Geothermal power is electrical power generated from geothermal energy, the term 'geothermal energy' refers to any heat
derived from the ground, from depths of a few metres to multiple kilometres beneath the Earth's surface, this energy is widely described as
'ground-source energy' or 'shallow geothermal energy', temperatures at the core–mantle boundary can reach over 4000 °C (7200 °F). Geothermal
power technologies in use include dry steam power stations, flash steam power stations and binary cycle power stations. Geothermal electricity
generation is currently used in 26 countries, while geothermal heating is in use in 70 countries. Geothermal power is considered to be a
sustainable, renewable source of energy because the heat extraction is small compared with the Earth's heat content. As a source of renewable
energy for both power and heating, geothermal has the potential to meet 3-5% of global demand by 2050. With economic incentives, it is estimated
that by 2100 it will be possible to meet 10% of global demand
Geothermal Electricity Production Basics
Geothermal power plants use steam to produce electricity. The thermal energy contained in the rocks and fluids can be
found from shallow depths right down to several miles below the Earth’s surface. Wells drilled into underground reservoirs tap into the
geothermal resources, Hot water is pumped from deep underground through the 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.
Dry Steam
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, 1) The Geysers in northern California - 2) 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
Flash steam power plants are the most common and 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 Steam
Binary cycle power plants operate on water at lower temperatures of about 225-360°F (107-182°C). Binary cycle 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. Currently, two types of geothermal resources
can be used in binary cycle power plants to generate electricity: enhanced geothermal systems (EGS) and low-temperature or co-produced
resources.
Enhanced Geothermal Systems
EGS provide geothermal power by tapping into the Earth's deep geothermal resources that are otherwise not economical
due to lack of water, location, or rock type. The U.S. Geological Survey estimates that potentially 500,000 megawatts of EGS resource is
available in the western U.S. or about half of the current installed electric power generating capacity in the United States.
Low-Temperature and Co-Produced Resources
Low-temperature and co-produced geothermal resources are typically found at temperatures of 300F (150C) or less.
Some low-temperature resources can be harnessed to generate electricity using binary cycle technology. Co-produced hot water is a byproduct
of oil and gas wells in the United States. This hot water is being examined for its potential to produce electricity, helping to lower
greenhouse gas emissions and extend the life of oil and gas fields.
Geothermal Power History
In the 20th century, demand for electricity led to the consideration of geothermal power as a generating source. Prince Piero Ginori Conti
tested the first geothermal power generator on 4 July 1904 in Larderello, Italy, it successfully lit four light bulbs, later, in 1911,
the world's first commercial geothermal power station was built there. Experimental generators were built in Beppu, Japan and the Geysers,
California in the 1920s, but Italy was the world's only industrial producer of geothermal electricity until 1958. In 1958, New Zealand became
the second major industrial producer of geothermal electricity when its Wairakei station was commissioned. Wairakei was the first station
to use flash steam technology. In 1960, Pacific Gas and Electric began operation of the first successful geothermal electric power station
in the United States at The Geysers in California. The original turbine lasted for more than 30 years and produced 11 MW net power.
Geothermal electric stations have until recently been built exclusively where high-temperature geothermal resources
are available near the surface. The development of binary cycle power plants and improvements in drilling and extraction technology may
enable enhanced geothermal systems over a much greater geographical range. Demonstration projects are operational in Landau-Pfalz, Germany,
and Soultz-sous-Foręts, France, while an earlier effort in Basel, Switzerland was shut down after it triggered earthquakes. Other
demonstration projects are under construction in Australia, the United Kingdom, and the United States of America.
Geothermal Heat Pumps
Geothermal heat pumps (GHPs), sometimes referred to as GeoExchange, earth-coupled, ground-source, or water-source heat
pumps, have been in use since the late 1940s. They use the relatively constant temperature of the earth as the exchange medium instead of
the outside air temperature, they work in the same way as a refrigerator, the compressed fluid heats up heating the radiator, and the decompressed
fluid cools down, absorbimg the grounds heat
Although many parts of the country experience seasonal temperature extremes, from scorching heat in the summer to sub-zero cold in the
winter, a few feet below the earth's surface the ground remains at a relatively constant temperature. Depending on latitude, ground
temperatures range from 45°F (7°C) to 75°F (21°C). Like a cave, this ground temperature is warmer than the air above it during the winter
and cooler than the air in the summer. The GHP takes advantage of these more favorable temperatures to become high efficient by exchanging
heat with the earth through a ground heat exchanger.
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