What
is the official government estimate of potential geothermal
electric resources in the U.S.?
What else can you tell
me about USGS Circular 790?
Is this estimates too high?
Too low? Just right?
How much energy is geothermal
electricity capable of supplying to the U.S. right now?
How much electricity can geothermal
supply worldwide?
Do you want more information
about developing geothermal power plants?
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 US 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): 23,000MWe
+/- 3,400 MWe
·Undiscovered Resource Bases: 72,000-127,000MWe
Total Identified and Undiscovered Resource Base: 95,000-150,000MWe
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 here.
The USGS is in the process of preparing a new national
geothermal resource assessment, which it expects to
complete by 2008.
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 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 worldwide?
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
geothermal systems.
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 regimes:
World Continental Resources
Geologic Regime: Joules BBL Oil Equivalent
Magmatic 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 109 bbl
Total Oil Reserves (for comparison) 5,300 x 109 bbl*
* 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 "developing" link under "information"
for statistics about developing geothermal power plants.
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