On January 16, 2006, the Energy Analysis Office (EAO) of the National
Renewable Energy Laboratory (NREL) issued for the Office of Science a
DRAFT analysis, for comment, of the technical potential for renewables.
EAO's preliminary analysis included a summary table representing
and ultimate technical potential for renewable energy resources
and market considerations are not taken into account). The seven-page
document is entitled "Near-Term Practical and Ultimate Technical
for Renewable Resources."
The representation for the near term potential is given in percentage
electric generation in the United States in 2020. Near-term potential
restricted by near-term challenges, such as infrastructure and
problems, electricity storage, and technological ability to use the
resource. Nonetheless, the "near-term practical" potential of
resources as a percent of U.S. electricity generation in 2020 is
to be 99-124 percent, or - in terms of primary energy - as 47-55
quads/year (electricity only).
The ultimate technical potential is a compilation of previous estimates
and calculations based on those estimates. While the analysis assumes
near-term challenges will be overcome, the ultimate potential does
for constraints on technologically insurmountable goals, such as
accepted restrictions on offshore wind facility distance from shore (200
meters), and on drilling capability for enhanced geothermal systems (10
of depth). The table suggests that the ultimate technical potential for
renewable resources could be as much as 8,529 quads/year
The resulting estimates offer rough estimates of the potential
contributions from renewable resources, not economically or
The text of the DRAFT paper reads as follows:
Current Renewable Resource Use
Currently used renewable energy resources are drawn from a variety of
sources. The current installed nameplate capacity total is a summation
verified, functioning electric-generation facilities (REPIS 2005).
Delivered electricity is based on 2004 electricity production (EIA
For all the renewable electric technologies except biomass, primary
energy required to produce electricity is calculated based on an average
heat rate of 10,000 Btu/kWh for existing thermal power plants (EIA
For biomass, a measured heat rate for power plants, 9,000 btu/kwh, is
used (EIA 2005b). For those renewable energy forms that also contribute
to heat and fuels markets, total primary energy shown is larger than the
thermal energy required to produce only electricity (EIA 2005a).
NEAR-TERM PRACTICAL POTENTIAL
The amount of electricity potentially produced by renewables is shown
percentage of the total projected U.S. generation in 2020: 5,085 billion
kWh (EIA 2005b).
Biomass is the only renewable energy form cited that can be used as
electricity or fuel. Because we cannot predict the distribution of
biomass use between electricity and fuel, we make two estimates. The
first assumes 100 percent of biomass is used for electricity, and the
second assumes that 100 percent is use for fuel. The baseline amount of
energy for these is the same, because it is limited by physical
availability of biomass. Perlack (2005) estimates 1.3 billion dry tons
biomass is possible with the use of non-food cropland and forestland in
the long run. To determine the near-term potential the mid-range
scenarios from Perlack (2005) to identify a near-term range of 593
to 968 million dry tons. The biomass-to-energy conversion used is an
average of energy from biomass types of just more than 12 million btus
ton (NREL 2005c). This range yielded a potential of between 8 and 13
quads of energy in the near term. To estimate the amount of electricity
that can be generated from the range, we assume a power plant heat rate
9,000 Btu/kWh (EIA 2005b). The result is 17-28 percent of total U.S.
electric generation. Biomass as a fuel potential is expressed as a
percentage of projected 2020 petroleum demand: 26 million barrels per
(EIA 2005b). Using 8-13 quads of available biomass energy, and a 49
percent fuel plant conversion efficiency, biomass could contribute 9-14
percent of the national petroleum demand in 2020.
Because of technology limitations, only hydrothermal energy is
in the short term. In 1979, the United States Geological Survey (USGS)
estimated that there were about 22 GW of discovered hydrothermal
(USGS 1979). While this estimate is dated, there has been no
authoritative study of the potential since that time. Using a 95
capacity factor (NREL 2005c), 22 GWs represents 2 quads of energy (or
percent of U.S. electric generation) in 2020.
Full hydroelectric potential is 140 GW (Hall et al 2003), which would
provide 9.4 percent of electric generation in 2020, assuming today's
national average capacity factor of 0.39 (NREL 2005c). Assuming a
Btu/kWh power plant heat rate conversion, this is equal to about 5.0
of primary energy.
In the short term, the full potential of mechanical (wave, tidal, and
current) electrical generation is assumed. This resource is estimated
have a full potential of 30 GW installed nameplate capacity. Assuming
constant power and a power plant conversion heat rate of 10,000 Btu/kWh,
this translates to 2.3 quads of primary energy (or 4.5 percent of the
electric generation) projected for 2020.
For the near-term technical photovoltaic potential, it is assumed that
there will be no storage for solar energy, and no PV generation will be
wasted. This implies that none of the nighttime loads can be met by
solar, and much of the load at dawn cannot be met (if PV capacity were
sufficient to meet such loads, PV output at midday would exceed loads,
wasting energy). These assumptions severely limit the impact of PV on
electric system. The PV impact would be even more limited if one also
took into account the many conventional fossil and nuclear plants that
must run all the time. In this case, the PV capacity would have to be
even smaller to keep from wasting PV generation.
The near-term potential for concentrated solar power (CSP) is assumed
be the minimum of the projected in-state electrical load and the actual
CSP resources in that state. In all cases, the projected state
load is the minimum. Therefore, the near-term CSP potential is the
electric load of the state in which the CSP resource resides. In 2020,
the projected load for states for CSP potential is expected to be 12
percent of the total U.S. generation, creating an upper bound for CSP
electrical generation. Assuming a 10,000 Btu/kWh heat rate for power
plants, the estimated primary energy to create this electricity is 6
The short-term wind potential is limited by grid reliability/stability
concerns to be 20 percent of total generation [based on Wan and Parsons
(1993) estimate of between 4 percent and 50 percent]. Assuming a power
plant heat rate of 10,000 Btu/kWh, the primary energy equivalent is 10
ULTIMATE TECHNICAL POTENTIAL
Ultimate technical potential differs from the short-term potential by
set of general assumptions for each resource type and one more general
assumption. The general assumption is that the electricity grid can
adjust to the diverse electricity fed into it by adding storage,
transmission, ancillary services, etc. Moreover, the ultimate
do not limit the amount of renewable electricity as a function of total
projected electricity demand. As with the short-term assumptions,
economic and market constraints are not accounted for in this long-term
Biomass is the only renewable energy form cited that can be used as
electricity or fuel. Because we cannot predict the distribution of
biomass use between electricity and fuel, we make no assumption
the differences between the use of biomass for electricity and biomass
fuel. The baseline amount of energy for these is the same, because it
limited by physical availability of biomass. Perlack (2005) estimates
billion dry tons of biomass is possible with the use of non-food
and forestland. The biomass-to-energy conversion used is an average of
energy from biomass types of just more than 13 million btus per ton
2005c). The total energy potential for biomass is 17 quads. To
the amount of electricity that can be generated from 17 quads, we assume
power plant heat rate of 9,000 BTU/kWh.
The hydrothermal estimate includes approximately 72-127 GW of as
yet-undiscovered resource (USGS 1979). The enhanced geothermal systems
estimate is based on an estimate of 42 TW, which includes the entire
potential heat source (Tester 1994).
The ultimate potential is assumed to be the same as the near-term
The ultimate potential estimate or ocean-based power expands the
potential to include power from ocean thermal energy of 0.11 TW (Sands
1980). The primary energy required for electricity generation, assuming
heat rate of 10,000 Btu/kWh, is 9 quads.
Unlike the near-term potential, the ultimate potentials for both PV and
CSP are not assumed to be constrained by grid limitations, e.g., storage
is assumed, transmission is assumed available, etc. For PV, the total
resource potential (NREL 2003b) was restricted by excluding federal and
sensitive lands, assuming only 30 percent of land area can be covered
PV, allowing only slopes that are less than 5 degrees, and requiring a
minimum resources of 6 kwh/m2/day. This results in an ultimate
potential of about 219 TW or 4,200 quads/year for PV systems, assuming
22 percent capacity factor.
The CSP resource is restricted to areas with resource potential -- the
southwestern United States. The potential reduces that amount of land
that can be used for CSP by federal and sensitive lands, land with a
greater than a 5 percent gradient, major urban areas and features, and
parcels less than 5 km2 in area. The remaining area determined the
technical potential for CSP, assuming 50 MW/km2 (Price et al 2003).
The ultimate wind potential is not limited to 20 percent for
and grid stability reasons, as battery storage is assumed. Instead,
potential is limited by appropriate land selection (exclusions for
land, etc.) and technical feasibility. For onshore wind potential,
estimated future capacity factors (NREL 2005b), and assuming complete
of Class 3 winds and better, the result is 324 quads of primary energy
from wind. For offshore wind, Class 5 and better with a distance
5 and 200 nautical miles (nm) were assumed. Between 5-20 nautical
only one-third of wind energy in Class 5 and better is captured, between
20 and 50 nautical miles, two-thirds; and between 50 and 200 nautical
miles, the entirety. Assuming future capacity factors, the potential
offshore wind primary energy is found to be 272 quads.
REFERENCES, DATA SOURCES, BACKGROUND MATERIAL
EIA 2005a - U.S. Department of Energy, Energy Information
Annual Energy Review 2004. DOE/EIA 0384-2004, Washington, DC: U.S.
Department of Energy
EIA 2005b - Assumptions to the Annual Energy Outlook 2005 with
for 2025. Washington DC: U.S. Department of Energy
EPRI/DOE. 1997. Renewable Energy Technology Characterizations,
Washington, D.C.: DOE
Hagerman, G., R. Bedard. 26-June-2005. "Ocean Kinetic Energy Resources
the United States and Canada." EnergyOceans 2005, Washington, D.C.
Hall, D., R. Hunt, K. Reeves, G. Carroll. 2003. Estimation of Economic
Parameters of U.S. Hydropower Resources. Idaho National Engineering and
Land and Water Fund of the Rockies. 2002. Renewable Energy Atlas of the
West. The Hewlett Foundation and The Energy Foundation. Page 10. http://energyatlas.org.
Morse, F. 2004. Presentations: The Concentrating Solar Power Global
Initiative (GMI) as a Result of Research and Development. Presented at
the Renewables 2004 Conference.
NREL 2003a - National Renewable Energy Laboratory. Assessing the
for Renewable Energy on Public Lands. 95 pp.; NREL Report No.
TP-550-33530; DOE/GO-102003-1704. Golden, CO: NREL
NREL 2003b - National Solar Photovoltaics (PV) Data. U.S. Data http://www.nrel.gov/gis/index_of_gis.html
NREL 2005a - Assessing the Potential for Renewable Energy on National
Forest Systems Lands. 123 pp; NREL Report No. BK-71036759. Golden, CO:
NREL 2005b - Potential Benefits of Federal energy Efficiency and
Energy Programs: FY 2006 Budget Request NREL-TP 620-37931. Golden, CO:
NREL 2005c - Power Technologies Energy Data Book. Golden, CO: NREL. URL:
Perlack, R., Wright, L., Tuhollow, A., Graham, R., Biomass as Feedstock
for a Bioenergy and Bioproducts Industry: The Technical Feasibility of
Billion-Ton Annual Supply, April 2005
Price, H.; Stafford, B.; Heimiller, D; Dahle, D. 2003. California Solar
Power Detailed Technical Report for Southern California Edison. 95 pp.;
NREL Report No. MP-710-35284
REPIS 2005 - Renewable Electric Plant Information System: http://www.nrel.gov/analysis/repis/
Sands, D. 1980. "Ocean thermal energy conversion programmatic
environmental assessment." Proceedings of the 7th Ocean Energy
Conference, Volume 1, Paper 4.1., Washington, D.C.: U.S. Department of
Energy, Publication No. Conf-800633-Vol 1.
Tester, J.W., H.J. Herzog, Z. Chen, R.M. Potter, and M.G. Frank. 1994.
Prospects for Universal Geothermal Energy from Heat Mining. Science &
Global Security. Volume 5, pp.99-121
Thresher, R. (NREL). 2005. E-mail communication to Elizabeth Brown.
October 14, 2005
TroughNet. 2005. TroughtNet CSP Projects Deployed Web page. http://www.eere.energy.gov/troughnet/deployed.html
USGS (United States Geological Survey) 1979, "Assessment of Geothermal
Resources of the United States - 1978". Geological Survey Circular
Edited by L.J.P. Muffler, United States Department of the Interior.
Wan Y. and Parsons, B. 1993. "Factors Relevant to Utility Integration
of Intermittent Renewable Technologies." NREL/TP-463-4953. National
Renewable Energy Laboratory: Golden, CO. Page 49
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The DRAFT document had earlier been available for inspection at:
but now appears to have been withdrawn. Comments on the draft had been
requested to be sent to Elizabeth Brown in NREL's Energy Analysis Office