is the official government estimate of potential geothermal
electric resources in the U.S.?
else can you tell me about USGS Circular 790?
this estimates too high? Too low? Just right?
much energy is geothermal electricity capable of supplying to
the U.S. right now?
much electricity can geothermal supply worldwide?
you want more information about developing geothermal power
What is the official
government estimate of potential geothermal electric resources
in the U.S.?
The U.S. Geological Survey (USGS), in
its Circular 790, estimates a hydrothermal resource base of
between 95,000 and 150,000 MWe. Hydrothermal resources are
those that support power in the U.S. today and are one of
several parts of the total geothermal resource base.
The report breaks the geothermal estimate into two
categories: Identified Resources Base, which locates each of
the sites included by latitude and longitude and presents
specific information on each in the appendix, and Undiscovered
Resource Base, which is limited by depth, heat, and locational
parameters. The potential, as assessed by USGS Circular 790,
are as follows:
Identified Resources Base (excluding Parks): 23,000 MWe +/-
Undiscovered Resource Bases: 72,000-127,000
Total Identified and Undiscovered Resource Base:
What else can you tell me
about USGS Circular 790?
The USGS Circular 790 is
the most thorough document assessing the potential of
geothermal resources, according to the majority of experts in
the geothermal industry. Published in 1978, this report
provides energy estimates for all identified geothermal
resources and features as well as yet to be identified
resources (undiscovered resources). It gives power potential
estimates for specific sites thought to be able to support
geothermal power production based upon specific and often
limited assumptions of reservoir heat, depth and producible
temperatures. To access an online copy of Circular 790, click
The USGS is in the process of preparing a new national
geothermal resource assessment, which it expects to complete
Is this estimate too high? Too
low? Just right?
Most geothermal industry experts,
including many of those from USGS who drafted the report, will
tell you that the report may have overestimated the shallow
hot resource while underestimating moderate and low
temperature potential. Also, the resource estimate made
involved many specific assumptions that limited the scope of
the projected resource base. For example, the report sites
that the resource estimates "are restricted to depths of less
than 3km," and that "any future change of this depth limit
that might be brought about by improved technology or more
favorable economics would increase the accessible resource
base proportionally." (USGS Circular 790, page 31, page 37 in
the on-line version). Today, oil and gas resources are
developed at depths more than three times the maximum
considered by the USGS in 1978. In addition, resources were
only considered developable for power production with
temperatures above 150°C (Table 4 and 5, p. 44-57), since
binary power, which can use lower temperatures to produce
electricity had not been commercially developed at that time
(see the basics
section for more information about binary power plants). Also,
heat (or fluid) below or to the side of identified reservoir
areas (page 19) was not considered. In its own words, the
report states that "all of our estimates are minima."
How much energy is geothermal
electricity capable of supplying to the U.S. right now?
The USGS assessment (cited above), found 20,000 -
26,000 megawatts of known geothermal sites that exist
throughout the United States. Of this, a recent report for the
Western Governors’ Association (WGA) estimates that 13,000MW
of identified resources are expected to be developable within
the next 10-20- years of which 5,600 megawatts can be
developed within the next five to ten years at competitive
prices with the production tax credit (for details about the
WGA estimate, please click the Excel file here).
That report notes: "This is a commercially achievable
capacity for new generation and does not include the much
larger potential of unknown, undiscovered resources." It also
notes that its market and cost assumptions "do not consider
advances in technology or any learning curve effects that
could reduce costs or expand available production." (WGA
Geothermal Task Force Report, pages 4 and 7 respectively,
January 2006, available at http://www.westgov.org/).
The total US geothermal resource is estimated to be much
larger. The Energy and Geosciences Institute of the University
of Utah estimates just the thermal aquifers contain 55 x 1018
Joules of energy, which would be roughly equivalent to the
energy needed to provide 15.3 Billion kilowatt hours of
electric power, or five times the total US electrical
production in 1990. Other geothermal systems -- magmatic
systems, geopressurized basins and resources available only
with enhanced geothermal techniques -- are estimated to
contain significantly even more energy.
How much electricity can geothermal supply
A 1999 study shows that geothermal
resources using existing technology have the potential to
support between 35,448 and 72,392 MW of worldwide electrical
generation capacity. Using enhanced technology, the geothermal
resources could support between 65,576 and 138,131 MW of
electrical generation capacity. Assuming a 90% availability
factor, which is well within the range experienced by
geothermal power plants, this electric capacity could produce
as much as 1,089 Billion kWh of electricity annually. The
estimates produced for world energy potential by this study
are comparable to the USGS estimate of the identified US
resource base. It did not assess the limits of geothermal
resource base, nor the potential for new development with
significantly different technologies, such as engineered
An estimate of world geothermal
resources made by the Energy and Geoscience Institute for the
President's Council of Advisors on Science and Technology
stated the following for different geologic
Geologic Regime: Joules BBL Oil Equivalent
Systems 15 x 1024 J 2,400,000 x 109 bbl
Crustal Heat 490 x
1024 J 79,000,000 x 109 bbl
Thermal Acquifers 810 x 1018 J
130 x 109 bbl
Geopressured Basins 2.5 x 1024 J 410,000 x
Total Oil Reserves (for comparison) 5,300 x 109
* National Academy of Sciences, 1990: includes crude oil,
heavy oil, tar sands, and oil shale.
Do you want more information about
developing geothermal power plants?
Please see the
link for statistics about developing geothermal power