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WHAT
DOES THE WORD "GEOTHERMAL" MEAN?
"Geothermal" comes
from the Greek words geo (earth) and therme (heat). So, geothermal
means earth heat.
WHAT IS GEOTHERMAL
ENERGY?
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 environment.
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 geothermal reservoir.
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 the reservoir.
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 ELECTRICITY?
- 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 local
wildlife.
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 the U.S.
- 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 shocks.
- 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 outside (agriculture);
- to shorten the
time needed for growing fish, shrimp, abalone and alligators to
maturity (aquaculture);
- to pasteurize milk,
to dry onions and lumber and to wash wool (industrial uses);
- Space 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 world.
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.
GEOTHERMAL HEAT 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 cooling.
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 Zealand.
- 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 U.S.); and
- 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 countries.
- 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 homes anywhere.
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.
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