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2
Resource Base
The United States has a significant amount of renewable energy resources. This
chapter details the resource base from wind, solar, geothermal, hydroelectric, and
biomass sources of energy that could make a material contribution to the nation’s
electricity supply. Discussion of this resource base sets the stage for the scenarios of
renewable energy deployment in Chapter 7.
Most renewable electricity generation must be located near the source of the
renewable energy flux1 being captured and converted into electricity. Hence, renewable
energy sources are by nature local or regional, and those that may be unable to contribute
significantly to total U.S. electricity generation, could still contribute to a substantial
share of the renewable-based electricity generated in regions where that specific type of
renewable energy flux is abundant and well suited for development.
2007 BASELINE VALUES
In 2007 total U.S. electricity generation was 4.2 million GWh and peak
generation capacity nationally was 998 GW (EIA, 2008); the average annual U.S. electric
generation load in 2007 was thus approximately 480 GW. For reference, total U.S.
primary energy consumption in 2007 was approximately 100 EJ. At approximately 35
percent generation efficiency, 42 EJ (corresponding to 11.7 million GWh at 100 percent
generation efficiency) was used to provide the 4.2 million GWh of electricity generated
in the United States in 2007.
WIND POWER
According to a study done by Pacific Northwest National Laboratory, the total
estimated electric energy potential of wind for the continental United States is 11 million
GWh per year from regions rated as Class 3 and higher2 (Elliott et al., 1991)—a value
greater than the 4.2 million GWh of electric energy generated in the United States in
2007. In energy units, 11 million GWh represents 40 EJ of energy, as compared to the
2007 domestic primary energy consumption of 100 EJ.
1
Energy flux is defined as the rate of energy transfer through a unit area.
2
Wind class is a measure of wind power density, which is measured in watts per square meter and is a
function of wind speed at a specific height.
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The domestic large-scale wind electric energy resource estimate of 11 million
GWh is uncertain, however, and the actual wind resource could be higher or lower. One
source of uncertainty is that the yearly wind electricity potential from the PNL study was
estimated from point-source measurements of the wind speed at a height of 50 m (Elliott
et al., 1986). Modern wind turbines can have hub heights of 80 m or higher, where more
wind energy resource is likely to be available. However, computer simulations of very
large scale wind farm deployment show that an agglomeration of point-source wind
speed data over large areas can significantly overestimate the actual wind energy resource
base (Roy et al., 2004). Just as a large wind turbine will overshadow a wind turbine
farther downwind, so a very extensive wind farm will also overshadow other wind farms
downwind. Specifically, when the downwind length of the wind farm is comparable to,
or larger than, the scale length of the atmosphere (approximately 50 km), then the point-
source measurement extrapolation is no longer valid, and significantly overestimates the
actual available wind energy resource (Keith et al., 2004).
Another consideration is that wind field deployment at levels needed to produce 5
million to 10 million GWh of electricity would entail extraction of a significant portion of
the energy from the wind field of the continental United States for conversion into
electric energy. Continental-scale simulations indicate that high levels of wind power
extraction could, to various degrees, affect regional weather as well as climate. In
addition to limiting the efficiency of large scale wind farms, model calculations suggest
that the extraction of wind energy from very large scale wind farms could have some
measurable effect on weather and climate at the local or even continental and global
scales (Roy et al., 2004; Keith et al., 2004).
More detailed meso-scale modeling and measurements are needed to clearly
delineate the total U.S. extractable wind energy potential and the portion that can be
extracted without significant environmental impacts. Modeling activities are under way
to determine the optimal distance between wind farms to minimize power loss (Frandsen
et al., 2007). Assuming an estimated upper limit of 20 percent of the energy in the wind
field for extraction, both regionally and on a continental scale, and a total U.S. onshore
wind electricity value of 11 million GWh/yr, an upper value for the extractable wind
electric potential would be about 2.2 million GWh/yr, equal to more than half of the
electricity generated in 2007. This estimate assumes that large scale wind farms are
installed over all suitable Class 3 and higher wind speed areas in the continental United
States, as mapped in Figure 2-1 (AWEA, 2007; DOE, 2008). The preceding analysis is
limited to onshore wind energy resources.
Significant offshore wind energy resources also exist, and Europe has begun to
develop its offshore resources. The available offshore wind capacity has been estimated
at 907 GW for distances 5-50 nautical miles offshore (NREL, 2004a), which corresponds
to 1.6 GWh/yr, assuming extraction of 20 percent of the energy in the wind field, i.e.,
almost 40 percent of 2007 U.S. electricity generation. The water at these locations varies
from less than 30 meters to greater than 900 meters deep. Since a large percentage of the
population lives along the coasts of the continental United States, offshore wind could be
a renewable resource located close to population centers. These resources are also
mapped in Figure 2-1 for the continental United States. Several states are now focusing
wind development efforts on offshore wind resources, especially where onshore wind
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resources are well developed. However, offshore projects have been fraught with siting
controversies, including the proposed development off Cape Cod, Massachusetts.
SOLAR POWER
The solar energy resource is extremely large. Taking 230 W/m2 as a
representative midlatitude, day/night average value for solar insolation3 and 8 × 1012 m2
as the area of the continental United States yields a yearly averaged, area-averaged,
power generation potential of 1.84 million GW (Clean Edge, 2008). The solar resource
thus provides annually to the continental United States the equivalent of about 16 billion
GWh of electric energy, and at a 10 percent average conversion efficiency would
therefore provide 1.6 billion GWh/yr of electricity. At a 10 percent conversion
efficiency, coverage of 0.25 percent of the land area of the continental United States
would be required to generate the 4.2 million GWh of electric energy generated
domestically in 2007.
Solar Photovoltaic Power
Flat-plate photovoltaic (PV) arrays effectively use both direct and diffuse
sunlight, thus enabling deployment over a larger geographic region than is possible with
concentrated solar power. Although the yearly averaged total insolation varies
significantly over the continental United States, the regional variation is approximately a
factor of two, as shown in Figure 2-2. Estimates of the rooftop area suitable for
installation of photovoltaic systems have been performed state-by-state for the whole
United States. An analysis by the Energy Foundation and Navigant Consulting
eliminated roofs on residences that were not generally facing southward and roofs that
had too high a slope for routine installation of solar PV panels; considered the impacts of
shading by trees, the presence of heating and air conditioning units, and other obstacles
on the remaining viable portion of the rooftops, but did not account for snow; and. added
suitable flat commercial building rooftop space to the total (Chaudhari et al., 2004). The
analysis concluded that 22 percent of the available residential rooftop space, and 65
percent of commercial building rooftop space, was technically suitable for PV system
installation. This total rooftop area, along with state-by-state values for the average
insolation, yielded a technical solar PV-based peak capacity of 1500-2000 GW at
commercially available PV system conversion efficiencies of 10-15 percent. At an
average 20 percent capacity factor, this peak-capacity value would thus result in the
production of 13 million to 17.5 million GWh/yr of electric energy, still much larger than
the 4.2 million GWh/yr of electricity generated in the United States in 2007. More
conservative estimates indicate that existing suitable rooftop space could provide 0.9
million to1.5 million GWh/yr of PV-generated electricity (ASES, 2007). Clearly, with
some (or perhaps no) amount of land set-aside for flat-plate PV-based solar electricity
generation beyond that already generated in existing rooftop areas, flat-plate solar PV has
3
Solar insolation is the amount of solar energy striking a flat surface per unit area per unit of time.
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the potential to supply significantly more electricity than was generated in 2008 in the
United States.
Concentrating Solar Power
Concentrating solar power (CSP) systems can only use the focusable, direct beam
portion of incident sunlight and is thus limited to favored sites, primarily in the
Southwest, that have abundant direct normal solar radiation. Figure 2-3 shows that
despite variations in radiation intensity in the Southwest, all six states there have
attractively high levels of insolation. A recent analysis by the Western Governors’
Association identified suitable land area that has a high average insolation of more than
6.75 kWm-2day-1; it excluded land areas having a slope greater than 1 percent or a
continuous area of smaller than 10 km2, and national parks, nature reserves, and urban
areas (WGA, 2006a). The analysis concluded that the Southwest has a concentrated solar
power electricity peak generation capacity of 7,000 GW. With an average annual
capacity factor of 25-50 percent for CSP, depending on the thermal storage used for a
plant, this land area could theoretically produce 15 million to 30 million GWh of electric
energy per year, again significantly more than the 4.2 million GWh total U.S. electricity
supply in 2007.4 Only a fraction of this land area at present could be developed
economically for CSP-based electricity generation due to factors such as generation and
transmission costs discussed in later chapters.
GEOTHERMAL POWER
Hydrothermal Energy
Geothermal energy exists as underground reservoirs of steam, hot water, and hot
dry rocks in Earth’s crust. Hydrothermal electric generating facilities use hot water or
steam extracted from these reservoirs, and supply this energy to turbines to generate
electricity. For reference, according to the U.S. Geological Survey (USGS, 1979),
thermal energy stored as hydrothermal resources ranges between 2,500 EJ (0.67 billion
GWh) and 9,700 EJ (2.7 billion GWh).
A regional study of known geothermal resources in the western United States
found that 13 GW of electric power capacity exists in 140 hydrothermal sites identified in
the region (Figure 2-4; WGA, 2006b). Of these 13 GW, the Western Governors’
Association reported that 5.6 GW of capacity was considered viable for commercial
development by 2015, which reflects the consensus of geothermal technology,
development, and power-generating operations experts. Since hydrothermal facilities
typically operate at 90 percent capacity during much of their operational life, the 13 GW
from identified hydrothermal resources could provide up to 0.1 million GWh/yr of
baseload electric energy. These same western states consumed slightly more than 1
million GWh/yr of electricity from 2000 through 2003 (WGA, 2006a). A nationwide
assessment of the shallow hydrothermal resource base estimates an availability of 30
4
See Figure 2 and Table 1 on page 83 of the ASES report (ASES, 2008).
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GW, with an additional 120 GW potential from unidentified hydrothermal resources that
show no surface manifestations (NREL, 2006). The NREL study estimated that 10 GW
could be developed by 2015.
Enhanced Geothermal Systems
Enhanced geothermal systems (EGSs) are engineered reservoirs created to extract
heat from low-permeability and/or low-porosity geothermal resources, as defined by the
Department of Energy. EGSs tap the vast heat resources available due to temperature
gradients between the surface and depths of up to 10 km, as shown in the maps in Figure
2-5. The geothermal energy resource base located beneath the continental United States,
defined as the total amount of heat trapped to 10 km depth, is estimated to be in excess of
13 million EJ (3.6 trillion GWh) (MIT, 2006). Figure 2-6 separates this heat content into
a function of temperature and depth. The heat stored is more than 130,000 times the total
2005 U.S. energy consumption of 106 EJ of energy. The extractable portion of this
resource has been estimated at 200,000 EJ, i.e., about 2,000 times more than the primary
energy consumed in the United States in 2005. At a conversion efficiency of 15 percent,
a reasonable value in view of the typical ~200 ºC temperature difference between the
temperature of the resource and the ambient temperature at the surface, the extractable
geothermal resource could then, in principle, provide 30,000 EJ of electric energy.
In addition to the total amount of available energy, the rate at which it is extracted
is also important. The mean geothermal heat flux over land at Earth’s surface is
approximately 60 mW/m2 and in many areas is significantly less. An efficiency of 15
percent is estimated for electricity generation from this relatively low temperature heat in
a turbine. Thus, on average, the extractable electric power density from the geothermal
resource on a renewable basis is about 10 mW/m2. At an extracted, producible electric
power density of 10 mW/m2, generation of 100 GW of electric power (22 percent of the
2005 average U.S. electric load and 10 percent of the 2005 U.S. electric generation
capacity) would thus require a minimum land area footprint of 1 × 1013 m2.5 For
comparison, the land area of the continental United States is 8 × 1012 m2, so the footprint
needed to provide 20 percent of the 2005 average electric load from sustainably produced
geothermal energy would exceed the total land area of the continental United States.
In practice, the in-place geothermal heat would be extracted at rates in excess of
the natural geothermal heat flux; such extraction rates are not sustainable in the long
term, because they would deplete the heat more rapidly than it would be restored by the
natural geothermal flux. Such heat mining would reduce the land area needed to be
tapped by allowing heat extraction to exceed the 10 mW/m2 replacement rate. Indeed, a
recent MIT report (2006) notes that some temperature drawdown should occur if such
reservoirs are used most efficiently. In its analysis of the resource potential for EGS, the
MIT report limited this heat mining by assuming that geothermal reservoirs would be
abandoned when the temperature of the rocks fell by 10-15 °C. Because heat extraction
may not be uniform, the MIT report assumes that reservoirs would have a lifetime of 30
years, with periodic re-drilling, fracturing, and hydraulic simulation. The report
estimates that reservoirs should be able to recover to their original temperature conditions
5
1 × 1011 W/(10-2 W m-2) = 1 × 1013 m2.
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within 100 years after abandonment. It contends that if only 10 percent or less of the
stored heat is mined at any time, enhanced geothermal energy could be considered a
renewable resource, because the huge resource base would support abandoning reservoirs
for the100 year-period needed to restore the original temperature.
HYDROPOWER
Conventional Hydroelectricity
Conventional hydroelectricity generation in 2007 provided 0.25 million GWh.
Hydroelectric generation capacity was 98 GW, representing about 9 percent of the total
U.S. electric generation capacity (EIA, 2009).
Because use of the conventional hydroelectric resource is generally accepted to be
near the resource base’s maximum capacity in the United States, further growth will
largely depend on non-conventional hydropower resources such as low-head power6 and
on microhydroelectric generation.7 A 2004 U.S. DOE study of total U.S. water-flow-
based energy resources, with emphasis on low-head/low-power resources, indicated that
the total U.S. domestic hydropower resource capacity was 170 GW of electric power, of
which 21 GW was from low-head/low-power, 26 GW was from high-head/low-power,
and 123 GW was from high-head/high-power (DOE, 2004). These numbers represent
only the identified resource base that was undeveloped and was not excluded from
development. A subsequent study assessed this identified resource base for feasibility of
development (DOE, 2006). After taking into consideration local land-use policies, local
environmental concerns, site accessibility, and power transmission, the total potential
domestic hydroelectric resource capacity was estimated to be100 GW of electric power.
This value was reduced to 30 GW of potential hydroelectric capacity after applying
development criteria (DOE, 2006). A report from EPRI determined that 10 GW of
additional hydroelectric resource capacity could be developed by 2025 (EPRI, 2007). Of
the 10 GW of potential capacity, 2.3 GW would result from capacity gains at existing
hydroelectric facilities, 2.7 GW would come from small and low-power conventional
hydropower facilities, and 5 GW would come from new hydropower generation at
existing, non-powered, dams.
Hydrokinetic Power—Wave, Tide, and River Energy
Hydrokinetic energy is the energy associated with the flow of water, such as wave
energy and the energy in water currents, including tides and rivers. As shown in Table 2-
1, there is significant interest in developing such energy resources, based on permits filed
with the Federal Energy Regulatory Commission. Permit activity is not a reliable
6
Vertical difference of 100 feet or less in the upstream surface water elevation (headwater) and the
downstream surface water elevation (tailwater) at a dam.
7
Hydroelectric power installations that produce up to 100 kW of power.
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predictor of future development of hydrokinetic resources, however, because often
developers will apply before planning the facility or obtaining financing.
TABLE 2-1 Permit Activity for Hydrokinetic Resources (in
megawatts of proposed capacity)
Issued Pending
Wave 170-330 1,270-2,150
Current 1,025-3,350 270-375
Tide 140-285 445
Inland 100 3,550
SOURCE: Federal Energy Regulatory Commission; presented in Miles
(2008).
According to an EPRI report that assessed total U.S. wave energy potential
(EPRI, 2005), all the wave energy in the coastal states of Washington and California
combined could produce 0.44 million GWh/yr, and the wave energy from the Maine,
New Hampshire, Massachusetts, Rhode Island, New York, and New Jersey coasts
combined could produce 0.12 million GWh/yr (Figure 2-7). These values should be
reduced by 10 to 15 percent to account for generation losses, resulting in a total electric
generation potential of about 0.07 million GWh from the entire continental U.S. wave
energy resource. Exhaustive use of the entire wave energy resource would therefore be
required to produce less than 2 percent of the 4.2 million GWh of the electricity
generated in the United States in 2007.
The largest U.S. wave resource lies off southern Alaska, which has an estimated
resource base of 1.25 million GWh/yr, as shown in Figure 2-7 (EPRI, 2005). Extraction
of this total amount of energy would involve tapping wave energy flows over relatively
large areas of ocean, and the EPRI report also does not indicate how the electric energy
over such a large area of the ocean would be collected or transmitted to consumers in the
lower 48 states.
The 2005 EPRI study also looked at tidal energy from a series of sites identified
in Alaska, Washington, California, Massachusetts, Maine, New Brunswick, and Nova
Scotia (EPRI, 2005). The total combined resource was estimated to have an annual
average electric generation potential of 152 MW, which corresponds to an annualized
electric energy production of 1,300 GWh/year (EPRI, 2005)—enough to provide, if the
stated resource were used in whole, 0.03 percent of the 2005 domestic generated electric
energy.
EPRI’s study of the electric energy potential in river currents yielded a value of
0.11 million GWh/year (EPRI, 2005). Thus, development of the entire U.S. river current
electricity potential would be required to produce 0.1 million GWh/year, which would
represent less than 3 percent of the 2005 domestic electric energy production.
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BIOPOWER
Biomass Resource Base
The USDA/DOE billion-ton study (2005) identified the potential for use of 1.3
billion dry tons (1 dry ton = 1,000 kg) per year of biomass without adversely affecting
food production. The area involved in producing this resource base comprises 448
million acres (1.8 × 1012 m2) of agricultural land (consisting of both cropland and
pasture), which is 23 percent of the land area of the continental United States, and 672
million acres of forestland (2.7 × 1012 m2), representing 34 percent of the land area of the
continental United States (USDA/DOE, 2005). Agricultural land totaled 455 million
acres in 1997, the year of the most recent complete inventory of land use. Hence, the
total land area assumed to be used for such biomass farms is just over 57 percent of the
total land area of the lower 48 states.
The amount of biomass sustainably removed from domestic agricultural lands and
forestlands is 190 million dry tons annually, with about 142 million dry tons coming from
forestland and the remainder coming from croplands. Only about 20 percent of this
biomass is now in use. The USDA/DOE report projected that approximately 370 billion
tons (double the present biomass production) could be made available sustainably for
biomass uses from 672 million acres of forestland. To accomplish this would require a
variety of methods, including using wood for electric power generation instead of
burning that wood for forest management (as is done at the present time), using pulp
residues, and logging residues.
The USDA/DOE report also projected that agricultural lands (cropland, idle
cropland, and cropland pasture), which produce approximately 50 million tons per year
for biomass uses, have the potential, within 35 to 40 years, to yield nearly 1 billion dry
tons of biomass. This represents a 20-fold increase in the sustainable biomass yield
relative to the present value. Of this projected 1 billion dry tons that might be available
in 35-40 years, 300million to 400 million tons would come from crop residues and 350
million tons would result from the substitution of high-yield perennial biomass crops for
other land uses on at least 40 million acres of land.
The geographical distribution of the biomass resource base shown in Figure 2-8
comes from Milbandt (2005), which estimated a lower overall biomass resource base
than does the USDA/DOE report. The geographic distribution of this resource assessment
is estimated from the locations of (1) Conservation Reserve Program lands suitable for
growth of switchgrass and mixed high-diversity prairie or other crops, (2) residuals from
agriculture and forestry, and (3) municipal solid waste.
According to the USDA/DOE study, providing 1.3 billion dry tons per year of
biomass would require increasing the yields of corn, wheat, and other small grains by 50
percent; doubling residue-to-grain ratios for soybeans; developing more efficient residue-
harvesting equipment; managing cropland with no-till cultivation; growing perennial
crops whose output is primarily dedicated to energy purposes on 55 million acres of
cropland, idle cropland, and cropland pasture; using animal manure in excess of what can
be applied on-farm for soil improvement; and using a larger fraction of other secondary
and tertiary residues for biomass production. Attaining these levels of crop yield
increases and collection would require research and new technologies such as genetic
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engineering to increase production. The ~50 million acres devoted to high-yield
perennials were projected to have an average annual crop yield of approximately 8 dry
tons/acre, in order to provide ~400 million dry tons of biomass annually from that portion
of land. Supporting the billion-ton estimate was the assumption that agricultural lands in
the United States could potentially provide in excess of 1 billion dry tons of sustainably
collectable biomass, while continuing to meet food feed and export demands. This
estimate included 446 million dry tons of crop residues (for example, more than 250
million tons from corn stover, as compared to the present value of 75 million tons
annually), 377 million dry tons of perennial crops,8 87 million dry tons of grains used for
biofuels, and 87 million dry tons of animal manure, process residues, and other residues
generated in the consumption of food products.
The forthcoming report of the America’s Energy Future (AEF) Panel on
Alternative Liquid Transportation Fuels (see Appendix A) provides another estimate of
the biomass resource base (NAS-NAE-NRC, 2009). It estimates that an annual supply of
400 million dry tons of cellulosic biomass could be produced sustainably, using
technologies and management practices available in 2008, an amount that could likely be
increased to about 550 million dry tons by 2020. The AEF alternative liquid fuels panel
judges that those estimated quantities of biomass can be produced from dedicated energy
crops, agricultural and forestry residues, and municipal solid waste with minimal impacts
on U.S. food, feed, and fiber production, and with minimal adverse environmental
impacts. The AEF alternative liquid fuels panel did not extend its estimate to 2035, as
did the 2005 USDA/DOE report.
Electricity Generation from Biomass
Based on 2005 biomass production levels, full use of the 190 million dry tons of
sustainable biomass produced in the United States, at 17 GJ (1 GJ = 1 × 109 J)/dry ton,
and at 35 percent efficiency for conversion of the heat produced from biomass
combustion into electric energy, would provide energy of 1.1 EJ9. In other words, 100
percent of the sustainable biomass produced domestically in 2005, if used entirely for
electricity generation, would produce 0.306 million GWh/yr of electricity, or 7.3 percent
of the 2007 domestic electricity generation of 4.2 million GWh/yr. Using the AEF
alternative liquid fuels panel’s more recent resource average value of ~500 million tons
of biomass (NAS-NAE-NRC, 2009), a total of 0.8 million GWh/yr of electricity could be
produced, which is 19 percent of 2007 U.S. electricity generation.
Increasing the available biomass production to 1 billion tons and using it solely
for electricity generation would produce 6 EJ, which is equal to 1.6 million GWh/yr of
electricity, representing approximately 40 percent of the domestic electric generation in
2007. If, however, 75 percent of this biomass were used to produce cellulosic ethanol or
other biofuels, then only 25 percent of the biomass would be available for electricity
generation. Thus, 250 million tons of biomass, projected as potentially available in 35-40
years through the use of more than 60 percent of the land area of the continental United
8
The perennial crops are crops dedicated primarily to energy and other products and will likely include
a combination of grasses and woody crops.
9
1.9 × 108 tonnes × (1.7 × 1010 J/tonne) at 35 percent electric generation efficiency.
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States, would be capable of producing 0.416 million GWh of electricity, or 10 percent of
the 2007 U.S. electricity generation. This potential represents more than 7 times the
actual electric generation from biomass in 2005 (0.054 million GWh, which accounted
for just above one percent of the 2007 U.S. electricity generation).
FINDINGS
Shown below in bold text are the most critical elements of the findings of the
AEF Panel on Electricity from Renewable Resources, based on its consideration of the
U.S. resource base for generation of renewable electricity.
In summary, the United States has significant renewable energy resources, which
combined together, have the potential, in principle, to provide more electric power than
the total existing installed peak capacity and more electric energy annually than the total
electricity consumed domestically in 2005. This resource base is spread widely across
the United States. However, as described in the remainder of this report, many other
factors will determine what portion of these resources will actually be incorporated into
the electricity system; some of these factors include the costs of technologies needed to
transform these resources into electricity; the expanded capacity and associated costs for
transmission to bring this electricity into load centers; and the need to compensate for
intermittency.
Solar and wind renewable resources offer significantly larger total energy
and power potential than do other domestic renewable resources. Although solar
intensity varies across the nation, the land-based solar resource provides a yearly average
of more than 5 × 1022 J (13.9 million TWh) and thus exceeds, by several thousand-fold,
present annual U.S. electrical energy demand, which totals 1.4 × 1019 J (~4,000 TWh).
Hence, at even modest conversion efficiency, solar energy is capable, in principle, of
providing enormous amounts of electricity without stress to the resource base. The land-
based wind resource is capable of providing at least 10 percent to 20 percent, and in some
regions potentially higher percentages, of current electrical energy demand. Other (non-
hydroelectric) renewable resources can contribute significantly to the electrical energy
mix in some regions of the country.
Renewable resources are not distributed uniformly in the United States.
Resources such as solar, wind, geothermal, tidal, wave, and biomass vary widely in space
and time. Thus, the potential to derive a given percentage of electricity from
renewable resources will vary from location to location. Awareness of such factors
is important in developing effective policies at the state and federal level to promote
the use of renewable resources for generation of electricity.
REFERENCES
ASES (American Solar Energy Society). 2007. Tackling Climate Change in the United
States: Potential Carbon Emission Reductions from Energy Efficiency and
Renewable Energy by 2030. Washington, D.C.
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AWEA (American Wind Energy Association). 2007. 20 Percent Wind Energy
Penetration in the United States: A Technical Analysis of the Energy Resource.
Washington, D.C.
Chaudhari, M., L. Frantzis, and T.E. Holff. 2004. PV Grid Connected Market Potential
Under a Cost Breakthrough Scenario. The Energy Foundation and Navigant
Consulting. San Francisco, Calif.
Pernick, R., and C. Wilder. 2008. Utility Solar Assessment (USA) Study: Reaching Ten
Percent Solar by 2025. Clean Edge Inc. and Co-op America Foundation,
Washington, D.C.
DOE (Department of Energy). 2004. Water Energy Resources of the United States with
Emphasis on Low Head/Low Power Resources. DOE/ID-11111. Washington,
D.C.
DOE. 2006. Feasibility Assessment of the Water Energy Resources of the United States
for New Low Power and Small Hydro Classes of Hydroelectric Plants.
Washington, D.C.
DOE. 2008. 20% Wind Energy by 2030: Increasing Wind Energy’s Contribution to U.S.
Electricity Supply. Washington, D.C.
DOE Energy Efficiency and Renewable Energy. 2008. United States—Wind Resource
Map. Washington, D.C. Available at
http://www.windpoweringamerica.gov/pdfs/wind_maps/us_windmap.pdf.
EIA (Energy Information Administration). 2008. Annual Energy Review 2007.
Washington, D.C
EIA. 2009. Electric Power Annual. Washington, D.C. Available at
http://www.eia.doe.gov/cneaf/electricity/epa/epa_sum.html; table available at
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