Geothermal
Energy... Power from the Depths
http://www.eere.energy.gov/erec/factsheets/geothermal.html
Summary:
This
fact sheet will provide you with an overview of how geothermal energy is
used to generate electricity and to heat buildings. To view
illustrations,
you can
download the PDF version (PDF 480 KB) of this fact sheet (Download
Acrobat
Reader).
See Related Links below for more publications and resources on related
topics, which
aren't included in the PDF version.
The Earth's crust is a bountiful source of energy—and fossil fuels are
only part of the
story. Heat or thermal energy is by far the more abundant resource. To
put it in
perspective, the thermal energy in the uppermost six miles of the
Earth's
crust amounts
to 50,000 times the energy of all oil and gas resources in the world!
The word "geothermal" literally means "Earth" plus "heat." The
geothermal
resource is
the world's largest energy resource and has been used by people for
centuries.
In
addition, it is environmentally friendly. It is a renewable resource
and
can be used in
ways that respect rather than upset our planet's delicate environmental
balance.
Geothermal power plants operating around the world are proof that the
Earth's
thermal
energy is readily converted to electricity in geologically active
areas.
Many communities,
commercial enterprises, universities, and public facilities in the
western
United States
are heated directly with the water from underground reservoirs. For the
homeowner or
building owner anywhere in the United States, the emergence of
geothermal
heat pumps
brings the benefits of geothermal energy to everyone's doorstep.
The Basics
There's a relatively simple concept underlying all the ways geothermal
energy is used:
The flow of thermal energy is available from beneath the surface of the
Earth and
especially from subterranean reservoirs of hot water. Over the years,
technologies
have
evolved that allow us to take advantage of this heat.
In fact, electric power plants driven by geothermal energy provide over
44 billion kilowatt
hours of electricity worldwide per year, and world capacity is growing
at approximately
9% per year. To produce electric power from geothermal resources,
underground
reservoirs of steam or hot water are tapped by wells and the steam
rotates
turbines that
generate electricity. Typically, water is then returned to the ground
to
recharge the
reservoir and complete the renewable energy cycle.
Underground reservoirs are also tapped for "direct-use" applications.
In
these instances,
hot water is channeled to greenhouses, spas, fish farms, and homes to
fill
space heating
and hot water needs.
Geothermal energy use extends beyond underground reservoirs. The soil
and
near-surface rocks, from 5 to 50 feet deep, have a nearly constant
temperature
from
geothermal heating. As a homeowner or business owner, you can use the
Earth
as a
heat source or heat sink with geothermal heat pumps. According to the
U.S.
Environmental Protection Agency (EPA), geothermal heat pumps are one of
the nation's
most efficient—and therefore least polluting—heating, cooling, and
water-heating
systems available. In winter, these systems draw on "earth heat" to
warm
the house, and
in summer they transfer heat from the house to the earth, which ranges
in temperature
from 50° to 70°F (10° to 21°C) depending on latitude.
A Clear Advantage
Geothermal energy delivers some powerful environmental and economic
benefits.
If you
live in an area that uses geothermal resources for electricity
production,
you're quite
fortunate. Consider Lake County, California, which is home to many of
the
geothermal
power plants at our nation's best-developed geothermal resource, The
Geysers.
It's no
coincidence that the Lake County air basin is the first and only one in
compliance with all
of California's stringent air quality regulations.
Perhaps you own a greenhouse and need to cut exorbitant energy bills in
order to stay in
business. If you are located near a geothermal resource, you should
know
that most
greenhouse growers estimate that direct use of geothermal resources
instead
of
traditional energy sources reduces heating costs by up to 80%. This can
save about 5%
to 8% in total operating cost.
Assume you're a home or business owner who has installed a geothermal
heat
pump.
You're not only doing your part to help make the world a cleaner place
to live and
breathe, you're rewarded with low operating and maintenance costs, and,
usually, lowest
life-cycle costs. (Life-cycle cost is the total cost of the equipment
spread
over the useful
life of the equipment.) In practical terms, your heat pump investment
may
cost you $15
per month more in mortgage payments, but it may save you $30 per month
on your
electric bill.
In all three of these cases, domestic, not foreign, resources are being
used—a practice
that has merits all its own. Nearly half of our nation's annual trade
deficit
would be
obliterated if we could displace imported oil with domestic energy
resources.
A nation's
trade deficit represents a permanent loss of wealth for the citizens of
that nation.
Keeping the wealth at home translates to more jobs and a robust
economy.
And not only
does our national economic and employment picture improve, but a vital
measure of
national security is gained when we control our own energy supplies.
Types of Geothermal Resources
The center of the Earth is 4000 miles (6400 kilometers) deep. How hot
is
this region?
Our best guess is 7200°F (4000°C) or higher. Partially molten
rock,
at temperatures
between 1200° and 2200°F (650° to 1200°C), is believed
to exist at depths of 50 to 60
miles (80 to 100 kilometers).
Heat is constantly flowing from the Earth's interior to the surface.
Most
types of
geothermal resources—hydrothermal, geopressured, hot dry rock, and
magma—result
from concentration of Earth's thermal energy within certain discrete
regions
of the
subsurface.
Hydrothermal resources are reservoirs of steam or hot water, which are
formed by
water seeping into the earth and collecting in, and being heated by
fractured
or porous
hot rock. These reservoirs are tapped by drilling wells to deliver hot
water to the surface
for generation of electricity or direct use. Hot water resources exist
in abundance around
the world. In the United States, the hottest (and currently most
valuable)
resources are
located in the western states, and Alaska and Hawaii. Technologies to
tap
hydrothermal
resources are proven commercial processes.
Geopressured resources are deeply buried waters at moderate temperature
that
contain dissolved methane. While technologies are available to tap
geopressured
resources, they are not currently economically competitive. In the
United
States, this
resource base is located in the Gulf coast regions of Texas and
Louisiana.
Hot dry rock resources occur at depths of 5 to 10 miles (8 to 16
kilometers)
everywhere
beneath the Earth's surface, and at shallower depths in certain areas.
Access to these
resources involves injecting cold water down one well, circulating it
through
hot fractured
rock, and drawing off the now hot water from another well. This
promising
technology has
been proven feasible, but no commercial applications are in use at this
time.
Magma (or molten rock) resources offer extremely high-temperature
geothermal
opportunities, but existing technology does not allow recovery of heat
from these
resources.
Earth energy is the heat contained in soil and rocks at shallow depths.
This resource is
tapped by geothermal heat pumps.
Geothermal Power Plants—from Water to Light
Flip a switch and light up a room—what could be easier? Push a button
on
the TV
remote control and be entertained. It all seems so simple that we are
often
unaware of
the true environmental and social cost of these conveniences—and who
would
want to
give them up even if we had to account for every penny?
But rather than thinking in terms of giving things up, let's think
positively:
in the United
States, right now, the installed generating capacity for geothermal
stands
at about 2700
megawatts. That's the equivalent of about 58 million barrels of oil,
and
provides enough
electricity for 3.7 million people. The cost of producing this power
ranges
from 4¢ to 8¢
per kilowatt hour. The geothermal industry is working to achieve a
geothermal
life-cycle
energy cost of 3¢ per kilowatt hour. And remember, this is clean
energy
produced from
domestic resources.
How clean? In terms of air emissions, geothermal power plants have an
inherent
advantage over fossil fuel plants because no combustion takes place.
Geothermal
plants emit no nitrogen oxides and very low amounts of sulfur
dioxide—allowing
them to
easily meet the most stringent clean air standards. The steam at some
steam
plants
contains hydrogen sulfide, but treatment processes remove more than
99.9%
of those
emissions. Typical emissions of hydrogen sulfide from geothermal plants
are less than 1
part per billion—well below what people can smell. The low levels of
air
emissions
produced are mostly carbon dioxide, which many people believe acts as a
greenhouse
gas to trap heat within Earth's atmosphere. Even so, geothermal plants
emit minimal
amounts of carbon dioxide—1/1000 to 1/2000 of the amount produced by
fossil-fuel
plants.
Geothermal water sometimes contains salts and dissolved minerals. In
the
United
States, the geothermal water is usually injected back into the
reservoir
from where it
came, at a depth well below groundwater aquifers, after its heat energy
has been
extracted. This recycles the geothermal water and replenishes the
reservoir.
However,
some geothermal plants also produce some solid materials, or sludges,
that
require
disposal in approved sites.
All U.S. geothermal power plants are located in the states of
California,
Nevada, Utah,
and Hawaii—home to some of the most majestic scenery on Earth. It's
fortunate,
then,
that these plants consume only a small amount of land, and can coexist
with numerous
other land uses, including agriculture, with minimal impact on the
surrounding
beauty.
They're reliable and efficient, too. Taken as a group, geothermal power
plants are
available to generate power 95% or more of the time; they are seldom
off-line
for
maintenance or repair. And, they have the highest capacity factors of
all
types of power
plants. Capacity factor is the ratio of the amount of electricity a
plant
produces to how
much electricity it is capable of producing.
Dry Steam Power Plants were the first type of geothermal power plant
(in
Italy in 1904).
The Geysers in northern California, which is the world's largest single
source of
geothermal power, is also home to this type of plant. These plants use
the steam as it
comes from wells in the ground, and direct it into the
turbine/generator
unit to produce
power.
Flash Steam Power Plants, which are the most common, use water with
temperatures
greater than 360°F (182°C). This very hot water is pumped under
high pressure to
equipment on the surface, where the pressure is suddenly dropped,
allowing
some of
the hot water to "flash" into steam. The steam is then used to power the
turbine/generator. The remaining hot water and condensed steam are
injected
back into
the reservoir.
Binary Cycle Power Plants operate on the lower-temperature waters,
225°
to 360°F
(107° to 182°C). These plants use the heat of the hot water to
boil a "working fluid,"
usually an organic compound with a low boiling point. This working
fluid
is then
vaporized in a heat exchanger and used to turn a turbine. The
geothermal
water and the
working fluid are confined to separate closed loops, so there are no
emissions
into the
air.
Because these lower-temperature waters are much more plentiful than
high-temperature
waters, binary cycle systems will be the dominant geothermal power
plants
of the future.
Developing and commercializing geothermal power technologies
contributes
not only to
a cleaner environment, but to a healthy U.S. industrial base, as well.
Around the
developing countries of the world, demand for electric power is
burgeoning—and
nearly
half of these countries have geothermal resources. These markets have
proven
particularly receptive to clean energy produced with indigenous
resources,
creating
attractive export options for geothermal technologies and expertise. In
fact, U.S.
geothermal companies have signed contracts worth more than $6 billion
in
the past few
years to build geothermal power plants in some of these developing
countries.
Direct Use of Geothermal Energy
If you've ever soaked in water from a natural hot spring, you're one of
the millions of
people around the world who has enjoyed the direct use of geothermal
energy.
And
while this naturally occurring hot water may be the perfect tonic for
frayed
nerves and
sore muscles, it's capable of much more. In the United States alone,
direct
geothermal
applications (not including geothermal heat pumps) have an installed
capacity
of 500
thermal megawatts, which is roughly equivalent to saving half a million
barrels of oil per
year. This includes approximately 40 greenhouses, 30 fish farms, 190
resorts
and spas,
125 space and district heating projects, and 10 industrial projects.
The resource required for these applications is widespread across the
western
third of
the United States. This is water in an underground reservoir, at
low-to-moderate
temperatures usually ranging from 68° to 302°F (20° to
150°C).
The consumer of
direct-use geothermal energy can count on savings in energy costs—as
much
as an
80% reduction from traditional fuel costs, depending on the application
and the industry.
Direct-use systems typically require a larger initial investment, but
have
lower operating
costs and no need for ongoing fuel purchases, therefore reducing
life-cycle
costs.
In a typical application, a well brings heated water to the surface; a
mechanical
system—piping, heat exchanger, controls—delivers the heat to the space
or process;
and a disposal system either injects the cooled geothermal fluid
underground
or
disposes of it on the surface.
The direct use of geothermal energy offers some heartening
possibilities.
Imagine an
entire community of people having their homes heated geothermally.
Sound
like
something way off in the future? Not at all. In 1893, the citizens of
Boise,
Idaho, put their
pioneering spirit to work and built the world's first geothermal
district
heating system by
piping water from a nearby hot spring. Within a few years, the system
was
providing heat
to 200 homes and 40 downtown businesses—and the system continues to
flourish
today.
There are now 18 district heating systems in the United States
(including
one in Klamath
Falls, Oregon, that melts snow from the city's downtown sidewalks), and
the potential for
more is tremendous. A recently updated resource inventory of 10 western
states
identified 271 communities located within 5 miles (8 kilometers) of a
geothermal
resource.
Greenhouse operators are taking advantage of geothermal direct use in
growing
numbers, with nearly 40 greenhouses (many of which are several acres in
size)
producing vegetables, flowers, houseplants, and tree seedlings in eight
western states.
Operators of fish farms are profiting from the lower energy costs and
improved
fish
growth rates that geothermal energy delivers. Other industrial and
commercial
applications that match well with geothermal direct use include food
dehydration,
laundries, gold processing, milk pasteurizing, and swimming pools and
spas.
The Heat Pump Solution
The geothermal heat pump doesn't create electricity—but it greatly
reduces
consumption of it. If you would like to reduce the cost of heating and
cooling your home,
you might want to consider installing a geothermal heat pump, an
economical
and
energy-efficient technology for space heating and cooling and water
heating.
Nationwide, more than 350,000 of these systems are in operation in
homes,
schools,
and businesses. And the geothermal heat pump industry expects to be
installing
40,000
systems per year by 2000.
In winter, heat pump systems draw thermal energy from the ambient
temperature
of the
shallow ground, which ranges between 50° and 70°F (10° to
21°C
) depending on
latitude. In summer, the process is reversed to a cooling mode, using
the
ground as a
sink for the heat contained within the building. The system does not
convert
electricity to
heat; rather, it uses electricity to move thermal energy between the
building
and the
ground and condition it to a higher or lower temperature according to
the
heating or
cooling requirements. Consumption of electricity is reduced 30% to 60%
compared to
traditional heating and cooling systems, allowing a payback of system
installation
in 2 to
10 years. And these low-maintenance systems have long lives of 30 years
or more.
Some systems are also capable of producing domestic hot water at no
cost
in summer
and at small cost in winter.
An analysis by the EPA found these systems to be among the most
efficient
space-conditioning technologies available—with the lowest environmental
cost of all that
were analyzed. But this might be the most compelling statistic: Surveys
show that the
number of satisfied geothermal heat pump customers stands at 95% or
higher.
Source List
The following organizations serve as excellent resources for
information
on geothermal
energy and its various applications.
Ask an Energy Expert
Energy Efficiency and Renewable Energy Clearinghouse (EREC)
P.O. Box 3048
Merrifield, VA 22116
(800) DOE-EREC (363-3732)
E-mail: doe.erec@nciinc.com
Provides free general and technical information to the public on the
many
topics and
technologies pertaining to energy efficiency and renewable energy.
DOE Geothermal Technologies Program
Office of Energy Efficiency and Renewable Energy
1000 Independence Ave., S.W.
Washington, DC 20585-0121
(202) 586-5340
Sponsors research to develop geothermal science and technology, and
works
closely
with industry to develop advanced technologies and help commercialize
research
discoveries. Publishes brochures and newsletters focused on geothermal
energy and
applications.
Energy and Geoscience Institute
423 Wakara Way, Suite 300
Salt Lake City, UT 84108
(801) 581-5126
Conducts applied geoscience research pertaining to geothermal
resources,
fossil fuels,
minerals, and environmental assessment; works cooperatively with
universities,
government agencies, national energy companies, and a global network of
collaborating
scientists. The institute has a professional staff of more than 40
scientists
and
engineers.
Geo-Heat Center
Oregon Institute of Technology
3201 Campus Drive
Klamath Falls, OR 97601-8801
(503) 885-1750
Provides technical information regarding direct-use geothermal energy
to
consultants,
developers, potential users, and the general public; information has
been
developed
through extensive research and firsthand experience with hundreds of
projects.
Publishes a quarterly bulletin. The center's resources are available to
the public through
the auspices of DOE.
Geothermal Education Office
664 Hilary Drive
Tiburon, CA 94920
(800) 866-4GEO
Focuses on helping students learn about geothermal energy. Provides
K-12
teachers
and other interested parties with free booklets, posters, global
statistical
maps, and
reference material. A grade school video, activity-packed curriculum ,
and a high school
video with curriculum supplement are available at cost.
Geothermal Heat Pump Consortium, Inc.
701 Pennsylvania, NW
Washington, DC 20004-2696
(202) 508-5500
Provides extensive information regarding geothermal heat pumps. Web
page
contains
case studies, published articles, list of service providers, and
workshop
schedules and
locations. The consortium, established under President Clinton's
"Climate
Change
Action Plan," has broad-based support and participation from DOE, the
utility
sector,
and geothermal associations and manufacturers.
Geothermal Resources Council
2001 Second Street, Suite 5
Davis, CA 95617-1350
(916) 758-2360
Publishes a monthly bulletin (11 issues a year); provides videos, maps,
and posters.
Develops and convenes special meetings, workshops, conferences,
courses,
and
symposia on a full range of subjects pertaining to geothermal
exploration,
development,
and use. Periodically schedules a basic introductory course on
geothermal
energy.
International Geothermal Association
c/o Institute of Geological and Nuclear Sciences
Wairakei Research Centre, Private Bag 2000
Taupo, New Zealand
64-7-374-8211
Publishes the "IGA News" (quarterly). Provides information about
geothermal
industry
associations worldwide. Encourages the development and use of
geothermal
resources
worldwide through the compilation, publication, and dissemination of
scientific
and
technical data and information. Organizes the international geothermal
congress every
five years.
International Ground Source Heat Pump Association
490 Cordell South
Stillwater, OK 74078-8018
(405) 744-5175
(800) 626-4747
Established in 1987 to advance geothermal/ground source heat pump
technology
on a
local, state, national, and international level. Publishes "The
Source,"
a bimonthly
newsletter. Sponsors the annual Geothermal Heat Pump Technical
Conference
and
Expo. Offers numerous booklets and brochures for contractors,
homeowners,
students,
and the general public.
Related Links
Here's more information about geothermal energy on DOE's Consumer Energy
Information Web site:
Geothermal Energy Information Sources
Geothermal Heat Pumps
Geothermal Heat Pump Information Sources
Geothermal Heat Pumps Make Sense for Homeowners
DOE/GO-10097-518
FS 188
December 1997
Last modified in April 2002
NOTICE
This report was prepared as an account of work sponsored by an agency
of
the United States
government. Neither the United States government nor any agency
thereof,
nor any of their employees,
makes any warranty, express or implied, or assumes any legal liability
or responsibility for the accuracy,
completeness, or usefulness of any information, apparatus, product, or
process disclosed, or represents
that its use would not infringe privately owned rights. Reference
herein
to any specific commercial
product, process, or service by trade name, trademark, manufacturer, or
otherwise does not necessarily
constitute or imply its endorsement, recommendation, or favoring by the
United States government or
any agency thereof. The views and opinions of authors expressed herein
do not necessarily state or
reflect those of the United States government or any agency thereof.
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