Geothermal Energy

Geothermal energy – literally heat from the earth – is a clean and versatile natural resource for the world’s steadily increasing energy needs.
GEOTHERMAL RESOURCES

When the rising hot water and steam is trapped in permeable and porous rocks under a layer of impermeable rock, it can form a geothermal reservoir.

© Geothermal Education Office, Tiburon, CA

Earth’s natural geologic processes, such as those associated with geysers and hot springs, allow magma to rise relatively close to the earth’s surface. In places like the “Pacific Ring of Fire,” the magma heats vast regions of underground rock located high above the magma chambers. Often porous and fractured, the hot rock can become saturated with rainwater that has seeped underground, creating geothermal reservoirs of hot water and steam. Geothermal reservoirs vary in temperature – sometimes reaching as high as 700°F (371°C).

Geothermal heat and geothermal reservoirs are generally referred to as geothermal resources and are located in many parts of the world. In the United States, they occur primarily in the western states including California.
ELECTRIC POWER GENERATION

Many areas have accessible geothermal resources, especially countries along the circum-Pacific “Ring of Fire,” spreading centers, continental rift zones and other hot spots.

© Geothermal Education Office, Tiburon, CA

High temperature geothermal resources, usually above 300°F (149°C), are generally used for electric power generation. To access the high-temperature geothermal resources, production wells are drilled. From the wells, the steam or hot water is brought to the surface and piped to a geothermal power plant where its energy is used by a steam turbine to generate electricity. After the geothermal water does its work in the power plant, it is piped back into the geothermal reservoir – and the cycle continues. Geothermal power plants operate 24 hours a day, since the “fuel” source is always available; these plants are therefore valued for their ability to provide us with baseload electricity.

Natural steam from the production wells power the turbine generator. The steam is condensed by evaporation in the cooling tower and pumped down an injection well to sustain production.

© Geothermal Education Office, Tiburon, CA

The methods and equipment used to drill geothermal wells in high-temperature water-dominated reservoirs are very similar to those used to drill oil and gas wells. Modern oil wells using rotary drills can reach depths of 38,000 ft. (11,600 meters). The deepest oil well penetrates a mere six miles (ten kilometers) into the crust while the center of the Earth is about 4,000 miles (6,400 kilometers) deeper (http://magma.nationalgeographic.com/ngm/0404/resources_who.html).

Geothermal wells usually range from 500 feet (152 meters) to 12,000 feet (3,700 meters) deep.

Because geothermal energy uses natural steam to operate the turbine-generator in a geothermal power plant, it is a clean energy resource. With geothermal energy no fossil fuels (such as coal or gas) are burned to create steam, so there are no smoky emissions. The cooling towers emit mostly water vapor (steam) as a by-product of generating electrical power.

Some geothermal power plants, Binary Power Plants, have no emissions at all.

Geothermal power plants emit water vapor (not smoke).

The first geothermal power plants in the U.S. were built in 1962 at The Geysers dry steam field, in northern California. It is still the largest producing geothermal field in the world.

© Geothermal Education Office, Tiburon, CA

Around the world there are about 11,000 MW of geothermal electricity generated in 22 countries. Current U.S. geothermal electric power generation totals approximately 2200 MW (or about the same as four large nuclear power plants). California’s geothermal power plants have a dependable installed capacity of over 1,800 megawatts – producing about 5 percent of California’s total electricity (more than all other renewables combined, excluding large hydro).

Geothermal power plants use three methods to generate electricity – dry stream, flash steam, and binary:
Dry Steam Power Plants

The first geothermal power plants in the U.S. were built in 1962 at The Geysers dry steam field, in northern California. It is still the largest producing geothermal field in the world. Located about 100 miles north of San Francisco, The Geysers is one of only two locations in the world (the other is Larderello, Italy) where a high-temperature, dry steam resource is used to turn turbines and generate electricity. In dry steam power plants, the steam (and no water) shoots up the wells and is passed through a rock catcher (not shown) and then directly into the turbine. Dry steam fields are rare.

In dry steam power plants, the steam (and no water) shoots up the wells and is passed through a rock catcher (not shown) and then directly into the turbine. Dry steam fields are rare.

© Geothermal Education Office, Tiburon, CA
Flash Steam Power Plants

Most geothermal plants today use a flash system, one which uses a resource of superheated water rather than steam only. In flash plants, as hot water is released from the pressure of the deep reservoir in a flash tank, some if it flashes to steam. Geothermal power plants in California that use flash steam are located in the Imperial Valley/Salton Sea area east of San Diego, and in the Coso Hot Springs area near Bakersfield.

Flash steam power plants use hot water reservoirs. In flash plants, as hot water is released from the pressure of the deep reservoir in a flash tank, some if it flashes to steam.

© Geothermal Education Office, Tiburon, CA
Binary Power Plants

The third geothermal power technology, found in binary power plants, takes advantage of resources that would not be hot enough to generate electricity in either a dry steam or flash plant. Binary technology uses a heat exchanger to transfer heat from the geothermal water to vaporize a “working fluid.” The vapor, like steam, powers the turbine. Because binary technology involves a “closed loop” system it is emission-free. Geothermal power plants in California that use the binary system are found in the southern Sierra area of Mammoth and near Honey Lake in the northeastern part of the state. There is also some use of binary technology in the Imperial Valley.

In a binary cycle power plant (binary means two), the heat from geothermal water is used to vaporize a “working fluid” in separate adjacent pipes. The vapor, like steam, powers the turbine generator.

© Geothermal Education Office, Tiburon, CA

It is estimated that California has a potential of more than 4,800 megawatts of additional power from geothermal energy, using these current technologies.

For more information about geothermal power plants in California, see Geothermal Electric Power Generation in California.
DIRECT (NON-ELECTRIC) USES

Bathing in hot pools like these at Hot Creek, Mammoth Lakes, California, has been practiced throughout history. Be careful – people and animals have been burned badly in unfamiliar pools.

© Geothermal Education Office, Tiburon, CA

Direct use projects use geothermal resources for their heat, applying the heat “directly” without generation of electricity. Such projects include space heating (individual buildings or whole districts), warming greenhouses, aquaculture (growing of fish), spas and swimming pools, and industrial processes.

Geothermal water flows through ceiling pipes to heat the plants in this greenhouse.

In several western US states, many long greenhouses are built and heated with geothermal water. This one is in New Mexico.

© Geothermal Education Office, Tiburon, CA

Pipes of geothermal water can be installed under sidewalks and roads to keep them from icing over in winter, like this sidewalk in Klamath Falls, Oregon.

© Geothermal Education Office, Tiburon, CA

Direct use projects generally use geothermal water at temperatures between 100°F (38°C) to 300°F (149°C). Current U.S. installed capacity of direct use systems totals enough to heat 40,000 average-sized houses. U.S. geothermal greenhouses today cover more than 110 acres, and domestic aquaculture annually yields about 40,000,000 pounds (18,000,000 kilograms) of fish.

Geothermal heating systems are remarkably durable. One system in Boise, Idaho, has been operating continuously since 1892, and its two original production wells are still in service.

Hot water from one or more geothermal wells is piped through a heat exchanger plant to heat city water in separate pipes. Hot city water is piped to heat exchangers in buildings to warm the air.

© Geothermal Education Office, Tiburon, CA

Depending upon water quality, the local environment, and project-permitting requirements, the used geothermal waters are either discharged at the surface or injected back into the geothermal reservoir to be reheated and reused.

Direct use of geothermal energy tends to make energy costs competitive and predictable. It is reliable, clean, sustainable, and helps to conserve fossil-fuel resources.

For more information about geothermal direct use projects in California, see Direct Use Projects in California.
GEOTHERMAL HEAT PUMPS

Another type of geothermal application – geothermal, or ground-source, heat pumps – uses underground heat that is relatively close to the surface. These systems — sometimes referred to as GeoExchange systems — do not depend on deep underground geothermal reservoirs, so they can be used almost everywhere in the world.

A geothermal heat pump is a unique mechanical device that conveniently heats and air conditions buildings and heats domestic hot water. It is one of the most efficient technologies available for home and workplace heating and cooling. These systems do the work that ordinarily requires two appliances, a furnace and an air conditioner.

The temperature of the ground, a few feet beneath the earth’s surface, remains relatively constant throughout the year, even though the outdoor temperature may fluctuate greatly with the change of seasons. Geothermal heat pumps rely on this relatively constant temperature of the earth (or groundwater) as a heat source in winter and a heat “sink” in summer. The resource temperatures, 37°F (2.7°C) to 74°F (23°C), are the natural temperatures just a few feet underground in many places in the world. In California, for example, at a depth of approximately six feet, underground temperatures remain stable between 52° F (11°C) and 74°F (23°C).

A geothermal heat pump transfers warmth from the underground to the house in winter and warmth from the house to the underground in summer. In the winter, the pump collects the earth’s natural heat through this configuration of closed pipes, called loops, installed below the surface of the ground — at 350 feet (107 meters) or less — or submersed in a pond or lake. Water circulating in the loop carries this heat to the building.

Different styles of pipes are installed beside a building. A liquid is piped through the pipes to pick up the heat FROM the ground or (in the summer) to bring heat from the building TO the ground.

© Geothermal Education Office, Tiburon, CA

In summer the process is reversed in order to cool the home. Excess heat is drawn from the home, expelled to the loop, and absorbed by the earth. Geothermal heat pumps provide cooling much the same way as a refrigerator, which keeps its contents cool by drawing heat from the interior of the refrigerator and expelling it outside.

Accurate data is not available on the current number of these systems; however, the rate of installation is thought to be between 10,000 and 40,000 per year. Geothermal heat pumps are becoming more popular as our need to conserve energy becomes more urgent. There is potential for much greater use of geothermal heat pumps in California.

Geothermal heat pumps provide clean energy, conserve fossil-fuel resources, and are both energy- and cost-efficient. The U.S. Environmental Protection Agency has declared these systems to be the most environmentally friendly and efficient heating and cooling systems available.

linkks:http://cgec.ucdavis.edu/pages/energy.html
en.wikipedia.org/wiki/Geothermal_power

cgec.ucdavis.edu/pages/energy.html

www1.eere.energy.gov/geothermal/powerplants.html

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About Rashid Faridi

I am Rashid Aziz Faridi ,Writer, Teacher and a Voracious Reader.
This entry was posted in Environment, interior of the Earth. Bookmark the permalink.

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