Environmental Impacts of Wind-Energy Projects (2007) / Chapter Skim
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2 Context for Analysis of Effects of Wind-Powered Electricity Generation in the United States and the Mid-Atlantic Highlands
2 Context for Analysis of Effects of Wind-Powered Electricity Generation in the United States and the Mid-Atlantic Highlands
Pages 28-66
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, with specific attention to the potential contribution to the electricity supply and air quality improvement as indicated by emission reductions. For context, a general overview is provided describing issues that should be considered when assessing potential wind-energy development and environmental benefits.
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Moreover, the only way to fully evaluate the environmental effects of generating electricity from wind energy is to understand all the adverse life-cycle effects of those electricity sources, and to compare them to all the adverse effects of wind energy. Because wind energy has some adverse impacts, the conclusion that a wind-powered EGU has net environmental benefits requires the conclusion that all its adverse effects are less than the adverse effects of the generation that it displaces.
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In practice, however, it is extremely difficult to perform the correct calculation. The following sections briefly discuss emissions from fossil-fuel-fired EGUs; the factors involved in calculating the extent to which wind energy reduces those emissions, today and in the future; and the committee's approach to the problem.
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. On March 15, 2005, the EPA issued the Clean Air Mercury Rule to permanently cap and reduce mercury emissions from coal-fired power plants for the first time (EPA 2006a)
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. The complex array of factors that affect how wind energy displaces other energy sources has been discussed in numerous publications (e.g., Smith et al.
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In addition to the characteristics of EGUs, electricity grids and transmission systems also have characteristics that affect the potential of wind energy to replace fossil fuel for generating electricity. Wind-powered EGUs are widely distributed in space, and to make matters more difficult, excluding offshore locations, the highest-quality largest-scale wind resources usually are far from the main centers of demand, i.e., where people live and work (DeCarolis and Keith 2006)
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. As a result, if electricity derived from wind energy is to be incorporated into a dispatch system, a certain amount of backup or reserve power is required.
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than if it is dominated by coal or nuclear plants, which have high capital costs and slow ramp rates.1 Not only wind energy receives government subsidies; all energy sources in the United States do. However, the subsidies vary from time to time, from one type of generator and its fuel to another, and from place to place, which further complicates understanding of how wind will displace other power sources in the mix.
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. NOTE: EIA, Energy Information Administration; MIT, Massachusetts Institute of Technology.
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. This is typically a large task: a variety of environmental, human-health, and ecological effects must be identified, quantified, and evaluated for all the life-cycle stages, often scattered geographically and over time.
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note that "despite the fact that the structure and technology of most modern wind turbines differ little over a wide range of power ratings, results from existing life-cycle assessments of their energy and CO2 intensity show considerable variations" due to different LCA approaches, scope, boundary assumptions, geographical distribution, and information used for embedded energy calculations of turbine and tower materials, recycling or overhaul of turbines after the service life, and national energy mixes. They review 72 studies focusing on energy and CO2 emissions associated with the life cycle of wind turbines and find that the energy intensity (kWh of energy input per kWh of electricity generated)
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In addition to technology applied to the generation and storage of electricity by wind energy, efforts continue in the development of better transmission lines and improved grid management, which would improve the incorporation into the grid of intermittent power sources like wind. Some research focuses on computer and modeling technology.
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2001; AWEA 2006c) , and the American Wind Energy Association (AWEA)
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. (The United States surpassed 11 GW of installed wind energy capacity in 2006.)
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attributes the decision to develop wind energy in Denmark and Germany -- among Europe's leaders in the amount of wind-energy capacity -- to the nuclear accident at Chernobyl in 1986 and the Brundtland Commission's report on sustainability in 1987. Today, the growing evidence of rapid climate change driven by GHG emissions is an important motivator (EWEA 2006)
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43 CONTEXT FOR ANALYSIS OF EFFECTS Energy Energy FIGURE 2-2 Installed wind-energy capacity in the contiguous United States in 1999 and 2005. SOURCE: Modified from Flowers 2006.
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The National Renewable Energy Laboratory (NREL) has assembled these more current maps and accounted for land use and other exclusions (technical, legal, and environmental)
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Wind-capacity forecasts are generated for 13 energy-market regions through application of a Wind Energy Submodule (Table 2-3)
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The Wind Energy Deployment System (WinDS) model was developed by NREL (NREL 2006b)
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installed electricity-generation capacity. If the average turbine size is 2 MW -- larger than most current turbines -- between 9,500 and 36,000 wind turbines would be needed to achieve that projected capacity.
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2-4 capital costs for every doubling of installed wind-energy capacity worldwide, the EIA-AEO forecasts are based on a 1% decrease in capital costs for every doubling of installed capacity nationwide. Fully understanding the differences in forecasts among the Metafile made from original Powerpoin.
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The highest projection in the table estimates about a seven-fold increase in installed capacity in 15 years. Given that only limited data are available for evaluation of both beneficial and adverse effects of existing development, especially in the MAH region, the
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Contribution of Wind-Powered Generation to Meeting Projected Electricity Demand Between 2005 and 2020, based on the WinDS model application (Table 2-3 and Figure 2-4) , installed wind-power capacity for generating electricity is projected to increase from 1 to 7% of the total installed U.S.
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Because wind-powered generators have an inherently low capacity factor, the percentage of total electricity generation from wind energy is substantially less than the percentage of total installed capacity. Based on records assembled for the EIA Annual Energy Outlook 2006 (EIA 2006a)
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Capacity factors for calculation of electricity generation are based on installed capacity and generation data for wind energy provided in the Annual Energy Outlook 2006 (EIA 2006a)
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Estimating the Effective Electricity Generation from Installed Wind-Energy Capacity In the absence of information concerning the need for increased reserve capacity or other effects of temporal variation in wind energy, annual average capacity factors provide a reasonable basis for approximating the effective amount of electricity generated from installed wind-energy capacity. However, this approximation may prove unreliable for specific projects or regions, and we acknowledge uncertainty concerning the effect of rapidly expanding wind development.
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4 ENVIRONMENTAL IMPACTS OF WIND-ENERGY PROJECTS BOX 2-4 Mid-Atlantic Highlands: Wind-Capacity Factor versus Electricity Demand 10% 50% maximum electricity demand Percent of Annual Demand 40% Wind Capacity Factor 9% 30% 8% 20% 7% 10% JAN FEB MAR APR MAY JUN JUL AUG SEP OCT NOV DEC monthly electricity use in 2004 wind power capacity factor Electricity demand and wind-power profiles in the MAH states. The electricity demand profile is based on 2004 monthly sales data (EIA 2004c)
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The forecasts, however, provide a context for evaluating both the electricity supply and air-quality benefits of future wind-energy development in the United States. The highest forecast for 2020 indicates that wind-energy development will provide 7.0% of total installed electricity-generation capacity, and 4.5% of electricity generation, which is consistent with the fact that wind turbines generally have a lower capacity factor than other electricity-generation sources.
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electricity generation by 2020 is expected to be obtained from generation sources other than wind. Contribution of Wind Energy to Air-Quality Improvement Our approach to assessing the benefits of wind-energy development for air-quality improvement focuses on displacement of several of the pollutant emissions from fossil-fueled EGUs (in this case, CO2, NOx, and SO2)
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electricity supply differ greatly in terms of their contributions to total generation and pollutant emissions (Figure 2-6)
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Identification of affected EGUs generally requires application of a system-dispatch model. This involves accounting for the temporal distribution of wind energy or actual wind generation, the identity and operational properties of EGUs operating on the margin, and transmission limits or other dispatch constraints.
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Given this lack of transparency, it can be difficult or impossible for independent parties to objectively review and verify emissions-displacement estimates based on system-dispatch modeling. System-average emission rates are commonly used for analysis of emissions displacement when the data and resources needed for system-dispatch modeling are unavailable (NESCAUM 2002; Keith et al.
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, marginalaverage emission rates would be weighted toward the higher emission rates associated with the coal-fueled EGUs, regardless of which type of EGU would actually be displaced by wind-energy generation. Emissions Displacement in Context In this section, the committee examines the potential for obtaining reductions in emissions of NOx, SO2, and CO2 through the increased use of wind energy to generate electricity.
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. The task of evaluating air-quality benefits of wind-powered electricity generation is complicated by increasing electricity use and changing emission rates for fossil-fuel-fired EGUs.
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2-7 U.S. emissions data for 1970-2003 indicate that emissions of SO2 from fossil-fuel-fired EGUs declined 37%, while emissions of NOx from those EGUs declined 9% (EPA 2005)
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The estimated offsets are based on the maximum forecasts for wind-powered generation of electricity provided in Table 2-4 and on the system-average emission rates for CO2 listed in Table 2.5. Based on this comparison, the effect of wind development by 2020 is expected to offset CO2 emissions from fossil-fuel-fired EGUs in the United States by 4.5%.
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CO2 emissions from EGUs and potential offsets associated with wind-energy development. CO2 emissions are based on forecasts reported in the Annual Energy Outlook 2006 (EIA 2006a)
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On average in the MAH, the capacity factor of wind turbines is about 30% for current technology, forecast to improve to near 37% by the year 2020. The projections the committee has used in this chapter suggest that onshore wind-energy development will contribute about 60 to 230 billion kWh, or 1.2 to 4.5% of projected U.S.
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• In the presence of more aggressive renewable-energy-development policies, potential increased energy conservation, and improving technology of wind-energy electricity generation and transmission, the above findings may underestimate wind energy's contribution to total electricity production. This would affect the committee's analysis, including projections for development and associated effects (e.g., energy supply, air pollution, development footprint)
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