Geothermal
energy can sometimes find its way to the surface in the form of:
The most active
geothermal resources are usually found along major plate boundaries
where earthquakes and volcanoes are concentrated. Most of the
geothermal activity in the world occurs in an area called the
Ring of Fire. This area rims the Pacific Ocean.
When magma
comes close to the surface it heats ground water found trapped
in porous rock or water running along fractured rock surfaces
and faults. Such hydrothermal resources
have two common ingredients: water (hydro) and heat (thermal).
Naturally occurring large areas of hydrothermal resources are
called geothermal reservoirs. Geologists
use different methods to look for geothermal reservoirs. Drilling
a well and testing the temperature deep underground is the only
way to be sure a geothermal reservoir really exists.
Most of the
geothermal reservoirs in the United States are located in the
western states, Alaska, and Hawaii. California is the state that
generates the most electricity from geothermal energy. The Geysers
dry steam reservoir in northern California is the largest known
dry steam field in the world. The field has been producing electricity
since 1960.
USES OF GEOTHERMAL
ENERGY
Some applications
of geothermal energy use the earth's temperatures near the surface,
while others require drilling miles into the earth. The three
main uses of geothermal energy are:
1)
Direct Use and District Heating Systems which use hot water
from springs or reservoirs near the surface.
2) Electricity
generation in a power plant requires water or steam at very
high temperature (300 to 700 degrees Fahrenheit). Geothermal power
plants are generally built where geothermal reservoirs are located
within a mile or two of the surface.
3) Geothermal
heat pumps use stable ground or water temperatures near the
earth's surface to control building temperatures above ground.
DIRECT USE
OF GEOTHERMAL ENERGY
The direct
use of hot water as an energy source has been happening
since ancient times. The Romans, Chinese, and Native Americans
used hot mineral springs for bathing, cooking and heating. Today,
many hot springs are still used for bathing, and many people believe
the hot, mineral-rich waters have natural healing powers.
After bathing,
the most common direct use of geothermal energy is for heating
buildings through district heating systems. Hot
water near the earth's surface can be piped directly into buildings
and industries for heat. A district heating system provides heat
for 95 percent of the buildings in Reykjavik, Iceland. Examples
of other direct uses include: growing crops, and drying lumber,
fruits, and vegetables.
GEOTHERMAL
POWER PLANTS
Geothermal
power plants use hydrothermal resources which
have two common ingredients: water (hydro) and heat (thermal).
Geothermal plants require high temperature (300 to 700 degrees
Fahrenheit) hydrothermal resources that may come from either dry
steam wells or hot water wells. We can use these resources by
drilling wells into the earth and piping the steam or hot water
to the surface. Geothermal wells are one to two miles deep.
The United
States generates more geothermal electricity than any other country
but the amount of electricity it produces is less than one-half
of a percent of electricity produced in United States. Only four
states have geothermal power plants:
-
California
- has 33 geothermal power plants that produce almost 90 percent
of the nation's geothermal electricity.
-
Nevada
- has 14 geothermal power plants.
-
Hawaii
and Utah - each have one geothermal plant
There are
three basic types of geothermal power plants:
-
Dry steam
plants - use steam piped directly from a geothermal reservoir
to turn the generator turbines. The first geothermal power
plant was built in 1904 in Tuscany, Italy at a place where
natural steam was erupting from the earth.
-
Flash
steam plants - take high-pressure hot water from deep inside
the earth and convert it to steam to drive the generator turbines.
When the steam cools, it condenses to water and is injected
back into the ground to be used over and over again. Most
geothermal power plants are flash plants.
-
Binary
power plants - transfer the heat from geothermal hot water
to another liquid. The heat causes the second liquid to turn
to steam which is used to drive a generator turbine.
GEOTHERMAL
HEAT PUMPS
While temperatures
above ground change a lot from day to day and season to season,
temperatures in the upper 10 feet of the Earth's surface hold
nearly constant between 50 and 60 degrees Fahrenheit. For most
areas, this means that soil temperatures are usually warmer than
the air in winter and cooler than the air in summer. Geothermal
heat pumps use the Earth's constant temperatures to heat and cool
buildings. They transfer heat from the ground (or water) into
buildings in winter and reverse the process in the summer.
According
to the U.S. Environmental Protection Agency (EPA), geothermal
heat pumps are the most energy-efficient, environmentally clean,
and cost-effective systems for temperature control. Although,
most homes still use traditional furnaces and air conditioners,
geothermal heat pumps are becoming more popular. In recent years,
the U.S. Department of Energy along with the EPA have partnered
with industry to promote the use of geothermal heat pumps.
GEOTHERMAL
ENERGY AND THE ENVIRONMENT
The environmental
impact of geothermal energy depends on how it is being used.
-
Direct
use and heating applications have almost no negative impact
on the environment.
-
Geothermal
power plants do not burn fuel to generate electricity, so
their emission levels are very low. They release less than
1 percent of the carbon dioxide emissions
of a fossil fuel plant. Geothermal plants use scrubber systems
to clean the air of hydrogen sulfide that is naturally found
in the steam and hot water. Geothermal plants emit 97 percent
less acid rain - causing sulfur compounds than are emitted
by fossil fuel plants. After the steam and water from a geothermal
reservoir have been used, they are injected back into the
earth.
-
Geothermal
features in national parks, such as geysers and fumaroles
in Yellowstone National Park, are protected by law, to prevent
the land from being disturbed.
SOURCE
: ENERGY INFORMATION ADMINISTRATION
-- DEPARTMENT OF ENERGY -- KIDS HOME PAGE
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