comparison on environmental impacts. Courtesy of Vestas Wind System A/S

Vattenfall Nordic Countries have carried out life cycle assessments of its electricity generation systems. The results of the study showed that:

• Construction is the most polluting phase for the technologies lacking fuel, instead using a flowing source of energy (hydro-, wind- and solar-power).
• The operational phase dominates for all fuel-burning power plants, followed by fuel production.
• Wind energy generates low environmental impact in all the parameters analysed: CO2, NOx, SO2 and particulate matter emissions; radioactive waste. Only the use of copper from mines presents a significant impact.
• The demolition/dismantling phase causes a comparatively low impact since, for example, metals and concrete can be recycled.

Avoided emissions

Environmental benefits of wind electricity can be assessed in terms of avoided emissions compared to other alternative electricity generation technologies.

Life cycle inventory results for some relevant emissions from electricity production in a coal condensing power plant and in a natural gas combined cycle power plant are shown in Figure 1.15 compared with the results obtained for onshore and offshore wind energy.

Figure 1.15. Comparison of the emissions produced in the generation of 1 kWh in a coal and a natural gas combined cycle power plant and the emissions produced in an onshore and offshore wind farm. Source: Results from CASES, Ecoinvent and NEEDS for the coal and natural gas power plants.

As observed in the Figure, emissions produced in the life cycle of wind farms are well below those produced in competing electricity generation technologies such as coal and gas. The only exception is the emissions of particles in the natural gas combined cycle which are of the same order of those from wind farms along the whole life cycle.

Emissions avoided using wind farms to produce electricity instead of coal or natural gas power plants are quantified in tables 1.2 and 1.3.

Table 1.2. Emissions of relevant pollutants produced by wind electricity and coal and natural gas electricity along the whole life cycle, and benefits of wind versus coal and natural gas.

Results show that as much as 828 g of CO2 can be avoided per kWh produced by wind instead of coal, and 391 g of CO2 per kWh in the case of natural gas. Quite significant nitrogen and sulphur oxides and non-methane VOC emission reductions can be obtained substituting coal or gas with wind energy as well. In the case of particles, natural gas emits less than wind energy along the whole life cycle although differences are only minor.

Table 1.3. Emissions and benefits of relevant pollutants produced by wind electricity and other renewable energies.

As in the case of fossil energies, results show in general lower emissions of CO2, methane, nitrogen and sulphur oxides, NMVOC's and particulates than other renewable sources. In this sense, it is possible to obtain avoided emissions, except for CO2 and NMVOC's by nuclear and sulphur oxides by solar technologies, using wind (onshore and offshore) technologies in the power generation.