||WHAT DOES THE WORD
"Geothermal" comes from the Greek
words geo (earth) and therme (heat). So, geothermal means earth
WHAT IS GEOTHERMAL
Our earth's interior - like the sun
- provides heat energy from nature. This heat - geothermal energy -
yields warmth and power that we can use without polluting the
Geothermal heat originates from
Earth's fiery consolidation of dust and gas over 4 billion years ago. At
earth's core - 4,000 miles deep - temperatures may reach over
9,000 degrees F.
HOW DOES GEOTHERMAL
HEAT GET UP TO EARTH'S SURFACE?
The heat from the earth's core
continuously flows outward. It transfers (conducts) to the surrounding
layer of rock, the mantle. When temperatures and pressures become
high enough, some mantle rock melts, becoming magma. Then,
because it is lighter (less dense) than the surrounding rock, the
magma rises (convects), moving slowly up toward the earth's
crust, carrying the heat from below.
Sometimes the hot magma reaches all
the way to the surface, where we know it as lava. But most often the
magma remains below earth's crust, heating nearby rock and water
(rainwater that has seeped deep into the earth) - sometimes as hot as
700 degrees F. Some of this hot geothermal water travels back up through
faults and cracks and reaches the earth's surface as hot springs
or geysers, but most of it stays deep underground, trapped in
cracks and porous rock. This natural collection of hot water is called a
HOW HAVE PEOPLE USED
GEOTHERMAL ENERGY IN THE PAST?
From earliest times, people have
used geothermal water that flowed freely from the earth's surface as hot
springs. The oldest and most common use was, of course, just relaxing in
the comforting warm waters. But eventually, this "magic water" was used
(and still is) in other creative ways. The Romans, for example, used
geothermal water to treat eye and skin disease and, at Pompeii, to heat
buildings. As early as 10,000 years ago, Native Americans used hot
springs water for cooking and medicine. For centuries the Maoris of New
Zealand have cooked "geothermally," and, since the 1960s, France has
been heating up to 200,000 homes using geothermal water.
HOW DO WE USE
GEOTHERMAL ENERGY TODAY?
Today we drill wells into the
geothermal reservoirs to bring the hot water to the surface. Geologists,
geochemists, drillers and engineers do a lot of exploring and testing to
locate underground areas that contain this geothermal water, so we'll
know where to drill geothermal production wells. Then, once the
hot water and/or steam travels up the wells to the surface, they can be
used to generate electricity in geothermal power plants or for energy
saving non-electrical purposes.
HOW IS ELECTRICITY
GENERATED USING GEOTHERMAL ENERGY?
In geothermal power plants
steam, heat or hot water from geothermal reservoirs provides the force
that spins the turbine generators and produces electricity. The
used geothermal water is then returned down an injection well
into the reservoir to be reheated, to maintain pressure, and to sustain
There are three kinds of
geothermal power plants. The kind we build depends on the
temperatures and pressures of a reservoir.
- A "dry'" steam reservoir produces
steam but very little water. The steam is piped directly into a
"dry" steam power plant to provide the force to spin the
turbine generator. The largest dry steam field in the world is The
Geysers, about 90 miles north of San Francisco. Production of
electricity started at The Geysers in 1960, at what has become the
most successful alternative energy project in history.
- A geothermal reservoir that
produces mostly hot water is called a "hot water reservoir" and is
used in a "flash" power plant. Water ranging in temperature
from 300 - 700 degrees F is brought up to the surface through the
production well where, upon being released from the pressure of the
deep reservoir, some of the water flashes into steam in a 'separator.'
The steam then powers the turbines.
- A reservoir with temperatures
between 250 - 360 degrees F is not hot enough to flash enough steam
but can still be used to produce electricity in a "binary" power
plant. In a binary system the geothermal water is passed through a
heat exchanger, where its heat is transferred into a second
(binary) liquid, such as isopentane, that boils at a lower temperature
than water. When heated, the binary liquid flashes to vapor, which,
like steam, expands across and spins the turbine blades. The vapor is
then recondensed to a liquid and is reused repeatedly. In this closed
loop cycle, there are no emissions to the air.
WHAT ARE SOME OF THE
ADVANTAGES OF USING GEOTHERMAL ENERGY TO GENERATE
- Clean. Geothermal power plants, like wind and
solar power plants, do not have to burn fuels to manufacture steam to
turn the turbines. Generating electricity with geothermal energy helps
to conserve nonrenewable fossil fuels, and by decreasing the use of
these fuels, we reduce emissions that harm our atmosphere. There is no
smoky air around geothermal power plants -- in fact some are built in
the middle of farm crops and forests, and share land with cattle and
For ten years, Lake County California, home to
five geothermal electric power plants, has been the first and only
county to meet the most stringent governmental air quality standards in
- Easy on the
land. The land area required
for geothermal power plants is smaller per megawatt than for almost
every other type of power plant. Geothermal installations don't require
damming of rivers or harvesting of forests -- and there are no mine
shafts, tunnels, open pits, waste heaps or oil spills.
- Reliable. Geothermal power plants are designed to run
24 hours a day, all year. A geothermal power plant sits right on top of
its fuel source. It is resistant to interruptions of power generation
due to weather, natural disasters or political rifts that can interrupt
transportation of fuels.
- Flexible. Geothermal power plants can have modular
designs, with additional units installed in increments when needed to
fit growing demand for electricity.
- Keeps Dollars at
Home. Money does not have to
be exported to import fuel for geothermal power plants. Geothermal
"fuel'" - like the sun and the wind - is always where the power plant
is; economic benefits remain in the region and there are no fuel price
- Helps Developing
Countries Grow. Geothermal
projects can offer all of the above benefits to help developing
countries grow without pollution. And installations in remote locations
can raise the standard of living and quality of life by bringing
electricity to people far from "electrified" population centers.
HOW MUCH ELECTRICITY
IS FROM GEOTHERMAL ENERGY?
Since the first
geothermally-generated electricity in the world was produced at
Larderello, Italy, in 1904 the use of geothermal energy for electricity
has grown worldwide to about 7,000 megawatts in twenty-one
countries around the world. The United States alone produces 2700
megawatts of electricity from geothermal energy, electricity comparable
to burning sixty million barrels of oil each year.
WHAT ARE SOME
NON-ELECTRIC WAYS WE CAN USE GEOTHERMAL ENERGY?
Geothermal water is used around the
world, even when it is not hot enough to generate electricity. Anytime
geothermal water or heat are used directly, less electricity is used.
Using geothermal water 'directly' conserves energy and
replaces the use of polluting energy resources with clean ones.
The main non-electric ways we use geothermal energy are DIRECT USES and
GEOTHERMAL HEAT PUMPS.
DIRECT USES Geothermal waters ranging from 50 degrees F to
over 300 degrees F, are used directly from the earth:
- 'to soothe aching muscles
in hot springs, and health spas (balneology);
- to help grow flowers,
vegetables, and other crops in greenhouses while snow-drifts pile up
- to shorten the time
needed for growing fish, shrimp, abalone and alligators to maturity
- to pasteurize milk, to
dry onions and lumber and to wash wool (industrial
heating of individual
buildings and of entire districts, is - besides hot spring bathing - the
most common and the oldest direct use of nature's hot water. Geothermal
district heating systems pump geothermal water through a heat
exchanger, where it transfers its heat to clean city water
that is piped to buildings in the district. There, a second heat
exchanger transfers the heat to the building's heating system. The
geothermal water is injected down a well back into the reservoir to be
heated and used again. The first modern district heating system was
developed in Boise, Idaho. (In the western U.S. there are 271
communities with geothermal resources available for this use.) Modern
district heating systems also serve homes in Russia, China, France,
Sweden, Hungary, Romania, and Japan. The world's largest district
heating system is in Reykjavik, Iceland. Since it started using
geothermal energy as its main source of heat Reykjavik, once very
polluted, has become one of the cleanest cities in the
Geothermal heat is being used in some creative ways; its
use is limited only by our ingenuity. For example, in Klamath Falls,
Oregon, which has one of the largest district heating systems in the
U.S., geothermal water is also piped under roads and sidewalks to keep
them from icing over in freezing weather. The cost of using any other
method to keep hot water running continuously through cold pipes would
be prohibitive. And in New Mexico and other places rows of pipes
carrying geothermal water have been installed under soil, where flowers
or vegetables are growing. This ensures that the ground does not freeze,
providing a longer growing season and overall faster growth of
agricultural products that are not protected by the shelter and warmth
of a greenhouse.
PUMPS Animals have always
known to burrow into the earth, where the temperature is relatively stable
compared to the air temperature, to get shelter from winter's cold and
summer's heat. People, too, have sought relief from bad weather in earth's
caves. Today, with geothermal heat pumps (GHP's), we take advantage of
this stable earth temperature - about 45 - 58 degrees F just a few feet
below the surface - to help keep our indoor temperatures comfortable.
GHP's circulate water or other liquids through pipes buried in a
continuous loop (either horizontally or vertically) next to a building.
Depending on the weather, the system is used for heating or
Heating: Earth's heat (the difference between the
earth's temperature and the colder temperature of the air) is
transferred through the buried pipes into the circulating liquid and
then transferred again into the building.
Cooling: During hot weather, the continually
circulating fluid in the pipes 'picks up' heat from the building - thus
helping to cool it - and transfers it into the earth.
GHP's use very little electricity and
are very easy on the environment.
In the U.S., the temperature inside
over 300,000 homes, schools and offices is kept comfortable by these
energy saving systems, and hundreds of thousands more are used worldwide.
The U.S. Environmental Protection Agency has rated GHP's as among the most
efficient of heating and cooling technologies.
WHAT PARTS OF THE
WORLD HAVE GEOTHERMAL ENERGY?
- For electricity and
direct use: Geothermal
reservoirs that are close enough to the surface to be reached by
drilling can occur in places where geologic processes have allowed magma
to rise up through the crust, near to the surface, or where it flows out
as lava. The crust of the Earth is made up of huge plates, which are in
constant but very slow motion relative to one another. Magma can reach
near the surface in three main geologic areas:
- where Earth's large oceanic and
crustal plates collide and one slides beneath another, called a
subduction zone The best example of these hot regions around plate
margins is the Ring of Fire -- the areas bordering the Pacific Ocean:
the South American Andes, Central America, Mexico, the Cascade Range
of the U.S. and Canada, the Aleutian Range of Alaska, the Kamchatka
Peninsula of Russia, Japan, the Philippines, Indonesia and New
- spreading centers, where these
plates are sliding apart, (such as Iceland, the rift valleys of
Africa, the mid-Atlantic Ridge and the Basin and Range Province in the
- places called hot spots-- fixed
points in the mantle that continually produce magma to the surface.
Because the plate is continually moving across the hot spot, strings
of volcanoes are formed, such as the chain of Hawaiian Islands.
The countries currently producing the most electricity from
geothermal reservoirs are the United States, New Zealand, Italy,
Iceland, Mexico, the Philippines, Indonesia and Japan, but geothermal
energy is also being used in many other
- For geothermal heat
pumps, use can be almost
world-wide. The earth's temperature a few feet below the ground surface
is relatively constant everywhere in the world (about 45 - 58 degrees
F), while the air temperature can change from summer to winter extremes.
Unlike other kinds of geothermal heat, shallow ground temperatures are
not dependent upon tectonic plate activity or other unique geologic
processes. Thus geothermal heat pumps can be used to help heat and cool
HOW MUCH GEOTHERMAL
ENERGY IS THERE?
Thousands more megawatts of power
than are currently being produced could be developed from
already-identified hydrothermal resources. With improvements in
technology, much more power will become available. Usable geothermal
resources will not be limited to the "shallow" hydrothermal reservoirs
at the crustal plate boundaries. Much of the world is underlain (3-6
miles down), by hot dry rock - no water, but lots of heat.
Scientists in the U.S.A., Japan, England, France, Germany and Belgium
have experimented with piping water into this deep hot rock to create
more hydrothermal resources for use in geothermal power plants. As
drilling technology improves, allowing us to drill much deeper,
geothermal energy from hot dry rock could be available anywhere. At such
time, we will be able to tap the true potential of the enormous heat
resources of the earth's crust.