U.S. Renewable Electricity Generation: Resources and Challenges
Congressional research reportAug 5, 2011
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U.S. Renewable Electricity Generation:
Resources and Challenges
(name redacted)
Analyst in Energy Policy
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Section Research Manager
August 5, 2011
Congressional Research Service
7-....
www.crs.gov
R41954
CRS Report for Congress
Prepared for Members and Committees of Congress
U.S. Renewable Electricity Generation: Resources and Challenges
Summary
The United States faces important decisions about future energy supply and use. A key question is
how renewable energy resources might be used to meet U.S. energy needs in general, and to meet
U.S. electricity needs specifically. Renewable energy sources are typically used for three general
types of applications: electricity generation, biofuels/bioproducts, and heating/cooling. Each
application uses different technologies to convert renewable energy sources into usable products.
The literature on renewable energy resources, conversion technologies for different applications,
and economics is massive. This report focuses on electricity generation from renewable energy
sources. In 2010, renewable sources of energy were used to produce almost 11% (7% from
hydropower and 4% from other renewables) of the 4 million gigawatthours of electricity
generated in the United States.
This report provides a summary of U.S. electricity generation potential from wind, solar,
geothermal, hydroelectric, ocean-hydrokinetic, and biomass sources of renewable energy. The
focus of this report is twofold: (1) provide an assessment of U.S. renewable electricity generation
potential and how renewables might satisfy electric power sector demand, and (2) discuss
challenges, issues, and barriers that might limit renewable electricity generation deployment.
Data sources from 15 different organizations were reviewed to derive estimates of electricity
generation potential. One key finding is that there exists no uniform national assessment of
renewable electricity generation potential. No standard methods or set of assumptions are used to
estimate renewable electricity generation potential. So even existing assessments for individual
energy sources are difficult to compare objectively. In order to compare various estimates on an
equivalent basis, CRS engaged experts in each renewable energy resource area to help normalize
electricity generation potential estimates into a common metric: gigawatthours per year.
After surveying, researching, and normalizing all of the third-party electricity generation
estimates, results indicate that renewable energy sources may, in principle, have the potential to
satisfy a large portion of U.S. electricity demand. However, a number of potential barriers to
large-scale deployment exist, including cost, power system integration, intermittency and
variability, land requirements, transmission access, possible limits to the availability of key
materials and resources, certain environmental impacts, specialized infrastructure requirements,
and policy issues. Ultimately, the amount of renewable electricity generation in the U.S. may be
dependent on the ability to address these deployment barriers. The Energy Information
Administration projects that U.S. renewable electricity generation will increase from 11% today
to between 14% and 15% in 2035.
As Congress considers policy options associated with increasing renewable electricity generation,
policy makers may assess potential benefits such as emissions reduction, job creation, and global
competitiveness, along with possible risks and consequences such as electricity cost and price
increases, electricity delivery reliability, and environmental impacts associated with large-scale
deployment of renewable electricity generation technologies.
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Contents
Introduction...................................................................................................................................... 1
Renewable Electricity Concepts and Units ...................................................................................... 3
Definition and Characteristics of Renewable Electricity........................................................... 3
Renewable Electricity Terminology and Units .......................................................................... 4
Measuring Energy: Fossil versus Renewable ...................................................................... 4
Expressing Renewable Electricity Generation Potential: Watthour .................................... 5
Authoritative Data Sources for Renewable Energy Resources ................................................. 5
U.S. Renewable Electricity Use and Potential ................................................................................. 8
Summary of Current U.S. Renewable Electricity...................................................................... 8
Future Renewable Electricity Generation Potential .................................................................. 8
Wind ........................................................................................................................................ 12
U.S. Resource Estimates ................................................................................................... 12
Technology and Cost Considerations ................................................................................ 14
Solar......................................................................................................................................... 15
U.S. Resource Estimates ................................................................................................... 15
Technology and Cost Considerations ................................................................................ 17
Geothermal .............................................................................................................................. 19
U.S. Resource Estimates ................................................................................................... 19
Technology and Cost Considerations ................................................................................ 21
Hydroelectric ........................................................................................................................... 22
U.S. Resource Estimates ................................................................................................... 22
Technology and Cost Considerations ................................................................................ 24
Ocean and Hydrokinetic .......................................................................................................... 25
U.S. Resource Estimates ................................................................................................... 25
Technology and Cost Considerations ................................................................................ 26
Biomass ................................................................................................................................... 27
U.S. Resource Estimates ................................................................................................... 27
Technology and Cost Considerations ................................................................................ 29
Challenges for Renewable Energy ................................................................................................. 30
Cost .......................................................................................................................................... 30
Levelized Cost of Energy (LCOE) .................................................................................... 30
Comparing Fossil and Renewable Energy Costs............................................................... 33
Power System Integration........................................................................................................ 34
Intermittency and Variability ................................................................................................... 35
Renewable Energy Footprint and Land-Use............................................................................ 35
Transmission Availability and Access ..................................................................................... 37
Materials and Resources .......................................................................................................... 38
Environmental Impact and Aesthetic Concerns....................................................................... 38
Infrastructure Requirements .................................................................................................... 39
Technology Development and Commercialization ................................................................. 39
Policy and Regulatory Challenges........................................................................................... 39
Related Issues ................................................................................................................................ 40
Energy Efficiency and Curtailment ......................................................................................... 40
Biofuels ................................................................................................................................... 42
Additional Considerations for Renewable Electricity in the United States ................................... 43
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The Scale of U.S. Energy Consumption .................................................................................. 43
Relationship Between Renewable Electricity and Imported Energy ....................................... 44
International Renewable Electricity Markets .......................................................................... 44
Future Trends in Renewable Electricity......................................................................................... 45
Conclusion ..................................................................................................................................... 46
Figures
Figure 1. U.S. Primary Energy Flow by Supply Source and Demand Sector, 2009 ........................ 1
Figure 2. Supply Sources for U.S. Electric Power Sector................................................................ 2
Figure 3. U.S. Electricity Generation from Various Renewable Sources, 2009 .............................. 8
Figure 4. U.S. Onshore Wind Energy Resources, 80 Meter Turbine Height ................................. 13
Figure 5. U.S. Offshore Wind Energy Resources, 90 Meter Turbine Height................................. 14
Figure 6. U.S. Concentrating Solar Resource ................................................................................ 16
Figure 7. U.S. Photovoltaic Solar Resource .................................................................................. 18
Figure 8. Geothermal Resource of the United States ..................................................................... 21
Figure 9. Existing and Potential Hydropower Projects in the Lower 48 United States ................. 24
Figure 10. U.S. Wave Energy Resources ....................................................................................... 26
Figure 11. U.S. Biomass Resource Availability ............................................................................. 29
Figure 12. EIA’s Levelized Cost of Energy (LCOE) Estimates for New Plants ............................ 32
Figure 13. NREL Supply Curve for Near-Hydrothermal Field
Enhanced Geothermal Systems (EGS) Resource ....................................................................... 33
Figure 14. Land-Use Intensity for Various Forms of Energy Production ...................................... 37
Figure 15. Total U.S. Energy Consumption and Energy Intensity, 1975-2009 .............................. 42
Figure 16. Total Net Renewable Electricity Generation, 2009 ...................................................... 45
Tables
Table 1. U.S. Renewable Electricity Generation Potential—Information Sources.......................... 6
Table 2. Summary of U.S. Renewable Electricity Resources and Challenges .............................. 10
Table 3. U.S. Geothermal Electricity Generation Potential ........................................................... 19
Table 4. U.S. Ocean Energy Resource Estimates .......................................................................... 25
Table 5. Annual U.S. Biomass Electricity Generation Potential .................................................... 28
Table 6. Total U.S. Electricity Generation, By Source, 2009 ........................................................ 43
Table 7. Existing Renewable Energy Capacities at the End of 2010 ............................................. 45
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Contacts
Author Contact Information........................................................................................................... 47
Acknowledgments ......................................................................................................................... 47
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Introduction
The U.S. energy sector is large and complex. Multiple energy sources, including fossil, nuclear,
and several renewable sources, are used to produce energy products for multiple demand sectors
(transportation, electricity, industrial, and residential/commercial). Today, fossil fuels are the
dominant sources of energy, comprising 83% of total U.S. primary energy supply. Renewable
energy sources, which can be used to generate electricity, produce liquid transportation fuels, and
provide heating and cooling for industrial and residential/commercial sectors, provided 8% of
total U.S. primary energy supply in 2009 (see Figure 1).
Figure 1. U.S. Primary Energy Flow by Supply Source and Demand Sector, 2009
(Values are in Quadrillion Btu and Percentage of Total)
Source: CRS adaptation of Energy Information Administration, Annual Energy Review 2009,
http://www.eia.doe.gov/totalenergy/data/annual/pdf/pecss_diagram_2009.pdf
The largest source of energy demand in the United States is the electric power sector, which
consumed just over 40% of total U.S. energy supply in 2009. The U.S. electric power sector
generates approximately 4 million gigawatthours of electricity each year. Like the total U.S.
energy sector, electricity generation is dominated (89%) by fossil fuels and nuclear power.
Renewable electricity generation, including hydro, wind, solar, geothermal, and biomass,
contributed 11% of total U.S. electric power in 2009 (Figure 2).1 Most U.S. renewable generation
1
Energy Information Administration, Annual Energy Review 2009, http://www.eia.doe.gov/totalenergy/data/annual/
(continued...)
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comes from conventional hydropower, which has limited growth potential. Other renewable
electricity sources constitute about 4% of U.S. generation, but have been growing more rapidly.
Figure 2. Supply Sources for U.S. Electric Power Sector
Source: Energy Information Administration, Annual Energy Review 2009, http://www.eia.doe.gov/totalenergy/
data/annual/pdf/pecss_diagram_2009.pdf.
The purpose of this report is to analyze the prospects, opportunities, and challenges for renewable
energy sources to increase their contribution to the electric power sector.
There is growing interest in increasing the amount of renewable electricity generation to reduce
the amount of fossil fuel consumption for U.S. electric power. That interest is driven by concerns
about greenhouse gas emissions, the realization that economically recoverable fossil fuel supplies
are ultimately finite, and the desire to position the United States as a global leader for renewable
energy technology and manufacturing.2 These concerns are counter-balanced by the fact that
fossil fuel electricity generation has long been—and generally continues to be—the least
expensive form of electricity generation, by the fact that the United States has access to
considerable resources of coal and natural gas for electricity generation, and from the economic
and cultural inertia of the existing infrastructure in place for coal and natural gas to be used in
large quantities for electricity generation. Renewable electricity generation provides two
advantages when compared to fossil generation: (1) it relies on energy sources that may not
(...continued)
pdf/pecss_diagram_2009.pdf.
2
Decreasing U.S. reliance on foreign oil is not included here because the focus of this report is on electricity
generation. Petroleum contributed 1% of electricity generation in 2009. Based on current U.S. energy infrastructure,
adding additional renewable electricity generation capacity will have a negligible, if any, impact on U.S. oil import
dependency. However, electrification of the transportation fleet could potentially result in decreasing total U.S. oil
demand. Renewable electricity generation combined with electric vehicle market penetration could potentially result in
lower oil import requirements.
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decline over time, and (2) it produces little or no net greenhouse gas emissions or other pollutants
during use.3 However, renewable electricity generation does have liabilities and implementation
challenges that will be further discussed in this report.
This report addresses two fundamental questions about U.S. renewable electricity generation
potential: (1) How much renewable electricity generation might be possible in the United States?4
and (2) What technical, operational, and economic challenges might renewables encounter when
considering large-scale deployment for electricity generation?
Renewable Electricity Concepts and Units
Definition and Characteristics of Renewable Electricity
Renewable electricity is derived from renewable energy sources that “regenerate and can be
sustained indefinitely.”5 This report does not use the term “clean energy” or “alternative energy,”
which are terms used by some to include renewable energy resources plus other sources that may
emit little or no carbon dioxide during use, such as nuclear plants and coal-fired power plants
equipped with carbon capture and sequestration capabilities. A discussion of biomass used to
generate electricity is included, but biofuels are mentioned only briefly. This study is focused on
wind, solar, hydroelectric, geothermal, biomass, and ocean/hydrokinetic energy sources used to
generate electricity.
“Renewable energy” sources for electricity generation are often discussed as if they were a single
entity, but renewable energy sources are more numerous and variable than fossil energy sources.
Fossil fuels comprise oil, natural gas, and coal. The three major types of fossil fuels are extracted
from the earth’s crust by drilling or mining. Each of these fuels has very high energy density and
is used primarily through combustion to exploit the heat produced. Renewable energy sources are
more numerous and diverse and, thus, harnessing renewable energy requires a number of different
technologies. Some of the distinctive characteristics of renewable energy are:
•
Renewable energy sources for electricity generation are numerous. Sun, wind, flowing
water in streams, flowing water in tidal channels, wave action in oceans, the earth’s
natural heat, biological materials, and others comprise the current portfolio of renewable
energy sources, and additional renewable sources may be identified in the future.
•
Each renewable energy source may be exploited in multiple ways to generate electricity
using different technologies and materials. For example, the energy of the sun may be
used by concentrating the energy to generate steam that drives electric turbines
(concentrating solar power), or the energy of the sun may be converted directly to
3
Biomass and biofuels release CO2 during combustion, but are considered by some to have zero net emissions because
the CO2 released was taken up from the atmosphere to grow the plants. However, there is debate about biomass being
considered carbon neutral. For more information see CRS Report R41603, Is Biopower Carbon Neutral?, by (name
redacted).
4
CRS is aware that the National Renewable Energy Laboratory (NREL) is in the process of publishing an analysis
about U.S. renewable electricity generation potential. However, the NREL work was not available to influence the
research for this report.
5
Energy Information Administration, http://www.eia.gov/energyexplained/index.cfm?page=renewable_home.
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electricity using semiconducting materials (photovoltaics). Furthermore, photovoltaic
electricity may be produced using solar panels that consist of crystalline silicon, cadmium
telluride, or other materials, and each material has unique characteristics.
•
Renewable energy sources for electricity generation are naturally dispersed with
relatively low energy densities. Fossil energy sources are typically concentrated as liquids
or solids by millions of years of natural heating and pressure processes, which result in
relatively high energy density that is accessible in wells or mines. In contrast, renewable
energy sources are typically diffuse and require multiple technologies and management
systems to gather and concentrate the resources.
•
Each renewable electricity generation project/installation can vary in size. Renewable
electricity generation systems are being installed in large, megawatt-scale projects that
feed electricity into the electric grid for consumption along with electricity from other
sources. In fact, the largest electric power plant in the United States is a hydroelectric
facility, Grand Coulee Dam, which has a capacity of 7.08 GW.6 At the same time,
individual homes are being powered by small, kilowatt-scale rooftop solar panels. Also,
wind turbines may be large, up to 5 megawatt (MW) utility-scale turbines, or small,
approximately 5 kilowatt (kW) residential scale units.
Renewable Electricity Terminology and Units
This section defines terms and units used to describe and quantify renewable energy sources, and
electricity generation potential from these sources, and how renewable energy might be compared
to other forms of energy. Although this report focuses on renewable energy, discussions of fossil
fuel units and consumption are included to facilitate comparisons with renewable forms of
energy.
Measuring Energy: Fossil versus Renewable
Fossil fuels have traditionally been measured and marketed in the units of the physical material—
barrels (42 gallons) of oil, short tons (2,000 pounds) of coal, or cubic feet of natural gas—
transported to the point of end use. The use of volume or weight for measuring fossil fuels makes
it challenging to compare the energy content among fossil fuels, and also contributes to the
difficulty in clearly communicating the amounts of renewable energy that will be needed to
replace fossil fuels. Each fossil fuel unit of measure has a corresponding energy content, which is
typically expressed in terms of British Thermal Units (Btu).7
With the exception of biomass (typically measured in tons), each renewable energy source has its
own unit of measure that may not be expressed as volume or weight. For example, wind energy is
typically expressed in terms of wind speed (reported as meters per second); solar energy is
typically expressed in terms of daily insolation (reported as kilowatthours per meter-square per
day); hydroelectric is derived from flowing water, typically expressed in terms of water flow rate
6
Energy Information Administration, http://www.eia.gov/state/state-energy-profiles-analysis.cfm?sid=WA.
A British thermal unit (Btu) is a measure of the energy (heat) content of fuels. It is the quantity of energy (heat)
required to raise the temperature of 1 pound of liquid water by 1°F at the temperature that water has its greatest density
(approximately 39°F), http://www.eia.doe.gov/energyexplained/index.cfm?page=about_btu.
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and velocity. In order to estimate annual electricity generation potential from renewable energy
sources, experts must make assumptions about conversion equipment efficiencies and annual
hours of operation.
Expressing Renewable Electricity Generation Potential: Watthour
Renewable electricity generation potential is typically expressed in terms of watthours (see text
box below). A watthour (Wh) is a unit of electrical energy that can be generated, distributed, and
consumed. A watthour can also be purchased and/or sold. For example, a residential electricity
bill is typically calculated by multiplying the number of kilowatthours (kWh) consumed by a
residence times the rate per kilowatthour charged by the electric power provider.8 In 2009, U.S.
total electricity net generation was approximately 4 million gigawatthours.9 For the purpose of
this report, renewable electricity generation potential, for all renewable energy sources, is
expressed in terms of annual gigawatthours (GWh).
Power versus energy: What’s the difference between a watt and a watthour?
Some energy reports provide statistics in units of power while other reports use units of energy. Power and energy
are related, but they are not the same thing. Energy equals power multiplied by the amount of time the power is
applied. Conversely, power is the rate at which energy is produced or consumed. Power is measured in watts, energy
is measured in watthours. An electrical generator with 50 megawatts of power (or nameplate capacity) would
generate 50 megawatthours of electrical energy for each hour it operates. The power capacity of a generator conveys
only the size of the device, thus, when it’s not operating, a generator does not produce any energy even though the
power capacity remains the same. Power capacity is a critical variable when selecting a device to do a specific job, but
the energy produced by the device depends on the amount of time it operates. The report examines total energy
production with little regard to the size of the devices that produce it.
Authoritative Data Sources for Renewable Energy Resources
Various renewable electricity resource estimates for the United States are calculated by different
institutions that use different processes, methodologies, and assumptions. No uniform
methodologies exist for estimating and comparing the resource potential of different forms of
renewable energy that might be used to generate electricity (see text box below).
Traditional fossil fuel energy resource assessments are conducted through detailed geologic
studies and the application of rigorously vetted methodologies. In contrast, most renewable
electricity generation resource estimates are subject to the unique methods and assumptions of the
organization conducting the assessment. Fossil energy resource estimates typically classify
resources into categories such as: resource base, technically recoverable, economically
recoverable, and reserves.10 In principle, renewable energy resources should be measurable using
similar analysis of the natural processes (wind, solar insolation, water flow, geothermal heat,
etc.), adjusted for the effectiveness of the respective energy extraction technologies, and then
couched in economic terms based on economic conditions and parameters.
8
A kilowatthour is equal to one thousand watthours. 1 kWh = 3,412 Btu.
A gigawatthour is equal to one billion watthours.
10
For more information on U.S. fossil fuel resources, see CRS Report R40872, U.S. Fossil Fuel Resources:
Terminology, Reporting, and Summary, by (name redacted), (name redacted), and (name redacted).
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In reality, it is very difficult, time consuming, and expensive to collect high quality data for wind,
solar, stream flow, geothermal and biomass energy at a fine scale over the entire nation on an
hourly, daily, or seasonal basis, as appropriate. In addition, the basic physics are different for
extracting energy from solar, wind, hydro, geothermal, and biomass sources. Those physical
differences give rise to different technologies, and many renewable energy technologies exhibit
dramatically different performance according to geographic location and time of day or time of
year. Therefore, estimating the amount of each type of renewable energy that is available to the
nation is a challenging task. Examination of the literature reveals that estimates of available
renewable energy resources vary widely. Attempting to compare estimates for different types of
renewable energy multiplies those challenges.
The most reliable data for the various renewable energy sources come from national data
collection programs from federal agencies. For example, the National Renewable Energy
Laboratory, funded by the Department of Energy and its partners, operates programs designed to
collect such data and has worked to identify the areas within the United States that are optimally
suited for exploitation of various renewable energy sources. Other federal and state agencies,
federal labs, and academic institutions also collect, analyze, and report renewable energy resource
data. These data and estimates change over time as data collection technologies advance and
understanding of the natural processes improves. Nevertheless, comparing renewable energy
assessments from different sources is difficult, and a complete and comprehensive assessment of
all available renewable energy resources for the nation does not yet exist. Collection of high
quality data on renewable energy sources at a fine scale over broad ranges of time and geography
will likely be an ongoing need for the nation. Table 1 summarizes sources of information
reviewed for this report.
Table 1. U.S. Renewable Electricity Generation Potential—Information Sources
Renewable Electricity Resource
Sources of Data Reviewed
Wind
National Renewable Energy Laboratory (NREL); American Wind Energy
Association (AWEA); Department of Energy (DOE) Office of Energy
Efficiency and Renewable Energy (EERE).
Solar
NREL; Solar Energy Industries Association (SEIA); DOE EERE.
Hydro
DOE EERE, Oak Ridge National Laboratory (ORNL); Idaho National
Laboratory (INL); National Hydropower Association (NHA).
Geothermal
United States Geological Survey (USGS); NREL; Massachusetts Institute of
Technology (MIT); Geothermal Energy Association (GEA).
Ocean-Hydrokinetic
Electric Power Research Institute (EPRI); DOE EERE; New York
University; Ocean Renewable Energy Coalition (OREC).
Biomass
DOE EERE; United States Department of Agriculture (USDA); NREL,
Biomass Power Association (BPA).
Source: CRS.
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How Much Renewable Energy Is Available? It Depends ... And It Can Change
The overriding goal of this report is to provide Congress with accurate, comparable, and current U.S. renewable
electricity resource estimates using currently available data. Answering the question “How much renewable electricity
is possible in the United States?” is the primary objective. However, the answer to this key question is “it depends,
and it will very likely change over time.”
No centralized authoritative body or organization currently exists to develop and enforce standards for renewable
electricity resource assessment methodologies and assumptions used to calculate estimates. Renewable electricity
resource estimates come from multiple organizations. As a result, renewable electricity generation potential estimates
are derived using different methodologies and different assumptions which, in turn, produce different estimates.
Estimates for renewable electricity generation potential in the United States depend on several factors such as the
methodology used to calculate the estimates and certain assumptions that can have a major impact on the calculation
results. With regard to methodologies used, resource estimates surveyed for this report came from several different
organizations that include federal labs, industry organizations, and academic institutions. Each organization typically
uses a unique methodology to calculate resource estimates. Therefore, comparing all of these estimates on an
“apples-to-apples” equivalent basis is a challenge.
Key assumptions made for calculating renewable electricity generation potential can also have a major impact on
resulting estimates. Geothermal electricity is a good example of how assumptions can impact renewable electricity
generation estimates. Both USGS and MIT have published reports that estimate the amount of electricity generation
potential from U.S. geothermal resources.11 However, MIT estimates are more than 10 times larger than those from
USGS. Two key assumptions explain most of this discrepancy: (1) Resource depth: The USGS geothermal study only
considered geothermal potential at depths of 6 kilometers below the earth’s surface whereas the MIT report
considered depths of 10 kilometers, and (2) Which U.S. states were included: The USGS study only included 14
western states, Alaska, and Hawaii, while the MIT study included all 50 states. Thus, understanding assumptions for
understanding and comparing the various resource potential estimates is critical.
Understanding certain exclusions for the various resource potential estimates is also important. Many of the studies
surveyed for this report excluded certain areas from development based on several factors (national parks, urban
areas, etc.). However, the types of exclusions and the constraints that result from exclusions vary. Comparing wind
estimates and hydroelectricity estimates is one example. Wind electricity generation potential estimates exclude
certain land areas. After these exclusions are taken into account, the NREL study referenced for this report assumes
that wind projects can be built anywhere as long as the wind resource is large enough to meet certain electricity
production levels. Hydroelectricity generation estimates, on the other hand, also include certain land area exclusions
but apply additional filters such as the location being within one mile of a road and a transmission line. If identical
exclusions were applied to all renewable electricity generation resource assessments, resource potential results may
be quite different.
Further, estimates for renewable electricity generation potential in the U.S. will likely change over time as resource
estimate methodologies improve, renewable electricity generation technologies are developed and commercialized,
and better information about the magnitude and quality of renewable energy resources is made available. As a result,
estimates of renewable electricity generation potential could either go up or down in the future.12
11
“Assessment of Moderate- and High-Temperature Geothermal Resources of the United States,” U.S. Geological
Survey, 2008, available at http://pubs.usgs.gov/fs/2008/3082/pdf/fs2008-3082.pdf, and “The Future of Geothermal
Energy: Impact of Enhanced Geothermal Systems (EGS) on the United States in the 21st Century,” Massachusetts
Institute of Technology, 2006, available at http://geothermal.inel.gov/publications/future_of_geothermal_energy.pdf.
12
Resource estimate changes are not unique to renewable energy. Fossil fuel estimates typically change in response to
technology, economic conditions, improved data sets, etc. Shale gas in the United States is an example of how resource
estimates can change over time.
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U.S. Renewable Electricity Use and Potential
This section provides a brief overview of current U.S. renewable electricity generation, followed
by a series of discussions of specific renewable electricity technologies. Current electricity
generation, estimated potential generation, and deployment challenges are discussed for wind,
solar, geothermal, hydroelectric (hydro), ocean-hydrokinetic, and biomass energy sources.
Summary of Current U.S. Renewable Electricity
In 2009 renewable energy resources provided 11% of U.S. electricity net generation. Renewable
electricity was derived from wind, solar, geothermal, hydro, and biomass energy sources. The
largest source of renewable electricity was hydro. Wind and biomass each contributed between
1% and 2% of total U.S. electricity net generation. Solar and geothermal electricity generation
contributed relatively small amounts to the renewable electricity portfolio mix (Figure 3).
Figure 3. U.S. Electricity Generation from Various Renewable Sources, 2009
(Percentage of each renewable source)
Source: Energy Information Administration, Annual Energy Review 2009, http://www.eia.doe.gov/totalenergy/
data/annual/pdf/pecss_diagram_2009.pdf.
Notes: Renewable electric power percentages may not add to 11% because of independent rounding error.
Future Renewable Electricity Generation Potential
The following sections discuss the estimated range of electricity generation potential from wind,
solar, geothermal, hydro, ocean-hydrokinetic, and biomass renewable energy sources. A
discussion of technology and cost considerations is presented for each respective renewable
source of electricity. As discussed above, comparing renewable electricity generation resource
estimates is a challenging task. The approach used to derive the resource estimate range for each
technology is described in the footnotes to each renewable energy source section. Table 2
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provides a summary of U.S. renewable electricity generation potential, based on the research and
analysis performed for this report, current and projected renewable electricity generation
potential, cost of electricity estimates, and a summary of key challenges for each renewable
energy source. As the table shows, renewable electricity generation potential is compared to 2009
total U.S. net generation of approximately 4 million gigawatthours (GWh). This approach was
used in order to indicate the maximum electricity generation contribution that might be available
from each renewable energy source. Furthermore, the reader is advised that levelized cost of
energy (LCOE) estimates presented in Table 2 only reflect electricity costs associated with
capacity additions in EIA’s Annual Energy Outlook 2011. For more information, see the
“Levelized Cost of Energy (LCOE)” section below.
Research and analysis conducted for this report indicates that renewable energy sources may,
theoretically, have the potential to satisfy a large portion of U.S. electric power needs. However,
numerous technical, operational, economic, and practical challenges will likely be encountered,
which may ultimately limit the potential contribution of renewable electricity generation. These
challenges are discussed in a following section. Furthermore, while the potential for renewable
electricity generation in the country is vast, EIA Annual Energy Outlook 2011 reference case
projections indicate that renewables will contribute between 14% and 15% of total U.S.
electricity generation by 2035.13 Also, the quality of resources estimates is different for each
renewable technology, and these estimates may change as new data are collected and new
assessments are conducted. The current estimates represent a snapshot in time and must be
continually updated as additional data become available.
13
For more information about the Annual Energy Outlook reference case see, Energy Information Administration,
“Annual Energy Outlook 2011,” Report Number: DOE/EIA-0383(2011), April 2011, available at http://www.eia.gov/
forecasts/aeo/pdf/0383(2011).pdf.
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Table 2. Summary of U.S. Renewable Electricity Resources and Challenges
Electricity Generation
Potential
Electricity Potential (GWh/yr)
Winda
Low
32,500,000
High
61,400,000
Solarb
Geothermal
Hydro
Ocean-Hydrokinetic
Biomassc
Low
4,000,000
High
56,300,000
Low
927,791
High
36,991,864
Low
558,145
High
613,333
Low
287,850
High
2,161,350
Low
125,730
High
1,428,780
100%
>100%
23%
>100%
14%
16%
7%
55%
3%
36%
* Total estimated resource potential
% of 2009 total U.S. generation
>100%
>100%
Current and Forecasted Generation
2009 Generation (GWh)
73,886
% of 2009 total U.S. generation
1.87%
$82 to $349
EIA LCOEd $/MWh
891
0.02%
$159 to $642
15,009
0.38%
$92 to $116
273,445
6.92%
$59 to $121
not available
not available
not available
54,493
1.38%
$99 to $134
3,970
49,190
310,590
not available
47,440
0.09%
1.06%
6.70%
not available
1.02%
Yes
Yes
Yes
- Currently the highest
cost source of renewable
electricity
No
Yes
Yes
- Enhanced geothermal
system (EGS) costs are
estimates only; NREL
indicates EGS LCOE could
be as high as $1,000/MWh
No
- Geothermal electricity
production can be
predictable and may
operate at high capacity
factors
Yes
- EGS, the largest potential
source of geothermal
electricity, technology is
not yet commercially
available
- Specialized drilling
equipment may be
No
Yes
No/Yes
- One of the oldest and
lowest-cost sources of
renewable electricity
- Emerging small/low-head
hydro costs unknown
Yes
- Hydropower resource
can vary based on annual
rain/snow fall
Yes
Yes
Yes
- Actual cost of ocean
and hydrokinetic
electricity is unknown
No
Yes
Yes
- Cost of electricity
can be impacted by
logistics and feedstock
quality
Yes/No
- Wave energy
resources can vary
based on the amount
of wind; tidal energy
may be predictable
Yes
- Ocean and
hydrokinetic energy
technologies are
considered “emerging"
with no commercially
available electricity
generation
No
- Biomass electricity
plants can operate at
high capacity factors
and may provide
baseload power
No/Yes
- Biomass combustion
technology might be
considered
commercial
- Some technical
issues (tar production,
equipment fouling,
** Only for capacity additions
forecasted in AEO 2011
2035 Generation (GWh)
160,880
*** EIA AEO 2011 forecast
(reference case)
% of 2035 total est. generation
3.48%
Deployment Challenges, Issues, and Barriers?
Power System Integration
Yes
Transmission
Yes
Cost
No/Yes
- Onshore wind costs
are in the range of fossil
electricity costs
- Offshore costs are
higher
Intermittency/Variability
Yes
- Wind resources can
vary on an hourly, daily,
and/or annual basis
Technology
CRS-10
No/Yes
- Onshore wind
technology considered
commercial
- Offshore wind may
require further
technology development
to operate in harsh
Yes
- Cloud coverage and
other weather events can
degrade solar technology
performance; solar energy
not available at night
Yes
- Emerging PV technologies
that may improve
efficiencies & reduce costs
- Some CSP technologies
may require further
engineering, development,
and demonstration before
Yes
- Small and low-head/lowpower technologies are
being developed and
matured but some are
not yet commercially
available
U.S. Renewable Electricity Generation: Resources and Challenges
Electricity Generation
Potential
Winda
Solarb
Geothermal
Low
High
being commercial
Low
required
Environmental Impact
Yes
- Land use, habitat and
scenic disturbance,
noise, and bird mortality
are potential
environmental issues
associated with wind
projects
Yes
- Water use requirements
for some solar thermal
technologies
- Land use and associated
habitat disturbance
- Mobilization of trace
metals
Yes
- Water use; discharge of
metals and toxic gas
- Ground/surface water
pollution
- Land subsidence and
seismicity
Yes
- Ecosystem changes; fish
migration and mortality
- Habitat damage; water
quality degradation
Infrastructure
Yes
- Offshore wind may
require specialized
vessels, portside
infrastructure, under-sea
transmission, etc.
Yes
- High volumes of steel,
concrete, and rare-earth
metals may be needed
to support large scale
wind deployment
Unknown
Information regarding
potential infrastructure
issues not available
Unknown
Information regarding
potential infrastructure
issues not available
Unknown
Information regarding
potential infrastructure
issues not available
Yes
- High volumes of steel and
concrete may be needed
to support large-scale
deployment of utility-scale
solar; silicon, tellurium,
cadmium, silver, and other
commodities may be
required for large-scale PV
deployment
Unknown
Information regarding
potential materials and
resources issues not
available
Unknown
Information regarding
potential materials and
resources issues not
available
Source: CRS; Various sources as identified and referenced in the respective sections of this report.
a. Includes both onshore and offshore wind.
b. Includes both photovoltaic and concentrating solar.
c. Does not include liquid biofuels used for transportation.
d. LCOE = Levelized Cost of Energy.
CRS-11
Low
Ocean-Hydrokinetic
Low
High
ocean environment
Materials and Resources
High
Hydro
High
Low
technologies
High
Yes
- Alteration of
currents and waves;
alteration of sediment
disposition; habitat
impacts; noise;
electromagnetic fields;
toxicity of lubricants
and other fluids; animal
injury from moving
parts; degradation of
water quality
Yes
- Specialized
infrastructure may be
needed to install and
maintain operational
projects
Yes
- Materials that can
operate for long
periods of time in a
corrosive ocean
environment may need
to be developed
Biomassc
Low
High
etc.) may have to be
addressed
Yes
- Biomass combustion
for electricity
generation emits
NOx, CO2, and other
emissions
- Land use/change
associated with
biomass production
- Carbon neutrality of
biomass combustion is
a possible issue
Yes
- Logistics
infrastructure may be
needed to gather and
process biomass
material
Yes
- Economical
electricity generation
from biomass may
require adequate
biomass resources
within a defined
geographic area
U.S. Renewable Electricity Generation: Resources and Challenges
Wind
U.S. Resource Estimates
U.S. wind energy resource estimates are highly dependent on certain assumptions used to
calculate them, and users of those estimates should pay careful attention to the underlying
assumptions. Turbine height and capacity factor assumptions can have major impacts on wind
resource estimates. For example, winds are generally stronger at greater heights above the
ground. As a result, wind resource estimates at 100 meters are likely to be greater than those at 50
meters.
Wind energy resources in the United States are typically categorized as either “onshore” or
“offshore.” According to National Renewable Energy Laboratory (NREL) estimates, onshore
wind electricity generation potential for the 48 contiguous United States ranges from 22.5 million
gigawatthours to 46.9 million gigawatthours annually.14 Wind resources can vary state by state
and region by region. Based on NREL estimates, the largest onshore U.S. wind energy resources
are located in the middle of the country (see Figure 4).
14
In February 2010, NREL and AWS Truepower released estimates for windy land area and wind energy potential for
the 48 contiguous United States. A revision to these estimates that includes data for Alaska and Hawaii was released in
April 2011. This is the first comprehensive update of wind energy potential since 1993. The NREL AWS study
evaluates three gross (no system losses included) capacity factor assumptions (30%, 35%, and 40%) and two hub
heights (80 meters and 100 meters). NREL/AWS also considered certain land area exclusions such as parks, urban
areas, and others. Study results, maps, and data tables available at http://www.windpoweringamerica.gov/
wind_maps.asp.
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U.S. Renewable Electricity Generation: Resources and Challenges
Figure 4. U.S. Onshore Wind Energy Resources, 80 Meter Turbine Height
Source: http://www.windpoweringamerica.gov/wind_maps.asp.
NREL has also calculated estimates for U.S. offshore wind energy resources.15 Based on NREL
estimates, offshore wind energy resource potential may range between 10 million GWh and 14.5
million GWh annually.16 Figure 5 illustrates how offshore wind energy resources vary by
location. However, in its February 2011 National Offshore Wind Strategy report, the DOE EERE
states that “the offshore wind resource is not well characterized.”17 This uncertainty indicates that
additional work may be needed to more accurately assess U.S. offshore wind potential.
15
NREL’s offshore wind study does not take into account any potential area exclusions. The offshore wind study also
does not include estimates for Florida, Mississippi, Alabama, or Alaska. For more information see Marc Schwartz,
Donna Heimiller, Steve Haymes, and Walt Musial, “Assessment of Offshore Wind Energy Resources for the United
States,” National Renewable Energy Laboratory, June 2010, available at http://www.windpoweringamerica.gov/pdfs/
offshore/offshore_wind_resource_assessment.pdf.
16
Gigawatthour estimates for offshore wind energy resources were calculated by CRS by applying average capacity
factor assumptions of 30% and 40% to megawatt installed capacity estimates from NREL.
17
“A National Offshore Wind Strategy: Creating an Offshore Wind Energy Industry in the United States,” U.S.
Department of Energy, Energy Efficiency and Renewable Energy, February 2011, available at
http://www1.eere.energy.gov/windandhydro/pdfs/national_offshore_wind_strategy.pdf.
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U.S. Renewable Electricity Generation: Resources and Challenges
Figure 5. U.S. Offshore Wind Energy Resources, 90 Meter Turbine Height
(Excluding Alaska)
Source: http://www.windpoweringamerica.gov/windmaps/offshore.asp.
Technology and Cost Considerations
Onshore wind energy conversion technology is generally considered to be commercially
available18 and many projects are able to attract debt and equity investment capital for project
development. General Electric and Siemens were the top two manufacturers of wind turbines
installed in the U.S. during 2010.19 Typical wind turbines have a rated capacity between 1
megawatt and 3 megawatts, and the general industry trend is to continue increasing the size and
capacity of individual wind turbines in order to operate at greater heights (taller towers) and
realize economies of scale by generating more watthours from a single unit. Offshore wind
energy technology faces some technical challenges associated with operating in a corrosive
marine environment and installation of equipment at various water depths. The Department of
Energy (DOE) operates a Wind Power Program aimed at wind research and development needs.20
18
For the purpose of this report, “commercially available” refers to renewable electricity generation technologies that
have achieved an adequate amount of operational time that allows for performance validation, accurate reliability
assessments, and an understanding of actual operations and maintenance requirements. These commercialization
parameters are typically validated by an independent engineering firm. This independent validation is typically
necessary for technologies, and projects that use these technologies, to obtain debt and equity for project development.
Furthermore, commercially available technologies typically have an established supply chain of companies that can
provide equipment to meet certain project and technology performance specifications.
19
American Wind Energy Association (AWEA) U.S. Wind Industry Annual Market Report Year Ending 2010.
20
More information on DOE’s Wind Power program is available at http://www1.eere.energy.gov/windandhydro/
wind_power.html.
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U.S. Renewable Electricity Generation: Resources and Challenges
The cost of wind-generated electricity can vary based on a number of technology, performance,
operational, and financial factors. These factors are discussed in the “Levelized Cost of Energy”
section below. Assumptions made for these factors can result in significant differences among
cost-of-electricity estimates. In its Annual Energy Outlook 2011, EIA estimates onshore wind
electricity costs to range from $82-$115 per megawatthour (MWh) and offshore electricity costs
between $187-$349 per MWh.21 Figure 12 provides a comparison of costs for conventional
(fossil and nuclear) and renewable electricity generation.
Solar
U.S. Resource Estimates
Every U.S. locale receives sunlight during a calendar year, of course, but the amount of radiation
that reaches a given point at a particular time can vary based on factors that might include
geography (including latitude), time of day, season, landscape, and weather.22 Two authoritative
sources for U.S. solar resources are the National Solar Radiation Database (NSRDB), and NREL
and State University of New York at Albany (SUNYA) satellite-derived solar resources.23
Quantifying solar resource data, in terms of annual electricity generation potential, is complicated
by several factors.24 First, two different methods are used for capturing and converting solar
energy into electricity: (1) concentrating solar power (CSP), and (2) photovoltaic (PV) solar
power.25 Second, solar radiation has different components that may be better suited for different
collector types.26 Third, different system configurations are used to collect data and calculate
solar resource estimates.27 Finally, different types of CSP and PV technologies, with different
cost, efficiency, and performance characteristics, are available for solar energy conversion.28
21
Levelized Cost of New Generation Resources in the Annual Energy Outlook 2011, U.S. Energy Information
Administration, available at http://www.eia.gov/oiaf/aeo/electricity_generation.html.
22
An overview of solar resources is provided by the Department of Energy at http://www.eere.energy.gov/basics/
renewable_energy/solar_resources.html.
23
For a comprehensive summary of current solar resource assessment information, see “Report to Congress on
Renewable Energy Resource Assessment Information for the United States,” U.S. Department of Energy, Office of
Energy Efficiency and Renewable Energy, 2011.
24
The approach used to quantify annual solar electricity generation potential was based on input from experts at NREL
and Sandia National Laboratory. If different methodologies for calculating solar resource potential, such as quantifying
the total amount of solar radiation exposure on the surface area of the United States, are employed, results may be
different (likely much higher) than the summary data presented in this section.
25
For an overview of CSP technology see http://www.eere.energy.gov/basics/renewable_energy/csp.html. For an
overview of PV technology see http://www.eere.energy.gov/basics/renewable_energy/photovoltaics.html.
26
Three solar radiation components are typically measured and reported: (1) direct beam solar radiation, (2) diffuse
solar radiation, and (3) global solar radiation (the sum of direct beam and diffuse). CSP systems are able to use only
direct beam solar radiation. PV systems are able to use both direct beam and diffuse radiation. More detail regarding
solar radiation components is available at http://www.eere.energy.gov/basics/renewable_energy/solar_resources.html.
27
Solar energy system configurations may include (1) south-facing flat-plate collectors at various tilt angles, (2) oneaxis flat-plate tracking, (3) two-axis flat-plate tracking collectors, and (4) direct-beam one and two-axis tracking
concentrating collectors. For more information regarding solar system configurations see, D. Renne, R. George, S.
Wilcox, T. Stoffel, D. Myers, and D. Heimiller, “Solar Resource Assessment,” National Renewable Energy Laboratory,
February 2008, available at http://www.nrel.gov/docs/fy08osti/42301.pdf.
28
For a description of various CSP technologies, see http://www.solarpaces.org/CSP_Technology/csp_technology.htm.
For a description of various PV technologies, see http://solarbuzz.com/going-solar/understanding/technologies.
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U.S. Renewable Electricity Generation: Resources and Challenges
CSP resources vary throughout the country, with most of the highest quality resource located in
the southwestern United States (see Figure 6). CSP electricity generation is typically better suited
for large-scale (greater than 10 MW) power generation projects. NREL and Sandia National
Laboratories estimate that U.S. CSP electricity generation potential is approximately 16.3 million
GWh.29 This estimate is the result of applying a set of filters to existing CSP resource data in
order to calculate CSP electricity generation potential.30 NREL and Sandia CSP estimates include
electricity generation potential in seven U.S. states.31
Figure 6. U.S. Concentrating Solar Resource
Source: National Renewable Energy Laboratory (NREL), available at http://www.nrel.gov/gis/images/
map_csp_national_lo-res.jpg.
Notes: Annual average direct normal solar resource data are shown. The data for Hawaii and the 48 contiguous
states are 10km satellite modeled dataset (SUNY/NREL, 2007) representing data from 1998-2005. The data for
Alaska are a 40 km dataset produced by the Climatological Solar Radiation Model (NREL, 2003); kWh/m2/Day =
kilowatthour per square meter per day.
Photovoltaic resources also vary throughout the country and, much like CSP, the highest quality
PV resources are located in the southwestern United States (see Figure 7). PV systems offer
29
Tom Mancini, “CSP Overview,” Sandia National Laboratories.
Ibid. Filters applied to derive these analysis results include (1) sites with >6.75 kwh/m2/day direct normal insolation,
(2) excluding environmentally sensitive lands, major urban areas, etc., (3) removing land with slope >1%, 4) only
including contiguous areas >10km2. Changing these filters (i.e. reducing the direct normal insolation threshold) would
yield different results.
31
Ibid. Arizona, California, Colorado, Nevada, New Mexico, Texas, and Utah.
30
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U.S. Renewable Electricity Generation: Resources and Challenges
flexibility in terms of project size and can be used for residential, commercial, and utility-scale
applications. As of July 2011, estimates of the technically available and economically recoverable
solar photovoltaic resource, in terms of annual GWh, were not available. However, previous work
by NREL provides some indication about solar generation potential. NREL researchers analyzed
land-use requirements for generating 100% of U.S. electricity and estimated that 0.6% of total
U.S. land area would be needed to satisfy current demand load using a “base system
configuration.”32 NREL has also estimated land-use requirements for a variety of other system
configurations.33 Calculating total PV generation based on this NREL analysis is somewhat
complicated, but it may be reasonable to assume that solar PV could theoretically generate 10
times the amount of current U.S. demand, although realizing this amount of electricity generation
may be limited by several factors, particularly cost and power system integration.34 Extrapolating
from the NREL analysis, U.S. annual solar PV generation potential may be equal to
approximately 40 million GWh. NREL has also evaluated the generation potential of residential
and commercial rooftop PV systems and estimates that, under a base-case scenario,
approximately 819,000 GWh of electricity could be generated each year using existing rooftop
space.35
Technology and Cost Considerations
The most commonly used CSP technology in the United States is the parabolic trough. Of the 509
megawatts of U.S. installed CSP capacity, approximately 98% uses parabolic trough technology.36
Crystalline silicon is the most commonly used PV technology.37 While some CSP and PV
technologies might be considered commercially available, there are a number of research and
development activities within CSP and PV markets.38 Generally speaking, most CSP and PV
R&D work is focused on improving system-level efficiencies and reducing system costs. Storage,
demand response, and other “smart-grid” technologies may further enable large-scale solar
deployment.39
32
P. Denholm and R. Margolis, “Land-use requirements and the per-capita solar footprint for photovoltaic generation
in the United States,” Energy Policy 36, 3531-3543, 2008.
33
For more information see P. Denholm and R. Margolis, “Impacts of Array Configuration on Land-Use Requirements
for Large-Scale Photovoltaic Deployment in the United States,” NREL, Conference paper presented at SOLAR 2008—
American Solar Energy Society (ASES), May 3-8, 2008.
34
Telephone interview with Robert Margolis at NREL.
35
P. Denholm and R. Margolis, “Supply Curves for Rooftop Solar PV-Generated Electricity for the United States,”
National Renewable Energy Laboratory, November 2008, available at http://www.nrel.gov/docs/fy09osti/44073.pdf.
36
The remaining 2% of installed capacity consists of power tower, linear fresnel, and dish-stirling technologies. See
Tom Mancini, “CSP Overview,” Sandia National Laboratories.
37
For more information about crystalline solar cells, see Y.S. Tsuo, T.H. Wang, and T.F. Ciszek, “Crystalline-Silicon
Solar Cells for the 21st Century,” NREL, May 1999, available at http://www.nrel.gov/docs/fy99osti/26513.pdf.
38
More information about DOE CSP R&D programs and projects is available at http://www1.eere.energy.gov/solar/
csp_program.html. More information about DOE PV R&D programs and projects is available at
http://www1.eere.energy.gov/solar/photovoltaics_program.html.
39
For more information on electrical energy storage, see “Energy Storage: Program Planning Document,” Department
of Energy, Office of Electricity Delivery and Energy Reliability, February 2011, available at
http://www.oe.energy.gov/DocumentsandMedia/OE_Energy_Storage_Program_Plan_Feburary_2011v3.pdf.
For more information on “smart-grid,” see “The Smart Grid: An Introduction,” Department of Energy, available at
http://www.oe.energy.gov/DocumentsandMedia/DOE_SG_Book_Single_Pages(1).pdf.
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U.S. Renewable Electricity Generation: Resources and Challenges
The cost of solar electricity has been a challenge faced by both CSP and PV technologies. Solar
electricity, according to the Energy Information Administration, is the highest-cost source of
electricity generation, with CSP costs ranging from $192-$642 per MWh and PV costs ranging
from $159-$324 per MWh.40 DOE is funding an initiative, known as the SunShot program, which
aims to reduce the cost of PV electricity generation to $60 per MWh.41 Figure 12 provides a
comparison of costs for conventional (fossil and nuclear) and renewable electricity generation.
Figure 7. U.S. Photovoltaic Solar Resource
Source: National Renewable Energy Laboratory (NREL), available at http://www.nrel.gov/gis/images/
map_pv_national_lo-res.jpg.
Notes: Annual average solar resource data are shown for a tilt-latitude collector. The data for Hawaii and the
48 contiguous states are a 10 km satellite modeled dataset (SUNY/NREL, 2007) representing data from 19982005. The data for Alaska are a 40 km dataset produced by the Climatological Solar Radiation Model (NREL,
2003); kWh/m2/Day = kilowatthour per square meter per day.
40
For more information on EIA assumptions and calculation methodology see http://www.eia.gov/oiaf/aeo/
electricity_generation.html.
41
More information about DOE’s SunShot initiative can be found at http://www1.eere.energy.gov/solar/sunshot/.
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U.S. Renewable Electricity Generation: Resources and Challenges
Geothermal
U.S. Resource Estimates
Geothermal energy is present throughout the entire country, with most of the highest-quality
geothermal resources generally located in the western United States, Alaska, and Hawaii.42
However, all states may have geothermal electricity generation potential through the use of
enhanced, or engineered, geothermal systems (EGS) technology.43 USGS, NREL, and the
Massachusetts Institute of Technology (MIT) each have published estimates for U.S. geothermal
electricity generation. Generally, geothermal electricity generation resources are classified into
three categories: (1) identified resources, (2) undiscovered resources, and (3) enhanced
geothermal systems.44 Table 3 provides a summary of USGS, NREL, and MIT potential
geothermal capacity estimates for these resource types along with annual electricity generation
potential in GWh.
Table 3. U.S. Geothermal Electricity Generation Potential
Identified Resource
Undiscovered Resource
Enhanced Geothermal
Systems
Low
High
Low
High
Low
High
Capacity
(MW-e)
3,675
16,457
7,917
73,286
345,100
727,900
Electricity
Generationb
(GWh/yr)
29,618
132,630
63,805
590,627
834,369
1,759,888
Capacity
(MW-e)
n/a
6,390
n/a
30,030
n/a
15,000,913
Electricity
Generationb
(GWh/yr)
n/a
51,498
n/a
242,018
n/a
36,268,607
USGSa
NRELc
42
There are three general applications for geothermal energy: (1) electricity production, (2) direct heating, and (3)
geothermal (ground source) heat pumps. Typically, the application selected depends in part on the resource
temperature. Geothermal electricity production typically uses moderate temperature (90-150°C) and high temperature
(greater than 150°C) resources. Direct heating typically uses low temperature (less than 90°C) resources. Heat pump
applications utilize shallow ground temperatures for heating and cooling. Geothermal energy for electricity production
is the focus of this report. More information about these three applications is available at http://www.nrel.gov/learning/
re_geothermal.html. For more information about low temperature geothermal energy resources, see M. Reed, R.
Mariner, C. Brook and M. Sorey, “Selected Data For Low-Temperature (Less Than 90°C) Geothermal Systems In The
United States; Reference Data For U.S. Geological Survey Circular 892,” U.S. Geological Survey, 1983, available at
http://energy.usgs.gov/PDFs/USGS_Open-File%20Report%2083-250_1983.pdf.
43
“Report to Congress on Renewable Energy Resource Assessment Information for the United States,” U.S.
Department of Energy, Office of Energy Efficiency and Renewable Energy, 2011.
44
NREL categorizes geothermal resources into four categories: (1) identified, (2) undiscovered, (3) near-hydrothermal
field EGS, and (4) deep EGS. For purposes of comparison, CRS combined “near-hydrothermal field EGS” and “deep
EGS” and classified them both as “Enhanced Geothermal Systems.”
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U.S. Renewable Electricity Generation: Resources and Challenges
Identified Resource
Undiscovered Resource
Enhanced Geothermal
Systems
Low
High
Low
High
Low
High
Capacity
(MW-e)
n/a
n/a
n/a
n/a
1,249,000
12,486,000
Electricity
Generationb
(GWh/yr)
n/a
n/a
n/a
n/a
3,019,782
30,188,151
MITd
Source: U.S. Geological Survey, National Renewable Energy Laboratory, MIT. See specific references below.
Notes: Electricity generation potential estimates represent what might be technically recoverable and do not
include any filters for economic factors. ”Identified” and “Undiscovered” resources generally represent
conventional geothermal resources where naturally occurring conditions (high temperature and permeability)
allow for extraction of geothermal energy. “Enhanced Geothermal Systems” require engineering of rock
permeability to create geothermal energy extraction conditions. Electricity generation numbers were calculated
by CRS using a 92% capacity factor for each geothermal capacity estimate. USGS low estimates for each resource
category represent resources that have a 95% probability of being available. USGS high estimates for each
resource category represent resources that have a 5% probability of being available. NREL analysis provided a
single number for identified, undiscovered, and EGS resource estimates, respectively. The MIT study focused on
the potential of EGS in the United States. The large difference between MIT’s low and high estimates reflect an
assumption made for the EGS energy recovery factor (2% for the low estimate, 20% for the high estimate).
a.
“Assessment of Moderate- and High-Temperature Geothermal Resources of the United States,” U.S.
Geological Survey, 2008, available at http://pubs.usgs.gov/fs/2008/3082/pdf/fs2008-3082.pdf.
b.
Annual electricity generation potential assumes that all potential geothermal resources are developed and
operating. This is highly unlikely since EGS systems may result in resource depletion over a 30-40 year
operating life; regeneration of this resource is estimated to take approximately 100 years. As a result, EGS
estimates for GWh/yr were discounted by a factor of 0.3 in order to calculate sustainable electricity
generation potential based on a 30-year depletion and 100-year regeneration profile
c.
C. Augustine, K. Young, and A. Anderson, “Updated U.S. Geothermal Supply Curve,” National Renewable
Energy Laboratory, Conference Paper presented at Stanford Geothermal Workshop, February 1, 2010,
available at http://www.nrel.gov/docs/fy07osti/41073.pdf.
d.
“The Future of Geothermal Energy: Impact of Enhanced Geothermal Systems (EGS) on the United States in
the 21st Century,” Massachusetts Institute of Technology, 2006, available at http://geothermal.inel.gov/
publications/future_of_geothermal_energy.pdf.
MW-e = megawatt electrical generating capacity.
GWh/yr = gigawatthours per year.
USGS, NREL, and MIT each have a different estimate for U.S. geothermal electricity generation
potential, especially with regard to enhanced geothermal systems. Two primary factors account
for the differences in estimates: (1) USGS estimates are confined to western U.S. states, Hawaii,
and Alaska, while NREL and MIT estimates include potential electricity generation from all 50
states, and (2) USGS estimates are for resource depths between 3 kilometers (km) and 6 km,
while NREL and MIT estimates are for resource depths between 3 km and 10 km.45 This disparity
in resource estimates illustrates how assumptions can significantly alter the assessment results.
Figure 8 shows conventional geothermal sites and the estimated relative suitability of EGS
geothermal energy recovery throughout the U.S.
45
Phone interview with Chad Augustine at NREL.
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Figure 8. Geothermal Resource of the United States
(Locations of identified hydrothermal sites and favorability of deep enhanced geothermal systems [EGS])
Source: NREL, available at http://www.nrel.gov/gis/images/geothermal_resource2009-final.jpg.
Notes: Map does not include shallow EGS resources located near hydrothermal sites or USGS assessment of
undiscovered hydrothermal resources. Source data for deep EGS includes temperature at depth from 3 to 10
km provided by Southern Methodist University Geothermal Laboratory (Blackwell & Richards, 2009) and analysis
(for regions with temperatures ≥150˚C) performed by NREL (2009). Source data identified hydrothermal sites
from USGS Assessment of Moderate- and High-Temperature Geothermal Resources of the United States
(2008).
* “N/A” regions have temperatures less than 150˚C at 10 km depth and were not assessed for deep EGS
potential.
** Temperature at depth data for deep EGS in Alaska and Hawaii not available.
Technology and Cost Considerations
For conventional hydrothermal geothermal resources, four commercially available technologies
are available for generating electricity: (1) flash power plants, (2) dry steam power plants, (3)
binary power plants, and (4) flash/binary combined cycle.46 As of April 2011, U.S. geothermal
installed capacity was 3,102 MW, which represents approximately 0.3% of total U.S. electricity
capacity. In 2009, 15,009 GWh of electricity was generated from geothermal energy sources. The
majority of existing geothermal capacity is located in California.47 Enhanced Geothermal Systems
46
47
Geothermal Energy Association, more information available at http://geo-energy.org/Basics.aspx.
Geothermal Energy Association, more information available at http://geo-energy.org/plants.aspx.
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(EGS) technology could potentially enable large-scale deployment of economically recoverable
geothermal electricity generation.48 However, EGS technology has not been demonstrated at scale
and is not yet commercially available.49
Several factors can influence the cost of geothermal electricity. These factors include the resource
quality (temperature and volume), resource depth, drilling costs, and geothermal equipment costs.
EIA estimates that the levelized cost of energy (LCOE) for conventional geothermal electricity
ranges from $92/MWh to $116/MWh.50 Figure 12 provides a comparison of costs for
conventional (fossil and nuclear) and renewable electricity generation. NREL has also estimated
geothermal electricity LCOE and concluded that, depending on the total amount of capacity
installed, geothermal (conventional and EGS) electricity costs could range between $50/MWh
and $1,200/MWh (2008 US$).51 Based on these cost of energy estimates, NREL indicates that the
amount of EGS resource “that can be economically produced is likely much smaller” than the
total resource potential.52
Hydroelectric
U.S. Resource Estimates
Hydropower is currently the largest source of renewable electricity production in the United
States. In 2010, approximately 257,000 GWh was generated from hydropower resources, equal to
roughly 7% of total U.S. electricity generation.53 Hydropower can be generated in many ways.
For the purpose of this report, hydropower refers to “conventional” hydropower54 and does not
include hydrokinetic energy, ocean energy, or pumped storage.55
48
An overview of Enhanced Geothermal Systems (EGS) technology is available at http://www1.eere.energy.gov/
geothermal/pdfs/egs_basics.pdf.
49
The Department of Energy has established EGS commercialization programs. More information available at
http://www1.eere.energy.gov/geothermal/enhanced_geothermal_systems.html.
50
For more information on EIA assumptions and calculation methodology see http://www.eia.gov/oiaf/aeo/
electricity_generation.html.
51
C. Augustine, K. Young, and A. Anderson, “Updated U.S. Geothermal Supply Curve,” National Renewable Energy
Laboratory, Conference Paper presented at Stanford Geothermal Workshop, February 1, 2010, available at
http://www.nrel.gov/docs/fy07osti/41073.pdf.
NREL LCOE estimates are in 2008 US$.
52
Ibid.
53
Energy Information Administration, more information available at http://www.eia.gov/cneaf/solar.renewables/page/
hydroelec/hydroelec.html.
54
“Conventional” hydropower resource assessments typically include large hydropower dams, increasing capacity at
existing facilities, non-powered dams, small hydro, and low-power hydro. Pumped storage hydroelectricity generation
potential is not included in the resource estimates included in this report.
55
Pumped storage generation potential was not included in the resource assessment literature reviewed for this report.
However, pumped-storage projects are being developed and the Federal Energy Regulatory Commission (FERC) has
issued pre-permits for about 33 gigawatts of pumped storage capacity (see http://www.ferc.gov/industries/hydropower/
gen-info/licensing.asp). The business case for pumped storage might be viewed as an arbitrage opportunity whereby
water is pumped to a reservoir when energy prices are low, and the stored water is used to generate electricity when
energy prices are high or an opportunity exists to receive a financial premium for stand-by or firm power. According to
EIA, more energy is required to pump water into a storage reservoir than is generated when electricity is produced by
releasing the stored water. However, pumped storage facilities can provide valuable ancillary on-demand energy
production services for electricity grid operators. For more information see http://www.ferc.gov/industries/hydropower/
(continued...)
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Since 1998, several Idaho National Laboratory (INL) reports have estimated the potential to
develop new hydropower generation capacity. Three of those reports trace a time-wise increase in
the estimates of potential generation capacity: 30 GW (1998),56 43 GW (2003),57 and 60 GW
(2006).58 A review of the INL reports revealed that estimates differed with regard to the
hydropower categories included in the calculations.59 After sorting through the studies and
attempting to remove duplicative and non-relevant data, CRS calculated additional hydropower
potential to be approximately 65 gigawatts, which equates to approximately 284,700 GWh of
additional annual electricity generation potential.60 A 2007 report by the Electric Power Research
Institute (EPRI) estimated that additional hydropower capacity potential was equal to 62.3
gigawatts.61 However, recently published Oak Ridge National Laboratory (ORNL) resource
potential estimates for non-powered dams may increase the total hydropower resource assessment
by as much as 12.6 gigawatts.62
Figure 9 provides summary information about the location of existing and potential
hydroelectricity facilities in the United States.
(...continued)
gen-info/regulation/pump.asp.
56
A. Conner, J. Francfort, and B. Rinehart, “U.S. Hydropower Resource Assessment Final Report,” Idaho National
Engineering and Environmental Laboratory, December 1998, available at http://hydropower.inl.gov/
resourceassessment/pdfs/doeid-10430.pdf.
57
D. Hall, R. Hunt, K. Reeves, and G. Carroll, “Estimation of Economic Parameters of U.S. Hydropower Resources,”
Idaho National Engineering and Environmental Laboratory, June 2003, available at http://hydropower.inl.gov/
resourceassessment/pdfs/project_report-final_with_disclaimer-3jul03.pdf.
58
D. Hall, K. Reeves, J. Brizzee, R. Lee, G. Carroll, and G. Sommers, “Feasibility Assessment of the Water Energy
Resources of the United States for New Low Power and Small Hydro Classes of Hydroelectric Plants,” Idaho National
Laboratory, January 2006, available at http://hydropower.inl.gov/resourceassessment/pdfs/
main_report_appendix_a_final.pdf. Note: This report quantified hydropower resource potential as megawatts-annual
(MWa) based on a 50% capacity factor assumption. As a result, CRS had to convert MWa estimates to megawatts
(MW) in order to have resource estimates on an equivalent basis.
59
The primary difference between the reports was the inclusion of low-power (<1MW) hydropower resources in the
INL 2006 report.
60
Electricity generation potential assumes a 50% capacity factor.
61
“Assessment of Waterpower Potential and Development Needs,” Electric Power Research Institute, 2007, available
at http://www.aaas.org/spp/cstc/docs/07_06_1ERPI_report.pdf.
62
Presentation by Brennan T. Smith to the National Hydropower Association Annual Conference, “U.S. Hydropower
Fleet and Resource Assessments,” Oak Ridge National Laboratory, April 5, 2011, available at http://hydro.org/wpcontent/uploads/2011/04/Brennan-Smith-PPT_NHA_April2011_Final.pdf.
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Figure 9. Existing and Potential Hydropower Projects in the Lower 48 United States
Source: DOE. “Feasibility Assessment of the Water Energy Resources of the United States for New Low
Power and Small Hydro Classes of Hydroelectric Plants,” DOE, Office of Energy Efficiency and Renewable
Energy, Wind and Hydropower Technologies, January 2006, available at http://www1.eere.energy.gov/
windandhydro/pdfs/doewater-11263.pdf.
Notes: Alaska and Hawaii were included in the DOE study, but were not included in the accompanying map.
DOE study results indicate that Alaska may have the potential to increase its hydropower capacity by as much as
16 times and Hawaii was distinguished as the state having the highest concentration (measured as kilowatt-annual
per square mile) of hydropower potential.
Technology and Cost Considerations
Hydroelectricity generation in the United States dates back to the 1880s and many technologies
are fully commercialized with proven operational performance.63 However, DOE is pursuing
efforts to further improve the performance, economics, and environmental impact of conventional
hydropower technologies.64 Low-head and low-power hydroelectricity technology that might be
used in constructed waterways, such as canals, may require additional research, development, and
demonstration before being commercially available.65
63
For more information on the history of hydroelectricity in the United States see http://www1.eere.energy.gov/
windandhydro/hydro_history.html.
For an overview of hydroelectricity technologies see CRS Report R41089, Small Hydro and Low-Head Hydro Power
Technologies and Prospects, by (name redacted).
64
For more information, see http://www1.eere.energy.gov/windandhydro/printable_versions/hydro_advtech.html.
65
DOE, in April 2011, announced $10.5 million of funding for small hydropower technologies that could be deployed
in constructed waterways. For more information see http://www.energy.gov/news/10255.htm.
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Hydroelectricity is generally considered to be one of the lowest-cost sources of renewable
electricity. EIA estimates that the LCOE for new hydroelectricity plants ranges from $59/MWh
and $121/MWh.66 Figure 12 provides a comparison of costs for conventional (fossil and nuclear)
and renewable electricity generation. However, due to their relatively early stage of development,
the cost of electricity from low-head and low-power technologies remains somewhat uncertain.
Ocean and Hydrokinetic
U.S. Resource Estimates
Ocean-based energy resources come in several forms, including (1) tidal, (2) wave, (3) current,
and (4) thermal (also known as Ocean Thermal Energy Conversion or OTEC).67 Each ocean
energy resource is fundamentally different in terms of the amount of available resources, location
of the resource, and the conversion technology used to generate electricity. While a limited
number of ocean energy resource assessments are available, the Electric Power Research Institute
(EPRI) published resource estimates for wave and tidal energy in 2006.68 DOE has funded several
resource assessments that are not yet available.69 Table 4 summarizes some of the resource
estimates for different categories of ocean energy.
Table 4. U.S. Ocean Energy Resource Estimates
Resource Estimate
(GWh/year)
Low
High
Resource Assessment Status
Wave
255,000
2,100,000
Tidal
n/a
6,600
Georgia Tech Research Corporation was awarded a grant
from DOE to assess tidal stream energy production potential.
Current
n/a
n/a
DOE awarded a grant to Georgia Tech Research Corporation
to create a database of ocean current energy potential.
OTEC
n/a
n/a
DOE awarded a grant to Lockheed Martin in 2009 to conduct
global and domestic ocean thermal resource assessments.
In 2008, DOE awarded a Marine Energy Grant to EPRI to
assess U.S. wave energy resources.
66
See EIA “Levelized Cost of New Generation Resources in the Annual Energy Outlook 2011,” available at
http://www.eia.gov/oiaf/aeo/electricity_generation.html.
67
For more information regarding these energy production approaches, see “Ocean Energy Technology Overview,”
Department of Energy, Office of Energy Efficiency and Renewable Energy, July 2009, available at
http://www1.eere.energy.gov/femp/pdfs/44200.pdf.
Osmotic, or salinity gradient, power is another possible source of ocean energy. However, this energy production
source has not yet been explored or analyzed in great detail. Background on osmotic power is available at
http://en.wikipedia.org/wiki/Osmotic_power.
68
For more information about EPRI’s wave energy resource assessment, see http://oceanenergy.epri.com/
waveenergy.html. For more information about EPRI’s tidal energy resource assessment see
http://oceanenergy.epri.com/streamenergy.html.
69
On July 6, 2011 DOE released a database, developed in partnership with the Georgia Institute of Technology, of tidal
energy resources in the United States. The interactive database is available online at
http://www.tidalstreampower.gatech.edu/.
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Source: EPRI (Resource Estimates); “Report to Congress on Renewable Energy Resource Assessment
Information for the United States,” DOE, Office of Energy Efficiency and Renewable Energy, January 28, 2011.
Notes: n/a = not available.
Figure 10 illustrates the location and magnitude of U.S. wave energy resources. The majority of
wave energy potential exists off the coasts of Alaska, Hawaii, and west coast states.
Figure 10. U.S. Wave Energy Resources
Source: R. Bedard, G. Hagerman, M. Previsic, O. Siddiqui, R. Thresher, and B. Ram, “Final Summary Report:
Project Definition Study – Offshore Wave Power Feasibility Demonstration Project,” Electric Power Research
Institute, September 22, 2005, available at http://oceanenergy.epri.com/attachments/wave/reports/
009_Final_Report_RB_Rev_2_092205.pdf.
Notes: TWh = terawatthours. 1 TWh = 1,000 gigawatthours.
Hydrokinetic energy, defined as river in-stream energy for the purpose of this report, can be
extracted from the natural water flow in rivers. The amount of electricity that can be generated
from this energy source is dependent on the volume and velocity of the water resource. A DOEfunded study by New York University estimates that approximately 12.5 GW of hydrokinetic
power potential might be possible.70 Assuming a capacity factor between 30% and 50%,
electricity generation potential from hydrokinetic resources may range from 32,850 GWh to
54,750 GWh.71
Technology and Cost Considerations
Ocean and hydrokinetic electricity generation technologies might be considered “emerging” as
they have yet to operate at a significant commercial scale. Nevertheless, demonstration and
commercial deployment of ocean and hydrokinetic projects is being pursued.72 Many technology
70
G. Miller, J. Franceschi, W. Lese, and J. Rico, “The Allocation of Kinetic Hydro Energy Conversion Systems
(KHECS) in USA Drainage Basins: Regional Resource Potential and Power,” New York University, Department of
Applied Science, August, 1986.
71
Capacity factor estimates for hydrokinetic devices were based on data reported by Argonne National Laboratory. See
http://teeic.anl.gov/er/hydrokinetic/restech/scale/index.cfm.
72
As of June 9, 2011, the Federal Energy Regulatory Commission (FERC) had issued 70 preliminary permits for tidal,
(continued...)
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concepts are being developed and demonstrated, including more than 100 ocean energy devices
worldwide, with approximately 30 under development in the United States.73
Given the early developmental status of ocean and hydrokinetic electricity production
technologies, estimating the levelized cost of energy is challenging.74 EIA did not include an
LCOE estimate for ocean and hydrokinetic electricity generation as part of the Annual Energy
Outlook (AEO) 2011.
Biomass
U.S. Resource Estimates
Accurate estimates for biomass electricity generation potential are somewhat challenging because
biomass material (forest, agriculture, solid waste, and landfill gases) can be used in a variety of
competing ways to include electricity generation, biofuel production, and space heating for
residential and commercial buildings.75 Also, unlike other renewable energy sources, biomass
might be considered a managed resource in that the quantity of biomass material available for
electricity generation can go up or down based on changes in management practices.76 As a result,
U.S. biomass electricity generation potential is highly dependent on how much biomass is
available and how much biomass material is dedicated for this specific use. In 2009 an estimated
54,493 GWh of electricity was generated from biomass, which represented approximately 1.2%
of total U.S. net electricity generation.77
According to DOE, approximately 190 million tons of biomass are consumed each year, with
roughly 25% to 35% of current biomass consumption being used for electricity generation. DOE
analysis and reports indicate that the potential may exist to produce about 1.3 billion tons of
biomass annually.78 However, estimating the amount of electricity that might be generated from
(...continued)
wave, and inland hydrokinetic projects. For more information, see http://www.ferc.gov/industries/hydropower/indusact/hydrokinetics.asp.
73
Remarks by Sean O’Neill, President—Ocean Renewable Energy Coalition, at the 14th Annual Congressional
Renewable Energy & Energy Efficiency EXPO + Forum, June 16, 2011.
DOE maintains an on-line database of ocean and hydrokinetic projects worldwide. For more information, see
http://www1.eere.energy.gov/windandhydro/hydrokinetic/default.aspx.
74
Challenges associated with calculating LCOE for ocean and hydrokinetic electricity generation technologies include
(1) unknown capital costs, (2) unknown operations and maintenance costs, (3) unknown technology performance
characteristics, etc.
75
For more information on biomass feedstock, see CRS Report R41440, Biomass Feedstocks for Biopower:
Background and Selected Issues, by (name redacted).
76
Biomass resource management practices may include land utilization intensity, fertilization, using more productive
and/or genetically modified crops, among others. NREL’s “Billion Ton” study makes some assumptions for resource
management changes needed in order to achieve that resource level. For more information, see “Biomass as Feedstock
for a Bioenergy and Bioproducts Industry: The Technical Feasibility of a Billion-Ton Annual Supply,” U.S.
Department of Energy and U.S. Department of Agriculture, April 2005, available at http://www1.eere.energy.gov/
biomass/pdfs/final_billionton_vision_report2.pdf.
77
Energy Information Administration, see http://www.eia.gov/totalenergy/data/monthly/pdf/sec7_5.pdf.
78
“Biomass as Feedstock for a Bioenergy And Bioproducts Industry: The Technical Feasibility of a Billion-Ton
Annual Supply,” U.S. Department of Energy and U.S. Department of Agriculture, April 2005, available at
http://www1.eere.energy.gov/biomass/pdfs/final_billionton_vision_report2.pdf.
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biomass depends on the amount of biomass material available and on the portion of that material
that might be used for electricity generation. Table 5 provides an estimate for potential generation
if DOE’s 1.3 billion ton estimate of biomass production were realized.
Table 5. Annual U.S. Biomass Electricity Generation Potential
(Based on DOE’s 1.3 billion ton biomass resource potential study)
50%
10%
100%
% of 1.3B
tons
Low
High
Low
High
Low
High
Electricity
Generation
(GWh)
125,730
142,880
628,660
714,390
1,257,330
1,428,780
Source: CRS analysis of scenarios based on, “Biomass as Feedstock for a Bioenergy and Bioproducts Industry:
The Technical Feasibility of a Billion-Ton Annual Supply,” U.S. Department of Energy and U.S. Department of
Agriculture, April 2005, available at http://www1.eere.energy.gov/biomass/pdfs/
final_billionton_vision_report2.pdf.
Notes: Calculations for this table were based on the following: (1) annual tons consumed for electricity
generation, (2) energy content (Btu) per ton of biomass, and (3) biomass-to-electricity conversion efficiency.
Estimates of annual tonnage were based on the percentages listed in the table (10%, 50%, and 100%). Energy
content per ton of biomass was assumed to be 15 million Btu/ton. Biomass-to-electricity conversion efficiency
ranged from 22% to 25%. This range is the reason for “low” and “high” estimates in the table. This conversion
efficiency is generally representative of biomass combustion technologies, which have a commercial operating
history. Other conversion technologies, such as certain gasification or biological conversion approaches, may
have different conversion efficiencies. Since there are competing uses for biomass material, it is unlikely that
100% of the potential biomass resource will be used for electricity generation. The “100%” scenario presented in
this table is provided for reference only.
Figure 11 indicates the relative concentration of current biomass resources throughout the United
States.
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Figure 11. U.S. Biomass Resource Availability
Source: NREL, available at http://www.nrel.gov/gis/images/map_biomass_total_us.jpg.
Notes: This NREL study estimates the biomass resources currently available in the United States by county. It
includes the following feedstock categories: crop residues (five year average: 2003-2007), forest and primary mill
residues (2007), secondary mill and urban wood waste (2002), methane emissions from landfills (2008), domestic
wastewater treatment (2007), and animal manure (2002). For more information on the data development, please
refer to http://www.nrel.gov/docs/fy06osti/39181.pdf. Although the document contains the methodology for the
development of an older assessment, the information is applicable to this assessment as well; the difference is
only in the data’s time period.
Technology and Cost Considerations
Combustion technologies used to convert biomass to electricity are generally considered
commercial, and there are approximately 80 operating biomass electricity generation facilities
located in the United States.79 Nevertheless, using biomass as a feedstock for electricity
generation can be challenging because each biomass type has different properties, such as water
content, ash content, and energy value.80 This variability in feedstock quality and characteristics
79
Biomass Power Association, see http://www.usabiomass.org/.
Biomass material might also be co-fired with coal in conventional coal electricity generation facilities. Biomass cofiring with coal may result in improved biomass conversion efficiencies when compared to combusting only biomass.
Co-firing biomass with coal may create some technical operating issues associated with tar production and fouling of
electricity generating equipment. The degree to which these technical problems might be realized is dependent on the
quality of the biomass material being combusted and the percentage of biomass blended and co-fired with coal. For
more information see http://www.iea.org/techno/essentials3.pdf.
80
R. Bain, W. Amos, M. Downing, and R. Perlack, “Highlights of Biopower Technical Assessment: State of the
(continued...)
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typically must be addressed in order to effectively operate biomass electricity generation
equipment. Further, some biomass materials contain certain alkali metal species, such as sodium
and potassium, that can potentially impede the operation of electricity generation equipment.81
EIA estimates that the levelized cost of energy for biomass electricity ranges from $99.50 per
MWh to $133.40 per MWh. Biomass accumulation and transportation and biomass feedstock
quality might be considered key cost drivers that can impact the levelized cost of energy for
biomass electricity.82 Figure 12 provides a comparison of costs for conventional (fossil and
nuclear) and renewable electricity generation.
Challenges for Renewable Energy
Each type of renewable energy technology has certain advantages and disadvantages relative to
each other and relative to fossil fuel energy sources. An extensive literature exists on these
advantages and disadvantages.83 This part of the report offers brief observations and discussion of
certain challenges that might affect the full development and deployment of renewable electricity
generation technologies. Many policies directed at renewable energy deployment are designed to
address these challenges.
Cost
Perhaps the most fundamental challenge to the deployment of renewable energy is the cost of
generating electricity from renewable sources. Energy producers and consumers seek the lowestcost energy, and fossil fuels have historically been the lowest-cost sources of energy, either
through end-use combustion or through the generation of electricity.
Levelized Cost of Energy (LCOE)
A common metric for measuring the financial cost of electricity production is Levelized Cost of
Energy, or LCOE.84 LCOE calculations are typically expressed in terms of dollars per unit of
(...continued)
Industry and the Technology,” National Renewable Energy Laboratory and Oak Ridge National Laboratory, April
2003, available at http://www.nrel.gov/docs/fy03osti/33502.pdf.
81
Ibid.
82
For more information about biomass feedstock characteristics see http://www1.eere.energy.gov/biomass/
feedstock_databases.html. For more information about biomass feedstock logistics see http://www1.eere.energy.gov/
biomass/feedstocks_logistics.html.
83
See, for example, National Academy of Sciences, National Research Council, Electricity from Renewable Resources:
Status, Prospects, and Impediments, National Academies Press, 2010.
84
Terms such as LCOE, Power Purchase Agreement (PPA), contract price, and others, are sometimes used when
discussing renewable electricity economics. Each of these terms has different, sometimes multiple, definitions. For
example, the Federal Energy Regulatory Commission (FERC) publishes contract prices for electricity, including
renewable electricity projects. Published contract prices for wind generated electricity can range between $40/MWh
and $60/MWh. Comparing these contract prices with EIA LCOE estimates ($82/MWh minimum) indicates that wind
electricity is being sold for less than cost. However, FERC published contract prices may not reflect any value that the
wind project might receive by selling renewable energy credits (RECs). It is important to understand what is being
reflected in LCOE, PPA, and contract price values.
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energy. The most common units of energy used for comparing the LCOE of different energy
sources are kilowatthour (kWh) and megawatthour (MWh). LCOE estimates can provide a
relative comparison of energy generation costs for different energy sources such as coal, natural
gas, wind, solar, and others. However, policy makers may want to exercise caution when
reviewing and considering LCOE estimates. Reasons for this caution include the following: (1)
no agreed-upon or standardized LCOE calculation methodology exists, and methods can be
tailored to skew results in favor of a particular technology or resource, (2) assumptions used to
calculate LCOE estimates can have a major impact on calculations results, and (3) LCOE
estimates may not reflect the variable time-of-day value of electricity generation. For example,
electricity at 2 p.m. may have more value than electricity at 2 a.m. Therefore, it is unlikely that
LCOE calculations performed by different organizations will be identical. Understanding the
methodology and assumptions used is often critical when considering LCOE estimates.
Although there is no standard LCOE calculation method, two fundamental methods are
commonly used. One method uses total life cycle costs (capital, operations and maintenance, etc.)
and total life cycle energy production to calculate a $/kWh or $/MWh cost of energy.85 Another
method uses a project cash flow model to calculate equity rates of return based on the price of
energy paid to the project. Typically, a target equity rate of return, expressed as a percentage, is
established and the price per unit of energy is adjusted in order to reach the equity return target.86
This cash-flow-based methodology is unique in that it may include specific project finance
constraints such as debt service coverage ratios, cash reserves, and other factors that may not be
reflected in the cost vs. energy production approach.
Furthermore, differences in several key assumptions can significantly alter calculations of LCOE
estimates. Assumptions that can impact LCOE estimates include (1) capital costs, (2) operation
and maintenance costs, (3) government incentives, (4) capacity factor, (5) financial structure
(debt/equity ratio), (6) financial costs for debt and equity, (7) project lifetime, and (8) technology
performance degradation. Several key assumptions must be included in each calculation of LCOE
estimates. Since different organizations often use different assumptions, the variation in LCOE
estimates is not surprising.87
For this report, LCOE estimates from the EIA Annual Energy Outlook (AEO) 2011 were used to
compare the cost of new electricity generation for various renewable energy resources. Figure 12
summarizes EIA’s range of LCOE estimates for several technologies.88
85
For a detailed description of this LCOE methodology, see “The Drivers of Levelized Cost of Energy for Utility-Scale
Photovoltaics,” SunPower Corporation, August 14, 2008, available at http://nl.sunpowercorp.be/downloads/
SunPower_levelized_cost_of_electricity.pdf.
86
For a description of the cash flow LCOE methodology, see P. Schwabe, S. Lensink, and M. Hand, “IEA Wind Task
26: Multi-National Case Study of the Financial Cost of Wind Energy,” IEA Wind, March 2011, available at
http://www.ieawind.org/IndexPagePOSTINGS/
IEA%20WIND%20TASK%2026%20FULL%20REPORT%20FINAL%203%2010%2011.pdf.
87
NREL has calculated LCOE estimates for wind and has summarized the sensitivity of LCOE values based on
different assumptions. For more information, see K. Cory and P. Schwabe, “Wind Levelized Cost of Energy: A
Comparison of Technical and Financing Input Variables,” National Renewable Energy Laboratory, October 2009.
88
For a description of EIA’s LCOE methodology and assumptions used for the estimates, see “Levelized Cost of New
Generation Resources in the Annual Energy Outlook 2011,” Energy Information Administration, December 2010,
available at http://www.eia.gov/oiaf/aeo/electricity_generation.html.
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Figure 12. EIA’s Levelized Cost of Energy (LCOE) Estimates for New Plants
(2009 $/Megawatthour)
Source: CRS adaptation of EIA’s “Levelized Cost of New Generation Resources in the Annual Energy Outlook
2011,” available at http://www.eia.gov/oiaf/aeo/electricity_generation.html.
Notes: EIA LCOE estimates are for new projects that are would be brought on line in 2016. LCOE estimates
do not incorporate any federal or state tax incentives.
* The LCOE range for Natural Gas includes four different technologies: (1) conventional combined cycle, (2)
advanced combined cycle, (3) conventional combustion turbine, and (4) advanced combustion turbine.
It is important to note that EIA LCOE estimates reflect only the projected amount of capacity
expected to be added to the electricity generation system during the forecast period. Costs for
renewable electricity typically follow a supply curve where costs increase as new capacity is
installed, which indicates that the lowest-cost capacity will be added first. Geothermal supply
curve estimates provide an example to consider. Figure 13 shows a supply curve for enhanced
geothermal electricity costs, developed by NREL. As indicated in the figure, depending on the
amount of geothermal capacity installed, the projected LCOE could be as high as $1,000 per
MWh. This example of how energy costs can change, as capacity additions increase, further
illustrates the importance of understanding all assumptions used for projecting future electricity
costs.
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Figure 13. NREL Supply Curve for Near-Hydrothermal Field
Enhanced Geothermal Systems (EGS) Resource
Source: NREL.
Notes: For more information see C. Augustine, K. Young, and A. Anderson, “Updated U.S. Geothermal Supply
Curve,” National Renewable Energy Laboratory, Conference Paper presented at Stanford Geothermal
Workshop, February 1, 2010, available at http://www.nrel.gov/docs/fy07osti/41073.pdf.
Comparing Fossil and Renewable Energy Costs
The current comparatively low cost of fossil fuel energy, as indicated in EIA’s LCOE estimates,
may not include any costs associated with the external impacts of fossil fuel consumption, which
has been stated this way:
But some energy costs are not included in consumer utility or gas bills, nor are they paid for
by the companies that produce or sell the energy. These include human health problems
caused by air pollution from the burning of coal and oil; damage to land from coal mining
and to miners from black lung disease; environmental degradation caused by global
warming, acid rain, and water pollution; and national security costs, such as protecting
foreign sources of oil.89
Accurately quantifying social costs of fossil energy associated with health problems, climate
change, and others can be difficult and complex. As with all cost calculations, assumptions used
for estimating social costs can have a dramatic effect on calculation results. Nevertheless, some
groups do attempt to place a value on the social costs of fossil energy as an alternative method for
89
Union of Concerned Scientists, 2002, The Hidden Cost of Fossil Fuels, available at http://www.ucsusa.org/
clean_energy/technology_and_impacts/impacts/the-hidden-cost-of-fossil.html.
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U.S. Renewable Electricity Generation: Resources and Challenges
comparing the cost of energy from fossil and renewable resources.90 Furthermore, an Interagency
Working Group was created under Executive Order 12866 to estimate the social cost of carbon
for regulatory impact analysis.91 Over time, the costs of mitigating some of these social costs may
be placed on the producers or consumers of fossil fuels.
Technology and cost are closely related because renewable energy developers seek technologies
that produce energy as inexpensively as possible in order to attain commercially viability. Today,
research continues to identify new, more efficient materials and to seek technologies that can be
manufactured at lower cost. Improvements continue as new technologies emerge and evolve.
Much of the current R&D on renewable technologies aims to reduce the manufacturing cost and
the electricity production cost, thereby making renewable electricity more competitive in the
marketplace.
Power System Integration
Connecting renewable electricity generation facilities to the electric power grid can raise potential
technical challenges. In particular, a high percentage penetration of variable sources—such as
solar and wind—can cause serious power quality and reliability problems. The power system
requires constant, 24/7 minute-by-minute monitoring and control. The introduction of variable
electricity generation may pose power system reliability challenges associated with moment-bymoment balancing of electricity supply and demand.92 A recent study by the International Energy
Agency (IEA) indicates that many existing power systems currently have infrastructure and
processes to manage some degree of variability, and these existing assets could potentially be
used to manage variable renewable energy resources.93 However, not all renewable sources of
electricity are classified as variable. Biomass, geothermal, and some hydropower sources have the
ability to generate electricity on a consistent and predictable basis. As a result, integrating these
renewable sources into the power system may not be difficult. However, the inherently variable
nature of wind, solar, and some ocean-hydrokinetic electricity may result in significant power
system operational challenges if these variable renewable energy sources achieve a high
percentage level of penetration.94
DOE funded two studies—the Eastern and Western grid interconnection studies—to evaluate the
challenges and opportunities associated with significant penetration of variable renewable sources
of electricity.95 The Eastern Wind Integration and Transmission Study assessed the impacts of
90
One study from the Brookings Institution attempts to quantify social costs, per unit of energy produced, associated
with energy production. For more information, see M. Greenstone and A. Looney, “A Strategy for America’s Energy
Future: Illuminating Energy’s Full Costs,” Brookings Institution, The Hamilton Project, May 2011, available at
http://www.brookings.edu/~/media/Files/rc/papers/2011/05_energy_greenstone_looney/
05_energy_greenstone_looney.pdf.
91
For more information, see “Social Cost of Carbon for Regulatory Impact Analysis Under Executive Order 12866,”
DOE, Office of Energy Efficiency and Renewable Energy, available at http://www1.eere.energy.gov/buildings/
appliance_standards/commercial/pdfs/sem_finalrule_appendix15a.pdf.
92
The term “power system,” for the purpose of this discussion, includes electricity generators, transmission
infrastructure, and electricity consumers. For more information about the North American power system, see
http://www.nerc.com/page.php?cid=1|15.
93
“Harnessing Variable Renewables: A Guide to the Balancing Challenge,” International Energy Agency, 2011.
94
Ibid.
95
North America has three distinct interconnections: (1) Eastern Interconnect, (2) Western Interconnect, and (3)
ERCOT (Electric Reliability Council of Texas) Interconnect. Each interconnect essentially operates as an independent
(continued...)
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integrating wind electricity generation at a 20% to 30% penetration level.96 The Western Wind
and Solar Integration Study evaluated potential power system impacts associated with a 35%
penetration comprised of wind (30%) and solar (5%).97 Both studies concluded that integrating
the respective penetration rates of variable renewable electricity is manageable, although
accommodating those penetration levels may require large amounts of transmission investment,
additional reserve capacity, and modifications to power system operations.
Intermittency and Variability
Some renewable energy sources are intermittent and variable. Geothermal, biomass, and some
hydropower energy sources usually can be delivered continuously over time. However, wind
power is usable only when the wind blows, solar power is usable only when the sun shines, and
some hydroelectric power is usable only when water is available to flow through the turbines, so
the production of renewable electricity from those sources varies over a period of minutes, hours,
days, or months. In addition, wind speed may vary over a period of seconds, minutes, or hours,
and solar energy may vary with cloud cover over a period of minutes or hours. This intermittent
and variable nature of renewables contrasts with fossil and nuclear power plants, which produce
electricity continuously and uniformly except during times of maintenance, fuel supply
disruptions, operational problems, or natural disasters. The intermittency and variability of
renewable energy might be partially overcome through the development of advanced storage
technologies that provide storage of various quantities of electrical energy for use during
renewable energy down time. A wide range of batteries, compressed-air storage, hydrogen
generation and fuel cells, and other means of storing and recovering intermittent energy are being
studied. Such storage is currently costly, and the combination of renewable electricity generation
and reliable storage—or backup reserve capacity from natural gas or other dispatchable sources—
will need to be considered by the electrical delivery system in order to maximize the potential
contributions of renewable technologies.98
Renewable Energy Footprint and Land-Use
Although the amount of renewable energy available from the sun, wind, and water may seem
unlimited, the land available for energy development is potentially limited by a number of factors.
As mentioned above, these sources are dispersed, and technologies are required to convert the
natural form of energy into electricity. For this reason, certain renewable energy technologies
available today require large areas of land—a large footprint—for each unit of energy produced.
Figure 14 displays different estimates of the land-use intensities of several energy production
technologies. Estimates of the land-use intensity for renewable and nonrenewable sources of
(...continued)
electrical grid system.
96
“Eastern Wind Integration and Transmission Study,” National Renewable Energy Laboratory, prepared by EnerNex
Corporation, February 2011, available at http://www.nrel.gov/wind/systemsintegration/pdfs/2010/
ewits_final_report.pdf.
97
“Western Wind and Solar Integration Study,” National Renewable Energy Laboratory, prepared by GE Energy, May
2010, available at http://www.nrel.gov/wind/systemsintegration/pdfs/2010/wwsis_final_report.pdf.
98
U.S. Department of Energy, Energy Storage Program Planning Document, http://www.oe.energy.gov/
DocumentsandMedia/OE_Energy_Storage_Program_Plan_Feburary_2011v3.pdf.
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energy vary significantly, depending on a number of assumptions. To date, there is no standard
methodology to produce these estimates. For example, the extent to which an energy site
exclusively “uses” an amount of land is debatable. Only a small portion of area within a wind
energy site is actually occupied by the turbines, so remaining land could potentially be—and
often is—dedicated to other uses. In contrast, fields of energy crops to be burned in the
production of electricity will fully occupy their allotted area. Further, energy production for
renewables varies substantially with geography. A solar photovoltaic plant of a certain capacity
will require less land if located in a region with more intense sunlight. In addition, it is difficult to
compare land-use intensities for renewable energy technologies with those of fossil fuel
technologies. For example, for fossil fuels, calculations of land-use intensity may include the
power plant footprint, plus mining or production area, plus areas occupied by transportation and
logistics infrastructure. Thus, the footprint for natural gas may include the gas power plant, but
also the areas occupied by gas wells, the roads that connect the gas wells, and the pipelines that
transport the gas to market. Also, the areal extent of infrastructure may not fully represent the
impact on the landscape. The degree to which such infrastructure divides or dissects ecosystems
may also be an important consideration. 99
The electric energy production technologies with the greatest land-use intensity (amount of land
per unit of electrical energy produced) are biomass, wind, hydropower, and solar photovoltaic.
Land-use intensities of natural gas, coal, geothermal, and nuclear power are likely significantly
smaller than those of other forms of energy production. As demand grows for utility-scale
installations of renewable energy, pressure will grow to integrate energy policy with land-use
policy.100 The integration of distributed generation technologies, such as rooftop solar, into
existing building structures will help mitigate land-use issues, but there will likely remain a
strong need for utility-scale renewable energy installations.
99
Uma Outka, The Renewable Energy Footprint, Stanford Environmental Law Journal, Vol. 30, p. 241, 2011.
Ibid.
100
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Figure 14. Land-Use Intensity for Various Forms of Energy Production
Source: CRS analysis of the following reports:
- McDonald RI, Fargione J, Kiesecker J, Miller WM, Powell J(2009) Energy Sprawl or Energy Efficiency: Climate
Policy Impacts on Natural Habitat for the United States of America. PLoS ONE 4(8): e6802.
doi:10.1371/journal.pone.0006802, Figure 3.
- David Pimentel et al., “Renewable Energy: Current and Potential Issues,” BioScience, vol. 52, no. 12 (December
2002), pp. 1111-1120.
- David V. Spitzley and Gregory A. Keoleian, Life Cycle Environmental and Economic Assessment of Willow
Biomass Electricity: A Comparison with Other Renewable and Non-Renewable Sources, Center for Sustainable
Systems, Report No. CSS04-05R, Ann Arbor, MI, March 25, 2004 (revised February 10, 2005).
- T.J. Dijkman and R.M.J. Benders, “Comparison of renewable fuels based on their land use using energy
densities,” Renewable and Sustainable Energy Reviews, vol. 14 (2010), pp. 3148-3155.
Notes: GWh = gigawatthours, yr = year; Acres per gigawatthour per year (GWh/yr) is the metric used to
compare results from the respective reports. GWh/yr indicates the amount of land required to generate a
certain amount of electricity, in this case a gigawatthour. Some studies report land use per unit of capacity, which
might be reported as acres per gigawatt (GW). Land use per capacity is somewhat misleading because each
energy technology has a different capacity factor, meaning that operational hours for each technology will vary
over the course of a year. Reflecting land use as a function of electricity generation takes into account capacity
factor differences.
Transmission Availability and Access
Though renewable energy technologies may be used across most of the nation, optimized use of
renewable energy must accommodate certain geographic controls. The wind energy resource is
richest in coastal areas and the Midwest. Solar energy is optimal in the relatively cloudless
southwestern United States. Hydroelectric power has historically been best deployed on large
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rivers with steep gradients. These geographic concentrations of renewable energy sources often
mean that the energy may be optimally produced far from the existing energy demand centers,
which are the large cities of the east and west coasts, upper Midwest, and South. Thus, large-scale
deployment of renewable energy technologies will likely be accompanied by the need for new
electricity transmission infrastructure from the new regions of energy supply to the demand
centers.101 For example, the NREL Eastern Interconnection Report concluded that 20% to 30%
wind generation is feasible, but would require “significant expansion of the transmission
infrastructure.”102 Not only must a new installation of renewable energy technology be connected
to the grid, but the new transmission infrastructure must be sized to the maximum rate of
electricity flow even though it may flow intermittently at that rate.
Materials and Resources
While renewable energy sources may provide a virtually infinite supply of energy, building and
installing the equipment necessary to convert renewable energy into usable electricity may
require significant quantities of materials and other natural resources. For example, wind turbine
manufacturing requires a number of materials and resources, the most critical being steel,
fiberglass, resins, blade core materials, permanent magnets, and copper.103 Current solar
photovoltaic technologies require materials such as silicon, cadmium, tellurium, silver, and
others.104 Large-scale wind and solar deployment would raise demand for these materials, which
in turn may impact their respective prices. This potential price impact may be an important
consideration, since the cost of renewable electricity generation is highly correlated with the cost
of the energy conversion system (i.e., wind turbines, solar panels, etc.).
Environmental Impact and Aesthetic Concerns
Capturing and converting any energy source—including renewable energy—will have some
degree of impact on the environment. Land use and habitat disturbance are potential
environmental issues for wind and solar electricity projects. Installation of wind turbines has
already attracted attention because of bird mortality, noise, and resulting NIMBY105 attitudes.
Some CSP technologies may require vast amounts of water, although dry-cooling CSP
technologies, with lower efficiencies, are available.106 Water use, land subsidence, and seismicity
may need to be addressed by geothermal power plants. Hydropower and ocean-hydrokinetic
101
On July 21, 2011, the Federal Energy Regulatory Commission (FERC) issued Order No. 1000—Final Rule on
Transmission Planning and Cost Allocation by Transmission Owning and Operating Public Utilities. This FERC order
may result in transmission capacity access for renewables, since transmission planning must take into account federal
and state public policy requirements (i.e., renewable portfolio standards, etc.).
102
“Eastern Wind Integration and Transmission Study,” National Renewable Energy Laboratory, February 2011,
available at http://www.nrel.gov/wind/systemsintegration/pdfs/2010/ewits_final_report.pdf.
103
“20% Wind Energy by 2030: Increasing Wind Energy’s Contribution to U.S. Electricity Supply,” U.S. Department
of Energy, Energy Efficiency and Renewable Energy, July 2008, available at http://www.nrel.gov/docs/fy08osti/
41869.pdf.
104
National Academy of Sciences, National Research Council, Electricity from Renewable Resources: Status,
Prospects, and Impediments, National Academies Press, 2010.
105
NIMBY = Not In My Back Yard.
106
For more information about potential water issues associated with CSP electricity generation, see CRS Report
R40631, Water Issues of Concentrating Solar Power (CSP) Electricity in the U.S. Southwest, by (name redacted) and
(name redacted).
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electricity generation systems may result in water quality degradation, ecosystem disruption, and
animal mortality. Biomass projects impact the environment through emissions such as nitrogen
oxides (NOx), carbon dioxide (CO2), and others, as well as land use changes associated with
producing biomass feedstock.107 These, and other, potential environmental impacts may need to
be considered as policy makers look to balance the desire to increase electricity production from
renewable sources of energy with environmental objectives.
Infrastructure Requirements
All forms of energy production and delivery require some form of infrastructure. Coal is
delivered by an extensive network of railroads, and natural gas is delivered via a large network of
pipelines. In addition to new transmission requirements, some renewable energy sources may
require investments in specialized infrastructure in order to provide a source of renewable
electricity. One example is offshore wind energy. Specialized vessels, purpose-built portside
infrastructure, undersea electricity transmission lines, and grid interconnections will likely be
required to support offshore wind development. According to DOE, “these vessels and this
infrastructure do not currently exist in the U.S.”108 Such specialized infrastructure requirements
may also be a consideration for policy decisions associated with certain other types of renewable
energy.
Technology Development and Commercialization
Some renewable electricity generation technologies are not yet commercially available. Private
and public investments are being made in renewable electricity generation technologies, to
include venture capital firms, private and public corporations, and the U.S. DOE through its
Advanced Research Projects Agency—Energy (ARPA-E) program office. While ARPA-E and
DOE’s Office of Energy Efficiency and Renewable Energy provide funds to support technology
R&D, concept demonstrations, and technology performance optimization, bridging the gap
between these activities and commercialization may require significant amounts of funding.
Commonly known as the commercialization “valley of death,” several additional market
development activities that might include technology performance characterization and
validation, operational reliability assessments, accurate quantification of maintenance and
operations costs, etc., may be necessary in order for new technologies to qualify for private equity
and bank/debt finance in support of commercial projects. Obtaining the funds necessary to
commercialize new technologies can be difficult and costly.109
Policy and Regulatory Challenges
Certain federal and state-level policies have served to stimulate growth of renewable electricity
generation. Federal policies such as production and investment tax credits for certain renewable
107
“Electricity from Renewable Source: Status, Prospects, and Impediments,” Chapter 5 – Environmental Impacts of
Renewable Energy, National Academy of Sciences, 2010.
108
“A National Offshore Wind Strategy: Creating an Offshore Wind Energy Industry in the United States.” U.S.
Department of Energy, Energy Efficiency and Renewable Energy, February 2011, available at
http://www1.eere.energy.gov/windandhydro/pdfs/national_offshore_wind_strategy.pdf.
109
For more information on the commercialization “valley-of-death,” see “Crossing the Valley of Death: Solutions to
the next generation clean energy project financing gap,” Bloomberg New Energy Finance, June 21, 2010.
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energy property, along with other tax-favored finance options, have created financial incentives
for building and operating renewable electricity generation projects.110 Other federal financial
incentives are also available for renewable energy.111 Furthermore, the American Recovery and
Reinvestment Act (ARRA) provided new policies such as the Section 1603 cash grant option for
renewable electricity generation projects and the Section 1705 Loan Guarantee Program that
provides government-backed debt financing for certain renewable energy projects.112 State-level
policies, such as renewable portfolio standards, have served to create market demand for
renewable electricity.113 Furthermore, there is some interest in establishing a federal renewable or
clean energy standard, which may create additional demand for renewable electricity
generation.114
Federal policies that support renewable electricity generation typically are available for a defined
period of time, at the end of which the policies expire. Some in the renewable electricity industry
argue that the sudden expiration of certain federal policies has resulted in market uncertainty and
downward pressure on renewable electricity market growth.115 The historical start-stop nature of
federal policies may be challenging to the renewable energy industry due to a lack of long-term
financial certainty for renewable electricity generation projects. On the other hand, some policy
makers may not wish to create a policy environment that results in a renewable energy industry
that is dependent on federal financial incentives. Balancing policy objectives that might stimulate
a solid base for renewable electricity, while at the same time eliminating a dependency on federal
subsidies, may be a consideration for policy makers.
Related Issues
Energy Efficiency and Curtailment
Although this report does not provide a detailed analysis of energy efficiency and conservation, it
is widely acknowledged that both energy efficiency (doing as much or more with less energy and
eliminating waste) and curtailment of demand (doing less with less energy) provide enormous
opportunities for reducing or controlling the energy resources of the nation. By addressing the
demand side of the energy equation, as well as the supply side, the United States can extend the
energy resources that it consumes. Efficiency and demand curtailment will not, by themselves,
110
For more information on energy tax policy see CRS Report R41769, Energy Tax Policy: Issues in the 112th
Congress, by (name redacted) and (name redacted).
For more information on tax favored finance options see CRS Report R41573, Tax-Favored Financing for Renewable
Energy Resources and Energy Efficiency, by (name redacted) and (name redacted).
111
For more information see CRS Report R40913, Renewable Energy and Energy Efficiency Incentives: A Summary of
Federal Programs, by (name redacted) and Beth A. Roberts.
112
For more information regarding Section 1603 of ARRA see CRS Report R41635, ARRA Section 1603 Grants in
Lieu of Tax Credits for Renewable Energy: Overview, Analysis, and Policy Options, by (name redacted) and (name red
acted).
113
For more information on state incentives for renewable energy, see the Database of State Incentives for Renewables
and Efficiency at http://www.dsireusa.org/.
114
For more information see CRS Report R41720, Clean Energy Standard: Design Elements, State Baseline
Compliance and Policy Considerations, by (name redacted).
115
One example of this scenario might be the expiration of production tax credits in 2000, 2002, and 2004. For more
information, see http://www.awea.org/issues/federal_policy/upload/PTC_April-2011.pdf.
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U.S. Renewable Electricity Generation: Resources and Challenges
meet the demand for energy in the future, but these strategies will likely reduce the amount of
new energy needed.116
The benefits of more efficient use of energy are being sought by a wide range of citizens,
homeowners, manufacturers, and governments. Lower costs, reduced greenhouse gas emissions,
and reduced need for expansion of supply are key motivators to increase energy efficiency and
conservation. Energy efficiency can be measured for individual devices such as appliances,
automobiles, and light bulbs, but derivative indicators are used to measure levels and trends in
energy efficiency at a national level. The most common national indicator of energy efficiency
and curtailment is energy intensity.117 Energy intensity is measured in units of energy per dollar of
Gross Domestic Product (GDP). As Figure 14 shows, the energy intensity of the United States
has been dropping steadily for decades, despite the steady growth in total energy consumption.
There are many reasons for this trend, of course, including a gradual change from a
manufacturing economy to a more service-oriented economy, but ongoing efforts to promote
energy efficiency and conservation are clearly succeeding in the United States. For example, one
study estimates that improving the energy efficiency of buildings in the United States could save
$170 billion per year in energy costs through 2030.118 Numerous other opportunities exist for
improving efficiency or curtailment in energy use in the United States.119
116
One concept worth noting here is known as the Jevons Paradox, which indicates that as efficiency increases the
amount of resources demanded will also increase, not decrease as might be expected. William Jevons, in 1865,
observed that as technology improved the efficiency of coal use, consumption of coal actually increased across several
industries. Whether or not the Jevons Paradox is applicable today is debatable, with experts presenting arguments that
support and refute the Jevons Paradox. A high level overview of the Jevons Paradox is available at
http://en.wikipedia.org/wiki/Jevons_paradox. For more information, see CRS Report RL31188, Energy Efficiency and
the Rebound Effect, by (name redacted).
117
Energy Information Administration, http://www.eia.gov/cfapps/ipdbproject/IEDIndex3.cfm?tid=92&pid=46&aid=2.
118
Rich Brown, Sam Borgeson, Jon Koomey, Peter Biermayer, “U.S. Building-Sector Energy Efficiency Potential”,
Environmental Energy Technologies Division, Ernest Orlando Lawrence Berkeley National Laboratory, Report LBNL1096E, September 2008.
119
U.S. Department of Energy, Office of Energy Efficiency and Renewable Energy, http://www.energy.gov/
energyefficiency/index.htm, and the U.S. Environmental Protection Agency, http://www.energystar.gov/.
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Figure 15. Total U.S. Energy Consumption and Energy Intensity, 1975-2009
Source: Energy Information Administration, http://www.eia.gov/emeu/aer/pdf/pages/sec1_13.pdf.
Note: Energy intensity is the total primary energy consumption per real dollar of Gross Domestic Product.
Biofuels
Biofuels are liquid fuels produced from plant materials, which makes them a renewable
commodity. The major biofuels are fuel ethanol and biodiesel, though other kinds of alcohols and
hydrocarbons can also be synthesized from biological materials. Both fuel ethanol and biodiesel
are currently used primarily as blending agents with conventional gasoline and diesel fuel, though
both can conceivably be used in their pure form with some modifications to engine fuel
systems.120 Unlike the other kinds of biomass discussed above, liquid biofuels are normally used
as transportation fuels and are not used to generate electricity. Liquid biofuels are important
because certain forms of transportation such as aircraft and heavy trucks cannot easily be
converted to electricity or other propulsion technologies. In 2009, the United States consumed 99
million gallons of fuel ethanol as an 85% blend (E85), 10.7 billion gallons of fuel ethanol as a
15% blend (E15) in gasoline, and 316 million gallons of biodiesel.121
For additional information on biofuels see the following CRS reports.
•
CRS Report R41282, Agriculture-Based Biofuels: Overview and Emerging
Issues, by (name redacted).
120
National Renewable Energy Laboratory, http://www.nrel.gov/learning/re_biofuels.html.
Energy Information Administration, http://www.eia.gov/renewable/alternative_transport_vehicles/pdf/afvatf2009.pdf
121
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•
CRS Report RL34738, Cellulosic Biofuels: Analysis of Policy Issues for
Congress, by (name redacted) et al.
•
CRS Report R41106, Meeting the Renewable Fuel Standard (RFS) Mandate for
Cellulosic Biofuels: Questions and Answers, by (name redacted).
•
CRS Report R40110, Biofuels Incentives: A Summary of Federal Programs, by
(name redacted).
•
CRS Report R40155, Renewable Fuel Standard (RFS): Overview and Issues, by
(name redacted) and (name redacted).
Additional Considerations for Renewable Electricity
in the United States
The Scale of U.S. Energy Consumption
One important aspect of the expansion of renewable forms of energy, often overlooked or underappreciated, is the scale or magnitude of energy use in the United States. It is not only what kind
of energy is used, but how much energy the United States uses on a daily, monthly, and annual
basis. By any measure, the amounts of energy used by the United States are prodigious, and
replacing a significant proportion of fossil fuels with renewable forms of energy would be a
formidable task. Alternatives to fossil fuels must be produced on a very large scale and must be
available to all parts of the nation to provide the enormous and increasing amounts of energy
demanded by the U.S. economy. Whether individual renewable energy installations are large
(utility-scale) or small (distributed), the total combined output must accommodate the very
large—and increasing—demand for energy. Current electricity generation is dominated by coal,
natural gas, and nuclear (see Table 6). Only 8% of total energy use in the United States is
renewable, and 53% of that is for electricity generation. In 2009, total U.S. energy use was 94.6
quadrillion Btu, and renewable electricity accounted for about 4 quadrillion Btu.122 Therefore, any
serious proposal to displace fossil fuels with renewable energy must include massive growth in
renewable energy technology deployment.
Table 6. Total U.S. Electricity Generation, By Source, 2009
122
Generation fuel
GWh
%
Coal
1,755,904
44.45
Petroleum
38,937
0.99
Natural Gas
920,979
23.31
Other Gases
10,632
0.27
Nuclear
798,855
20.22
Hydroelectric Conventional
273,445
6.92
Wind
73,886
1.87
U.S. energy use at the national scale is measured in quadrillion British thermal units (Btu), or “quads.”
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Generation fuel
GWh
%
Solar Thermal and Photovoltaic
891
0.02
Wood and Wood Derived Fuels
36,050
0.91
Geothermal
15,009
0.38
Other Biomass
18,443
0.47
Pumped Storage
-4,627
-0.12
Other
11,928
0.30
3,950,332
100.00
All Energy Sources
Source: EIA, http://www.eia.doe.gov/cneaf/electricity/epa/epaxlfilees1.pdf.
Notes: Electricity generation from pumped storage is negative since pumping water into a storage reservoir
requires more electricity than that generated when the stored water is used to operate a turbine. Pumped
storage projects are typically based on opportunities to pump water into a reservoir when electricity prices are
low (typically at night), then use the stored water to generate electricity when prices are high (typically during
peak demand hours).
Relationship Between Renewable Electricity and Imported Energy
Petroleum consumption may be displaced by the production of biofuels, but most renewable
energy technologies are designed to generate electricity. Therefore, the use of renewable energy
to generate electricity in today’s U.S. market would displace only those fossil fuels that are used
to generate electricity, and the United States uses almost no imported fossil fuels to generate
electricity. For example, the U.S. transportation system is 94% reliant on petroleum (Figure 1),
and the use of renewable electricity for transportation might require increased electrification of
the transportation system. Consequently, the only way that increasing production of renewable
electricity would affect oil imports is if the U.S. transportation system is electrified so that
domestically generated electricity substitutes for oil. Likewise, any process in which the burning
of natural gas is used for direct heating would need to be electrified in order for renewable energy
to substitute. More than 93% of U.S. coal consumption is used to generate electricity, so adopting
renewable energy sources to generate electricity could potentially reduce demand for coal, but
would have no effect on energy imports because virtually all of U.S. coal is produced
domestically.
International Renewable Electricity Markets
Recent news reports emphasize how successful China and other nations have become in
developing and deploying renewable energy technologies. Indeed, China is constructing
impressive amounts of renewable energy installations, but the United States remains one of the
world leaders in renewable energy capacity and deployment. For example, Table 7 shows that the
United States leads the world in installed non-hydropower renewable electricity generation
capacity, biomass power, and geothermal power. While the United States ranked second, behind
China, in total wind power capacity, the United States ranked first in 2010 in terms of operational
wind power capacity.123 In 2009, the United States generated more electricity from non-hydro
123
REN21. 2011. Renewables 2011 Global Status Report (Paris: REN21 Secretariat), http://www.ren21.net/
REN21Activities/Publications/GlobalStatusReport/GSR2011/tabid/56142/Default.aspx.
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U.S. Renewable Electricity Generation: Resources and Challenges
renewable energy sources than any other country in the world. However, when hydropower is
included, China led the world in terms of total renewable electricity generation (see Figure 16).
Table 7. Existing Renewable Energy Capacities at the End of 2010
(Country ranking for selected categories)
Rank
Renewables
power
capacity
(not
including
hydro)
Renewables
power capacity
(including hydro)
1
United States
China
2
China
3
Wind
power
Biomass
power
Geothermal
power
Solar PV
Solar hot
water/heat
China
United States
United States
Germany
China
United States
United States
Brazil
Philippines
Spain
Turkey
Germany
Canada
Germany
Germany
Indonesia
Japan
Germany
4
Spain
Brazil
Spain
China
Mexico
Italy
Japan
5
India
Germany/ India
India
Sweden
Italy
United States
Greece
Source: REN21. 2011. Renewables 2011 Global Status Report (Paris: REN21 Secretariat), available at
http://www.ren21.net/REN21Activities/Publications/GlobalStatusReport/GSR2011/tabid/56142/Default.aspx.
Figure 16. Total Net Renewable Electricity Generation, 2009
(Selected Countries)
Source: Energy Information Administration, International Energy Statistics, http://www.eia.gov/cfapps/
ipdbproject/IEDIndex3.cfm?tid=6&pid=29&aid=12.
Notes: Non-hydro includes generation from wind, solar, geothermal, tide and wave, and biomass and waste.
Future Trends in Renewable Electricity
The potential for renewable electricity generation in the United States is very large, yet current
use of renewable energy for electricity production is relatively modest, constituting only 11% of
total electricity generation and 8% of total energy consumption. Based on the current status of
Congressional Research Service
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U.S. Renewable Electricity Generation: Resources and Challenges
renewables in the United States, policy makers may consider some key questions about the future
of renewable energy:
•
Should the United States actively seek greater use of renewable energy to supply
electricity, or should the energy and electricity markets be allowed to work
without further interference with the existing structure of subsidies and
incentives?
•
If greater use of renewable energy for electricity is desired, what are the key
barriers or actions that should be addressed by federal policy?
Future trends in renewable electricity will depend heavily on the cost of both renewable
technologies and fossil fuel costs, and on government incentives for renewable energy. In the
absence of subsidies for renewable electricity technologies, and in the absence of accounting for
external costs of using fossil fuel combustion to generate electricity, several renewable electricity
technologies are currently not commercially viable, or only marginally so. Reference case
projections by EIA of growth in wind and solar electricity to 2035 are predicated on the use of
renewable portfolio standards, renewable fuel standards, and subsidies in the tax code.124 With
low coal and natural gas prices, and high renewable energy technology costs, and the absence of
regulation or subsidies, renewable electricity may not increase significantly. Without some form
of carbon pricing or other consideration of the externalities of fossil fuel combustion, the United
States may remain in an era of relatively low-cost fossil fuel electricity for decades.
However, policy makers may decide that growth in renewable electricity is desirable because of
concerns about greenhouse gas emissions and climate change, because fossil fuel supplies are
ultimately finite, and because of a desire to position the United States as a global leader for
renewable energy technology and manufacturing. Renewables could be made more cost
competitive by means of improved renewable technologies or revised cost of carbon-based fuels,
but financial or regulatory incentives may be required to make certain renewable sources more
economically viable in the short term.
In the event that levelized costs of renewable electricity become competitive with those of fossil
fuel electricity, the additional issues of intermittency/variability, land-use and footprint, the need
for additional transmission, plus other resource and environmental impacts of renewable
electricity will need to be addressed by local, state, and federal officials and policy makers.
Conclusion
Cumulative U.S. renewable electricity generation capacity more than doubled from 2006 to 2010,
increasing from approximately 22 GW to nearly 55 GW.125 In 2010, renewable sources of energy
provided approximately 11% (7% from hydropower and 4% from other renewables) of total net
electricity generation and the EIA AEO 2011 reference case projects that renewable electricity
124
Energy Information Administration, Annual Energy Outlook 2011, http://www.eia.gov/forecasts/aeo/pdf/
0383(2011).pdf.
125
Eckhart, M. “Renewable Energy Exceeds 50 GW and Enters Decade of Scale-Up,” Infrastructure Solutions
Magazine, April 2011, available at http://www.acore.org/wp-content/uploads/2011/04/Infrastructure-Magazine-ArticleV4.pdf.
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U.S. Renewable Electricity Generation: Resources and Challenges
generation will increase to between 14% and 15% by 2035.126 The renewable electricity
generation research conducted for this report indicates that the potential may exist for renewable
energy sources to make a sizeable contribution toward total U.S. electricity generation demand.
However, renewable electricity generation will likely encounter serious challenges, issues, and
barriers as technologies and projects look to realize large-scale deployment. As Congress
evaluates various energy policy objectives, policy makers may move to holistically evaluate the
potential intended benefits, such as emissions reduction and job creation, with potential risks and
consequences, such as electricity cost/price increases and electricity delivery reliability issues
associated with increasing renewable electricity generation.
Author Contact Information
(name redacted)
Analyst in Energy Policy
/redacted/@crs.loc.gov, 7-....
(name redacted)
Section Research Manager
/redacted/@crs.loc.gov, 7-....
Acknowledgments
The authors would like to recognize the valuable contributions from Steven Deitz and Amber Wilhelm
during the preparation of this report.
126
Energy Information Administration, “Annual Energy Outlook 2011: with projections to 2035,” DOE/EIA0383(2011), April 2011, available at http://www.eia.gov/forecasts/aeo/pdf/0383(2011).pdf.
Congressional Research Service
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