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
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:
- California - has 33 geothermal power plants that produce almost 90 percent of the nation's geothermal electricity.
- Nevada - has 15 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.
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.
- 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 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.
1951 - 1960
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