- Geothermal energy
is a renewable and sustainable power source that comes from the
heat generated by the earth. "Geo" means earth and "thermal"
means heat. The Earth has four main layers, as is shown in the
first picture below (Geothermal
Education Office). Each layer has different compositions,
functions and temperatures, as is illustrated in the second figure
Education office). The heat of the earth radiates outward
and sometimes melts the mantle at temperatures of 300° F-
700°F. When the mantle becomes melted magma is created. Sometimes
magma reaches the surface of the crust and is then called lava.
The magma reaches the crust and heats nearby rocks and water.
The heated water can reach the surface and form hot springs and
creates less environmental pollution, is renewable and sustainable,
avoids importing energy resources, benefits remote areas, adds
to energy source diversity, creates less waste disposal and
has a long life span.
is produced by drilling a well into the ground where thermal
activity is occuring. Once a well has been identified and a
well head attached, the steam is separated from the water, the
water is diverted through a turbine engine which turns a generator.
Usually the water is injected back into the ground to resupply
the geothermal source. The pictures below illustrate how the
set-up of a geothermal site collecting energy looks like (EIA
kids site) and (Geothermal
Locations of Geothermal Energy Use
Geothermal energy is
generally harnessed in areas of volcanic activity. The Pacific
Ring is a prime spot for the harnessing of geothermal activity
because it is an area where the tectonic processes
are always taking place. The picture below shows the general location
of the Ring of Fire (EIA
defines tectonic processes as a series of actions and changes relating
to, causing, or resulting from structural deformation of the earth's
crust. [Adapted from American Heritage Dic. of the English Language,
4th ed.] This picture illustrates the term tectonic processes
Geothermal power plants
are used all over the world, but can not be located just anywhere.
They are located where tectonic plates collide and generate volcanic
activity. The map below shows where plate
boundaries are located and the following map illustrates the
general location of geothermal
power plants being used around the world.
The table below shows
MW of Geothermal Energy in different countries around the world.
For more information on the countries below, click on the name.
For further information on other geothermal plants throughout the
world visit this website, Selected
Geothermal Power Plants (ORMAT GreEnergy Power).
below shows the countries that are using Geothermal Energy and
the number of Megawatts that their power plants produce.
countries in 1999
Within the United States,
the West (and specifically California) are major producers of
Geothermal Energy. Each state has different regulations on geothermal
energy. According to the Bureau
of Land Management in California, , "The Geothermal Steam
Act of 1970, as amended, (84 Stat, 1566; 30 U.S.C. 1001-1025)
provides the Secretary of the Interior with the authority to lease
public lands and other federal lands, including National Forest
lands, for geothermal exploration and development in an environmentally
sound manner. This authority has been delegated to the Bureau
of Land Management (BLM). BLM implements the Act through the regulations
contained in 43 Code of Federal Regulations (CFR) Part 3200."
The table below shows the amount of money, leases and megawatts
produced in California during the Fiscal
Year 2000 (October 1, 1999-September 30, 2000).
of Geothermal Power Plants
technology has three varied ways of taking geothermal energy and
turning it in to useable energy for humans to use. The most common
systems are steam and binary power plants. There are two different
types of steam power plants: dry steam and flash steam. The following
definitions and pictures are from Geothermal
Technologies Program or Godfrey Boyle in Renewable Energy:
Power for a Sustainable Future.
Steam Power Plants or Hot Dry Rock Power Plants
- Vapor dominated resources
where steam production is not contaminated
is 1050°F - 1220° F
- Steam passes through
- Steam expands
- Blades and shaft rotate
and generate power
- Cooling towers generate
- Most common and most
commercially attractive (Godfrey Boyle)
- Used in areas where
geysers do not exist
- Need water to inject
down into rock
- Well is deep
- Takes more time to
inject water in well
- Uses lower-temperatures,
but much more common, hot water resources (100° F – 300°
water is passed through a heat exchanger in conjunction with a secondary
(hence, "binary plant") fluid with a lower boiling point
(usually a hydrocarbon such as isobutane or isopentane).
- Secondary fluid vaporizes,
which turns the turbines, which drive the generators.
- Remaining secondary
fluid is simply recycled through the heat exchanger.
- Geothermal fluid is
condensed and returned to the reservoir.
- Binary plants use
a self-contained cycle, nothing is emitted.
- Energy produced by
binary plants currently costs about 5 to 8 cents per kWh.
reservoirs are far more common, which makes binary plants more prevalent.
Flash or Steam
very hot (more than 300° F) steam and hot water resources (as
found at The Geysers plants in northern California)
either comes directly from the resource, or the very hot, high-pressure
water is depressurized ("flashed") to produce steam.
- Steam then turns turbines,
which drive generators that generate electricity.
- Only significant emission
from these plants is steam (water vapor).
- Minute amounts of carbon
dioxide, nitric oxide, and sulfur are emitted, but almost 50 times
less than at traditional, fossil-fuel power plants.
- Energy produced this
way currently costs about 4-6 cents per kWh.