Geothermal Energy | National Geographic Society (2023)

Geothermal energyis heat that is generated within the Earth. (Geomeans “earth,” andthermalmeans “heat” in Greek.) It is arenewable resourcethat can be harvested for human use.

About 2,900 kilometers (1,800 miles) below the Earth’s crust, or surface, is the hottest part of our planet: thecore. A small portion of the


’s heat comes from thefrictionandgravitational pullformed when Earth was created more than 4 billion years ago. However, the vast majority of Earth’s heat is constantly generated by the decay ofradioactiveisotopes, such as potassium-40 and thorium-232.


are forms of an element that have a different number ofneutrons than regular versions of the


’s atom.

Potassium, for instance, has 20


in its nucleus. Potassium-40, however, has 21


. As potassium-40 decays, its nucleus changes, emitting enormous amounts of energy (radiation). Potassium-40 most often decays to


of calcium (calcium-40) and argon (argon-40).


decay is a continual process in the


. Temperatures there rise to more than 5,000° Celsius (about 9,000° Fahrenheit). Heat from the


is constantly radiating outward and warming rocks, water, gas, and other geological material.

Earth’s temperature rises with depth from the surface to the


. This gradual change in temperature is known as thegeothermal gradient. In most parts of the world, the

geothermal gradient

is about 25° C per 1 kilometer of depth (1° F per 77 feet of depth).

If underground rock formations are heated to about 700-1,300° C (1,300-2,400° F), they can become magma.


is molten (partly melted) rock permeated by gas and gas bubbles.


exists in themantleand lower crust, and sometimes bubbles to the surface aslava.

Magma heats nearby rocks and undergroundaquifers. Hot water can be released throughgeysers,hot springs, steamvents, underwaterhydrothermalvents, andmud pots.

These are all sources of

geothermal energy

. Their heat can be captured and used directly for heat, or their


can be used to generateelectricity.

Geothermal energy

can be used to heat structures such as buildings, parking lots, and sidewalks.

Most of the Earth’s

geothermal energy

does not bubble out as


, water, or


. It remains in the


, emanating outward at a slow pace and collecting as pockets of high heat. This dry geothermal heat can be accessed by drilling, and enhanced with injected water to create



Many countries have developed methods of tapping into

(Video) Energy 101: Geothermal Energy

geothermal energy

. Different types of

geothermal energy

are available in different parts of the world. In Iceland, abundant sources of hot, easily accessible underground water make it possible for most people to rely on geothermal sources as a safe, dependable, and inexpensive source of energy. Other countries, such as the U.S., must drill for

geothermal energy

at greater cost.

Harvesting Geothermal Energy: Heating and Cooling

Low-Temperature Geothermal Energy
Almost anywhere in the world, geothermal heat can be accessed and used immediately as a source of heat. This heat energy is called


geothermal energy



geothermal energy

is obtained from pockets of heat about 150° C (302° F). Most pockets of


geothermal energy

are found just a few meters below ground.


geothermal energy

can be used for heating greenhouses, homes, fisheries, and industrial processes. Low-temperature energy is most efficient when used for heating, although it can sometimes be used to generate



People have long used this type of

geothermal energy

forengineering, comfort, healing, and cooking. Archaeological evidence shows that 10,000 years ago, groups ofNative Americans gathered around naturally occurring

hot springs

torecuperateor takerefugefrom conflict. In the third century BCE, scholars and leaders warmed themselves in a

hot spring

fed by a stone pool near Lishan, a mountain in central China. One of the most famous

hot spring

spas is in the appropriately named town of Bath, England. Starting construction in about 60 CE, Roman conquerors built an elaborate system of


rooms and pools using heat from the region’s shallow pockets of


geothermal energy



hot springs

of Chaudes Aigues, France, have provided a source of income and energy for the town since the 1300s. Tourists flock to the town for its elite


. The


geothermal energy

also supplies heat to homes and businesses.

The United States opened its first geothermal district heating system in 1892 in Boise, Idaho. This system still provides heat to about 450 homes.

Co-Produced Geothermal Energy

geothermal energy

technology relies on other energy sources. This form of

geothermal energy

uses water that has been heated as a byproduct in oil and gas wells.

In the United States, about 25 billion barrels of hot water are produced every year as a


. In the past, this hot water was simply discarded. Recently, it has been recognized as a potential source of even more energy: Its


(Video) How Iceland produces Geothermal Energy

can be used to generate


to be used immediately or sold to the grid.

One of the first


geothermal energy

projects was initiated at the Rocky Mountain Oilfield Testing Center in the U.S. state of Wyoming.



has allowed


geothermal energy

facilities to beportable. Although still in experimental stages, mobile power plants hold tremendous potential for isolated or impoverished communities.

Geothermal Heat Pumps
Geothermal heat pumps (GHPs) take advantage of the Earth’s heat, and can be used almost anywhere in the world. GHPs are drilled about 3 to 90 meters (10 to 300 feet) deep, much shallower than most oil and natural gas wells. GHPs do not require fracturingbedrockto reach their energy source.

A pipe connected to a GHP is arranged in a continuous loop—called a "slinky loop"—that circles underground and above ground, usually throughout a building. The loop can also be contained entirely underground, to heat a parking lot or landscaped area.

In this system, water or other liquids (such as glycerol, similar to a car’santifreeze) move through the pipe. During the cold season, the liquid absorbs underground geothermal heat. It carries the heat upward through the building and gives off warmth through a duct system. These heated pipes can also run through hot water tanks and offset water-heating costs.

During the summer, the GHP system works the opposite way: The liquid in the pipes is warmed from the heat in the building or parking lot, and carries the heat to be cooled underground.

The U.S. Environmental Protection Agency has called geothermal heating the most energy-efficient and environmentally safe heating and cooling system. The largest GHP system was completed in 2012 at Ball State University in Indiana. The system replaced a coal-fired boiler system, and experts estimate the university will save about $2 million a year in heating costs.

Harvesting Geothermal Energy: Electricity

In order to obtain enough energy to generate electricity, geothermal power plants rely on heat that exists a few kilometers below the surface of the Earth. In some areas, the heat can naturally exist underground as pockets steam or hot water. However, most areas need to be “enhanced” with injected water to create steam.

Dry-Steam Power Plants


power plants

take advantage of natural underground sources of


. The


is piped directly to a power plant, where it is used to fuelturbines and generate





is the oldest type of power plant to generate



geothermal energy

. The first



power plant

was constructed in Larderello, Italy, in 1911. Today, the



power plants

at Larderello continue to supply


to more than a million residents of the area.

There are only two known sources of underground


in the United States: Yellowstone National Park in Wyoming and The


in California. Since Yellowstone is a protected area, The


(Video) GeoThermal energy

is the only place where a



power plant

is in use. It is one of the largest

geothermal energy

complexes in the world, and provides about a fifth of all renewable energy in California.

Flash-Steam Power Plant

Flash-steam power plants use naturally occurring sources of underground hot water and steam. Water that is hotter than 182° C (360° F) is pumped into a low-pressure area. Some of the water “flashes,” or evaporates rapidly into steam, and is funneled out to power a turbine and generate electricity. Any remaining water can be flashed in a separate tank to extract more energy.



power plants

are the most common type of geothermal power plants. The volcanically active island nation of Iceland supplies nearly all its electrical needs through a series of flash-


geothermal power plants. The


and excess warm water produced by the flash-


process heat icy sidewalks and parking lots in thefrigidArctic winter.

The islands of the Philippines also sit over a tectonically active area, the "Ring of Fire" that rims the Pacific Ocean. Government and industry in the Philippines have invested in



power plants

, and today the nation is second only to the United States in its use of

geothermal energy

. In fact, the largest single geothermal power plant is a flash-


facility in Malitbog, Philippines.

Binary Cycle Power Plants
Binary cycle power plants

use a unique process to conserve water and generate heat. Water is heated underground to about 107°-182° C (225°-360° F). The hot water is contained in a pipe, which cycles above ground. The hot water heats a liquid organic compound that has a lower boiling point than water. The organic liquid creates


, which flows through a


and powers a generator to create


. The only emission in this process is


. The water in the pipe is recycled back to the ground, to be re-heated by the Earth and provide heat for the organic compound again.

The Beowawe Geothermal Facility in the U.S. state of Nevada uses the binary cycle to generate


. The organic compound used at the facility is an industrial refrigerant (tetrafluoroethane, agreenhouse gas). This refrigerant has a much lower boiling point than water, meaning it is converted into gas at low temperatures. The gas fuels the


, which are connected to electrical generators.

Enhanced Geothermal Systems
The Earth has virtually endless amounts of energy and heat beneath its surface. However, it is not possible to use it as energy unless the underground areas are "


." This means the underground areas are not only hot, but also contain liquid and arepermeable. Many areas do not have all three of these components. Anenhanced geothermal system (EGS)uses drilling, fracturing, and injection to provide fluid and permeability in areas that have hot—but dry—underground rock.

To develop an EGS, an “injection well” is drilled vertically into the ground. Depending on the type of rock, this can be as shallow as 1 kilometer (0.6 mile) to as deep as 4.5 kilometers (2.8 miles). High-pressure cold water is injected into the drilled


, which forces the rock to create new fractures, expand existing fractures, or dissolve. This creates a reservoir of underground fluid.

Water is pumped through the injection well and absorbs the rocks’ heat as it flows through the reservoir. This hot water, calledbrine, is then piped back up to Earth’s surface through a “production well.” The heated


is contained in a pipe. It warms a secondary fluid that has a low boiling point, which


(Video) Geothermal 101



and powers a


. The


cools off, and cycles back down through the injection well to absorb underground heat again. There are no gaseous


besides the water vapor from the



Pumping water into the ground for EGSs can cause seismic activity, or smallearthquakes. In Basel, Switzerland, the injection process caused hundreds of tiny


that grew to more significant seismic activity even after the water injection was halted. This led to the geothermal project being canceled in 2009.

Geothermal Energy and the Environment

Geothermal energy is a renewable resource. The Earth has been emitting heat for about 4.5 billion years, and will continue to emit heat for billions of years into the future because of the ongoing radioactive decay in the Earth’s core.

However, most wells that extract the heat will eventually cool, especially if heat is extracted more quickly than it is given time to replenish. Larderello, Italy, site of the world’s first electrical plant supplied by geothermal energy, has seen its steam pressure fall by more than 25% since the 1950s.

Re-injecting water can sometimes help a cooling geothermal site last longer. However, this process can cause “micro-earthquakes.” Although most of these are too small to be felt by people or register on a scale of magnitude, sometimes the ground can quake at more threatening levels and cause the geothermal project to shut down, as it did in Basel, Switzerland.

Geothermal systems do not require enormous amounts of freshwater. In binary systems, water is only used as a heating agent, and is not exposed or evaporated. It can be recycled, used for other purposes, or released into the atmosphere as non-toxic steam. However, if the geothermal fluid is not contained and recycled in a pipe, it can absorb harmful substances such as arsenic, boron, and fluoride. Thesetoxicsubstances can be carried to the surface and released when the water evaporates. In addition, if the fluid leaks to other underground water systems, it can contaminate clean sources of drinking water and aquatichabitats.

There are many advantages to using geothermal energy either directly or indirectly:

  • Geothermal energy is renewable; it is not a fossil fuel that will be eventually used up. The Earth is continuously radiating heat out from its core, and will continue to do so for billions of years.
  • Some form of geothermal energy can be accessed and harvested anywhere in the world.
  • Using geothermal energy is relatively clean. Most systems only emit water vapor, although some emit very small amounts of sulfur dioxide, nitrous oxides, and particulates.
  • Geothermal power plants can last for decades and possibly centuries. If a reservoir is managed properly, the amount of extracted energy can be balanced with the rock’s rate of renewing its heat.
  • Unlike other renewable energy sources, geothermal systems are “baseload.” This means they can work in the summer or winter, and are not dependent on changing factors such as the presence of wind or sun. Geothermal power plants produce electricity or heat 24 hours a day, 7 days a week.
  • The space it takes to build a geothermal facility is much morecompactthan other power plants. To produce a GWh (a gigawatt hour, or one million kilowatts of energy for one hour, an enormous amount of energy), a geothermal plant uses the equivalent of about 1,046 square kilometers (404 square miles) of land. To produce the same GWh,wind energyrequires 3,458 square kilometers (1,335 square miles), a solarphotovoltaiccenter requires 8,384 square kilometers (3,237 square miles), andcoalplants use about 9,433 square kilometers (3,642 square miles).
  • Geothermal energy systems are adaptable to many different conditions.

They can be used to heat, cool, or power individual homes, whole districts, or industrial processes.

Harvesting geothermal energy still poses many challenges:

  • The process of injecting high-pressure streams of water into the Earth can result in minor seismic activity, or small earthquakes.
  • Geothermal plants have been linked tosubsidence, or the slow sinking of land. This happens as the underground fractures collapse upon themselves. This can lead to damaged pipelines, roadways, buildings, and natural drainage systems.
  • Geothermal plants can release small amounts of greenhouse gases such as hydrogen sulfide and carbon dioxide.
  • Water that flows through underground reservoirs can pick up trace amounts of toxic elements such as arsenic, mercury, and selenium. These harmful substances can be leaked to water sources if the geothermal system is not properly insulated.
  • Although the process requires almost no fuel to run, the initial cost of installing geothermal technology is expensive. Developing countries may not have the sophisticated infrastructure or start-up costs to invest in a geothermal power plant. Several facilities in the Philippines, for example, were made possible by investments from American industry and government agencies. Today, the plants are Philippine-owned and operated.

Geothermal Energy and People

Geothermal energy exists in different forms all over the Earth (by steam vents, lava, geysers, or simply dry heat), and there are different possibilities for extracting and using this heat.

In New Zealand, natural geysers and steam vents heat swimming pools, homes, greenhouses, and prawn farms. New Zealanders also use dry geothermal heat to dry timber and feedstock.

Other countries, such as Iceland, have taken advantage of molten rock and magma resources from volcanic activity to provide heat for homes and buildings. In Iceland, almost 90% of the country’s people use geothermal heating resources. Iceland also relies on its natural geysers to melt snow, warm fisheries, and heat greenhouses.

The United States generates the most amount of geothermal energy of any other country. Every year, the U.S. generates at least 15 billion kilowatt-hours, or the equivalent of burning about 25 million barrels of oil. Industrial geothermal technologies have been concentrated in the western U.S. In 2012, Nevada had 59 geothermal projects either operational or in development, followed by California with 31 projects, and Oregon with 16 projects.

The cost of geothermal energy technology has gone down in the last decade, and is becoming more economically possible for individuals and companies.

Fast Fact

Balneotherapy is the treatment of disease by spa watersusually bathing and drinking. Some famous spas in the United States that offer balneotherapy include Hot Springs, Arkansas, and Warm Springs, Georgia. The most famous balneotheraputic spa in the world, Iceland's Blue Lagoon, is not a natural hot spring. It is a manmade feature where water from a local geothermal power plant is pumped over a lava bed rich in silica and sulfur. These elements react with the warm water to create a bright blue lake with alleged healing properties.

Fast Fact

Geothermal Powers

Since 2015 the three countries with the greatest capacity for geothermal energy use have included the United States, Indonesia, and the Philippines. Turkey and Kenya have been steadily building geothermal energy capacity as well.

Fast Fact

Ring of Geothermal
Geothermal energy sources are often located on plate boundaries, where the Earths crust is constantly interacting with the hot mantle below. The Pacifics so-called Ring of Fire and East Africas Rift Valley are volcanically active areas that hold enormous potential for geothermal power generation.

Fast Fact

The Fumaroles
There are no geysers at The Geysers, one of the most productive geothermal plants in the world. The California facility sits on fumarolesvents in the Earths crust where steam and other gases (not liquids) escape from the Earths interior.


How does geothermal energy work National Geographic? ›

Magma heats nearby rocks and underground aquifers. Hot water can be released through geysers, hot springs, steam vents, underwater hydrothermal vents, and mud pots. These are all sources of geothermal energy. Their heat can be captured and used directly for heat, or their steam can be used to generate electricity.

What is the biggest problem with geothermal energy? ›

Cons of geothermal energy: generates waste, reservoirs require proper management, it's location-specific, has high initial cost, and can cause earthquakes in extreme cases. Geothermal has the potential to become a major global energy source, but is held back by its high upfront costs.

What are the top 3 countries that use geothermal energy? ›

In favour of geothermal
Geothermal electricity production, 2010
United States16,603China
Philippines10,311United States
12 more rows

What are the 3 main uses of geothermal energy? ›

Geothermal energy can heat, cool, and generate electricity: Geothermal energy can be used in different ways depending on the resource and technology chosen—heating and cooling buildings through geothermal heat pumps, generating electricity through geothermal power plants, and heating structures through direct-use ...

What are 3 advantages of geothermal energy? ›

Thanks to long-lasting, safe, reliable plants, geothermal energy is increasingly low risk and brimming with untapped potential. It is silent, always available, has little impact on the landscape and is versatile. It can even be used for cooling and creates more jobs than any other green energy.

How long do geothermal systems last? ›

How long do geothermal heat pumps last? Geothermal heat pumps last significantly longer than conventional equipment. They typically last 20-25 years. In contrast, conventional furnaces generally last anywhere between 15 and 20 years, and central air conditioners last 10 to 15 years.

Is residential geothermal worth it? ›

As stated by the U.S. Department of Energy, investing in a geothermal heat pump can mean a 25% to 50% decrease in energy consumed compared to traditional systems that use air. In addition, your geothermal system can be as much as 300% to 600% more efficient, making this a great HVAC investment long term.

Why is geothermal energy not used? ›

Here are some of the disadvantages that come with using geothermal energy. Extracting geothermal energy does cause some greenhouse gas emissions during the extraction of steam. For instance, hydrogen sulfide, methane, and ammonia are often released in the process of extracting geothermal power.

How warm does geothermal heating get? ›

High-efficiency geothermal systems tend to operate between 100 to 120℉. Your traditional HVAC system is designed to operate at 180 to 200℉.

Can you put geothermal in an existing home? ›

The answer is simple! Yes, you can use geothermal technology in most homes. At Hoffmann Brothers Heating and Air Conditioning, we work alongside the GeoComfort team to install geothermal systems in existing homes every week.

Can geothermal energy run out? ›

Myth: We could run out of geothermal energy

Geothermal energy is a renewable energy and will never deplete. Abundant geothermal energy will be available for as long as the Earth exists.

Where is the world's largest geothermal field? ›

The Geysers Complex is located roughly 72 miles north of San Francisco in California's Mayacamas Mountains and sits on the world's largest geothermal field. Spanning approximately 30 square miles, it houses a magma chamber that's four miles deep beneath the surface and greater than eight miles in diameter.

What is the biggest geothermal plant in the world? ›

The largest geothermal plant in the world is called the Geysers Geothermal Complex, located in the United States, with a capacity of 900 megawatts. It is made up of 22 power plants and spread over several kilometers, located north of San Francisco.

Which country uses the most geothermal energy 2022? ›

Indonesia is still second to the United States, who leads the world with a geothermal energy capacity of 3,772 megawatts. The Phillipines, Turkey, and New Zealand make up the rest of the top 5 geothermal countries in 2022.

Which country has 90% of heating demand covered by geothermal energy? ›

This key renewable source covers a significant share of electricity demand in countries like Iceland, El Salvador, New Zealand, Kenya, and Philippines and more than 90% of heating demand in Iceland.

Where is geothermal most used? ›

Most of the geothermal power plants in the United States are in western states and Hawaii, where geothermal energy resources are close to the earth's surface. California generates the most electricity from geothermal energy.

How much does it cost to install geothermal heating? ›

On average, a homeowner can expect total expenses to reach between $18,000 to $30,000 on geothermal heating and cooling cost. This cost would cover a complete geothermal installation. The price can range from $30,000 to $45,000 with high-end ground-source heat pump systems for large homes.

How does a geothermal power plant work step by step? ›

How a Geothermal Power Plant Works (Simple) - Text Version
  1. Wells Are Drilled. A production well is drilled into a known geothermal reservoir. ...
  2. Steam Turns the Turbine. ...
  3. The Turbine Drives the Electric Generator. ...
  4. Transmission - Power Lines Deliver Electricity.

How does geothermal energy work for kids? ›

“Geo” means “earth,” and “thermal” means “heat,” so geothermal energy means “heat from the earth”. Geothermal energy is produced during the slow decay of radioactive elements in the earth's core. This process is continuous and it never stops, this is why geothermal energy is a renewable energy source.

What is the process of geothermal heat? ›

Hot water is pumped from deep underground through a well under high pressure. When the water reaches the surface, the pressure is dropped, which causes the water to turn into steam. The steam spins a turbine, which is connected to a generator that produces electricity.

What are the 5 parts of a geothermal power plant? ›

The main components in a geothermal power plant at The Geysers are the steam turbine, generator, condenser, cooling tower, gas removal system and hydrogen sulfide abatement system.

What country is the largest producer of geothermal energy? ›

Iceland: World's highest share of geothermal power

Unlike the other countries in the Nordic region, Iceland's electricity grid is isolated. Most small island economies rely on oil-fired power plants to provide steady electricity supply, but Iceland has…

What is the main source of geothermal energy? ›

Geothermal energy comes from deep inside the earth

The slow decay of radioactive particles in the earth's core, a process that happens in all rocks, produces geothermal energy.

What are the five activities that make use of geothermal energy? ›

8 uses of geothermal energy include:
  • Generating electricity.
  • Home heating and cooling using ground-source heat-pumps.
  • Heating greenhouses directly.
  • Pasteurizing milk.
  • Heating water for fish farms.
  • Cooking.
  • Health uses (as in health spas)
  • Drying food.
10 Oct 2022

Is geothermal clean energy? ›

Geothermal energy is heat derived below the earth's surface which can be harnessed to generate clean, renewable energy. This vital, clean energy resource supplies renewable power around the clock and emits little or no greenhouse gases -- all while requiring a small environmental footprint to develop.

What are some interesting facts about geothermal energy? ›

Key Facts:
  • Geothermal energy comes from the heat in the Earth's core. ...
  • Geothermal energy is the third largest source of renewable energy, behind hydropower and biomass. ...
  • The United States is the world's largest producer of geothermal energy.
1 May 2006

Is geothermal energy renewable? ›

Why is geothermal energy a renewable resource? Answer: Because its source is the almost unlimited amount of heat generated by the Earth's core. Even in geothermal areas dependent on a reservoir of hot water, the volume taken out can be reinjected, making it a sustainable energy source.

Why is geothermal energy not used more often? ›

Extracting geothermal energy resources comes with a significantly higher investment compared to other sources of energy. As a result, geothermal power often costs slightly more than other sources of power.

How much electricity does a geothermal heat pump use? ›

That's why it takes only one kilowatt-hour of electricity for a geothermal heat pump to produce nearly 12,000 Btu of cooling or heating. (To produce the same number of Btus, a standard heat pump on a 95-degree day consumes 2.2 kilowatt-hours.)

Does geothermal use water? ›

The Standard Geothermal uses a mix of water, antifreeze (Propylene Glycol), and refrigerant.

How much land does a geothermal power plant need? ›

An entire geothermal field uses 1-8 acres per megawatt (MW) versus 5-10 acres per MW for nuclear operations and 19 acres per MW for coal power plants.

How many types of geothermal energy are there? ›

There are three types of geothermal power plants: dry steam, flash steam, and binary cycle.

What is the difference between a geothermal power plant and a geothermal heat pump? ›

Geothermal power plants generate electricity by forcing hot steam or hot steam from the earth's interior through a turbine. This electricity can be used to power, heat, and cool homes, among other uses. Meanwhile, geothermal heat pumps circulate fluid through underground pipes, where they absorb heat.


1. Iceland's Volcanic World | National Geographic
(National Geographic)
2. Renewable Energy 101 | National Geographic
(National Geographic)
3. Geothermal energy coming to North Dakota through TERRACOH
(KX News)
4. Could the Earth's core help save us? - BBC REEL
(BBC Reel)
5. How Canada can become a deep geothermal superpower
(Energi Media)
6. Flame Drill | National Geographic
(National Geographic)
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