What is Geothermal Energy?
Geothermal Energy comes from the heat within the
earth. The word geothermal comes from the Greek words geo,
meaning earth and therme, meaning heat. People
around the world use geothermal energy to produce
electricity, to heat buildings, and for other purposes.
The earth's core lies almost 4,000 miles beneath the
earth's surface. The double-layered core s made up of
very hot molten iron surrounding a solid iron center.
Estimates of the temperature of the core range from 5,000
to 11,000 degrees Fahrenheit.
Surround the earth's core is the mantle, thought to be
partly rock and partly magma. The mantle is about 1,800
miles thick. The outermost layer of the earth, the
insulating crust, is not one continuous sheet of rock,
like the shell of an egg, but is broken into pieces
called plates.
These slabs of continents and ocean floor drift apart and
push against each other at the rate of about one inch per
year in a process called plate tectonics. This process
can cause the crust to become faulted (cracked),
fractured or thinned, allowing plumes of magma to rise up
into the crust.
This magma can reach the surface and form volcanoes, but
most remains underground, where it can underlie regions
as large as huge mountain ranges. The magma can take from
1,000 to 1,000,000 years to cool, as its heat is
transferred to surrounding rocks.
In areas where there is underground water, it can fill
rock fractures and porous rocks. The water becomes heated
and can circulate back to the surface to create hot
springs, mud pots and fumaroles, or it can become tapped
underground, forming deep geothermal reservoirs.
Geothermal energy is called a renewable energy source
because the water is replenished by rainfall, and the
heat is continuously produced within the earth by the
slow decay of radioactive particles that occurs naturally
in all rocks.
Where is Geothermal Energy Found?
Geologists use many methods to find geothermal
reservoirs. They study aerial photographs and geological
maps. They analyze the chemistry of local water sources
and the concentration of metals in the soil. They may
measure variations in gravity and magnetic fields. Yet
the only way they can be sure there is a geothermal
reservoir is by drilling an exploratory well.
The hottest geothermal regions are found along major
plate boundaries where earthquakes and volcanoes are
concentrated. Most of the world's geothermal activity
occurs in an area know as the Ring of Fire, which rims
the Pacific Ocean and is bounded by Indonesia, the
Philippines, Japan, the Aleutian Islands, North America,
Central America, and South America.
High Temperature: Producing Electricity
When geothermal reservoirs are located near the surface,
we can reach them by drilling wells. Some wells are more
than two miles deep. Exploratory wells are drilled to
search for reservoirs. Once a reservoir had been found,
production wells are drilled. Hot water and steam-at
temperatures of 250 to 700 degrees Fahrenheit-are used to
turn turbines to generate electricity.
There are several different types of geothermal power
plants:
Flashed Steam Plants: Most geothermal plants are flashed
steam plants. How water from production wells flashes
(explosively boils) into steam when it is released from
the underground pressure of the reservoir. The force of
the steam is used to spin the turbine generator. To
conserve water and maintain the pressure in the
reservoir, the steam is condensed into water and injected
back into the reservoir to be reheated.
Dry Steam Plants: A few geothermal reservoirs produce
mostly steam and very little water. In dry steam plants,
the steam from the reservoir shoots directly through a
rock-catcher into the turbine generator. The rock-catcher
protects the turbine from small rocks that may be carried
along with the steam from the reservoir.
The first geothermal power plant was a dry steam plant
build at Larderallo in Tuscany, Italy, in 1904. The
original buildings were destroyed during World War II,
but have since been rebuilt and expanded. The Larderallo
field is still producing electricity today.
The Geysers dry steam reservoir in northern California
has been producing electricity since 1960. It is the
largest known dry steam field in the world and, after 40
years, still produces enough electricity to supply a city
the size of San Francisco.
Binary Power Plants: Binary power plants transfer
the heat from geothermal hot water to other liquids to
produce electricity. The geothermal water is passed
through a heat exchanger in a closed pipe system, and
then reinserted into the reservoir. The heat exchanger
transfers the heat to a working fluid-usually isobutene
or isopentane-that boils at a lower temperature than
water. The vapor from the working fluid is used to turn
the turbines.
Binary systems can, therefore, generate electricity from
reservoirs with lower temperatures. Since the system is
closed, there is little heat loss and almost no water
loss, and virtually no emissions.
Hybrid Power Plants: In some power plants, flash
and binary systems are combined to make use of both the
steam and the hot water. A hybrid system provides about
25 percent of the electricity to the big island of
Hawaii.
GeoExchange Systems: Heating and Cooling
Once you go about twenty feet below the Earth's surface,
the temperature is remarkably constant year round. In
temperate regions, the temperature stays about 52 degrees
Fahrenheit. In tropical regions, it can range as high as
65-70 degrees, while certain arctic regions stay near
freezing all year.
For most areas, this means that soil temperatures are
usually warmer than the air in winter and cooler than the
air in summer. Geothermal exchange systems use the
Earth's constant temperature to hear and cool buildings.
These heat pumps transfer feat from the ground into
buildings in winter and reverse the process in the
summer.
A geothermal exchange system does not look like a
tradition furnace or air conditioner. For one thing, most
of the equipment is underground. A liquid-usually a
mixture of water ad antifreeze-circulates through a long
loop of plastic pipe buried in the ground. This liquid
absorbs hear and carries it either into or out of the
building.
One advantage of a geothermal exchange system is that is
does not have to manufacture hear. The heat is free,
renewable, and readily available in the ground. The only
energy this system needs is the electricity to pump the
liquid through the pipes and deliver the conditioned air
to the building. The pump itself is usually a small unit
located inside the building.
The geothermal exchange pipe can be buried in several
ways. If space is limited, holes for the pipe can by dug
straight into the ground as far down as 300 feet. In very
rocky areas, this method might not be an option.
If there is land available, the pipes can be buried in
shallow trenches four to six feet underground. Once the
pipes are in place the surface can be used as a front
lawn, football field, or parking lot. The pipes should
last up to 50 years without maintenance.
If a large lake or pond is nearby, the pipes can be
buried in the water. The water must be a least six feet
deep, though, or the temperature of the water will change
too much. Deep, flowing water provides especially good
heat exchange for a geothermal system.
Geothermal systems cost more to install than conventional
heating and cooling systems. Over the life of the system,
however, they can produce a significant cost savings.
They can reduce heating costs by 50-70 percent, and
cooling costs by 20-40 percent. If the cost of the
installation is spread out over several years, users see
savings from the day they begin using the system. Over
the life of the system, the average homeowner can
anticipate saving about $20,000.
In addition, geothermal systems are low maintenance and
should last twice as long as conventional systems. The
pumps should last 20 years, since they are located
inside, away form the weather. And most of the energy
they use is free, renewable energy. Electricity is used
only to move the heat, not to produce it.
Today, more than 300,000 homes and buildings in the
United States use geothermal heat exchange systems. They
are an efficient, economical alternative to conventional
heating and cooling systems. The U.S. Environmental
Protection Agency has rated geothermal heat pump systems
among the most efficient heating and cooling
technologies.
Geothermal Energy and the Environment
Geothermal energy is a renewable energy source that does
little damage to the environment. Geothermal steam and
hot water do contain naturally occurring traces of
hydrogen sulfide (a gas that smells like rotten eggs) and
other gases and chemicals that can be harmful in high
concentrations. Geothermal power plants use scrubber
systems to clean the air of hydrogen sulfide and the
other gases. Sometimes the gases are converted into
marketable products, such as liquid fertilizer.
Geothermal power plants do not burn fuel to generate
electricity, so their emission levels are very low. They
release about one percent of the carbon dioxide emitted
by comparable fossil fuel plants. Emissions of sulfur
compounds from motor vehicles and fossil fuel plants also
contribute to acid rain. Geothermal power plants, on the
other hand, emit only one to three percent of the sulfur
compounds that coal and oil-fired power plants do.
Well-designed binary cycle power plants have no emissions
at all.
Geothermal power plants are compatible with many
environments. They have been built in deserts, in the
middle of crops, and in mountain forests.
Development is often allowed on federal lands because is
does not significantly harm the environment. Before
permission is granted, studies must be made to determine
impact. Law, so geothermal energy is not tapped in these
areas, protects geothermal features in national parks,
such as the geysers and fumaroles in Yellowstone and
Lassen National Parks.
Geothermal Reserves
The earth has no shortage of geothermal activity, but not
all geothermal resources are easy or economical to use.
Geothermal energy comprises four percent of the total
U.S. domestic energy reserves, an amount exceeded only by
coal (83 percent) and biomass (5 percent).
Because energy sources are counted as reserves only when
they are economical to develop, geothermal reserves will
increase as the price of other fuels increases.
Improvements in technology will make it easier to use
geothermal resources. This will also bring costs down and
increase geothermal reserves,
Today, there are 250 geothermal power plants in 21
countries, supplying 8,200 megawatts of electricity to 15
million people. Direct uses of geothermal reservoirs
amount to over 11,000 megawatts of thermal energy in 35
countries. And an additional 40 countries use hot springs
and spas, but have not yet commercially developed their
geothermal reservoirs.
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The earth is the most
precious resource the we have. It can be used to produce
almost anything that we need to survive. It can even
produce energy. Read on to find out how.
A geyser is one of the most commonly used resources to
collect geothermal energy. Here is a picture of the most
famous geyser in the world - Old Faithful!
Here are geothermal exchange pipes as they rise above the
surface of the earth. Read the section to the right to
find out what they are carrying when they return to the
surface.
Areas like these are oozing with geothermal energy. Many
of these areas have not even been discovered yet. This is
why we will almost certainly never run out of geothermal
energy. |
