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Electricity from Renewable Resources: Status, Prospects, and Impediments (2010)

Chapter: 5 Environmental Impacts of Renewable Electricity Generation

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Suggested Citation:"5 Environmental Impacts of Renewable Electricity Generation." National Academy of Sciences, National Academy of Engineering, and National Research Council. 2010. Electricity from Renewable Resources: Status, Prospects, and Impediments. Washington, DC: The National Academies Press. doi: 10.17226/12619.
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5
Environmental Impacts of Renewable Electricity Generation

Environmental impacts are an inherent part of electricity production and energy use. Electricity generated from renewable energy sources has a smaller environmental footprint than power from fossil-fuel sources, which is arguably the major impetus for moving away from fossil fuels to renewables. However, although the types and magnitude of environmental effects differ substantially from fossil-fuel sources and from one renewable source to another, using renewables does not avoid impacts entirely. An understanding of the relative environmental impacts of the various electric power sources is essential to the development of sound energy policy.

This chapter reviews and compares the environmental impacts of various fossil-fuel and renewable sources of electricity. It applies life-cycle analyses in discussing impacts that occur typically on regional or larger scales, such as air, water, and global warming pollution. This chapter then addresses local impacts that are often considered and assessed as part of the siting and permitting processes.

LARGE-SCALE IMPACTS FROM LIFE-CYCLE ASSESSMENT

Life-cycle assessment (LCA) attempts to estimate the overall energy usage and environmental impact from the energy produced by a given technology by assessing all the life stages of the technology: raw materials extraction, refinement, construction, use, and disposal. Here, LCA is used to compare the relative impacts of various fossil-fuel-based and renewable sources of electricity. To place all analyses on a common footing, impacts are expressed in terms of emission or usage rate Environmental Impacts of

Suggested Citation:"5 Environmental Impacts of Renewable Electricity Generation." National Academy of Sciences, National Academy of Engineering, and National Research Council. 2010. Electricity from Renewable Resources: Status, Prospects, and Impediments. Washington, DC: The National Academies Press. doi: 10.17226/12619.
×

per kilowatt-hour (kWh). Finally, it should be noted that developing complete LCAs of electricity sources is beyond the scope of this panel. There are, however, a wide range of earlier assessments, and these form the basis of this section.

A major complication in comparing LCAs is that there is no set standard for carrying out such analyses. While it is the goal in using LCAs to cover technologies from cradle to grave in a systematic way, there is variability in the assumptions, boundaries, and methodologies used in these assessments. Therefore, caution should be used in comparing LCAs; each is an approximation of a technology’s actual impact. Discussion of the attributes and assumptions used in life-cycle analysis is found in Appendix E.

The renewable energy technologies are wind, solar, geothermal, hydroelectric, tidal, biopower, and storage. Appendix F contains LCA studies for coal, natural gas, and nuclear technologies as a benchmark against which to assess the performance of renewables. LCA information for solar energy is limited to photovoltaic (PV) technologies, and no LCA studies were reviewed for concentrating solar power (CSP) technologies such as solar trough, power tower, or dish–engine technologies. No LCA information is included for enhanced geothermal systems. The life-cycle impacts considered here include net energy usage; atmospheric emissions of greenhouse gases expressed in units of carbon dioxide (CO2) equivalents (CO2e);1 atmospheric emissions of sulfur dioxide (SO2), nitrogen oxides (NOx), and particulate matter;2 land use; and water withdrawals and consumption. To provide a sense of the variability of the LCAs found in the literature, the maximum, minimum, and average energy usage and environmental impact for each technology are shown in figures discussed below in this chapter.

Energy

Energy input and output calculations, the basic building blocks for any life-cycle evaluation of greenhouse gas emissions, can be used to evaluate the energy inten-

1

Equivalent carbon dioxide emissions (CO2e) are the amount of greenhouse gas emissions expressed as carbon dioxide, taking into account the global warming potential of non-carbon dioxide greenhouse gases (e.g., methane and nitrous oxides).

2

All energy technologies are included in the CO2 section even if CO2 emissions were low. Other pollutants with emissions less than 100 mg/kWh are not included in the data and discussion. Studies used to compile CO2 data often make up a different data set from the studies used to compile other emissions. Often LCA studies focus only on CO2. This required building another data set for other emissions.

Suggested Citation:"5 Environmental Impacts of Renewable Electricity Generation." National Academy of Sciences, National Academy of Engineering, and National Research Council. 2010. Electricity from Renewable Resources: Status, Prospects, and Impediments. Washington, DC: The National Academies Press. doi: 10.17226/12619.
×

sity and resource consumption of the energy technology itself. The literature is replete with assessments of life-cycle energy usage from renewable and non-renewable sources of electricity. However, these assessments adopt a wide range of energy metrics, making internal comparisons problematic. Spitzley and Keoleian (2005) describe eight distinct energy metrics defined in the literature.

Energy metrics should therefore be used with cautions and caveats. No single metric defines the ideal energy generation technology without an accompanying statement of the core value for assessment. For example, a metric such as capacity factor will effectively measure for intermittence or dispatchability. A metric such as price per unit of energy produced measures economic value according to conventional accounting, financing, and cost-accounting assumptions.

This review focuses on two of the more commonly used energy metrics: (1) net energy ratio (NER), which quantifies how much net energy a technology produces over its life cycle, and (2) energy payback time, which defines how long it takes for a given energy technology to recoup the lifetime energy invested in its development once the technology starts generating electricity. These metrics offer insight into the overall energy and environmental performance of generation technologies, especially in making macro-level resource acquisition and development decisions.

Net Energy Ratio

The NER is defined as the ratio of useful energy output to the grid to the fossil-fuel energy consumed during the lifetime of the technology. As such, it is critical to assessing whether or not a renewable energy source reduces our use of fossil fuel.

Renewable energy sources generally have an NER value greater than one. For fossil-fuel energy technologies, the NER is commonly referred to as the lifecycle efficiency. However, there is some inconsistency in the literature on how the NER is defined when the energy technology itself is based on a fossil fuel. In these cases, some researchers include only indirect (external) energy inputs and not the (primary) energy inherent in the fuel (Meier, 2002; White, 2006; Denholm and Kulcinski, 2003). However, this interpretation of the ratio is not an accurate reflection of the total resource consumption of the energy technology in question. For example, the energy consumed by combusting coal in a coal-fired plant is not included in this alternate use of the term. In cases where the primary energy of the fuel is not included in the energy inputs, the NER is more accurately defined as an

Suggested Citation:"5 Environmental Impacts of Renewable Electricity Generation." National Academy of Sciences, National Academy of Engineering, and National Research Council. 2010. Electricity from Renewable Resources: Status, Prospects, and Impediments. Washington, DC: The National Academies Press. doi: 10.17226/12619.
×

external energy ratio (EER). The EER is also widely referred to in the literature as the energy payback ratio.

For renewable energy sources such as wind and solar, the NER and EER are very similar, since the energy technology’s use of fuel (e.g., wind or solar radiation) does not deplete the energy resource. For the purposes of this text, the ratio is referred to as the EER when primary fossil energy inputs are not included.

Figure 5.1 illustrates the range of NERs and EERs found in the literature. NER values are influenced by a number of factors, including plant capacity factor, plant life expectancy, choice of plant materials (e.g., steel versus concrete for wind towers), and fuel mix during material construction. For wind and solar technologies, the location and the strength of the resource at that location also constitute an important variable. For example, a wind farm sited in a location with higher average wind speeds will generate more energy than will a wind farm sited at a

FIGURE 5.1 Net energy ratio (NER) and external energy ratio (EER) for various renewable and non-renewable energy sources.

FIGURE 5.1 Net energy ratio (NER) and external energy ratio (EER) for various renewable and non-renewable energy sources.

Source: Developed from data provided in Denholm (2004), Denholm and Kulcinski (2003), Meier (2002), Pacca et al. (2007), Spath et al. (1999), Spath and Mann (2000), Spitzley and Keoleian (2005), and White (1998, 2006).

Suggested Citation:"5 Environmental Impacts of Renewable Electricity Generation." National Academy of Sciences, National Academy of Engineering, and National Research Council. 2010. Electricity from Renewable Resources: Status, Prospects, and Impediments. Washington, DC: The National Academies Press. doi: 10.17226/12619.
×

location with lower average wind speeds. In the same way, solar installations in areas with greater solar radiation will typically have higher NERs. Additional factors for PV technologies include position of module, solar conversion efficiency of module, and manufacturing energy intensity.

Figure 5.1 shows that NERs for renewable technologies tend to be higher than for conventional energy technologies, because they consume fewer resources. Of the technologies reviewed, wind has the highest NERs, with values that range from 11 to 65. The lower values tend to be for relatively small wind farms with low-capacity turbines and slower winds. Net energy ratios of 47 and 65 were reported for two large wind farms with higher-capacity turbines and higher average wind speeds. The NER for wind is very dependent on assumptions related to the frequency of blade and turbine replacement, because so much life-cycle energy is consumed in material manufacturing for this technology.

Figure 5.1 also indicates a relatively high NER for hydroelectric power, but this should be interpreted with caution, as it is based on only one LCA study (with a NER of 31) for a large reservoir facility in the United States with a 50-year lifetime. NERs for biopower reported here range from 10 to 16, based on analysis of four power plants that use cropping to supply biomass. Biopower from waste would be expected to have higher NERs, but no LCAs for this fuel stock appear to be available at this time. No NER data were reviewed for geothermal, tidal, or energy storage technologies.

While the NERs for solar PV plotted in Figure 5.1 tend to be relatively low, rapid innovation should improve this ratio in the coming years. For example, Pacca et al. (2007) developed an optimal case for multicrystalline and thin-film (a-Si) PV technologies (using the highest possible solar insolation and conversion efficiency, the least possible manufacturing energy, and maximum plant life) to evaluate the future potential of this technology and found that PV NERs improved to 43 and 132, respectively.

Unlike renewable sources, conventional energy technologies have NERs of less than 1. Their EERs, however, tend to be comparable to or even greater than the NERs for solar PV and biopower. Of the three non-renewable sources of energy considered here, nuclear has the highest average EER.

Energy Payback Time

The energy payback time (EPBT) is a measure of how much time it takes for an energy technology to generate enough useful energy to offset energy consumed

Suggested Citation:"5 Environmental Impacts of Renewable Electricity Generation." National Academy of Sciences, National Academy of Engineering, and National Research Council. 2010. Electricity from Renewable Resources: Status, Prospects, and Impediments. Washington, DC: The National Academies Press. doi: 10.17226/12619.
×

during its lifetime. As such it provides an indication of the temporal fossil-fuel needs and emissions as an energy infrastructure is transformed from a carbon-intensive to a low-carbon system.

In the LCA literature, the EPBT is most commonly applied to wind and PV technologies as an additional measure of the economic viability of these newer technologies. Wind EPBT of 0.26 and 0.39 years were reported for two large wind farms with higher-capacity turbines and higher average wind speeds (Schleisner, 2000). The lower value is for a land-based wind farm, while the higher value reflects the additional materials needs for offshore installations. EPBT values for PV range from 7.5 years to less than 1 year. As illustrated in Figure 5.2, this range in EPBT for PV largely reflects a downward trend in time as each successive generation becomes less energy intensive. The EPBT of less than 1 year is from analysis of a hypothetical future generation of PV.

The length of the EPBT has important implications for how long it will take to displace fossil-fuel sources of energy with renewable sources. Consider a simple example. Suppose it takes four units of fossil-fuel energy to produce one unit of energy with a renewable energy technology (such as a wind turbine), and suppose that the unit of renewable technology displaces one unit of fossil-fuel energy.

FIGURE 5.2 Estimated PV energy payback time decreases as a function of the vintage year of the technology.

FIGURE 5.2 Estimated PV energy payback time decreases as a function of the vintage year of the technology.

Source: Developed from data provided in Fthenakis et al. (2006), Keoleian and Lewis (2003), Meier (2002), and Pacca et al. (2007).

Suggested Citation:"5 Environmental Impacts of Renewable Electricity Generation." National Academy of Sciences, National Academy of Engineering, and National Research Council. 2010. Electricity from Renewable Resources: Status, Prospects, and Impediments. Washington, DC: The National Academies Press. doi: 10.17226/12619.
×
FIGURE 5.3 Simple illustrative example of total fossil-fuel energy expended (red), renewable energy generated (green), and net fossil-fuel energy displaced (blue) for a scenario when one unit of a renewable technology with an energy payback time of 4 years is deployed each year over a 5-year period.

FIGURE 5.3 Simple illustrative example of total fossil-fuel energy expended (red), renewable energy generated (green), and net fossil-fuel energy displaced (blue) for a scenario when one unit of a renewable technology with an energy payback time of 4 years is deployed each year over a 5-year period.

Thus, the EPBT for the technology is 4 years. The renewable technology does not begin to displace fossil-fuel energy used per year until 4 years after its initial deployment.

However, the preceding example omits the reality that low-carbon technologies will be deployed over time, so that the energy costs of each successive installation accumulate and effectively extend the time it takes before the energy benefits of the renewable technology are realized. For example, suppose that one unit of the renewable technology discussed above is deployed each year for a period of 5 years. In this scenario, the break-even point between the expenditure of fossil-fuel energy and displacement of the same does not occur until 1 year after the completion of the deployment or 6 years after the first unit is deployed (see Figure 5.3). By the same token, large-scale deployment of renewable technologies with long EPBTs, such as PV, will likely not begin to provide a net displacement of fossil-fuel energy until some years after the deployment has begun. Since CO2 emission reductions depend on displacing fossil-fuel energy, this means that the greenhouse gas emissions reductions from using renewable energy may not be realized for quite some time after the deployment begins. On the other hand, in terms of greenhouse gas emissions, adding new capacity using

Suggested Citation:"5 Environmental Impacts of Renewable Electricity Generation." National Academy of Sciences, National Academy of Engineering, and National Research Council. 2010. Electricity from Renewable Resources: Status, Prospects, and Impediments. Washington, DC: The National Academies Press. doi: 10.17226/12619.
×

renewables is preferable to adding new capacity using CO2-emitting fossil-fuel sources regardless of the EPBT because of the lifetime commitment to fossil-fuel use made by such plants.

Greenhouse Gas Emissions

Concern about climate change and greenhouse gas (GHG) emissions is a major driver in the push for use of renewable energy sources. This section reviews the LCAs of GHG or CO2e for relevant renewable and non-renewable sources of electricity. Figure 5.4 illustrates the range of estimates of CO2e emissions that appear in the literature. Table 5.A.1 (in the annex at the end of the chapter) provides a compilation of studies that estimate life-cycle emission of GHG in CO2e.

Not surprisingly, renewables are estimated to have significantly less CO2e emissions than coal and gas; most estimates of emissions from nuclear power use are similar in magnitude to those from the use of renewables. Adding carbon capture and storage (CCS) to coal and gas systems, however, significantly reduces the relative advantage renewables have in terms of carbon and energy savings. This relative advantage is also modestly reduced by adding energy storage to a renewable technology.

Solar Photovoltaic

Of the renewable technologies included in this review, solar PV technologies have the highest CO2e emissions, ranging from 21 to 71 g CO2e/kWh. CO2e emissions from PV are sensitive to innovations in conversion efficiencies and to the energy mix used to generate electricity during manufacturing. Older systems have conversion efficiencies as low as 5 percent. In 2007, efficiencies had increased to 8–13 percent depending on the type of PV used. A study of newer PV systems dating from 2004–2006 by Fthenakis et al. (2008) puts CO2e emissions at the lower end of the range (21–54 g CO2e/kWh). By 2010 conversion efficiencies for CdTe PV are expected to increase from 9 percent to 12 percent, and efficiencies for crystalline silicon modules are expected to increase to 16 percent in the next few years, lowering emissions even further (Fthenakis and Kim, 2007).

Suggested Citation:"5 Environmental Impacts of Renewable Electricity Generation." National Academy of Sciences, National Academy of Engineering, and National Research Council. 2010. Electricity from Renewable Resources: Status, Prospects, and Impediments. Washington, DC: The National Academies Press. doi: 10.17226/12619.
×
FIGURE 5.4 Life-cycle emissions of greenhouse gases (in CO2 equivalents) for various sources of electricity. Average, maximum, and minimum emissions are shown for each technology based on a review of the literature. Note that the inset provides a smaller scale and more details for sources that are not distinguishable in the main figure. Note: Values for biomass, coal, and natural gas include data for carbon capture and storage (CCS).

FIGURE 5.4 Life-cycle emissions of greenhouse gases (in CO2equivalents) for various sources of electricity. Average, maximum, and minimum emissions are shown for each technology based on a review of the literature. Note that the inset provides a smaller scale and more details for sources that are not distinguishable in the main figure. Note: Values for biomass, coal, and natural gas include data for carbon capture and storage (CCS).

Source: Developed from data provided in Berry et al. (1998), Chataignere et al. (2003), Denholm (2004), Denholm and Kulcinski (2003), European Commission (1997a,b,c,d), Frankl et al. (2004), Fthenakis and Kim (2007), Hondo (2005), Mann and Spath (1997), Meier (2002), Odeh and Cockerill (2008), Spath et al. (1999), Spath and Mann (2000, 2004), Spitzley and Keoleian (2005), Storm van Leeuwen and Smith (2008), Vattenfall AB (2004), and White (1998, 2006).

Suggested Citation:"5 Environmental Impacts of Renewable Electricity Generation." National Academy of Sciences, National Academy of Engineering, and National Research Council. 2010. Electricity from Renewable Resources: Status, Prospects, and Impediments. Washington, DC: The National Academies Press. doi: 10.17226/12619.
×
Biopower

The CO2e emissions from biopower are affected not only by the feedstocks used but also by the yield, fertilizer, and fuel used to cultivate and harvest the feed-stock, as well as the specifics of the power plant itself (Mann and Spath, 1997). Most CO2e values for biopower range from 15 to 52 g CO2e/kWh for biomass derived from cultivated feedstocks. Spath and Mann (2004) claim that biopower can actually lead to “negative” CO2e emissions (i.e., act as a greenhouse gas sink). Their estimate of a negative emission of −410 g C2e/kWh for biopower was based on using waste residues as the feedstock and giving credit for the avoided GHG emissions that would have occurred as a result of normal waste disposal. Negative emissions of −6667 g C2e/kWh and −1368 g C2e/kWh were estimated for biopower combined with carbon capture and storage using crops and residues, respectively. However, none of these studies considered CO2 emissions from initial land conversion, which can be considerable (Searchinger et al., 2008; Fargione et al., 2008).

Wind

Among the renewable energy technologies, wind is estimated to be among the lowest life-cycle emitters of greenhouse gases, with emissions ranging from 2 to 29 g CO2e/kWh. The high value corresponds to a wind farm with a 20 percent generating capacity (Hondo, 2005). This capacity factor is lower than the range of capacity factors (24–40 percent) used in other studies. The two lowest values of 1.7 and 2.5 g CO2e/kWh are for two larger wind farms (with 50 or more 500-kW turbines) set in an area with good wind production (Class 6 and 4 wind areas, respectively) (Spitzley and Keoleian, 2005). While wind speed is a key factor in determining life-cycle CO2e emissions, other variables such as generation capacity per unit of materials are also important. For example, Berry et al. (1998) found that a U.K. wind farm with 103 lower-capacity turbines (250 kW) located in an area with higher average wind speeds (Class 7) emitted 9 g CO2e/kWh. This result, while still very low, is more than three times higher than that seen for the U.S. farm with 50 500-kW turbines located in an area with Class 4 winds.

In spite of producing very low life-cycle carbon emissions, wind is often discounted as a viable source of electricity because of its intermittent availability. Addressing this limitation, Denholm (2004) evaluated CO2 emissions from wind generation with different storage options. The study found that a combination of wind and pumped hydropower storage (PHS) emitted only 24 g CO2e/kWh, which

Suggested Citation:"5 Environmental Impacts of Renewable Electricity Generation." National Academy of Sciences, National Academy of Engineering, and National Research Council. 2010. Electricity from Renewable Resources: Status, Prospects, and Impediments. Washington, DC: The National Academies Press. doi: 10.17226/12619.
×

is within the range of CO2 emissions for wind technology alone. A combination of wind and compressed air energy storage (CAES) technology showed a higher value of 105 g CO2e/kWh, but still far less than emissions seen with fossil-fuel electricity generation. The life-cycle data from Denholm (2004) demonstrate that current technologies for storage are capable of overcoming the limitations of wind generation intermittency without significant carbon emissions.

Geothermal

The total for CO2e emissions from geothermal electricity generation incorporates the emissions associated with production of the facility and emissions during operation. The latter emissions depend on both the reservoir gas composition and whether the gas is vented to the atmosphere during electricity generation. In 2003, only 14 percent of geothermal facilities were closed-loop binary systems that did not vent gases to the atmosphere (Bloomfield et al., 2003). The analysis presented here considers hydrothermal plants and does not discuss enhanced geothermal systems.

The panel’s review found only one LCA study of geothermal technologies that considered emissions from both facility construction and operation. Hondo (2005) reported a value of 15 g CO2e/kWh for a double-flash geothermal facility. Other data from non-LCA literature show a range of CO2e emissions from 0 to 740 g CO2e/kWh for reservoir emissions only.

Hydropower

Most studies conclude that the life-cycle emissions of CO2e from conventional hydropower technologies are quite small. For example, Hondo (2005) reported a value of 11 g CO2e/kWh for a river system with a small reservoir. Spitzley and Keoleian (2005) evaluated a large-capacity, efficient U.S. reservoir system located in a semiarid region and estimated an emission rate of 26 g CO2e/kWh that did not include emissions from flooded biomass. A limitation of most LCAs of hydroelectric generation is that they do not consider the CO2 and CH4 emissions that arise from the flooding of large quantities of biomass when the facility is first developed. Some studies suggest that these emissions may be significant for large and/or inefficient tropical hydroelectric projects that flood large quantities of biomass (Fearnside, 1995, 2002) or hydroelectric reservoirs sited on more temperately located peat lands (Gagnon and van de Vate, 1997). Ranges in the literature for carbon emissions from tropical reservoirs can be several hundred to several

Suggested Citation:"5 Environmental Impacts of Renewable Electricity Generation." National Academy of Sciences, National Academy of Engineering, and National Research Council. 2010. Electricity from Renewable Resources: Status, Prospects, and Impediments. Washington, DC: The National Academies Press. doi: 10.17226/12619.
×

thousand grams CO2e/kWh, but they do not reflect normalized life-cycle emissions. Gagnon et al. (1997) addressed this issue by deriving a theoretical life-cycle emission value of 237 g CO2e/kWh for a hydroelectric reservoir located in Brazil. In this calculation, Gagnon et al. (1997) assumed that 100 percent of the flooded biomass would decay completely over 100 years and that 20 percent of the biomass carbon would be emitted as methane. This calculation does not include emissions from turbines and spillways. More study is needed of the impact of flooded biomass on life-cycle emissions associated with hydroelectric plants.

Hydrokinetic (Tidal/Wave)

No LCA data were reviewed for tidal or wave electricity-generating technologies, which are still very much in the pilot or demonstration stage. One source reported a value of 25 g CO2e/kWh for the steel used to manufacture turbines for tidal generation installations (CarbonTrust, 2008). One would expect LCA emissions to be low and to occur primarily during material manufacturing and plant construction.

Storage

Storage is not a generating system, but it can be combined with generating technologies to provide backup power for intermittent and peak power needs. Storage options reviewed in the LCA literature included pumped hydropower storage, compressed air energy storage, and battery energy storage (BES) (Denholm and Kulcinski, 2003; Denholm, 2004). The estimate for PHS was a low 3 g CO2e/kWh. When transmission and distribution (T&D) were included, the estimate increased to 6 g CO2e/kWh. A variety of BES technologies were reviewed with values ranging from 33 to 81 g CO2e/kWh. A subset of the BES data with values from 33 to 50 g CO2e/kWh includes T&D. CAES had the highest emission values, 291 and 292 g CO2e/kWh, primarily because it relies on natural gas.3 The second example includes T&D.4

3

Natural gas is used to reheat the air coming from the cavern in diabatic CAES.

4

Most LCA studies cited here do not include T&D.

Suggested Citation:"5 Environmental Impacts of Renewable Electricity Generation." National Academy of Sciences, National Academy of Engineering, and National Research Council. 2010. Electricity from Renewable Resources: Status, Prospects, and Impediments. Washington, DC: The National Academies Press. doi: 10.17226/12619.
×

SO2Emissions

Figure 5.5 shows the range from the literature for life-cycle SO2 emissions from power sources. Wind, hydropower, and nuclear technologies have extremely low life-cycle SO2 emissions, less than 100 mg/kWh.

FIGURE 5.5 Estimated life-cycle emissions of SO2 in milligrams per kilowatt-hour for various renewable and non-renewable energy sources. No data on SO2 emissions were found for tidal or energy storage technologies.

FIGURE 5.5 Estimated life-cycle emissions of SO2in milligrams per kilowatt-hour for various renewable and non-renewable energy sources. No data on SO2emissions were found for tidal or energy storage technologies.

Note: Asterisk indicates facility emissions only.

Source: Developed from data provided in Berry et al. (1998), Chataignere et al. (2003), Dones et al. (2005), European Commission (1997a,b,c,d), Frankl et al. (2004), Fthenakis et al. (2008), Green and Nix (2006), Mann and Spath (1997), Odeh and Cockerill (2008), Spath et al. (1999), Spath and Mann (2000), Spitzley and Keoleian (2005), and Vattenfall AB (2004, 2005).

Suggested Citation:"5 Environmental Impacts of Renewable Electricity Generation." National Academy of Sciences, National Academy of Engineering, and National Research Council. 2010. Electricity from Renewable Resources: Status, Prospects, and Impediments. Washington, DC: The National Academies Press. doi: 10.17226/12619.
×
Solar Photovoltaic

Rates of SO2 emissions associated with electricity generation from PV are most affected by the energy intensity of the manufacturing process and the efficiency of the PV material, as well as the energy mix used to manufacture the PV material and the solar insolation at the site where the PV is installed. SO2 emissions for PV installations in Europe range from 73 to 215 mg/kWh and include a range of PV technologies (single crystalline, multicrystalline, amorphous silicon, copper-indium-gallium-diselenide [CIGS] and CdTe) with conversion efficiencies of 6–14 percent, and insolation rates of 1700–1740 kWh m2/yr over assumed lifetimes of 20–30 years. SO2 emissions shown from studies in the United States have a wider range of values, from 158 to 540 mg/kWh. The high value of 540 mg SO2/kWh is from an older U.S. PV installation with lower insolation rates and a greater reliance on coal for electricity generation compared to that of Europe (Spitzley and Keoleian, 2005). Fthenakis et al. (2008) compared 2004–2006 PV technologies for similar systems using the average U.S. and European inventory data and electricity mix. For the European cases, SO2 emission values ranged from 73 to 146 mg/kWh, whereas for the U.S. cases the values ranged from 158 to 378 mg/kWh.

Interestingly, studies suggest that the most efficient PV material is not necessarily the best for minimizing emissions. For example, cadmium telluride (CdTe) technologies have the lowest conversion efficiencies (9 percent) yet produce lower SO2 emissions because less energy is consumed during CdTe manufacturing than with other PV technologies that have higher conversion efficiencies (11.5–14 percent) (Fthenakis et al., 2008). This relationship may change as technology innovations decrease energy consumption during manufacturing.

Biopower

For biopower, reported values for SO2 emissions range from 40 to 940 mg/kWh. Mann and Spath (1997) suggest that much of this variation arises from differences in power plant efficiency. The low end of the range, from 40 to 45 mg/kWh, is from two European studies cited by Mann and Spath (1997). The four remaining studies, with values ranging from 302 to 940 mg/kWh, are from the United States. Cases with results in the mid-range include two hypothetical integrated gasification combined cycle (IGCC) plants with different fuels. Both plants are based on models developed by the National Renewable Energy Laboratory (NREL). A plant using hybrid poplar as fuel has an estimated SO2 emission rate of 302 mg/kWh (Mann and Spath, 1997), and a willow feedstock plant has an estimated SO2 emis-

Suggested Citation:"5 Environmental Impacts of Renewable Electricity Generation." National Academy of Sciences, National Academy of Engineering, and National Research Council. 2010. Electricity from Renewable Resources: Status, Prospects, and Impediments. Washington, DC: The National Academies Press. doi: 10.17226/12619.
×

sion rate of 370 mg/kWh (Spitzley and Keoleian, 2005).5 Mann and Spath (1997) include no special emission controls on combustion plants and assume that all SO2 in the biomass is converted to emissions. The other U.S. examples include a direct-fired boiler and a high-pressure IGCC system, based on Electric Power Research Institute (EPRI) models, that emit SO2 at rates of 930 and 940 mg/kWh, respectively (Spitzley and Keoleian, 2005). The base models developed by NREL and EPRI have very different emission profiles for plant combustion (Heller et al., 2004); the EPRI plant is assumed to emit approximately three times more SO2 than is assumed for the NREL plant.

Geothermal

No LCA data were found that included SO2 emissions for geothermal technologies. Data from Green and Nix (2006) show reservoir-only emissions ranging from 0 to 160 mg/kWh.

Emissions of Nitrogen Oxides

Figure 5.6 illustrates the range of life-cycle NOx emissions estimated from various electrical generation technologies. Among these technologies, hydroelectric, wind, geothermal, and nuclear technologies have low estimated NOx emissions (<100 mg/kWh) and are not discussed in detail in this section.

As a rule, energy sources based on combustion have significantly higher levels of NOx emissions than do those that do not involve combustion. The NOx produced from combustion arises from two sources: the oxidation and volatilization of the nitrogen contained in the fuel, and the high-temperature reactions involving atmospheric nitrogen and oxygen. The production of NOx from atmospheric sources can be reduced or even completely eliminated by carrying out the combustion under high-oxygen conditions, so-called oxy-fuel combustion. Because of a lack of LCAs, the levels of NOx emissions described here do not reflect the performance of these systems.

5

Spitzley and Keoleian (2005) attributed incorrect SO2 and NOx emission data to the base model IGCC plants from Heller et al. (2004). SO2 and NOx emission results cited here have been corrected to be consistent with Heller et al. (2004).

Suggested Citation:"5 Environmental Impacts of Renewable Electricity Generation." National Academy of Sciences, National Academy of Engineering, and National Research Council. 2010. Electricity from Renewable Resources: Status, Prospects, and Impediments. Washington, DC: The National Academies Press. doi: 10.17226/12619.
×
FIGURE 5.6 Estimates of life-cycle emissions of NOx from various technologies. No LCA data on emissions of NOx were found for geothermal, tidal, or energy storage technologies.

FIGURE 5.6 Estimates of life-cycle emissions of NOxfrom various technologies. No LCA data on emissions of NOxwere found for geothermal, tidal, or energy storage technologies.

Note: Asterisk indicates facility emissions only.

Source: Developed from data provided in Berry et al. (1998), Chataignere et al. (2003), Dones et al. (2005), European Commission (1997a,b,c,d), Frankl et al. (2004), Fthenakis et al. (2008), Green and Nix (2006), Mann and Spath (1997), Odeh and Cockerill (2008), Spath et al. (1999), Spath and Mann (2000), Spitzley and Keoleian (2005), and Vattenfall AB (2004, 2005).

Suggested Citation:"5 Environmental Impacts of Renewable Electricity Generation." National Academy of Sciences, National Academy of Engineering, and National Research Council. 2010. Electricity from Renewable Resources: Status, Prospects, and Impediments. Washington, DC: The National Academies Press. doi: 10.17226/12619.
×
Solar

NOx emission data for PV technologies range from 40 to 260 mg/kWh. This range largely reflects the differing mixes of grid energy used to produce the PV material as well as the conversion efficiencies and life expectancies of the PV facility. The high value of 260 mg/kWh is for an older U.S. PV installation with lower insolation; the greater reliance on coal for electricity generation in the United States as compared to Europe leads to greater life-cycle emissions in the United States (Spitzley and Keoleian, 2005). NOx values from European studies ranged from 40 to 99 mg/kWh. A study by Fthenakis et al. (2008) demonstrates how the carbon intensity of the grid can affect emissions from PV technologies. They compared 2004–2006 PV technologies for similar systems using the average U.S. and European inventory data and electricity mix. For the European cases, NOx values ranged from 40 to 82 mg/kWh, whereas for the U.S. cases reported values ranged from 79 to 188 mg/kWh.

Biopower

Of all the renewable electricity technologies, biopower can have the highest NOx emissions, with estimates ranging from 290 to 820 mg/kWh. Mann and Spath (1997) found that NOx emissions are most sensitive to variations in crop yield, feedstock fuel used, and power plant efficiency, and that most NOx emissions in the biopower life cycle (about 70 percent) are from combustion. Whether the feedstock is a fossil fuel or is biomass, the amount of NOx produced during combustion depends on the nitrogen content of the fuel and the temperature of combustion. The higher the temperature, the more NOx is produced. As a result, production of electricity from biopower produces NOx at rates comparable to that of fossil fuels.

Emissions of Particulate Matter

Figure 5.7 illustrates the range of estimated life-cycle emissions of particulate matter (PM) from various renewable and non-renewable energy sources. PM emissions tend to be low (<100 mg/kWh) for all the energy technologies considered here, with the exception of coal, natural gas, and PV. However, many LCAs do not report on emissions of PM.

Suggested Citation:"5 Environmental Impacts of Renewable Electricity Generation." National Academy of Sciences, National Academy of Engineering, and National Research Council. 2010. Electricity from Renewable Resources: Status, Prospects, and Impediments. Washington, DC: The National Academies Press. doi: 10.17226/12619.
×
FIGURE 5.7 Estimates of life-cycle particulate matter emissions for various electrical power generations technologies. No LCA data on emissions of particulate matter were found for geothermal, tidal, or energy storage technologies.

FIGURE 5.7 Estimates of life-cycle particulate matter emissions for various electrical power generations technologies. No LCA data on emissions of particulate matter were found for geothermal, tidal, or energy storage technologies.

Note: Asterisk indicates facility emissions only.

Source: Developed from data provided in Berry et al. (1998), Chataignere et al. (2003), Dones et al. (2005), European Commission (1997a,b,c,d), Frankl et al. (2004), Green and Nix (2006), Mann and Spath (1997), Odeh and Cockerill (2008), Spath et al. (1999), Spath and Mann (2000), and Spitzley and Keoleian (2005).

Solar Photovoltaic

Five LCAs for PM emissions from PV were found by the panel. Only one, a U.S. study, reported results higher than 100 mg/kWh: Spitzley and Keoleian (2005) reported a value for particulate matter of 610 mg/kWh for an older U.S. PV installation with lower insolation rates and a relatively large reliance on coal in electricity from the grid. The European data, on the other hand, showed emissions of PM ranging from 6 to 55 mg/kWh.

Suggested Citation:"5 Environmental Impacts of Renewable Electricity Generation." National Academy of Sciences, National Academy of Engineering, and National Research Council. 2010. Electricity from Renewable Resources: Status, Prospects, and Impediments. Washington, DC: The National Academies Press. doi: 10.17226/12619.
×

Land Use

Some have proposed that land use may be a limiting factor for the use of renewable energy technologies (Pimentel et al., 2002; Grant, 2003), supporting this argument with non-LCA land-use data based on calculations of power plant size and quantity of electricity generated. Other studies have focused on one aspect of an energy technology (e.g., reservoir size for hydropower) to derive a land-use estimate. These estimates of land use can be misleading because they fail to present an accurate understanding of the entire life-cycle land-use requirements of a technology. The LCA land-use data discussed here are from Spitzley and Keoleian (2005), whose land-use metric accounts for the total surface area occupied by the materials and products of an energy technology, including the time of land occupation over the total life-cycle energy generated. Figure 5.8 shows the results of this 2005

FIGURE 5.8 Life-cycle cost assessment of land use for various renewable and non-renewable technologies in square meters per megawatt-hour per year. Note that the inset provides a smaller scale and more details for sources that are not distinguishable in the main figure.

FIGURE 5.8 Life-cycle cost assessment of land use for various renewable and non-renewable technologies in square meters per megawatt-hour per year. Note that the inset provides a smaller scale and more details for sources that are not distinguishable in the main figure.

Source: Developed from data provided in Spitzley and Keoleian, 2005.

Suggested Citation:"5 Environmental Impacts of Renewable Electricity Generation." National Academy of Sciences, National Academy of Engineering, and National Research Council. 2010. Electricity from Renewable Resources: Status, Prospects, and Impediments. Washington, DC: The National Academies Press. doi: 10.17226/12619.
×

study’s estimates of LCA land use for renewables and other electricity-generating technologies. Key assumptions in the Spitzley and Keoleian (2005) analysis are (1) exclusion of fuels and materials with insignificant land acquisition requirements compared to other life-cycle stages, and (2) inclusion of end-of-life land disposal requirements for nuclear fuel only. The Spitzley and Keoleian analysis does not allow for distinctions for intensity of land use.

A key factor affecting land use is the generating efficiency of the technology per unit area. By design, technologies using high energy density power sources use less land to produce more electricity at the point of generation than do the more diffuse renewable technologies. For this reason, analyses such as the ones cited here find that renewables have relatively large land-use requirements. To operate fossil-fuel and nuclear plants, however, the fuel must first be extracted or mined. Most LCAs, including those used in this study, do not account for that process in their assessment of land-use requirements. Moreover, the land used by some diffuse renewable electricity technologies usually allows for multiple uses, or the technology makes use of sites that also serve an alternate purpose (e.g., PV installations on roofs or sides of buildings, wind turbines on farms, and hydroelectric reservoirs that provide flood control, recreation, and water supply).

Figure 5.8 shows that studies found in the literature give natural gas, coal, and nuclear technologies low land-use values: 0.45 m2/(MWh/yr), 4.4–5.8 m2/(MWh/yr), and 6.5 m2/(MWh/yr), respectively (without counting resource extraction). Of the renewable energy technologies, solar has the lowest land-use values, ranging from 9 to 14.3 m2/(MWh/yr). The lowest estimated value for PV is for an installation in Phoenix where higher insolation rates yield more energy potential per unit area.

The two wind farms in the Spitzley and Keoleian (2005) study report landuse values of 69 and 94 m2/(MWh/yr). The lower land-use value is from the wind farm with higher wind speed and reflects the greater power generation potential per unit area and per unit of equipment. Additionally, only about 1 percent of wind farm land is used by the turbines and associated facilities, thus allowing for multiple uses (e.g., grazing and agriculture).

Spitzley and Keoleian (2005) included one LCA example of hydroelectric power with a land-use value of 122 m2/(MWh/yr) for a high-capacity, large-reservoir facility in the United States with a 50-year lifetime. The literature also contains a wide range of non-LCA land-use data for hydroelectric power. The range includes very small values for run-of-river hydroelectric facilities to very

Suggested Citation:"5 Environmental Impacts of Renewable Electricity Generation." National Academy of Sciences, National Academy of Engineering, and National Research Council. 2010. Electricity from Renewable Resources: Status, Prospects, and Impediments. Washington, DC: The National Academies Press. doi: 10.17226/12619.
×

large values for low-capacity hydroelectric plants associated with very large reservoirs in developing nations.

Biopower is estimated to have the highest land-use requirements, with estimates ranging from 360 to 488 m2/(MWh/yr). The highest value is from a direct-fired boiler biopower facility with a small generating capacity. The other facilities all use IGCC and show very similar results of 360–375 m2/(MWh/yr). All four examples cited in the Spitzley and Keoleian (2005) study use cropping to supply biomass. Biopower from waste would be expected to have much lower land-use values.

Water Use

Water Use by Renewable Technologies

Although most renewable technologies use only a fraction of the water used by thermoelectric plants, some renewables, such as geothermal, hydroelectric, and solar thermal, can be water intensive. For example, flash geothermal plants consume reservoir water and require makeup water.6 One plant in California uses 2,000 gal/MWh and requires 1,400 gal/MWh of makeup water (Table 5.1). This facility uses water recycled from a wastewater facility as an innovative makeup water source (DOE, 2006). Newer geothermal plant designs such as binary plants use little water. Hydroelectric power, which generates electricity from the kinetic energy of water itself, uses vast quantities of water. Evaporative loss from hydroelectric reservoirs has been estimated at 4,500 gal/MWh (DOE, 2006). CSP technologies can also be water intensive (see Table 5.1). Concentrated solar thermal power uses 770–920 gal/MWh, and solar power tower technologies use about 750 gal/MWh for evaporative cooling (DOE, 2006). Parabolic dish-engine solar technologies are air-cooled and use minimal water (DOE, 2006).

Energy technologies that withdraw and consume less water will have both public benefit and economic advantages in the marketplace moving forward. One option is to develop electricity from sources that use very little water, such as wind and PV. Other options include developing technologies that limit the use of water with fossil-fuel electricity sources or use alternate sources of water, such as reclaimed or saline water. For example, some power plants use mine water and/or

6

Makeup water is the water added to the existing flow of cooling water to replace the water lost during passage through the cooling towers or other power plant processes.

Suggested Citation:"5 Environmental Impacts of Renewable Electricity Generation." National Academy of Sciences, National Academy of Engineering, and National Research Council. 2010. Electricity from Renewable Resources: Status, Prospects, and Impediments. Washington, DC: The National Academies Press. doi: 10.17226/12619.
×

TABLE 5.1 Water Use by Energy Technology

Technology

 

Consumption (Withdrawal) (gal/MWh)

DOE (2006)a

Feeley III et al. (2008)

Geothermal

Cooling tower

~1,400 (~2,000)

 

Nuclear

Once through

~400 (25,000–60,000)

140 (31,500)

 

Cooling tower

720 (800–1,100)

620 (1,100)

 

Cooling pond

400–720 (500–1,100)

 

Fossil/biopower

Once through

~300 (20,000–50,000)

60–140 (22,500–27,000)

 

Cooling tower

480 (500–600)

460–520 (500–650)

 

Cooling pond

300–480 (300–600)

4–800 (15,000–18,000)

NGCC

Once through

100 (7,500–20,000)

20 (9,000)

 

Cooling tower

~180 (~230)

130 (150)

 

Cooling pond

 

240 (6,000)

 

Air cooled

 

4 (4)

IGCC, coal

Cooling tower

~200 (~380)

170 (230)

Concentrated solar power

Solar thermal

770–920 (770–920)

 

 

Power tower

760 (760)

 

 

Dish-engine

Minimal

 

Hydroelectric

 

4,500 (reservoir evaporation)

 

aDOE (2006) inaccurately reports water consumption for recirculating cooling system from EPRI (2002).

gray water from wastewater treatment plants. Other alternative sources of water include produced water from oil and gas operations and brackish groundwater aquifers. Developing alternate water sources requires careful consideration of economic and ecosystem impacts. For example, brackish groundwater requires additional conditioning to meet power plant water chemistry specifications. At the same time, groundwater withdrawals can affect freshwater aquifers and lead to saltwater intrusion. Relying on marine water has the same impacts for fish and other aquatic organisms as freshwater use.

Water Use by Thermoelectric Technologies

Generating electricity from energy technologies that rely on water to produce electricity from steam (thermoelectric generation) is very water-intensive. In recent years, concerns regarding water use have led to the denial of water permits for new power plant construction in various locations throughout the United States (Feeley III et al., 2008; DOE, 2006). In areas of the United States experiencing

Suggested Citation:"5 Environmental Impacts of Renewable Electricity Generation." National Academy of Sciences, National Academy of Engineering, and National Research Council. 2010. Electricity from Renewable Resources: Status, Prospects, and Impediments. Washington, DC: The National Academies Press. doi: 10.17226/12619.
×

drought and population growth, thermoelectric power plants may be forced to reduce output as they compete with other users for a limited supply of water (Vinluan, 2007; MSNBC, 2008). The benefits of present and future water use by energy technologies must be carefully weighed in examining the implications of a finite water resource. Competition over water is intensifying, because water supports agricultural, industrial, and domestic needs, as well as the need for electricity.

Thermoelectric plants generate electricity using steam from a variety of fuel sources including fossil fuels, geothermal energy, concentrated solar power, and biopower. However, most thermoelectric power in the United States is generated from conventional fossil sources. Water use by thermoelectric power plants is categorized as water withdrawn or consumed. Thermoelectric power plants use large quantities in each category but withdraw more than is actually consumed. According to the U.S. Geological Survey (USGS, 2004), thermoelectric power plants withdrew about 136 billion gallons per day (billion gal/d) of freshwater for use and consumed about 3 billion gal/d of this amount. This accounted for about 40 percent of all freshwater withdrawals in the United States, and almost 15 percent of all non-agricultural consumption.

The USGS (2004) estimated that power plants withdrew an additional 59 billion gal/d of saline water, bringing the total daily water use in 2000 by power plants to 195 billion gal/d. However, Dziegielewski et al. (2006) argued that this was an underestimation. They reported that water-use data for thermoelectric power plants compiled by the USGS did not include water from public water supplies, nor was it clear whether water use by independent non-utility power plants was included. Independent non-utility power plants generated an additional 16 percent of electricity in 2000. On average, approximately 26 gallons of water is used to produce 1 kWh of electricity. Total per capita water withdrawals for electricity in 2000 amounted to 686 gallons per person per day, which is about four and a half times the direct per capita use (Table 5.2) (Dziegielewski et al., 2006).

Figure 5.9 illustrates the range of water withdrawal and consumption rates for a variety of technologies as compiled by DOE (2006). Power plants use water primarily for cooling, but significant quantities of water are also used in other plant activities. Because of this dependency, power plants have traditionally been sited near rivers, lakes, or oceans. Most of the water consumed by thermoelectric power plants is lost through evaporation. Cooling system options include once-through, recirculating, or air-cooled systems. Water use by thermoelectric technologies with these cooling options is shown in Table 5.2.

Suggested Citation:"5 Environmental Impacts of Renewable Electricity Generation." National Academy of Sciences, National Academy of Engineering, and National Research Council. 2010. Electricity from Renewable Resources: Status, Prospects, and Impediments. Washington, DC: The National Academies Press. doi: 10.17226/12619.
×

TABLE 5.2 Water Intensity of Thermoelectric Generators as Compared to Other Water Users

Category

Water Consumption (Withdrawal) (gal/d)

Average person U.S., total (indoor and outdoor), 2002

152

Average person Germany, total, 2002

51

Average person U.K., total, 2002

39

Washington, D.C., and area, 2005 (about 2 million people)

123.6 million

New York City, 2006 (about 8 million people)

1069 million

Average 500 MW coal plant, cooling tower

6.1 million (6.4–7.6 million)

Average 500 MW coal plant, once-through cooling

4 million (240–600 million)

Average 1 GW nuclear plant, cooling tower

17.3 million (19.9–27.1 million)

Average 1 GW nuclear plant, once-through cooling

10.3 million (600–1440 million)

Average 500 MW NGCC plant, cooling tower

2.2 million (2.8 million)

FIGURE 5.9 Estimates of water withdrawal and consumption rates for various thermoelectricity generating technologies.

FIGURE 5.9 Estimates of water withdrawal and consumption rates for various thermoelectricity generating technologies.

Source: DOE, 2006.

Suggested Citation:"5 Environmental Impacts of Renewable Electricity Generation." National Academy of Sciences, National Academy of Engineering, and National Research Council. 2010. Electricity from Renewable Resources: Status, Prospects, and Impediments. Washington, DC: The National Academies Press. doi: 10.17226/12619.
×

LOCAL ENVIRONMENTAL IMPACTS—SITING AND PERMITTING

It is critical to consider siting and permitting issues. The permitting process addresses the wide range of localized impacts that might result from the construction of a renewables facility or related infrastructure, such as transmission lines. New renewable electric facilities can affect water supplies, ecosystems, and the natural landscape and hence can meet with local opposition. Though renewable facilities are obtaining permits and completing impact assessments, the knowledge of the full impacts of renewables and the guidance for permitting projects are nascent in comparison to those for fossil fuels. Further, renewable energy resources are generally more distributed than concentrated, especially those powering the technologies dominating the near term (wind power, solar PV, and CSP). As noted previously, renewables have relatively large land-use requirements. The process of siting and permitting these facilities has the potential to place burdens on local jurisdictions that regulate land use and create a hodgepodge of rules and requirements for renewable energy deployment.

Siting

Siting issues could be a significant concern with renewables. The NIMBY (not in my back yard) effect, which describes local opposition to a new development intended to distribute broad benefits, has delayed the construction of several major renewable energy projects in the United States. While proponents cite the environmental, economic, and energy security benefits to be gained from these projects, opponents cite the negative impacts, which often include potential damage to local ecosystems, loss of aesthetic value to the natural landscape, and the opportunity cost of land use. Biomass and biofuels, for example, require large amounts of land that could instead be used for agricultural purposes. Hydropower is becoming increasingly difficult to site; most major potential sites are already being used, and ecological considerations are preventing the exploitation of remaining ones. Siting renewable energy projects can also pit environmentalists against one another. In Cape Cod, Massachusetts, local residents who fear harm to aquatic life have fought the construction of 130 wind turbines; in southern California, advocates of solar power face resistance from environmental groups that fear potential disruption to the Mojave Desert ecosystem (Barringer, 2009). Local opposition has also stymied the development of new transmission lines (Silverstein, 2008). Review of siting issues occurs during the permitting process discussed below.

Suggested Citation:"5 Environmental Impacts of Renewable Electricity Generation." National Academy of Sciences, National Academy of Engineering, and National Research Council. 2010. Electricity from Renewable Resources: Status, Prospects, and Impediments. Washington, DC: The National Academies Press. doi: 10.17226/12619.
×

Permitting

Most if not all technologies for generating electricity will require multiple permits. These permits are intended to consider the local impacts on the land, water, and air that occur during the installation and operation of these technologies. Depending on the size and location of the generating facility, permits from local zoning boards, state agencies, and federal agencies may be required. In the case of traditional electricity-generating facilities, such as those that use coal and natural gas, there is a long and evolving permitting process that has been applied across the country. For most renewable technologies, the process is more in the developmental stage. As of January 2008, at least two states, California and Wisconsin, have enacted state laws preempting or limiting local siting jurisdiction for wind power (Green, 2008). Because wind power has been the most extensively deployed renewable electricity technology in recent times, guidance for permitting a wind power project is more advanced. A National Research Council (NRC) report contains a fairly extensive review of guidelines that have been developed for such projects (NRC, 2007). For biomass, geothermal, and solar, the guidance for permitting is less well developed. However, there are many current regulations that apply to all generating facilities. Table 5.3 summarizes some of the most important regulations that apply to all large electricity-generating facilities. Although an exhaustive review of local impacts and permitting issues is beyond the scope of this study, a short summary of permitting issues for wind, geothermal, and CSP is presented below.

Wind Power

Due to the increasing number of wind power projects, more information is being developed concerning the process for permitting them. The most prominent issues of concern are land use and the possible impacts on birds and bats. In addition, concerns have been raised about noise, aesthetics, and the use of herbicides to clear and maintain sites, particularly where endangered species are involved. Recent reports and references on permitting wind power projects include the American Wind Energy Association (AWEA) siting handbook, which presents information about regulatory and environmental issues associated with developing and siting wind energy projects in the United States (AWEA, 2008). The AWEA handbook covers the components of a typical wind power project: the stages of a wind power project; the federal, state, and local regulatory frameworks relevant for wind power; and the array of environmental and human impacts to consider

Suggested Citation:"5 Environmental Impacts of Renewable Electricity Generation." National Academy of Sciences, National Academy of Engineering, and National Research Council. 2010. Electricity from Renewable Resources: Status, Prospects, and Impediments. Washington, DC: The National Academies Press. doi: 10.17226/12619.
×

TABLE 5.3 Some of the Important Regulations That Apply to All Electricity Generating Facilities

Topic

Law: Statutory Citation

Regulation Name:

Code of Federal Regulations Citation

Air Quality

Clean Air Act conformity

Clean Air Act (CAA), Section 176(c)(1): P.L. 88-206, as amended; 42 USC 7401, et seq.

Determining Conformity of Federal Actions to State or Federal Implementation Plans:

40 CFR Part 51, Subpart W

40 CFR Part 93, Subpart B

Biota

Eagles

Bald and Golden Eagle Protection Act: 16 USC 668a-668d, as amended

General Provisions (for taking, possession, etc. of wildlife and plants):

50 CFR Part 10

Eagle Permits:

50 CFR Part 22

Endangered and threatened species and critical habitats

Endangered Species Act (ESA), Section 7: P.L. 93-205, as amended; 16 USC 1536(a)-(d)

Interagency Cooperation:

50 CFR Part 402

Endangered Species Exemption Process:

50 CFR Parts 450–453

Essential fish habitat

Magnuson–Stevens Fishery Conservation and Management Act (also known as the Sustainable Fisheries Act): P.L. 104-297 (major amendments to P.L. 94-265); 16 USC 1801, et seq.

Magnuson–Stevens Act Provisions:

50 CFR Part 600

The following subparts deal with Essential Fish Habitat (EFH): Table of contents; Subpart A–General (purpose and scope, definitions, other acronyms); Subpart D–National Standards, section 600.305 General, particularly subsection 600.305(c); Subpart J–Essential Fish Habitat; Subpart K–EFH coordination, consultation, and recommendations

Fish and wildlife

Fish and Wildlife Coordination Act (FWCA): P.L. 85-624, as amended; 16 USC 661, et seq.

No implementing regulations

Suggested Citation:"5 Environmental Impacts of Renewable Electricity Generation." National Academy of Sciences, National Academy of Engineering, and National Research Council. 2010. Electricity from Renewable Resources: Status, Prospects, and Impediments. Washington, DC: The National Academies Press. doi: 10.17226/12619.
×

Topic

Law: Statutory Citation

Regulation Name:

Code of Federal Regulations Citation

Marine mammals

Marine Mammal Protection Act (MMPA), Sections 103 and 104: P.L. 92-522; 16 USC 1361-1407

Fish and Wildlife Service General Permit Procedures:

50 CFR Part 13

Marine Mammals:

50 CFR Part 18

National Marine Fisheries Service Regulations Governing the Taking and Importing of Marine Mammals:

50 CFR Part 216

Migratory birds

Migratory Bird Treaty Act (MBTA): 16 USC 703-712

General Provisions (for taking, possession, etc. of wildlife and plants):

50 CFR Part 10

Migratory Bird Permits:

50 CFR Part 21

Cultural Resources

Archaeological resources

Archaeological Resources Protection Act (ARPA): P.L. 96-95; 16 USC 470aa–mm

Protection of Archaeological Resources:

43 CFR Part 7

Historic resources

National Historic Preservation Act (NHPA), Sections 106 and 110: P.L. 89-665, as amended; 16 USC 470

Protection of Historic Properties: 36 CFR Part 800

Native American graves

Native American Graves Protection and Repatriation Act (NAGPRA): P.L. 101-601; 25 USC 3001, et seq.

Native American Graves Protection and Repatriation Regulations:

43 CFR Part 10

Native American religions

American Indian Religious Freedom Act (AIRFA): P.L. 95-341; 42 USC 1996 and 1996a

No implementing regulations

Land Use and Special Land and Water Designations

Coastal zone areas

Coastal Zone Management Act (CZMA): P.L. 92-583, as amended; 16 USC 1451, et seq.

Federal Consistency with Approved Coastal Management Programs: 15 CFR Part 930

Farmland

Farmland Protection Policy Act (FPPA): P.L. 97-98, as amended; 7 USC 4201, et seq.

Prime and Unique Farmlands:

7 CFR Part 657

7 CFR Part 658

Suggested Citation:"5 Environmental Impacts of Renewable Electricity Generation." National Academy of Sciences, National Academy of Engineering, and National Research Council. 2010. Electricity from Renewable Resources: Status, Prospects, and Impediments. Washington, DC: The National Academies Press. doi: 10.17226/12619.
×

Topic

Law: Statutory Citation

Regulation Name:

Code of Federal Regulations Citation

National marine sanctuaries

Marine Protection, Research, and Sanctuaries Act (MPRSA), Title III: P.L. 92-532, as amended; 16 USC 1431-1445

National Marine Sanctuary Program Regulations:

15 CFR Part 922

National natural landmarks

Historic Sites Act: P.L. 74-292, as amended; 16 USC 461-467

National Natural Landmarks Program:

36 CFR Part 62

Wild and scenic rivers

Wild and Scenic Rivers Act (WSRA), Sections 5 and 7: P.L. 90-524, as amended; 16 USC 1271-1287

Wild and Scenic Rivers:

36 CFR Part 297

Wilderness areas

Wilderness Act: P.L. 88-577; 16 USC 1131-1133

Forest Service Regulations:

Prohibitions:

36 CFR Part 261

Special Areas:

36 CFR Part 294

Note: Contents are listed by environmental topic.

Source: U.S. Department of Energy; see http://www.eh.doe.gov/nepa/tools/guidance/volume3/laws_regulations_table.html.

when siting wind power. An example of a state handbook on wind power permitting is the guidance developed by the Kansas Energy Council for siting wind power projects in that state (Kansas Energy Council, 2005). In terms of impacts on wildlife, the New York State Department of Environmental Conservation recently proposed guidelines on how to characterize bird and bat resources at onshore wind energy sites and how to estimate and document impacts (New York Department of Environmental Conservation, 2008). Although bird deaths are often characterized as one critical potential impact from wind turbines, the NRC (2007) study cited above concluded that, while the impacts on bat populations were unclear, there was no evidence that bird fatalities caused by wind turbines result in measurable demographic changes to bird populations in the United States (NRC, 2007).

One purpose of the NRC (2007) study was to develop an analytical framework for impact evaluation to inform siting decisions for wind-energy projects. The study organized impacts assessment into a three-dimensional action space that includes the relevant spatial jurisdictions (local, state/regional, and federal),

Suggested Citation:"5 Environmental Impacts of Renewable Electricity Generation." National Academy of Sciences, National Academy of Engineering, and National Research Council. 2010. Electricity from Renewable Resources: Status, Prospects, and Impediments. Washington, DC: The National Academies Press. doi: 10.17226/12619.
×

project stage (pre-project, construction, operational, and post-operational), and environmental and human impacts (NRC, 2007). The NRC (2007) study found that because wind energy is new to many state and local governments, the quality of the permitting process is uneven, and it pointed out that a coordinated and consistent process would greatly aid planning and regulating wind-energy development at smaller scales. The report recommended that representatives of federal, state, and local governments work with wind developers and interested parties to develop guidance and permitting guidelines (NRC, 2007).

In order to better assess possible wildlife impacts of wind power, Secretary of the Interior Dirk Kempthorne in 2007 announced the creation of the Wind Turbine Guidelines Advisory Committee, which will function in accordance with the Federal Advisory Committee Act (FACA). The scope and objective of the committee, as outlined in its charter, is to provide advice and recommendations to the Interior secretary on developing effective measures to avoid or minimize impacts on wildlife and habitats related to land-based wind energy facilities. The committee members represent the varied interests associated with wind energy development and wildlife management.7

Another group that will address fauna issues is the recently formed American Wind Wildlife Institute, created through cooperation between members of the environmental community and the wind industry. The institute will focus on efforts to facilitate timely and responsible development of wind energy while protecting wildlife and wildlife habitat. It will do this through research, mapping, mitigation, and public education on best practices in wind farm siting and wildlife-habitat protection.

Geothermal

Because of the long history of geothermal (hydrothermal) projects in the western United States, there is a mature record of the permitting of these plants. Battocletti (2005) provides an overview of the geothermal permitting process. Most federal statutes listed in Table 5.3 that apply to geothermal development are similar to the statutes for fossil-fuel plants. Because much of the geothermal resources occur on lands managed by the U.S. Bureau of Land Management (BLM), the agency

7

For additional information on the activities of the Wind Turbine Guidelines Advisory Committee, see http://www.fws.gov/habitatconservation/windpower/wind_turbine_advisory_committee.html.

Suggested Citation:"5 Environmental Impacts of Renewable Electricity Generation." National Academy of Sciences, National Academy of Engineering, and National Research Council. 2010. Electricity from Renewable Resources: Status, Prospects, and Impediments. Washington, DC: The National Academies Press. doi: 10.17226/12619.
×

has developed a set of reporting and permitting requirements that includes a notice of intent to conduct geothermal explorations, a geothermal drilling permit, and a monthly report of operations. California has its own geothermal permitting requirements, which are issued by the California Energy Commission (CEC, 2007).

Concentrating Solar Power

Permitting for CSP plants falls under general requirements for utility-scale solar projects. At present, CSP plants are the only utility-scale solar plants that have been built. Figure 2.3 shows that the U.S. resource base for CSP is located in the Southwest. As with geothermal energy, BLM manages much of this land and must issue permits for these plants. Because of concerns about the potentially large land resources needed for CSP projects, the BLM recently announced that it would produce a programmatic environmental impact statement to evaluate the environmental, social, and economic impacts associated with the 125 applications for solar energy development on BLM-managed public land (BLM, 2008). The announcement also called for a moratorium on the acceptance of any new applications for CSP development on BLM lands, but this policy was rescinded. In California, CSP plants greater than 50 MW in size require approvals from both the BLM and the CEC. To provide joint National Environmental Protection Act and California Environmental Quality Act review and a more efficient process, the BLM and the California Energy Commission have entered into a memorandum of understanding that contains projects of joint jurisdiction and provides a timeline for the joint review process.

Hydrokinetic (Tidal/Wave)

Hydrokinetic technologies are still very much in the pilot/demonstration stage. However, the Department of Energy, in conjunction with the Departments of Commerce and the Interior, is studying these issues at the request of the U.S. Congress8 and will issue a report that is scheduled for publication in July 2009. The goal of that report is to address the potential effects of marine and hydrokinetic energy projects, options to prevent adverse impacts, and potential roles and components for environmental monitoring and adaptive management. For the pur-

Suggested Citation:"5 Environmental Impacts of Renewable Electricity Generation." National Academy of Sciences, National Academy of Engineering, and National Research Council. 2010. Electricity from Renewable Resources: Status, Prospects, and Impediments. Washington, DC: The National Academies Press. doi: 10.17226/12619.
×

poses of the report, the term “marine and hydrokinetic renewable energy” refers to electrical energy that comes from a wide range of sources, including waves, tides, and currents in oceans, estuaries, and tidal areas; free-flowing water in rivers, lakes, and streams; free-flowing water in man-made channels; and differentials in ocean temperature (ocean thermal energy conversion). The report will not address energy from impoundments or other diversionary structures. Given the scarcity of real operational data, the report will not constitute a definitive impact assessment but will highlight areas of potential concern and areas of research and monitoring necessary to gain needed data.

Other Localized Environmental Impacts

A wide spectrum of other environmental impacts are not addressed by LCA and are not discussed here. They are nevertheless of potential importance and, in some particular locations, can include the impact that raises the greatest concern on the part of local populations and regulators. For example, all large power plants and transmission corridors require large tracts of land that must be kept at least partially clear of unwanted vegetation to maintain security, operational performance, and access for maintenance. To the extent that herbicides are used to clear and maintain areas for such sites, localized impacts will occur. Other technology-specific impacts associated with the use of renewable sources of electricity include the following:

  • Hydroelectric— Ecosystem changes including impacts on fish migration and mortality, habitat damage, degradation of water quality, and loss of sediment transport to delta systems (Goodwin et al., 2006; ORNL, 1993).

  • Solar (PV)—Mobilization of trace metals (Fthenakis, 2004; EPRI, 2003).

  • Wind—Potential climatic and meteorological perturbations, especially in the vicinity of large wind farms; noise pollution; aesthetic impacts; and bird and bat deaths (Keith et al., 2004; NRC, 2007; Morrison and Sinclair, 2004; GAO, 2005).

  • Biopower—Ground and surface water pollution from fertilizers and depletion of water for irrigation (cultivated biomass); removal of organic material from soil (waste biomass) (Marland and Obersteiner, 2008).

Suggested Citation:"5 Environmental Impacts of Renewable Electricity Generation." National Academy of Sciences, National Academy of Engineering, and National Research Council. 2010. Electricity from Renewable Resources: Status, Prospects, and Impediments. Washington, DC: The National Academies Press. doi: 10.17226/12619.
×
  • Geothermal—Metals (arsenic) and gas (H2S) from power plant operations, groundwater and surface water pollution, and potential for land subsidence and induced seismicity (DiPippo, 2007).

FINDINGS

Shown below in bold text are the most critical elements of the panel’s findings, based on its consideration of environmental impacts associated with generation of renewable electricity.

Energy is essential for modern life as we know it, and all energy use implies environmental impacts upstream of the point at which work is done. These impacts range widely in locus, intensity, and significance depending on the primary source of the energy and means used to deliver and convert it into useful work. Today’s electric generation and delivery system already imposes significant impacts on the environment at the local, regional, and global levels.

Understanding of these impacts has improved with advancements in environmental sciences and in analytical processes used to assess present and future environmental impacts. These improvements in the ability to understand environment impacts, including advances made in life-cycle assessment, have advanced society’s ability to improve the overall efficiency of energy resource decisions by improving the metrics that allow the comparison of impacts and potentially internalizing previously externalized costs.

Armed with better analytical tools and a greater appreciation of the systematic and long-term impacts of energy resource decisions, the basic question we face regarding environmental impacts, then, is the extent to which the continuation of impacts is acceptable to society, and more importantly, how the evaluation and consideration of potential environmental impacts should influence the policy that affects energy resource decisions. This panel’s high-level assessment leads to a number of important conclusions when considering scenarios involving significant increases in the deployment of renewable energy.

Renewable electricity technologies have inherently low life-cycle CO2emissions as compared to fossil-fuel-based electricity production, with most emissions occurring during manufacturing and deployment. Renewable electricity generation also involves inherently low or zero direct emissions of other regulated atmospheric pollutants, such as sulfur dioxide, nitrogen oxides, and mercury. Biopower is an exception because it produces NOx emissions at levels similar to those asso-

Suggested Citation:"5 Environmental Impacts of Renewable Electricity Generation." National Academy of Sciences, National Academy of Engineering, and National Research Council. 2010. Electricity from Renewable Resources: Status, Prospects, and Impediments. Washington, DC: The National Academies Press. doi: 10.17226/12619.
×

ciated with fossil-fuel power plants. Renewable electricity technologies (except biopower, high-temperature concentrated solar power, and some geothermal technologies) also consume significantly less water and have much smaller impacts on water quality than do nuclear, natural gas-, and coal-fired electricity generation technologies.

Because of the diffuse nature of renewable resources, the systems needed to capture energy and generate electricity (i.e., wind turbines and solar panels and concentrating systems) must be installed over large collection areas. Land is also required for the transmission lines needed to connect this generated power to the electricity system. But because of low levels of direct atmospheric emissions and water use, land-use impacts tend to remain localized and do not spread beyond the land areas directly used for deployment, especially at low levels of renewable electricity penetration. Moreover, some land that is affected by renewable technologies can also be used for other purposes, such as the use of land between wind turbines for agriculture.

However, at a high level of renewable technologies deployment, land-use and other local impacts would become quite important. The land-use impacts have caused, and will in the future cause, instances of local opposition to the siting of renewable electricity-generating facilities and associated transmissions lines. State and local government entities typically have primary jurisdiction over the local deployment of electricity generation, transmission, and distribution facilities. Significant increases in the deployment of renewable electricity facilities will thus entail concomitant increases in the highly specific, administratively complex, environmental impact and siting review processes. While this situation is not unique to renewable electricity, nevertheless, a significant acceleration of its deployment will require some level of coordination and standardization of siting and impact assessment processes.

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Suggested Citation:"5 Environmental Impacts of Renewable Electricity Generation." National Academy of Sciences, National Academy of Engineering, and National Research Council. 2010. Electricity from Renewable Resources: Status, Prospects, and Impediments. Washington, DC: The National Academies Press. doi: 10.17226/12619.
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×

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Suggested Citation:"5 Environmental Impacts of Renewable Electricity Generation." National Academy of Sciences, National Academy of Engineering, and National Research Council. 2010. Electricity from Renewable Resources: Status, Prospects, and Impediments. Washington, DC: The National Academies Press. doi: 10.17226/12619.
×

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Suggested Citation:"5 Environmental Impacts of Renewable Electricity Generation." National Academy of Sciences, National Academy of Engineering, and National Research Council. 2010. Electricity from Renewable Resources: Status, Prospects, and Impediments. Washington, DC: The National Academies Press. doi: 10.17226/12619.
×

ANNEX

TABLE 5.A.1 Estimates of Life-Cycle Greenhouse Gas Emissions in CO2 Equivalent (g/kWh) for Electricity Generation Technologies

Technology

CO2

Notes

Solar

 

 

 

39

Meier 2002. 8 kW, a-Si, 20% capacity, 30 yr lifetime. 157 m2. Colorado.

 

70 w/BES

Denholm 2004. Storage (10-50% capacity, 20 yr lifetime) added to Meier (2002) PV system with T&D.

 

53

Hondo 2005. 15% capacity, 30 yr lifetime. Rooftop 3 kW, p-Si, 10 MW/yr, system efficiency 10%.

 

44 or 26

Future scenarios Hondo 2005. 1% capacity, 30 yr lifetime. Case 1, p-Si w/production rate 1 GW/yr, 10% system efficiency. Case 2, a-Si, 1 GW/yr, 8.6% system efficiency.

 

55

European Commission 1997d. ExternE. Germany. 4.8 kW, mc-Si (technology from 1990), 25 yr lifetime.

 

51

European Commission 1997d. ExternE. Germany. 13 kW, mc-Si (technology from 1993), 25 yr lifetime.

 

43

Frankl et al. 2004. ECLIPSE. Italy. 1 kW, sc-Si, 25 yr lifetime, 13% conversion efficiency. Insolation 1740 kWh/m2/yr.

 

51

Frankl et al. 2004. ECLIPSE. Italy. 1 kW, mc-Si, 25 yr lifetime, 10.7% conversion efficiency. Insolation 1740 kWh/m2/yr.

 

44

Frankl et al. 2004. ECLIPSE. Italy. 1 kW, a-Si, 20 yr lifetime, 6% conversion efficiency. Insolation 1740 kWh/m2/yr.

 

45

Frankl et al. 2004. ECLIPSE. Italy. 1 kW, CIGS, 20 yr lifetime, 9% conversion efficiency. Insolation 1740 kWh/m2/yr.

 

66

Spitzley and Keoleian 2004. Data from Keoleian and Lewis 2003. 2 kW, a-Si. 20 yr lifetime. Detroit. 6% conversion efficiency. Insolation 1380 kWh/m2/yr (technology from 1900s).

 

44

Spitzley and Keoleian 2005. 2 kW, a-Si, 20 yr lifetime. Phoenix, Arizona.

 

71

Spitzley and Keoleian 2005. 2 kW, a-Si, 20 yr lifetime. Portland, Oregon.

 

35

Fthenakis et al. 2008. UTCE, ribbon Si, 11.5% conversion efficiency. (This case and the next seven all have the same assumptions for the following parameters: solar insolation of 1700 kWh/m2 per yr, performance ratio of .8, 30 yr lifetime. Did not include a case with crystal-clear project energy mix (natural gas and hydroelectric).)

 

43

Fthenakis et al. 2008. UTCE, mc-Si, 13.2% conversion efficiency.

 

44

Fthenakis et al. 2008. UTCE, s-Si, 14% conversion efficiency.

 

21

Fthenakis et al. 2008. UTCE, CdTe, 9% conversion efficiency.

 

44

Fthenakis et al. 2008. U.S., ribbon Si, 11.5% conversion efficiency.

 

52

Fthenakis et al. 2008. U.S., mc-Si, 13.2% conversion efficiency.

 

54

Fthenakis et al. 2008. U.S., s-Si, 14% conversion efficiency.

 

26

Fthenakis et al. 2008. U.S., CdTe, 9% conversion efficiency.

Suggested Citation:"5 Environmental Impacts of Renewable Electricity Generation." National Academy of Sciences, National Academy of Engineering, and National Research Council. 2010. Electricity from Renewable Resources: Status, Prospects, and Impediments. Washington, DC: The National Academies Press. doi: 10.17226/12619.
×

Technology

CO2

Notes

Wind

15

White 1998. 25 yr lifetime. Capacity 24% actual. Class 2 to 4 wind. Includes replacement of all blades. Note: White (2006) updated LCA on actual performance and found similar results—14. Wind results specific to site; hard to generalize and dependent on energy used to produce materials—in the United States, coal. Wind dismantling assumed to be same as construction. No recycling of metals taken into account.

 

24 w/PHS

Denholm 2004. PHS (10-50% capacity).

 

105 w/CAES

Denholm 2004. CAES (70-85% capacity, 30 yr lifetime).

 

29 (20 future)

Hondo 2005. 20% capacity both. 300 kW (future case 400 kW).

 

7

European Commission 1997d. ExternE. Germany. 0.25 MW, 20 yr lifetime. Recycle metals.

 

7

Chataignere et al. 2003. ECLIPSE. Europe. 0.6 MW, 20 yr lifetime. 1995-19980. technology, onshore.

 

12

Chataignere et al. 2003. ECLIPSE. Europe. 1.5 MW, 20 yr, onshore.

 

9

Chataignere et al. 2003. ECLIPSE. Europe. 2.5 MW, 20 yr, offshore.

 

14.5

European Commission 1997b. ExternE. Denmark. 0.5 MW turbine, onshore.

 

22

European Commission 1997b. ExternE. Denmark. 0.5 MW turbine, offshore.

 

8

European Commission 1997a. ExternE. Greece. Onshore.

 

9

Berry et al. 1998. 0.3 MW, onshore.

 

1.7

Spitzley and Keoleian 2005. Turbine data from Schleisner 2000. 30 yr lifetime,

 

25

MW, Class 6 wind, 36% capacity.

 

2.5

Spitzley and Keoleian 2005. Turbine data from Schleisner 2000. 30 yr lifetime,

 

25

MW, Class 4 wind, 24% capacity.

Biopower

49

Mann and Spath 1997. IGCC with 80% capacity, 30 yr lifetime. Assumes 95% carbon closure. Biopower from energy crops. 600 MW via several small plants.

 

−667

Spath and Mann 2004. Added CO2 capture and storage (CCS) to Mann and Spath (1997) example from above.

 

−410

Spath and Mann 2004. 0.6 GW direct-fire boiler with biomass from waste streams.

 

−1368

Spath and Mann 2004. 0.6 GW direct-fire boiler with biomass from waste streams with CCS.

 

18

European Commission 1997c. ExternE. France. Cropping.

 

15

Berry et al. 1998. Biopower source mainly willow and poplar. Lp IGCC.

 

49

Spitzley and Keoleian 2005. 30 yr lifetime. 113 MW, hybrid poplar based on Mann and Spath 1997. Lp IGCC.

40

Spitzley and Keoleian 2005. 20 yr lifetime. 75 MW, willow based on Heller et al. 2003. Hp IGGC. EPRI model.

39

Spitzley and Keoleian 2005. 20 yr lifetime. 113 MW, willow based on Heller et al. 2003. Lp IGGC. NREL model.

 

52

Spitzley and Keoleian 2005. 20 yr lifetime. 50 MW, willow based on Heller et al. 2003. Direct fire. EPRI model.

Suggested Citation:"5 Environmental Impacts of Renewable Electricity Generation." National Academy of Sciences, National Academy of Engineering, and National Research Council. 2010. Electricity from Renewable Resources: Status, Prospects, and Impediments. Washington, DC: The National Academies Press. doi: 10.17226/12619.
×

Technology

CO2

Notes

Geothermal

 

 

 

15

Hondo 2005. 60% capacity, 30 yr lifetime. Double flash type.

 

47–97*

Serchuk 2000. Only includes reservoirs emissions, not LCA.

 

91*

Bloomfield et al. 2003. A weighted average of all geothermal capacity (including binary plants with no CO2 emissions) per unit of electricity produced (not LCA).

 

122*

Bertani and Thain 2002. A weighted average of existing plant operation per unit of electricity produced not LCA. Actual range 4–740 g CO2 e/kWh from 85 plants in 11 countries.

Hydroelectric

 

 

 

20

Gagnon et al. (1997) present summary of a hydropower LCA survey using data from Finland, Canada, China, Japan, and Switzerland. Range in data 15 to 165 g CO2e/kWh; average 20 g CO2e/kWh. 100 yr lifetime. Includes data from river run and reservoir systems, alpine and prairie, small and large plants. Emissions very dependent on climate, topography, size of reservoir, construction materials, type of ecosystem flooded. Lowest case: 15 CO2e from large reservoir in cold climate where emissions from flooded biomass drop to 0 at year 50. Worst case was in Finland where peat land flooded. LCA includes plant construction and decaying biomass from reservoir. A Brazilian reservoir is mentioned that due to very large size and low generation capacity has an estimated CO2e of 237 (Fearnside’s estimate is even higher).

 

11

Hondo 2005. 45% capacity, 30 yr lifetime. Assumed river run w/small reservoir and did not include CO2 from flooded biomass.

 

26

Spitzley and Keoleian 2005. 50 yr lifetime. 1296 MW. Large reservoir type. Used data from Pacca and Horvath (2002).

Tidal

 

 

 

25–50

Preliminary, not rigorous. NOTE: production of steel for turbine is 25 g/kWh of CO2. ETSO (1999) from Carbon Trust website.

Suggested Citation:"5 Environmental Impacts of Renewable Electricity Generation." National Academy of Sciences, National Academy of Engineering, and National Research Council. 2010. Electricity from Renewable Resources: Status, Prospects, and Impediments. Washington, DC: The National Academies Press. doi: 10.17226/12619.
×

Technology

CO2

Notes

Coal

 

 

 

974

White 1998. 75% capacity, 40 yr lifetime. Average U.S. plant with SO2 control.

 

1050

Denholm 2004. With T&D based on White 1998.

 

975

Hondo 2005. 70% capacity, 30 yr lifetime. Average Japanese plant with SCR and FGD.

 

1042

Spath et al. 1999. Average, 360 MW, 60% capacity, 1995, 30 yr lifetime. FGC and ESP (same as baghouse?).

 

960

Spath et al. 1999. NSPS, 425 MW, 60% capacity, 1995, 30 yr lifetime. Same as average but with low NOx burners or staged combustion for increased removal of airborne pollutants.

 

757

Spath et al. 1999. Future LEBS, 404 MW, 60% capacity, 30 yr lifetime, 1995. Unspecified technologies used to decrease emissions.

 

681

Spath and Mann 2004. Biomass residue co-fired w/coal.

 

43

Spath and Mann 2004. Biomass residue co-fired w/coal w/CCS.

 

847

Spath and Mann 2004. Coal based on Hendriks 1994.

 

247

Spath and Mann 2004. Coal w/CCS.

 

861

Odeh and Cockerill 2008. IGCC.

 

167

Odeh and Cockerill 2008. IGCC w/CCS via selexol.

 

984

Odeh and Cockerill 2008. Subcritical pulverized coal with SRC, ESP, FGD.

 

879

Odeh and Cockerill 2008. Supercritical pulverized coal with SRC, ESP, FGD.

 

255

Odeh and Cockerill 2008. Supercritical pulverized coal (same as above) w/CCS via MEA.

Gas

 

 

 

469

Meier 2002. 75% capacity over 30 yr lifetime. Average 620 MW, NGCC. Assumed CH4 release rate of 1.4% (can range from 1 to 11%). Missouri plant.

 

500

Denholm 2004. NGCC w/T&D based on Meier 2002.

 

608

Hondo 2005. 70% capacity, 30 yr lifetime, LNG-fired.

 

518

Hondo 2005. 70% capacity, 30 yr lifetime, LNGCC.

 

499

Spath and Mann 2000. Average case NGCC with SCR.

 

245

Spath and Mann 2004. Added CCS to Spath and Mann 2000.

 

488

Odeh and Cockerill 2008. NGCC.

 

200

Odeh and Cockerill 2008. NGCC w/CCS via MEA.

Suggested Citation:"5 Environmental Impacts of Renewable Electricity Generation." National Academy of Sciences, National Academy of Engineering, and National Research Council. 2010. Electricity from Renewable Resources: Status, Prospects, and Impediments. Washington, DC: The National Academies Press. doi: 10.17226/12619.
×

Technology

CO2

Notes

Nuclear

 

 

 

15

White 1998. PWR. 75% capacity, 40 yr lifetime. Enrichment by gas centrifuge (not normally used in United States). Data for construction, operations, decommissioning, and waste disposal from others. Only fuel considered in land reclamation. Spent fuel disposal data 30 yrs old.

 

25

White (2006) updates value to reflect 100% enrichment by gas diffusion—25.

 

16

Denholm 2004. With T&D based on White 1998.

 

24 (22)

Hondo 2005. Disposal costs not included, only 50 yr dry storage for spent fuel. Assumes 67% enrichment in United States. Analysis very sensitive to enrichment conditions, e.g., values range from 30 to 10 g CO2/kWh if all U.S. versus all Japan enrichment. 70% capacity, 30 yr lifetime. Accounted for CH4 leakage during resource extraction. Did not include decommissioning land for mining and milling, just electricity to mine and mill. LLW stored w/o maintenance in near-surface waste disposal sites. Note: Future case 22 w/recycling includes HLW disposal but not disposal transport. Lower due to enrichment savings. Includes one-time MOX reprocessing of spent fuel.

 

20

European Commission 1997d. ExternE. Germany. Capacity 1375 MW. PWR.

 

3

Vattenfall 2004. Sweden. Industry EDP. PWR and BWR. Two sites. 85% capacity, 40 yr lifetime.

 

108

Storm van Leeuwen and Smith 2008. Average lifetime baseline case. 30 years at 82% capacity. Very detailed LCA.

 

24

Fthenakis and Kim 2007. Baseline case represents average United States.

 

55

Fthenakis and Kim 2007. Worst case, poor ores typical of Australia (0.05% U), most energy for enrichment from coal requiring 3000 kWh/SWU of energy, EIO method for construction.

 

16

Fthenakis and Kim 2007. Best case, rich Canadian ores (12.7% U), 20% energy for enrichment from coal, rest U.S. grid mix requiring 2400 kWh/SWU of energy, process analysis for construction.

Storage

 

 

PHS

 

 

 

3

Denholm and Kulcinski 2003. 74% efficient (?=capacity), 60 yr lifetime. Assumes dams and reservoirs permanent.

 

5.6

Denholm 2004. With T&D. 74% efficient, 60 yr lifetime. Assumes dams and reservoirs permanent.

CAES

 

 

 

291

Denholm and Kulcinski 2003. 40 yr lifetime.

 

292

Denholm 2004. With T&D. 65% efficient, 40 yr lifetime. Excludes primary electricity generation. Based on a 2.7 GW proposed facility in Ohio. Assumes negligible leaks, no energy intensive maintenance on cavern. Uses natural gas to compress air.

Suggested Citation:"5 Environmental Impacts of Renewable Electricity Generation." National Academy of Sciences, National Academy of Engineering, and National Research Council. 2010. Electricity from Renewable Resources: Status, Prospects, and Impediments. Washington, DC: The National Academies Press. doi: 10.17226/12619.
×

Technology

CO2

Notes

BES

 

 

 

80.5 Pb-acid

Denholm and Kulcinski 2003. 20 yr lifetime.

 

64.9 V redox

 

 

50.4 Pb-acid

Denholm 2004. With T&D. 20 yr lifetime, excludes the stored electricity. Assumes large system w/energy:power ratio of 8 hr. Pb-acid oversized 30% due to limited depth of discharge. VRB 75%, PSB 63%, Pb-acid 66% efficient.

 

32.6 PSB

 

 

40.2 V redox

 

Note: a-Si, amorphous silicon; BES, battery energy storage; CAES, compressed air energy storage; CCS, carbon capture and storage; CIGS, copper indium gallium selenide; FGC, flue gas clean-up; FGD, flue gas desulphurization; LEBS, low emission boiler system; mc-Si, multicrystalline silicon; MEA, monoethanolamine; PB-acid, lead acid; pc-Si, polycrystalline silicon; PHS, pumped hydro storage; PSB, sodium-bromide/sodium-polysulfide battery; sc-Si, single-crystalline silicon; SCR, selective catalytic reduction; T&D, transmission and distribution; V redox, vanadium acid; VRB, vanadium redox battery. All studies listed use LCA method. Not all studies are comparable. Denholm (2004) includes all life-cycle costs plus T&D emissions in LCA (most LCAs do not include T&D).

Suggested Citation:"5 Environmental Impacts of Renewable Electricity Generation." National Academy of Sciences, National Academy of Engineering, and National Research Council. 2010. Electricity from Renewable Resources: Status, Prospects, and Impediments. Washington, DC: The National Academies Press. doi: 10.17226/12619.
×

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Suggested Citation:"5 Environmental Impacts of Renewable Electricity Generation." National Academy of Sciences, National Academy of Engineering, and National Research Council. 2010. Electricity from Renewable Resources: Status, Prospects, and Impediments. Washington, DC: The National Academies Press. doi: 10.17226/12619.
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Suggested Citation:"5 Environmental Impacts of Renewable Electricity Generation." National Academy of Sciences, National Academy of Engineering, and National Research Council. 2010. Electricity from Renewable Resources: Status, Prospects, and Impediments. Washington, DC: The National Academies Press. doi: 10.17226/12619.
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Suggested Citation:"5 Environmental Impacts of Renewable Electricity Generation." National Academy of Sciences, National Academy of Engineering, and National Research Council. 2010. Electricity from Renewable Resources: Status, Prospects, and Impediments. Washington, DC: The National Academies Press. doi: 10.17226/12619.
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Suggested Citation:"5 Environmental Impacts of Renewable Electricity Generation." National Academy of Sciences, National Academy of Engineering, and National Research Council. 2010. Electricity from Renewable Resources: Status, Prospects, and Impediments. Washington, DC: The National Academies Press. doi: 10.17226/12619.
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Suggested Citation:"5 Environmental Impacts of Renewable Electricity Generation." National Academy of Sciences, National Academy of Engineering, and National Research Council. 2010. Electricity from Renewable Resources: Status, Prospects, and Impediments. Washington, DC: The National Academies Press. doi: 10.17226/12619.
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Suggested Citation:"5 Environmental Impacts of Renewable Electricity Generation." National Academy of Sciences, National Academy of Engineering, and National Research Council. 2010. Electricity from Renewable Resources: Status, Prospects, and Impediments. Washington, DC: The National Academies Press. doi: 10.17226/12619.
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Suggested Citation:"5 Environmental Impacts of Renewable Electricity Generation." National Academy of Sciences, National Academy of Engineering, and National Research Council. 2010. Electricity from Renewable Resources: Status, Prospects, and Impediments. Washington, DC: The National Academies Press. doi: 10.17226/12619.
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Suggested Citation:"5 Environmental Impacts of Renewable Electricity Generation." National Academy of Sciences, National Academy of Engineering, and National Research Council. 2010. Electricity from Renewable Resources: Status, Prospects, and Impediments. Washington, DC: The National Academies Press. doi: 10.17226/12619.
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Suggested Citation:"5 Environmental Impacts of Renewable Electricity Generation." National Academy of Sciences, National Academy of Engineering, and National Research Council. 2010. Electricity from Renewable Resources: Status, Prospects, and Impediments. Washington, DC: The National Academies Press. doi: 10.17226/12619.
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Suggested Citation:"5 Environmental Impacts of Renewable Electricity Generation." National Academy of Sciences, National Academy of Engineering, and National Research Council. 2010. Electricity from Renewable Resources: Status, Prospects, and Impediments. Washington, DC: The National Academies Press. doi: 10.17226/12619.
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Suggested Citation:"5 Environmental Impacts of Renewable Electricity Generation." National Academy of Sciences, National Academy of Engineering, and National Research Council. 2010. Electricity from Renewable Resources: Status, Prospects, and Impediments. Washington, DC: The National Academies Press. doi: 10.17226/12619.
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A component in the America's Energy Future study, Electricity from Renewable Resources examines the technical potential for electric power generation with alternative sources such as wind, solar-photovoltaic, geothermal, solar-thermal, hydroelectric, and other renewable sources. The book focuses on those renewable sources that show the most promise for initial commercial deployment within 10 years and will lead to a substantial impact on the U.S. energy system.

A quantitative characterization of technologies, this book lays out expectations of costs, performance, and impacts, as well as barriers and research and development needs. In addition to a principal focus on renewable energy technologies for power generation, the book addresses the challenges of incorporating such technologies into the power grid, as well as potential improvements in the national electricity grid that could enable better and more extensive utilization of wind, solar-thermal, solar photovoltaics, and other renewable technologies.

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