America's Energy Future Technology and Transformation (2009) / Chapter Skim
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6 Renewable Energy
6 Renewable Energy
Pages 271-330
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From page 271... ...
Rep resenting about 71 percent of the electric power derived from renewable sources, hydropower generated 6 percent of the electricity -- almost 250,000 GWh out of a total of 4.2 million GWh -- produced by the electric power sector in 2007.1 The nonhydropower sources of renewable electricity together contributed 2.5 percent of the 2007 total. Within this group, biomass electricity generation (called 1The electric power sector includes electricity utilities, independent power producers, and large commercial and industrial generators of electricity.
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From page 272... ...
The largest growth in the use of renewable resources for electricity genera tion is currently in wind power and, to a lesser extent, in solar power. Wind power technology, having matured over the last two decades, now accounts for an increasing fraction of total electricity generation in the United States.
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From page 273... ...
Federal policies are also contributing to this era of strong growth in renewable-energy development. The major incentive, particularly for wind power, is the Federal Renewable Electricity Production Tax Credit (referred to simply as the PTC)
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From page 274... ...
Figure 6.1 shows the impact of the PTC on the price of wind power versus that of natural-gas-fired electricity, though it should be noted that other current electricity sources, such as coal, hydropower, and nuclear, have lower operating costs than do natural gas combined-cycle plants.
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From page 275... ...
The United States has significant wind energy resources in particular; Figure 6.2 shows their distribution across the country. The total estimated electri Wind Resource Wind Power Wind Speed Wind Speed Power Potential Density at 50 m at 50 m at 50 m Class W/m2 m/s mph 2 Marginal 200–300 5.6–6.4 12.5–14.3 3 Fair 300–400 6.4–7.0 14.3–15.7 4 Good 400–500 7.0–7.5 15.7–16.8 5 Excellent 500–600 7.5–8.0 16.8–17.9 6 Outstanding 600–800 8.0–8.8 17.9–19.7 7 Superb 800–1600 8.8–11.1 19.7–24.8 FIGURE 6.2 U.S wind resource map showing various wind power classes.
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From page 276... ...
This potential resource base is about half of the current electrical power use in the United States, and significant offshore wind energy resources also exist and increase the wind resource base considerably. The solar energy resource also is very large indeed.
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From page 277... ...
. Only a fraction of rooftops and other lands can be developed economically at present for solar-based electricity generation, however; it is the economics of solar technologies, not the size of the potential resource, that
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From page 278... ...
There is some potential for expanding electricity production from the hydrothermal resources and thus affecting regional electricity generation -- for example, a regional study of known hydrothermal resources in the western states found that 13 GW of electric power capacity exists in identified resources within this region (WGA, 2006) -- but in general, the resources are too small to have a major overall impact on total electricity genera tion in the United States.
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From page 279... ...
Awareness of such factors is important in developing effective policies at the state and federal level to promote the use of renewable resources for generation of electricity. RENEWABLE TECHNOLOGIES A renewable electricity-generation technology harnesses a naturally existing energy flux, such as wind, sun, or tides, and converts that flux into electricity.
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From page 280... ...
; (3) oppor tunities for achieving economies of scale are greater at the manufacturing stage than at the generating site -- larger-generation units do not necessarily reduce the average cost of electricity generation as much as they do for coal-fired or nuclear plants; and (4)
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From page 281... ...
It should be noted that future capital costs also will be greatly influenced by global supply and demand for wind turbines. Some of these issues are discussed in the section titled "Deployment Potential" later in this chapter, as well as in the report by the Panel on Electricity from Renewable Resources (NAS-NAE-NRC, 2009)
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From page 282... ...
rotors • Advanced materials • Improved structural aerodynamic design • Active controls • Passive controls • Higher tip speed/lower noise levels Reduced energy losses and • Reduced blade-soiling losses +7/+5/0 0/0/0 improved availability • Damage-tolerant sensors • Robust control systems • Prognostic maintenance +8/+4/0 –11/–6/+1 Drive train • Fewer gear stages or direct-drive (gear boxes, generators, and • Medium/low speed generators power electronics) • Distributed gearbox topologies • Permanent-magnet generators • Medium-voltage equipment • Advanced gear-tooth profiles • New circuit topologies • New semiconductor devices • New materials (gallium arsenide [GaAs]
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From page 283... ...
This type of solar cell is attractive because of its low cost and simplicity in manufacturing, but the device's efficiency and stability will need to be closely monitored before largescale deployment is possible. In organic solar cells, which also are in the early developmental stage, the sunlight creates an exciton, which separates into an electron on one side and a hole on the other side of a material interface within the device.
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From page 284... ...
Concentrating Solar Power CSP systems -- sometimes referred to as solar thermal -- employ optics to con centrate beam radiation, which is the portion of the solar spectrum that is not scattered by the atmosphere. The concentrated solar energy produces high temperature heat, which can be used to generate electricity or to drive chemical reactions to produce fuels (syngas or hydrogen)
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From page 285... ...
For the long term, thermochemical production of fuels using CSP is a promising mechanism for storing solar energy. Geothermal Geothermal electricity is currently produced by conventional power-generating technologies utilizing hydrothermal resources (hot water or steam)
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From page 286... ...
Significant chal lenges include a general lack of experience in drilling to depths approaching 10 km, even in oil and natural gas exploration, and the need to enhance heat transfer performance for lower-temperature fluids in power production. Another challenge is to improve reservoir-stimulation techniques so that sufficient con nectivity within the fractured rock can be achieved; in that way, the injection and production well system may realize commercially feasible and sustainable produc tion rates (MIT, 2006)
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From page 287... ...
As a result, the costs of their commercial-scale operation are unknown. Biopower Biopower is the generation of electricity by extracting the solar energy stored in biomass -- that is, by burning it.
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From page 288... ...
rarely reach 50 MW in size, whereas conventional coal-fired plants typically range from 100 MW to 1500 MW. Similarly, power plants based on landfill gas -- a methane-containing product of the anaerobic decomposition of solid waste -- have capacities in the 0.5 MW to 5 MW range, whereas those operating on natural gas may be some 100 times larger, in the 50 MW to 500 MW range.
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From page 289... ...
In addition, the long-term potential of biomass is currently limited by the low conversion efficiency of the photosynthesis process. For more details on the timing, costs, and impediments to the development and deployment of all of these technologies, the reader is referred to the report by the Panel on Electricity from Renewable Resources (NAS-NAE-NRC, 2009)
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From page 290... ...
With conventional hydropower's contribution remaining at current levels, total electricity generation from renewables could account for more than 25 percent by 2035. The significant issues raised in reaching this level of renewables penetration are discussed later in this chapter and in NAS-NAE NRC (2009)
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From page 291... ...
Beyond the continuing needs for improvements in cost, scalability, and performance of renewable electricity-generation technologies, some combination of intelligent two-way electric grids, cost-effective methods for large-scale and distributed storage (either direct electricity energy storage or generation of chemical fuels) , widespread implementation of rapidly dispatchable fossil electricity technologies (for backup)
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From page 292... ...
Because some of the technologies that tap renewable resources to produce electricity must operate under temporal and spatial constraints, special consider ation of systems-integration and transmission issues will be needed in order for the penetration of renewable electricity to grow. Such considerations become espe cially important at sizable penetrations (greater than ~20 percent)
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From page 293... ...
For intermittent technologies such as concentrating solar thermal, solar PV, and wind power, the capacity factor can vary considerably, depending on the quality of the resource (e.g., hours and intensity of sunlight or speed and constancy of wind) , which varies by location.
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From page 294... ...
Limited Portfolio Onshore wind DOE (2008a) , Black & DOE 20% Wind Energy 1630 Veatch (2007)
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From page 295... ...
295 Renewable Energy Variable Total O&M/ Fixed Levelized O&M Cost of Energy Fuel Costs Capacity Factor Capital Cost ($/MWh)
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From page 296... ...
, tend to be more optimistic than those from other sources; the SEIA and EERE estimates reflect how full funding of renewable-energy research at the DOE and elsewhere is expected to affect the future costs of renewable electricity generation. Thus these estimates tend to represent aspirations.
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From page 297... ...
Generally, these studies have found that, when the average cost of wind generation is about $80/MWh, the impact of grid integration costs is estimated to be less than 15 percent where wind produced 20 percent or less of total electricity generation. Renewable Supply Curve: Example for Wind Power Single national-average estimates of LCOEs fail to communicate how such costs vary with the quality of the resource.
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From page 298... ...
FIGURE 6.5 Supply curve for wind accounting for transmission costs but no integration costs. Sources: DOE, 2008a; Black & Veatch, 2007.
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From page 299... ...
Supply-side utility-based renewable-electricity technologies, such as concen trated solar power, wind, and biomass, must compete on a cost basis with other technologies for utility electricity generation. But the future of distributed renew ables generation, such as from residential PV, will depend more on policy, on how costs compare to the retail price of power delivered to residential or other custom ers, on whether prices fully reflect variations in cost over the course of the day, and on whether the full costs of using fossil-fuel generation -- particularly their externalities, such as CO2 emissions -- are incorporated into prices.
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From page 300... ...
. Much higher values are found for fossil-fuel sources of electricity, upward of 500 g CO2 eq per kilowatt-hour for natural gas and 1000 g CO2 eq per kilowatt-hour for coal, though the relative advantage of renewables would be significantly reduced by adding carbon capture and storage (CCS)
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From page 301... ...
On the other hand, because renewable-energy resources are more diffuse than fossil and nuclear energy resources, the land areas needed to collect renewable energy and convert it to electricity are, on an energy-equivalent basis, much larger than those of fossil and nuclear. Spitzley and Keoleian (2005)
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From page 302... ...
Findings: Impacts Renewable electricity-generation technologies have inherently low life-cycle emis sions of carbon dioxide and other atmospheric pollutants compared to those of fossil-fuel-based technologies. Most of the CO2 emissions from renewable electricity generation are incurred during the manufacturing and deployment stages.
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From page 303... ...
There are constraints on such growth, how ever, which are related to restricted supplies of raw materials, limitations on man ufacturing capacity, competition from other construction projects, and workforce shortages. These constraints have the potential to impede or even derail the large scale deployment and integration of renewable electricity-generation technologies.
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From page 304... ...
. Consider also the limitations on production capacity for wind turbines.
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From page 305... ...
Renewable Electricity Integration Because renewable resources such as solar and wind have temporal (including short- and long-term) and spatial variability, they introduce intermittencies that
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From page 306... ...
. These studies also show that electricity storage is not needed for integrating intermittent renewable energy sources as long as they do not account for more than 20 percent of total electricity generation.
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From page 307... ...
The key risks engendered by this pervasive regime relate to whether future policies will conform to reasonable expectations. For example, Figure 6.8 shows the impact that an off-and-on policy can have on wind power investment: the intermittency of the PTC for wind power generation has led to large fluctuations in demand for wind turbines and in annual installations of new wind power capacity.
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From page 308... ...
Significant increases in renewable electricity-generation deployments are also dependent on concomitant improvements in several areas, including labor and workforce development, transmission and distribution grids, and the frameworks and regulations under which the electric systems are operated. One important ele ment is that accommodation of the intermittent characteristics of wind and solar electricity into the overall system is critical for large-scale deployment.
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From page 309... ...
DEPLOYMENT SCENARIOS Scenarios of how renewables might significantly increase their contribution to the electricity system provide a quantitative and conceptual framework to help describe and assess issues related to greatly increasing the scale of renewables deployment. Such scenarios are a primary way of quantifying the materials and manufacturing requirements, human and financial resources, and environmental impacts associated with greatly expanding renewables' electricity generation.
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From page 310... ...
electricity generation by 2030. The DOE developed this scenario in collaboration with the National Renewable Energy Lab oratory (NREL)
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From page 311... ...
Under the scenario, wind power would produce about 1.2 million GWh/yr out of a total electricity generation of 5.8 million GWh. Figure 6.9 shows the amounts of annual installed capacity needed to meet 300 GW by 2030, starting with the approximately 12 GW of total wind power capacity that was available in 2006; the scenario limited the annual capacity increase to 20 percent.
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From page 312... ...
Even assuming that growth outside the United States is more modest, this scenario would still require a continued large expansion of the manufacturing base. Addi tionally, the scenario assumes that wind turbines have an average life of 25 years; sustaining annual installations at approximately 16 GW/yr beyond 2030 would be needed to accommodate repowering of aging turbines and meeting increasing electricity demand to continue the 20 percent wind generation level (Laxson et al., 2006; DOE, 2008a)
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From page 313... ...
However, the impacts on NOx and SOx emissions are expected to be less than what would be estimated from simply assuming that electricity generation from fossil fuels is replaced with a non-carbon-emitting technology such as wind power. Emissions of both NOx and SOx are subject to caps on emissions; thus emissions reductions from wind-generated electricity may be reallocated to other plants.
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From page 314... ...
. The impact on the energy mix is largest for natural gas, with the 20 percent wind sce nario displacing about 50 percent of electricity-utility natural gas consumption (DOE, 2008a)
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From page 315... ...
As with the DOE's 20 percent wind scenario, the JCSP study did not envision the need for electricity storage to be necessary for integrating 20 percent wind power into the study region. Using Multiple Renewables to Reach 20 Percent Electricity Generation The 20 percent wind scenario discussed in the previous section shows the potential for renewables to increase electricity generation and the scale and integration associated with rapid expansion of wind power only.
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From page 316... ...
The mix of renewable resources shown in Table 6.5 is not presented as the opti mal set to meet the target of obtaining 20 percent of total electricity generation from additions of renewable resources. This set is merely one mix that could be considered, given the available resource base, readiness of renewable-electric ity technologies, and what might be practicable for an aggressive but achievable expansion of market penetration.
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From page 317... ...
However, simply continuing the level of deployment for wind that occurred in 2008 and assuming a capacity factor of 35 percent would have wind power contributing almost 14 percent of total projected electricity demand in 2035.8 But, as emphasized in the 20 percent wind scenario, greatly enhancing the penetration of renewable electricity will require large increases over current levels of manufacturing, employment, investment, and installation. The numbers from the 20 percent wind study demonstrate the potential challenges and opportunities: 100,000 wind turbines, up to $100 billion in additional capital costs and transmission upgrades, thousands of miles of new transmission lines, 100,000-plus jobs, and an 800-million-tonne annual reduction in CO2 emissions.
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From page 318... ...
Solar Thermal Applications for distributed solar thermal include water heating, space heating and cooling, and heat for industry and agriculture. Because the solar collector does not rely on concentrating the sun's energy and can use both direct and diffuse radia tion, distributed solar thermal systems are applicable to the entire United States.
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From page 319... ...
The Interstate Renewable Energy Council and the North Carolina Solar Energy Center maintain a database of state incentives for distributed renewable energy.12 The use of solar thermal systems to yield space heating and cooling in residential and commercial buildings could provide a greater reduction of fossil fuels than do water heaters, but at present these systems are largely an untapped opportunity. Recently there has been limited deployment of liquid-based solar collectors for radiant floor-heating systems and solar air heaters, but the challenge with these applications is the relatively large collector area required in the absence of storage.
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From page 320... ...
installed capacity of direct-use systems is 620 MWthermal(MWt) .13 Municipalities and smaller communities provide district heating by circulating hot water from aquifers through a distribution pipeline to the points of use, though this applica tion of geothermal energy remains modest, with systems in only seven states.14 The barriers to increased penetration of direct geothermal heating and cooling systems are the high initial investment costs and the challenges associated with locating and developing appropriate sites.
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From page 321... ...
2008 Build ings Energy Data Book, downloadable at buildingsdatabook.eere.energy.gov/. This figure does not include biomass that is used in electricity generation.
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From page 322... ...
CONCLUSION A future characterized by a large penetration of renewable electricity represents a paradigm shift from the current electricity generation, transmission, and dis tribution system. There are many reasons why renewable electricity represents such a shift, including the spatial distribution and intermittency of some renew able resources, as well as issues related to greatly increasing the scale of deploy ment.
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From page 323... ...
Nevertheless, the promise of renewable resources is that they offer significant potential for low-carbon generation of elec tricity from domestic sources of energy that are much less vulnerable to fuel cost increases than are other electricity sources. Overall success thus depends on having technology, capital, and policy working together to enable renewable-electricity technologies to become a major contributor to America's energy future.
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From page 324... ...
2003. Net Energy Balance and Greenhouse Gas Emissions from Renewable Energy Storage System.
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From page 325... ...
1997a. External Costs of Electricity Generation in Greece.
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From page 326... ...
2001. Biomass for Electricity Generation.
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From page 327... ...
2002. Life-Cycle Assessment of Electricity Generation Systems and Applications for Climate Change Policy Analysis.
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From page 328... ...
Presentation to the Panel on Electricity from Renewable Resources, Washington, D.C., December 7. Smith, J.C., and B
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From page 329... ...
Presentation at the fourth meeting of the Panel on Electricity from Renewable Resources, Washington, D.C., March 11, 2008. Wiser, R., and G
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