" Geothermal energy "

Geothermal energy is thermal energy in the Earth's crust. It

combines energy from the formation of the planet and from
radioactive decay. Geothermal energy has been exploited as a
source of heat and/or electric power for millennia

Geothermal heating, using water from hot springs, for example,

has been used for bathing since Paleolithic times and for space
heating since Roman times. Geothermal power, (generation of
electricity from geothermal energy), has been used since the
20th century. Unlike wind and solar energy, geothermal plants
produce power at a constant rate, without regard to weather
conditions. Geothermal resources are theoretically more than
adequate to supply humanity's energy needs. Most extraction
occurs in areas near tectonic plate boundaries

The cost of generating geothermal power decreased by 25%

during the 1980s and 1990s. Technological advances continued
to reduce costs and thereby expand the amount of viable
resources. In 2021, the U.S. Department of Energy estimated that
.power from a plant "built today" costs about $0.05/kWh

In 2019, 13,900 megawatts (MW) of geothermal power was

available worldwide. An additional 28 gig watts provided heat for
district heating, space heating, spas, industrial processes,
desalination, and agricultural applications as of 2010

As of 2019 the industry employed about 100 thousand

people. Pilot programs like EWEB's customer opt-in Green
Power Program suggest that customers would be willing to pay a
little more for renewable energy
History :
Hot springs have been used for bathing since at least Paleolithic
times. The oldest known spa is at the site of the Huaqing Chi
palace. In the first century CE, Romans conquered Aquae Sulis,
now Bath, Somerset, England, and used the hot springs there to
supply public baths and underfloor heating. The admission fees
for these baths probably represent the first commercial use of
geothermal energy. The world's oldest geothermal district
heating system, in Chaudes-Aigues, France, has been operating
since the 15th century. The earliest industrial exploitation began
in 1827 with the use of geyser steam to extract boric acid from
.volcanic mud in Larderello, Italy

In 1892, the US's first district heating system in Boise, Idaho was
powered by geothermal energy. It was copied in Klamath Falls,
Oregon in 1900. The world's first known building to utilize
geothermal energy as its primary heat source was the Hot Lake
,Hotel in Union County, Oregon

beginning in 1907. A geothermal well was used to heat

greenhouses in Boise in 1926, and geysers were used to heat
greenhouses in Iceland and Tuscany at about the same time.
Charles Lieb developed the first downhole heat exchanger in
1930 to heat his house. Geyser steam and water began heating
home in Iceland in 1943

In the 20th century, geothermal energy came into use as a

generating source. Prince Piero Ginori Conti tested the first
geothermal power generator on 4 July 1904, at the Larderello
steam field. It successfully lit four light bulbs. In 1911, the world's
first commercial geothermal power plant was built there. It was
the only industrial producer of geothermal power until New
Zealand built a plant in 1958. In 2012, it produced some 594
megawatts

In 1960, Pacific Gas and Electric began operation of the first US

geothermal power plant at The Geysers in California. The
original turbine lasted for more than 30 years and produced 11
MW net power

A binary cycle power plant was first demonstrated in 1967 in the

USSR and introduced to the US in 1981. This technology allows
the generation of electricity from much lower temperature
resources than previously. In 2006, a binary cycle plant in Chena
Hot Springs, Alaska, came on-line, producing electricity from a
)record low temperature of 57 °C (135 °F

In 2021 Quaise Energy announced the idea of using a gyrotron as

a boring machine to drill a hole 20 kilometers in depth. The
technique used frequencies of 30-300 GHz to transfer energy to
rock 1012 (1 trillion) times more efficiently than a laser. Lasers
would be disrupted by the vaporized rock, which would affect
the gyrotron's longer-wavelength much less. Drilling rates of 70
meters/hour were claimed to be possible with a 1 MW gyrotron
Global geothermal electric capacity. Upper red line is installed
capacity; lower green line is realized production

Resources :
The Earth has an internal heat content of 10^31 joules , About
20% of this is residual heat from planetary accretion; the
remainder is attributed to past and current radioactive decay of
naturally occurring isotopes. For example, a 5275 m deep
borehole in United Downs Deep Geothermal Power Project in
Cornwall, England, found granite with very high thorium
content, whose radioactive decay is believed to power the high
temperature of the rock

Earth's interior temperature and pressure are high enough to

cause some rock to melt and the solid mantle to behave
plastically. Parts of the mantle convect upward since it is lighter
than the surrounding rock. Temperatures at the core–mantle
.)boundary can reach over 4000 °C (7200 °F

The Earth's internal thermal energy flows to the surface by

conduction at a rate of 44.2 terawatts (TW), and is replenished
.by radioactive decay of minerals at a rate of 30 TW

These power rates are more than double humanity's current

energy consumption from all primary sources, but most of this
energy flux is not recoverable. In addition to the internal heat
flows, the top layer of the surface to a depth of 10 m (33 ft) is
heated by solar energy during the summer, and cools during the
winter

Outside of the seasonal variations, the geothermal gradient of .

temperatures through the crust is 25–30 °C (45–54 °F) per km of
depth in most of the world. The conductive heat flux averages 0.1
MW/km2. These values are much higher near tectonic plate
boundaries where the crust is thinner. They may be further
augmented by combinations of fluid circulation, either through
.magma conduits, hot springs, hydrothermal circulation

The thermal efficiency and profitability of electricity generation

is particularly sensitive to temperature. Applications receive the
greatest benefit from a high natural heat flux most easily from a
hot spring. The next best option is to drill a well into a hot
aquifer. An artificial one may be built by injecting water to
hydraulically fracture bedrock. This last approach is called hot
dry rock geothermal energy in Europe, or enhanced geothermal
. systems in North America

estimates of the potential for electricity generation from 0202

geothermal energy vary sixfold, from 0.035to2TW depending on
the scale of investments. Upper estimates of geothermal
resources assume wells as deep as 10 kilometres (6 mi), although
20th century wells rarely reached more than 3 kilometres (2 mi)
deep. Wells of this depth are common in the petroleum industry

Enhanced geothermal system :

0- Reservoir

2 - Pump house

3 - Heat exchanger

4 - Turbine hall

5 - Production well

6 - Injection well

7 - Hot water to district heating

8 - Porous sediments

9 - Observation well

10 - Crystalline bedrock
Geothermal power :
Geothermal power is electrical power generated from
geothermal energy. Dry steam, flash steam, and binary cycle
power stations have been used for this purpose. As of 2010
. geothermal electricity was generated in 26 countries

As of 2019, worldwide geothermal power capacity amounted to

15.4 gigawatts (GW), of which 23.86 percent or 3.68 GW were in
the United States

Geothermal energy supplies a significant share of the electrical

power in Iceland, El Salvador, Kenya, the Philippines and New
Zealand

Geothermal power is considered to be renewable energy because

the heat extraction is insignificant compared with the Earth's
heat content .The greenhouse gas emissions of geothermal
electric stations are on average 45 grams of carbon dioxide per
kilowatt-hour of electricity, or less than 5 percent of that of coal-
.fired plants

Geothermal heating :
Geothermal heating is the use of geothermal energy to heat
buildings and water for human use. Humans have done this
since the Paleolithic era. Approximately seventy countries made
direct use of a total of 270 PJ of geothermal heating in 2004. As
of 2007, 28 GW of geothermal heating satisfied 0.07% of global
primary energy consumption. Thermal efficiency is high since no
energy conversion is needed, but capacity factors tend to be low
.(around 20%) since the heat is mostly needed in the winter

Even cold ground contains heat: below 6 metres (20 ft) the
undisturbed ground temperature is consistently at the Mean
Annual Air Temperature that may be extracted with a ground
source heat pump

Types :
Liquid-dominated plants

Liquid-dominated reservoirs (LDRs) are more common with

temperatures greater than 200 °C (392 °F) and are found near
volcanoes in/around the Pacific Ocean and in rift zones and hot
spots. Flash plants are the common way to generate electricity
from these sources. Steam from the well is sufficient to power
the plant. Most wells generate 2–10 MW of electricity. Steam is
separated from liquid via cyclone separators and drives electric
generators. Condensed liquid returns down the well for
reheating/reuse. As of 2013, the largest liquid system was Cerro
Prieto in Mexico, which generates 750 MW of electricity from
.)temperatures reaching 350 °C (662 °F

Lower-temperature LDRs (120–200 °C) require pumping. They

are common in extensional terrains, where heating takes place
via deep circulation along faults, such as in the Western US and
Turkey. Water passes through a heat exchanger in a Rankine
cycle binary plant. The water vaporizes an organic working fluid
that drives a turbine. These binary plants originated in the Soviet
Union in the late 1960s and predominate in new plants. Binary
plants have no emissions
Enhanced geothermal systems :
Enhanced geothermal systems (EGS) actively inject water into
wells to be heated and pumped back out. The water is injected
under high pressure to expand existing rock fissures to enable
the water to flow freely. The technique was adapted from oil and
gas fracking techniques. The geologic formations are deeper and
no toxic chemicals are used, reducing the possibility of
environmental damage. Drillers can employ directional drilling
to expand the reservoir size

Economics :
As with wind and solar energy, geothermal power has minimal
operating costs; capital costs dominate. Drilling accounts for
over half the costs, and not all wells produce an exploitable
resources. For example, a typical well pair (one for extraction
and one for injection) in Nevada can produce 4.5 megawatts
(MW) and costs about $10 million to drill, with a 20% failure
rate, making the average cost of a successful well $50 million

1 - Geothermal reservoirs are usually in igneous or metamorphic

rock, which is harder to penetrate than the sedimentary rock of
.typical hydrocarbon reservoirs

2 - The rock is often fractured, which causes vibrations that

.damage bits and other drilling tools
3 - The rock is often abrasive, with high quartz content, and
sometimes contains highly corrosive fluids the rock is hot ,
which limits use of downhole electronics

4 - Well casing must be cemented from top to bottom, to resist

the casing's tendency to expand and contract with temperature
changes. Oil and gas wells are usually cemented only at the
.bottom

5 - Well diameters are considerably larger than typical oil and

gas wells

Sustainability :
Geothermal energy is considered to be sustainable because the
heat extracted is so small compared to the Earth's heat content,
which is approximately 100 billion times 2010 worldwide annual
energy consumption. Earth's heat flows are not in equilibrium;
the planet is cooling on geologic timescales. Anthropic heat
.extraction typically does not accelerate the cooling process

Wells can further be considered renewable because they return

the extracted water to the borehole for reheating and re-
.extraction, albeit at a lower temperature

Replacing material use with energy has reduced the human

environmental footprint in many applications. Geothermal has
the potential to allow further reductions. For example, Iceland
has sufficient geothermal energy to eliminate fossil fuels for
electricity production and to heat Reykjavik sidewalks and
eliminate the need for gritting

However, local effects of heat extraction must be considered .

Over the course of decades, individual wells draw down local
temperatures and water levels. The three oldest sites, at
Larderello, Wairakei, and the Geysers experienced reduced
output because of local depletion. Heat and water, in uncertain
proportions, were extracted faster than they were replenished.
Reducing production and injecting additional water could allow
these wells to recover their original capacity. Such strategies
have been implemented at some sites. These sites continue to
provide significant energy.

The Wairakei power station was commissioned in November

1958, and it attained its peak generation of 173 MW in 1965, but
already the supply of high-pressure steam was faltering. In 1982
it was down-rated to intermediate pressure and the output to 157
MW. In 2005 two 8 MW isopentane systems were added,
boosting output by about 14 MW. Detailed data were lost due to
re-organisations

Environmental effects :
Fluids drawn from underground carry a mixture of gasses,
notably carbon dioxide (CO2), hydrogen sulfide (H2S), methane
(CH4) and ammonia (NH3). These pollutants contribute to
global warming, acid rain and noxious smells if released. Existing
geothermal electric plants emit an average of 122 kilograms (269
lb) of CO2 per megawatt-hour (MW.h) of electricity, a small
fraction of the emission intensity of fossil fuel plants.[44][needs
update] A few plants emit more pollutants than gas-fired power,
at least in the first few years, such as some geothermal power in
Turkey. Plants that experience high levels of acids and volatile
chemicals are typically equipped with emission-control systems
to reduce the exhaust
Water from geothermal sources may hold in solution trace
amounts of toxic elements such as mercury, arsenic, boron, and
antimony. These chemicals precipitate as the water cools, and
can damage surroundings if released. The modern practice of
returning geothermal fluids into the Earth to stimulate
production has the side benefit of reducing this environmental
impact

Construction can adversely affect land stability. Subsidence

occurred in the Wairakei field In Staufen im Breisgau, Germany,
tectonic uplift occurred instead. A previously isolated anhydrite
layer came in contact with water and turned it into gypsum,
doubling its volume. Enhanced geothermal systems can trigger
earthquakes as part of hydraulic fracturing. A project in Basel,
Switzerland was suspended because more than 10,000 seismic
events measuring up to 3.4 on the Richter Scale occurred over
.the first 6 days of water injection

Geothermal power production has minimal land and freshwater

requirements. Geothermal plants use 3.5 square kilometres (1.4
sq mi) per gigawatt of electrical production (not capacity) versus
32 square kilometres (12 sq mi) and 12 square kilometres (4.6 sq
mi) for coal facilities and wind farms respectively. They use 20
litres (5.3 US gal) of freshwater per MW·h versus over 1,000 litres
(260 US gal) per MW·h for nuclear, coal, or oil
Production :
Philippines

The Philippines began geothermal research in 1962 when the

Philippine Institute of Volcanology and Seismology inspected
the geothermal region in Kiwi, Albany. The first geothermal
power plant in the Philippines was built in 1977, located in Tong
nan, Leyte. The New Zealand government contracted with the
Philippines to build the plant in 1972. The Tong nan Geothermal
Field (TGF) added the Upper Mania, Malabo, and South Samba
.loran plants, which resulted in a 508 MV capacity

The first geothermal power plant in the Kiwi region opened in

1979, while two other plants followed in 1980 and 1982. The Kiwi
geothermal field is located about 450 km from Manila. The three
geothermal power plants in the Kiwi region produce 330 Me,
putting the Philippines behind the United States and Mexico in
geothermal growth. The Philippines has 7 geothermal fields and
continues to exploit geothermal energy by creating the
Philippine Energy Plan 2012-2030 that aims to produce 70% of
the country's energy by 2030