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Geothermal Energy
The word geothermal comes
from the Greek words geo (earth) and therme (heat). So, geothermal energy is
heat from within the earth. We can use the steam and hot water produced inside
the earth to heat buildings or generate electricity. Geothermal energy is a renewable
energy source because the water is replenished by rainfall and the heat is
continuously produced inside the earth.
Geothermal energy is generated in
the earth's core, about 4,000 miles below the surface. Temperatures hotter than
the sun's surface are continuously produced inside the earth by the slow decay
of radioactive particles, a process that happens in all rocks. The earth has a
number of different layers: The core itself has two layers: a solid iron core
and an outer core made of very hot melted rock, called magma. The mantle which
surrounds the core and is about 1,800 miles thick. It is made up of magma and
rock. The crust is the outermost layer of the earth, the land that forms the
continents and ocean floors. It can be three to five miles thick under the
oceans and 15 to 35 miles thick on the continents. The earth's crust is broken
into pieces called plates. Magma comes close to the earth's surface near the
edges of these plates. This is where volcanoes occur. The lava that erupts from
volcanoes is partly magma. Deep underground, the rocks and water absorb the heat
from this magma. The temperature of the rocks and water get hotter and hotter as
you go deeper underground. People around the world use geothermal energy to heat
their homes and to produce electricity by digging deep wells and pumping the
heated underground water or steam to the surface. Or, we can make use of the
stable temperatures near the surface of the earth to heat and cool buildings.
Most geothermal reservoirs are
deep underground with no visible clues showing above ground. Geothermal energy
can sometimes find its way to the surface in the form of: volcanoes and
fumaroles (holes where volcanic gases are released) hot springs and geysers. 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.
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.
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.
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.
In Iceland, there are five major
geothermal power plants which produce about 26% (2006) of the country's
electricity. In addition, geothermal heating meets the heating and hot water
requirements for around 87% of the nation's housing. In 2006, 26.5% of
electricity generation in Iceland came from geothermal energy, 73.4% from hydro
power, and 0.1% from fossil fuels
http://www.worldatlas.com
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 1 percent of electricity produced in United States. Only
four states have geothermal power plants:
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California - has 33
geothermal power plants that produce almost 90 percent of the nation's
geothermal electricity.
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Nevada - has 15 geothermal
power plants.
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Hawaii and Utah - each have
one geothermal plant
There are three basic types of
geothermal power plants:
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.
Types of
Geothermal Heat Pump Systems
There are four basic types of
ground loop systems. Three of these—horizontal, vertical, and pond/lake—are
closed-loop systems. The fourth type of system is the open-loop option. Which
one of these is best depends on the climate, soil conditions, available land,
and local installation costs at the site. All of these approaches can be used
for residential and commercial building applications.
Closed-Loop Systems
Horizontal
This type of installation is
generally most cost-effective for residential installations, particularly for
new construction where sufficient land is available. It requires trenches at
least four feet deep. The most common layouts either use two pipes, one buried
at six feet, and the other at four feet, or two pipes placed side-by-side at
five feet in the ground in a two-foot wide trench. The Slinky™ method of
looping pipe allows more pipe in a shorter trench, which cuts down on
installation costs and makes horizontal installation possible in areas it would
not be with conventional horizontal applications.
Vertical
Large commercial buildings and
schools often use vertical systems because the land area required for horizontal
loops would be prohibitive. Vertical loops are also used where the soil is too
shallow for trenching, and they minimize the disturbance to existing
landscaping. For a vertical system, holes (approximately four inches in
diameter) are drilled about 20 feet apart and 100–400 feet deep. Into these
holes go two pipes that are connected at the bottom with a U-bend to form a
loop. The vertical loops are connected with horizontal pipe (i.e., manifold),
placed in trenches, and connected to the heat pump in the building.
Pond/Lake
If the site has an adequate water
body, this may be the lowest cost option. A supply line pipe is run underground
from the building to the water and coiled into circles at least eight feet under
the surface to prevent freezing. The coils should only be placed in a water
source that meets minimum volume, depth, and quality criteria.
Open-Loop System
This type of system uses well or
surface body water as the heat exchange fluid that circulates directly through
the GHP system. Once it has circulated through the system, the water returns to
the ground through the well, a recharge well, or surface discharge. This option
is obviously practical only where there is an adequate supply of relatively
clean water, and all local codes and regulations regarding groundwater discharge
are met.
GEOTHERMAL ENERGY
AND THE ENVIRONMENT
The environmental impact of
geothermal energy depends on how it is being used.
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Direct use and heating
applications have almost no negative impact on the environment.
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Geothermal power plants do
not burn fuel to generate electricity, so their emission levels are very
low. They release about 1 to 3 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.
A History of
Geothermal Energy in the United States
Archaeological evidence shows
that the first human use of geothermal resources in North America occurred more
than 10,000 years ago with the settlement of Paleo-Indians at hot springs. The
springs served as a source of warmth and cleansing, their minerals as a source
of healing. While people still soak in shallow pools heated by the Earth,
engineers are developing technologies that will allow us to probe more than 10
miles below the Earth's surface in search of geothermal energy. We invite you to
study the timeline of the recent history of geothermal energy in the United
States.
Important Events
in the History of Geothermal Energy in the United States
Human beings have used geothermal
energy in North America for at least 10,000 years. Paleo-Indians used hot
springs for cooking, and for refuge and respite. Hot springs were neutral zones
where members of warring nations would bathe together in peace. Native Americans
have a history with every major hot spring in the United States.
1800 - 1850
1807
As European settlers moved
westward across the continent, they gravitated toward these springs of warmth
and vitality. In 1807, the first European to visit the Yellowstone area, John
Colter, probably encountered hot springs, leading to the designation "Colter's
Hell". Also in 1807, settlers founded the city of Hot Springs, Arkansas,
where, in 1830, Asa Thompson charged one dollar each for the use of three
spring-fed baths in a wooden tub, and the first known commercial use of
geothermal energy occurred.
1847
William Bell Elliot, a member of
John C. Fremont's survey party, stumbles upon a steaming valley just north of
what is now San Francisco, California. Elliot calls the area The Geysers-a
misnomer-and thinks he has found the gates of Hell.
1851 - 1900
1852
The Geysers is developed into a
spa called The Geysers Resort Hotel. Guests include J. Pierpont Morgan, Ulysses
S. Grant, Theodore Roosevelt, and Mark Twain.
1862
At springs located southeast of
The Geysers, businessman Sam Brannan pours an estimated half million dollars
into an extravagant development dubbed "Calistoga," replete with
hotel, bathhouses, skating pavilion, and racetrack. Brannan's was one of many
spas reminiscent of those of Europe.
1864
Homes and dwellings have been
built near springs through the millennia to take advantage of the natural heat
of these geothermal springs, but the construction of the Hot Lake Hotel near La
Grande, Oregon, marks the first time that the energy from hot springs is used on
a large scale.
1892
Folks in Boise, Idaho, feel the
heat of the world's first district heating system as water is piped from hot
springs to town buildings. Within a few years, the system is serving 200 homes
and 40 downtown businesses. Today, there are four district heating systems in
Boise that provide heat to over 5 million square feet of residential, business,
and governmental space. Although no one imitated this system for some 70 years,
there are now 17 district heating systems in the United States and dozens more
around the world.
1900
Hot springs water is piped to
homes in Klamath Falls, Oregon.
1901 - 1950
1921
John D. Grant drills a well at
The Geysers with the intention of generating electricity. This effort is
unsuccessful, but one year later Grant meets with success across the valley at
another site, and the United States' first geothermal power plant goes into
operation. Grant uses steam from the first well to build a second well, and,
several wells later, the operation is producing 250 kilowatts, enough
electricity to light the buildings and streets at the resort. The plant,
however, is not competitive with other sources of power, and it soon falls into
disuse.
Hot Springs National Park in
Arkansas is created.
1927
Pioneer Development Company
drills the first exploratory wells at Imperial Valley, California.
1930
The first commercial greenhouse
use of geothermal energy is undertaken in Boise, Idaho. The operation uses a
1000-foot well drilled in 1926. In Klamath Falls, Charlie Lieb develops the
first downhole heat exchanger (DHE) to heat his house. Today, more than 500 DHEs
are in use around the country.
1940
The first residential space
heating in Nevada begins in the Moana area in Reno.
1948
Geothermal technology moves east
when Professor Carl Nielsen of Ohio State University develops the first
ground-source heat pump, for use at his residence. J.D. Krocker, an engineer in
Portland, Oregon, pioneers the first commercial building use of a groundwater
heat pump.
1960
The country's first
large-scale geothermal electricity-generating plant begins operation. Pacific
Gas and Electric operates the plant, located at The Geysers. The first turbine
produces 11 megawatts (MW) of net power and operates successfully for more than
30 years. Today, 69 generating facilities are in operation at 18 resource sites
around the country.
1961 - 1970
1970
The Geothermal Resources Council
is formed to encourage development of geothermal resources worldwide.
The Geothermal Steam Act is
enacted, which provides the Secretary of the Interior with the authority to
lease public lands and other federal lands for geothermal exploration and
development in an environmentally sound manner.
1971 - 1980
1972
The Geothermal Energy Association
is formed. The association includes U.S. companies that develop geothermal
resources worldwide for electrical power generation and direct-heat uses.
1973
The National Science Foundation
becomes the lead agency for federal geothermal programs.
1974
The U.S. government enacts the
Geothermal Energy Research, Development and Demonstration (RD&D) Act,
instituting the Geothermal Loan Guaranty Program, which provides investment
security to public and private sectors using developing technologies to exploit
geothermal resources.
1975
The Energy Research and
Development Administration (ERDA) is formed. The Division of Geothermal Energy
takes over the RD&D program. The Geo-Heat Center is formed. The center,
located at the Oregon Institute of Technology, disseminates information to
potential users and conducts applied research on using low- to
moderate-temperature geothermal resources. The U.S. Geological Survey releases
the first national geothermal resource estimate and inventory.
1977
The U.S. Department of Energy
(DOE) is formed.
1978
The Public Utility Regulatory
Policies Act (PURPA) is enacted. PURPA encourages the development of
independent, nonutility cogeneration and small power projects by requiring
electric utilities to interconnect with them. The act results in the development
of several water-dominated resources.
Geothermal Food Processors, Inc.,
opens the first geothermal food-processing (crop-drying) plant in Brady Hot
Springs, Nevada. The Loan Guaranty Program provides $3.5 million for the
facility.
A hot dry rock geothermal
facility is created and tested in Fenton Hill, New Mexico, with financial
assistance from DOE. The facility generates electricity two years later, in
1980.
1979
The first electrical development
of a water-dominated geothermal resource occurs, at the East Mesa field in the
Imperial Valley in California. The plant is named for B.C. McCabe, the
geothermal pioneer who, with his Magma Power Company, did field development work
at several sites, including The Geysers.
DOE institutes funding of
direct-use demonstration projects. Among the beneficiaries of this effort are
several office buildings, district heating systems, and agribusinesses.
1980
TAD's Enterprises of Nevada
pioneers the use of geothermal energy for the cooking, distilling, and drying
processes associated with alcohol fuels production. UNOCAL builds the country's
first flash plant, generating 10 MW at Brawley, California.
1981 - 1990
1981
With a supporting loan from DOE,
Ormat successfully demonstrates binary technology in the Imperial Valley of
California. This project establishes the technical feasibility of larger-scale
commercial binary power plants. The project is so successful that Ormat repays
the loan within a year.
The first electricity is
generated from geothermal resources in Hawaii. The Department of Energy
demonstrates the production of electricity from moderate temperature geothermal
resources using binary technology at Raft River, ID.
1982
Economical electrical generation
begins at California's Salton Sea geothermal field through the use of
crystallizer-clarifier technology. The technology resulted from a
government/industry effort to manage the high-salinity brines at the site.
1984
A 20-MW plant begins generating
power at Utah's Roosevelt Hot Springs. Nevada's first geothermal electricity is
generated when a 1.3-MW binary power plant begins operation.
The Heber dual-flash power plant
goes online in the Imperial Valley of California with 50 MW.
1987
Geothermal fluids are used in the
first geothermal-enhanced heap leaching project for gold recovery, near Round
Mountain, Nevada.
1989
The world's first hybrid (organic
Rankine/gas engine) geopressure-geothermal power plant begins operation at
Pleasant Bayou, Texas, using both the heat and the methane of a geopressured
resource.
1991 - 2000
1991
The Bonneville Power
Administration selects three sites in the Pacific Northwest for geothermal
demonstration projects.
1992
Electrical generation begins at
the 25-MW geothermal plant in the Puna field of Hawaii.
1993
A 23-MW binary power plant is
completed at Steamboat Springs, Nevada.
1994
DOE creates two
industry/government collaborative efforts to promote the use of geothermal
energy to reduce greenhouse gas emissions. One effort is directed toward the
accelerated development of geothermal resources for electric power generation;
the other is aimed toward the accelerated use of geothermal heat pumps.
1995
Integrated Ingredients dedicates
a food-dehydration facility that processes 15 million pounds of dried onions and
garlic per year at Empire, Nevada. A DOE low-temperature resource assessment of
10 western states identifies nearly 9000 thermal wells and springs and 271
communities collocated with a geothermal resource greater than 50ºC.
2000
DOE initiates its GeoPowering the
West program to encourage development of geothermal resources in the western U.
S. An initial group of 21 partnerships with industry is funded to develop new
technologies.
2001 - 2002
2001
GeoPowering the West brings
together representatives from industry and agencies such as the U.S. Bureau of
Land Management and U.S. Forest Service to identify major barriers to geothermal
development in the west. The report of the proceedings listed specific action
items and recommendations. Several of the recommendations pertained to leasing,
permitting, and access to federal lands.
Secretary of the Interior Gail
Norton convened a renewable energy summit with officials from DOI, DOE, and
other agencies to identify actions required to support renewable energy
development. Recommendations specific to geothermal emerged from the meeting,
including a mandate to BLM to accelerate issuing leases and permits on federal
lands.
2002
Organized by GeoPowering the
West, geothermal development working groups are active in five states —
Nevada, Idaho, New Mexico, Oregon, and Washington. Group members represent all
stakeholder organizations. The working groups are identifying barriers to
geothermal development in their state, and bringing together all interested
parties to arrive at mutually beneficial solutions.
2003
2003 The Utah Geothermal Working
Group is formed.
Credit: Department Of Energy,
Oregon Institute of Technology, International Geothermal Association, NOAA, USGS
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