We live between two great sources of energy, the hot rocks beneath the surface of the earth and
the sun in the sky. Our ancestors knew the value of geothermal energy; they bathed and cooked in hot
springs. Today we have recognized that this resource has potential for much broader application.
The term geothermal comes geo meaning earth and thermal meaning heat. Heat from the Earth,
or geothermal from the Greek — Geo (Earth) + thermal (heat) — energy can be and already is accessed

by drilling water or steam wells in a process similar to drilling for oil.
The core of the earth is very hot and it is possible to make use of this geothermal energy (in
Greek it means heat from the earth). These are areas where there are volcanoes, hot springs, and geysers,
and methane under the water in the oceans and seas. In some countries, such as in the USA water
is pumped from underground hot water deposits and used to heat people’s houses.
Geothermal energy is an enormous, underused heat and power resource that is clean (emits little
or no greenhouse gases), reliable (average system availability of 95%), and homegrown (making us
less dependent on foreign oil). The geothermal fields were first discovered in 1847 by William Bell
Elliot, an explorer surveyor who was hiking in the mountains between Cloverdale and Calistoga, California,
in search of grizzly bears. He discovered steam seeping out of the ground along a quarter of a
mile on the steep slope of a canyon near colb Mountain, an extinct volcano, now known as the Geysers.
The first application of geothermal energy was for space heating, cooking, and medicinal purposes.

The center of the earth is estimated at temperature up to 10,000 K due to decay process of
radioactive isotopes. The total steady geothermal energy flow towards earth's surface is 4.2 × 1010 kW.
But the average flow energy is only 0.063 W/m2.
The utilization of geothermal energy for the production of electricity dates back to the early part
of the twentieth century. For 50 years the generation of electricity from geothermal energy was confined
to Italy and interest in this technology was slow to spread elsewhere. In 1943 the use of geothermal
hot water was pioneered in Iceland.
The following general objectives of geothermal energy:
(1) Reduction of dependence on nonrenewable energy and stimulation of the state’s economy
through development of geothermal energy.
(2) Mitigation of the social, economic, and environmental impacts of geothermal development.
(3) Financial assistance to counties to offset the costs of providing public services and facilities
necessitated by the development of geothermal resources within their jurisdictions.
(4) Maintenance of the productivity of renewable resources through the investment of proceeds
from these resources.

The first mechanical conversion was in 1897 when the steam of the field at Larderello, Italy, was
used to heat a boiler producing steam which drove a small steam engine. The first attempt to produce
electricity also took place at Larderello in 1904 with an electric generator that powered four light bulbs
In the United States, the first attempt at developing the geysers field was made in 1922. Steam
was successfully tapped, but the pipes and turbines of the time were unable to cope with the corrosive
and abrasive steam. The effort was not revived until 1956 when two companies, Magma Power and
Thermal Power, tapped the area for steam and sold it to Pacific Gas and Electric Company. By that time
stainless steel alloys were developed that could withstand the corrosive steam, and the first electricgenerating
unit of 11 mW capacity began operation in 1960. Since then 13 generally progressively
larger units have been added to the system. The latest is a 109 mW unit that began operation in September
1982 and which brought the Geysers total capacity to 909 mW. Two more units are under construction
and four more are planned, which will bring the total capacity to 1514 mW by the late 1980s.
Other electric-generating fields of note are in New Zealand (where the main activity at Wairakei
dates back to 1958), Japan, Mexico (at Cerro Prieto), the Phillipines, the Soviet Union, and Iceland (a

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large space-heating program).
Future world projections for geothermal electric production, based on the decade of the 1970s,
are 7 percent per year. In the last four years of that decade, however, the growth rate was 19 percent per
year. In the United States, the projections are for growth between 13.5 and 22 percent per year through
the 1980s, which is 2.5 to 4 times the 5.3 percent per year growth rate of the total electric-generating
capacity. This includes the steam field at the Geysers and other fields of different types.
The U.S. Geological Survey predicts a U.S. potential from currently iden-tified sources to be
around 23,000 mW of electric power and around 42 × 10 SkJ of space and process heat for 30 years
with existing technology, and 72,000 to 127,000 mW of electricity and 144 to 294 × 1015 Btu of heat
from unidentified sources. Areas of geothermal potential in the North American continent, Geysers
Region in Northern California, the Imperial Valley in Southern California, and the Yellowstone Region
in Idaho, Montana, and Wyoming.
Most power plants need steam to generate electricity. The steam rotates a turbine that activates

a generator, which produces electricity. Many power plants still use fossil fuels to boil water for steam.
Geothermal power plants, however, use steam produced from reservoirs of hot water found a couple of
miles or more below the Earth’s surface. There are three types of geothermal power plants: dry steam,
flash steam, and binary cycle.

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