Geothermal Energy Facts

Geothermal energy is a renewable energy source that derives from the heat of the earth’s core and has long been used for a variety of purposes. In this article you will find various geothermal energy facts surrounding what this energy source is, how we can use it and the history behind it.

Some interesting facts about geothermal energy

These facts provide a good top-level overview of geothermal energy:

    Geothermal energy has been around since the earth formed and is a renewable energy source.

    The term “Geothermal” derives from the Greek words “geo” (meaning earth” and “therme” (meaning heat).

    Geothermal activity provides the energy behind volcanoes, hot springs and geysers.

    Civilisations have been using hot springs heated by geothermal activity for thousands of years.

    Geothermal energy is greater along the fault lines in the earth’s crust as liquid rock (magma) can be found closer to the earth’s surface, thus providing more geothermal activity.

    The best place for geothermal activity is along the “Ring of Fire”.

    Unlike solar, wind and other renewable energy sources, geothermal energy doesn’t rely on solar activity.

Facts specific to geothermal power

These facts are specific to how we can produce electricity from geothermal energy:

    The process of generating geothermal power has been in existence for over a hundred years and was first tested in Italy by Piero Ginori Conti in 1903.

    Today, geothermal power is only responsible for a small amount of global electricity capacity.

    Modern geothermal power generation is performed at either dry steam, flash steam or binary cycle power stations.

    Geothermal power can be highly price competitive.

    Geothermal power can only be generated cost-effectively in specific areas with enough geothermal activity.

    Geothermal power is considered clean and highly efficient.

    Geothermal power stations do still produce greenhouse gases but on a very small scale when compared with fossil fuel power stations.

    Geothermal power stations are often small and have minimal visual impact on the surrounding environment.

    Geothermal power stations can work both day and night with a high uptime.

    There are over 40 geothermal power plants in the USA alone with many more dotted across the globe.

    In the USA, California has the highest geothermal power capacity and generates just over 80% of the nations geothermal power supply.

    Iceland has the world’s most efficient geothermal power stations and is responsible for a large percentage of global geothermal electricity production.

    Iceland produces around 26% of its electricity supply from geothermal energy.

    New Zealand generates around 13% of its electricity from geothermal activity.

    Other countries that generate significant levels of geothermal power are; Indonesia, Italy, Japan, Kenya, Mexico and Philippines.

Facts specific to geothermal heating

These facts are specific to how we can use geothermal energy for heating purposes:

    Geothermal energy can also be used to provide heating for homes. This technique makes use of ground source heat instead of the geothermal activity described above.

    Geothermal heat pumps can be used to produce part or all of a buildings hot water supply.

    Geothermal heat pumps work by burying hundreds of meters of water pipes under ground so that the water absorbs the heat from the earth.

Fact Sheet On Geothermal Energy

	Fact 1	Geothermal Energy is created and stored inside the Earth.

Fact 2

The Geothermal Energy stored inside our Earth, was produced when our planet was formed millions of years ago and from the decay of minerals.

Fact 3

The core of the Earth is extremely hot. Hotter than you could ever imagine, sometimes reaching more than 4000 degrees Celsius! The heat from the core travels to the surface of the Earth.

Fact 4

The word 'geothermal' comes from Greek words: Geo means Earth and Thermal (Thermos) means heat. You will have heard the word 'thermal' many times as it's often used in reference to heat and insulating heat e.g. thermal gloves or a thermal flask which are devices that store heat similar to the geothermal energy of planet Earth.

Fact 5

Geothermal Energy from the Earth can be used in many ways in pumping systems and power stations where the energy can be converted to electricity.

Fact 6

One of the heat sources from the Earth is mineral water which can be heated by geothermal energy. For centuries, people have bathed in natural hot water springs.

Fact 7

Hot water can be run from geothermal power plants. When the water runs underground, it can help to melt ice away. This is particularly useful in countries such as Iceland.

Fact 8

Geothermal Energy has many benefits over many other types of energy and fossil fuels. This is a clean type of energy which doesn't pump harmful chemicals into our atmosphere when it is processed into electricity.

Fact 9

Although geothermal energy is not used as much as it could be, the future is looking brighter as it is being used more and more across the world. The more geothermal energy we can use, the less use of fossil fuels there will be. Fossil fuels can damage our planet as they are rich in carbon and release harmful chemicals when they are burned.

Fact 10

Geothermal Energy is reliable as it is constantly produced. Not all energies are the same, some are inconsistent such as solar power which relies on the sun. During night hours or poor weather conditions, solar energy cannot be received in all places on Earth.

Fact 11

Geothermal is a renewable energy source unlike many other types of energy. Renewable means it can be replenished and it isn't going to run out.

Fact 12

Electricity can be generated from geothermal energy at different types of power plants including binary cycle, dry steam and flash steam power plants.

Fact 13

Flash steam power plants usually function through the use of turbines to generate electricity. This type of power plant uses hot water from the ground which produces steam when it is released from the reservoir to the power plant. Steam is produced due to a decrease in temperature and it is used to power the turbine.

Fact 14

The oldest type of geothermal power plant runs on dry steam. It uses steam without water droplets (the molecules are in gas state not liquid).

Fact 15

Binary cycle power plants, like flash steam power plants, also uses steam from water to power turbines in order to generate electricity. However, the water is not as hot as the water used in flash steam power plants.

Geothermal Electricity Production

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.

Dry steam power plants draw from underground resources of steam. The steam is piped directly from underground wells to the power plant, where it is directed into a turbine/generator unit. There are only two known underground resources of steam in the United States: The Geysers in northern California and Yellowstone National Park in Wyoming, where there's a well-known geyser called Old Faithful. Since Yellowstone is protected from development, the only dry steam plants in the country are at The Geysers.

Flash steam power plants are the most common. They use geothermal reservoirs of water with temperatures greater than 360°F (182°C). This very hot water flows up through wells in the ground under its own pressure. As it flows upward, the pressure decreases and some of the hot water boils into steam. The steam is then separated from the water and used to power a turbine/generator. Any leftover water and condensed steam are injected back into the reservoir, making this a sustainable resource.

Binary cycle power plants operate on water at lower temperatures of about 225°-360°F (107°-182°C). These plants use the heat from the hot water to boil a working fluid, usually an organic compound with a low boiling point. The working fluid is vaporized in a heat exchanger and used to turn a turbine. The water is then injected back into the ground to be reheated. The water and the working fluid are kept separated during the whole process, so there are little or no air emissions.

Small-scale geothermal power plants (under 5 megawatts) have the potential for widespread application in rural areas, possibly even as distributed energy resources. Distributed energy resources refer to a variety of small, modular power-generating technologies that can be combined to improve the operation of the electricity delivery system.

Low Temerature and Direct Geothermal Energy Use

According to the National Renewable Energy Laboratory, "The Earth houses a vast energy supply in the form of geothermal resources. Domestic resources are equivalent to a 30,000-year energy supply at our current rate for the United States! In fact, geothermal energy is used in all 50 U.S. states today. But geothermal energy has not reached its full potential as a clean, secure energy alternative because of issues with resources, technology, historically low natural gas prices, and public policies. These issues affect the economic competitiveness of geothermal energy."

Besides use of geothermal energy in power plants, hot water from geothermal resources can be used for a number of purposes (also see Figure 1) including:

• Heating buildings or districts (either individually or whole towns)
• Raising plants in greenhouses
• Drying crops
• Heating water at fish farms
• Industrial processes, such as pasteurizing milk

Geothermal direct use dates back thousands of years, when people began using hot springs for bathing, cooking food, and loosening feathers and skin from game. Today, hot springs are still used as spas, but there are now more sophisticated ways of using this geothermal resource.

In modern direct-use systems, a well is drilled into a geothermal reservoir to provide a steady stream of hot water. The water is brought up through the well, and a mechanical system -- piping, a heat exchanger, and controls -- delivers the heat directly for its intended use. A disposal system then either injects the cooled water underground or disposes of it on the surface. In the United States, most geothermal reservoirs are located in the western states, Alaska, and Hawaii.

The direct-use geothermal reservoirs have relatively low to moderate temperatures - 68° to 302°F (20° to 150°C)

Direct use of geothermal energy in homes and commercial operations is much less expensive than using traditional fuels. Savings can be as much as 80% over fossil fuels. Direct use is also very clean, producing only a small percentage (and in many cases none) of the air pollutants emitted by burning fossil fuels.

District and Space Heating

The primary uses of low-temperature geothermal resources are in district and space heating, greenhouses, and aquaculture facilities. A 1996 survey found that these applications were using nearly 5.8 billion megajoules of geothermal energy each year - the energy equivalent of nearly 1.6 million barrels of oil!

In the U.S., more than 120 operations, with hundreds of individual systems at some sites, are using geothermal energy for district and space heating. District systems distribute hydrothermal water from one or more geothermal wells through a series of pipes to several individual houses and buildings, or blocks of buildings. Space heating uses one well per structure. In both types, the geothermal production well and distribution piping replace the fossil-fuel-burning heat source of the traditional heating system.

Geothermal district heating systems can save consumers 30% to 50% of the cost of natural gas heating. The tremendous potential for district heating in the western U.S. was illustrated in a 1980s inventory which identified 1,277 geothermal sites within 5 miles of 373 cities in 8 states.

Greenhouse and Aquaculture Facilities

Greenhouses and aquaculture (fish farming) are the two primary uses of geothermal energy in the agribusiness industry. Thirty-eight greenhouses, many covering several acres, are raising vegetables, flowers, houseplants, and tree seedlings in 8 western states. Twenty-eight aquaculture operations are active in 10 states.

Most greenhouse operators estimate that using geothermal resources instead of traditional energy sources saves about 80% of fuel costs - about 5% to 8% of total operating costs. The relatively rural location of most geothermal resources also offers advantages, including clean air, few disease problems, clean water, a stable workforce, and, often, low taxes.

Industrial and Commercial Uses

Industrial applications include food dehydration, laundries, gold mining, milk pasteurizing, spas, and others. Dehydration, or the drying of vegetable and fruit products, is the most common industrial use of geothermal energy. The earliest commercial use of geothermal energy was for swimming pools and spas. In 1990, 218 resorts were using geothermal hot water.

Permits for Direct Use

Direct use projects are not regulated by the California Energy Commission, and usually fall under the jurisdiction of local government unless on federal lands or tribal lands. Depending on the type of project and the specifics of the resource such as temperature, flow and chemistry there may be variations in the permitting requirements. The local government most likely would require a Conditional Use Permit. Additional permits would depend on the type of use. If there are structures, local building permits may be needed. Balneology may require a public pool permit from a local health department, district heating systems may need permits for disposal (National Pollution Discharge Elimination Permit - NPDES) of the resource from the Regional Water Quality Control Board if there is not an injection well, etc. These permits can take just as long as two years in the case of the NPDES permit and are in addition to the CEQA or National Environmental Policy Act environmental review process needed.

Sources (all accessed 9/22/08):

• NREL: Learning - Geothermal Direct Use, http://www.nrel.gov/learning/re_geo_direct_use.html
• Geothermal Direct-Use Case Studies, Geothermal Direct-Use Case Studies, http://geoheat.oit.edu/casestudies.htm
• Direct Use of Geothermal Energy, http://www1.eere.energy.gov/geothermal/pdfs/directuse.pdf
• Geothermal Technologies Program: Direct Use of Geothermal Energy, http://www1.eere.energy.gov/geothermal/directuse.html
• Geothermal Direct Use - Geothermal Energy, http://www.renewableenergyworld.com/rea/tech/geodirectuse

Types of Geothermal Power Plants

All geothermal power plants use steam to turn large turbines, which run electrical generators. In the Geysers Geothermal area, dry steam from below ground is used directly in the steam turbines. In other areas of the state, super-hot water is "flashed" into steam within the power plant, and that steam turns the turbine.

 

Direct Dry Steam

Steam plants use hydrothermal fluids that are primarily steam. The steam goes directly to a turbine, which drives a generator that produces electricity. The steam eliminates the need to burn fossil fuels to run the turbine. (Also eliminating the need to transport and store fuels!)

This is the oldest type of geothermal power plant. It was first used at Lardarello in Italy in 1904. Steam technology is used today at The Geysers in northern California, the world's largest single source of geothermal electricity. These plants emit only excess steam and very minor amounts of gases.

Flash and Double Flash Cycle

Hydrothermal fluids above 360°F (182°C) can be used in flash plants to make electricity.

Fluid is sprayed into a tank held at a much lower pressure than the fluid, causing some of the fluid to rapidly vaporize, or "flash." The vapor then drives a turbine, which drives a generator.

If any liquid remains in the tank, it can be flashed again in a second tank (double flash) to extract even more energy.

Binary Cycle

Most geothermal areas contain moderate-temperature water (below 400°F). Energy is extracted from these fluids in binary-cycle power plants.

Hot geothermal fluid and a secondary (hence, "binary") fluid with a much lower boiling point than water pass through a heat exchanger. Heat from the geothermal fluid causes the secondary fluid to flash to vapor, which then drives the turbines.

Because this is a closed-loop system, virtually nothing is emitted to the atmosphere. Moderate-temperature water is by far the more common geothermal resource, and most geothermal power plants in the future will be binary-cycle plants.

Text and graphics from U.S. Department of Energy's Energy Efficiency and Renewable Energy Program.

Geothermal Heat Pump Basics

Geothermal heat pumps take advantage of the nearly constant temperature of the Earth to heat and cool buildings. The shallow ground, or the upper 10 feet of the Earth, maintains a temperature between 50° and 60°F (10°–16°C). This temperature is warmer than the air above it in the winter and cooler in the summer.

Geothermal heat pump systems consist of three parts: the ground heat exchanger, the heat pump unit, and the air delivery system (ductwork). The heat exchanger is a system of pipes called a loop, which is buried in the shallow ground near the building. A fluid (usually water or a mixture of water and antifreeze) circulates through the pipes to absorb or relinquish heat within the ground.

Heat pumps work much like refrigerators, which make a cool place (the inside of the refrigerator) cooler by transferring heat to a relatively warm place (the surrounding room), making it warmer. In the winter, the heat pump removes heat from the heat exchanger and pumps it into the indoor air delivery system, moving heat from the ground to the building's interior. In the summer, the process is reversed, and the heat pump moves heat from the indoor air into the heat exchanger, effectively moving the heat from indoors to the ground. The heat removed from the indoor air during the summer can also be used to heat water, providing a free source of hot water.

Geothermal heat pumps use much less energy than conventional heating systems, since they draw heat from the ground. They are also more efficient when cooling your home. Not only does this save energy and money, it reduces air pollution.

Geothermal Heat Pumps

The shallow ground, the upper 10 feet of the Earth, maintains a nearly constant temperature between 50° and 60°F (10°-16°C). Like a cave, this ground temperature is warmer than the air above it in the winter and cooler than the air in the summer. Geothermal heat pumps take advantage of this resource to heat and cool buildings.

Geothermal heat pump systems consist of basically three parts: the ground heat exchanger, the heat pump unit, and the air delivery system (ductwork). The heat exchanger is basically a system of pipes called a loop, which is buried in the shallow ground near the building. A fluid (usually water or a mixture of water and antifreeze) circulates through the pipes to absorb or relinquish heat within the ground.

In the winter, the heat pump removes heat from the heat exchanger and pumps it into the indoor air delivery system. In the summer, the process is reversed, and the heat pump moves heat from the indoor air into the heat exchanger. The heat removed from the indoor air during the summer can also be used to heat water, providing a free source of hot water.

Geothermal heat pumps use much less energy than conventional heating systems, since they draw heat from the ground. They are also more efficient when cooling your home. Not only does this save energy and money, it reduces air pollution.

All areas of the United States have nearly constant shallow-ground temperatures, which are suitable for geothermal heat pumps.