PHYS 1110

Lecture 20 Professor Stephen Thornton November 13, 2012

Reading Quiz Which country has the greatest amount of geothermal produced electricity installed?

A) Philippines B) Iceland C) Italy D) Turkey E) United States

Reading Quiz Which country has the greatest amount of geothermal produced electricity installed?

A) Philippines B) Iceland C) Italy D) Turkey

E) United States

Homework 4 due Tuesday, November 13, 2012.

Quiz on solar (Ch. 7) and wind energies (Ch. 8) on Thursday, Nov. 13 Homework 5 on Ch. 8 due Thursday, Nov. 13.

Geothermal energy has been used for cooking and bathing for centuries, but can also be used in large power plants to produce electricity, and the steady temperatures just under the ground in our backyards can be used as thermal reservoirs to both heat and cool our homes using a heat pump. Geothermal energy accounts for at least 25% of the electrical capacity in Iceland, the Philippines, and El Salvador. The United States produces more geothermal electricity than any country in the world, more than 3 GW in eight states.

Geothermal heat – used in 78 countries Geothermal power – 11 GW in 24 countries Geothermal heat includes heat pump ground based thermal reservoirs.

Geothermal electrical power capacity for US and World.

The upper 3 m of the Earth has a nearly constant temperature between 50 0 F (10 0 C) and 60 0 F (16 0 C), but below that are large resources.

Crust: 5 – 70 km thick Mantle: 3000 km thick, rocks Core: outer (2300 km) is liquid. inner (1200 km) is solid.

The Earth’s temperature gradient is ~22 0 C/km. Radioactive decay heating of 40 K, 232 Th, 235 U, and 238 U are primarily responsible for the heating. The center of the Earth has a temperature of at least 5000 0 C (maybe as high as 7000 0 C) with a pressure as high as 360 GPa, which causes the inner core to still be a solid instead of melting into a liquid.

Hot springs occur when the rising heated water is collected on Earth’s surface into a pool. The springs can be calm or boiling, depending on the temperature. The hot water dissolves material as it rises to the surface and often contains minerals, which people use for medicinal purposes. Many hot springs are too hot or too acidic for bathing, but others are very relaxing. This one is in Japan.

Fumaroles are vents that emit steam and other gases (such as sulfur dioxide and hydrogen sulfide formed after interacting with sulfur). When superheated water emerges from the ground, the pressure drops turning the hot water into steam. This is sometimes associated with chemical activity and brightly colored rocks in the surface water. They contain water hotter than hot springs.

Mud pots are similar to hot springs or fumaroles but have only a small amount of water. This results in an acidic, viscous, often bubbling, slurry (Yellowstone).

Volcanoes and their eruptions are the most obvious visualizations of geothermal energy. They occur due to an opening in the Earth’s surface, often releasing huge amounts of lava, ash, and gases to escape to the Earth’s surface. Iceland is on the Mid Atlantic Ridge of the Ring of Fire and did not even exist as an island 20 million years ago.

Quiz The upper 3 m of the Earth has approximately what temperature?

A) 55 0 F B) 55 0 C C) 5 0 F D) 5 0 C E) 5 K

Quiz The upper 3 m of the Earth has approximately what temperature?

A) 55 0 F

B) 55 0 C C) 5 0 F D) 5 0 C E) 5 K

Quiz The temperature about 4000 km inside the Earth from its surface has approximately what temperature?

A) 40 0 F B) 400 0 C C) 40000 0 F D) 4000 0 C E) 50000 K

Quiz The temperature about 4000 km inside the Earth from its surface has approximately what temperature?

A) 40 0 F B) 400 0 C C) 40000 0 F

D) 4000 0 C

E) 50000 K

Quiz Which of the following is not directly due to geothermal processes?

A) hot springs B) volcanoes C) earthquakes D) geysers E) fumaroles

Quiz Which of the following is not directly due to geothermal processes?

A) hot springs B) volcanoes

C) earthquakes

D) geysers E) fumaroles

History Hot springs: US Indians, Chinese spa, Romans District heating system: Boise (1892), Klamath Falls, Oregon (1900) The first geothermal electricity was produced in 1904 in Lardello in Southern Tuscany, Italy. Steam and hot water springs were known to be produced at this site since Roman times. Hot steam escaping the Earth’s surface turned a turbine that powered five light bulbs in 1904. By 1911 a geothermal power station was constructed at Lardello. It remained the world’s only industrial geothermal power plant until a plant was built in New Zealand in 1958. A 250 kW power plant was constructed in 1913 to provide power for the Italian electric railroad system. Today, almost 5,000 GWh are produced at Lardello each year, enough to provide electricity to about one million homes. Surface water is pumped down to very hot granite rocks that are located close to the surface. The water is warmed to more than 200 0 C, and the returning steam turns turbines that produce electricity.

The Pacific Gas and Electric Company built the United State’s first successful geothermal power plant at the Geysers in California in 1960. Its successors remain in operation today and will be discussed shortly.

Ground Source Heat Pump

W

=

Q h

-

Q c

=

Q h

ж 1 -

Q c Q h

ц ч =

Q h

ж 1 -

T c T h

ч ш

Q c

is the heat removed from a cold reservoir at temperature

T c

and

Q h

is the heat deposited to a hot reservoir at temperature

T h

. If we want to minimize the work done, and therefore the amount of electricity we have to pay for, we want the cold and hot reservoirs to have approximately the same temperature. When it is very cold outside, heat pumps have to do a considerable amount of work. The work done to heat our houses to 72 0 F inside is much less when the cold reservoir is 57 0 F (underground thermal reservoir) rather than 5 0 F in the atmosphere.

Heat pumps are classified by their coefficient of performance COP =

Q h

/

W

There are more than 600,000 ground source heat pumps in operation in the United States today, and they are increasing at the rate of 60,000 new ones each year. They have higher initial capital costs, but the savings make them cost effective after only a few years. They are relatively easy to install, especially in new construction. They do require digging up yards in order to place the pipes in the ground. Even now, many heating and cooling contractors are not familiar with the installation procedures. Mostly the heat exchange is done with the ground, but it can also be done with a pond or even a swimming pool that does not freeze over in the winter.

Geothermal reservoirs close to the surface of Earth having temperatures up to about 150 0 C (300 0 F) are used for direct heat in residences, industry and commerce. Its use is widespread in the United States for a wide variety of applications including food processing, gold mining, greenhouses, and fish and alligator farms. Useful geothermal resources are plentiful in the western United States. A survey of 10 western states in the US identified almost 1000 low- to moderate- temperature geothermal sources with hundreds of direct use sites in the more than 9,000 thermal known wells and springs. In 2004 approximately 70 countries used 270,000 GJ of geothermal energy directly for space heating, heating swimming pools, and for industrial and agricultural applications.

• • Direct-use systems normally have three components: A production facility, usually a well, to bring hot water to the surface.

A mechanical system (pipes, heat exchanger, controls) to deliver the heat to a place of use.

• A disposal system (injection well or storage pond) for the spent geothermal fluid.

A district heating system melts the snow on a sidewalk in Klamath Falls, Oregon. Note the snow is not melted on the sidewalk beyond, the road, or the parking lot.

The hottest known geothermal regions on Earth are shown in red. These are likely to be best sources for electrical production.

Quiz Which of the following countries gets the largest percentage of its electricity from geothermal sources?

A) Philippines B) United Kingdom C) Italy D) Turkey E) United States

Quiz Which of the following countries gets the largest percentage of its electricity from geothermal sources?

A) Philippines

B) United Kingdom C) Italy D) Turkey E) United States

Estimated temperatures over the United States at a depth of 6 km.

Satellite imaging and aerial photography must be closely examined for prospective geothermal sites.

Geothermal exploration is similar to that of oil and gas – but 50 years behind!

Geologists and geophysicists examine closely volcanic regions like this one on a hillside in El Hoyo, Nicaragua for likely places for power plants.

Data from all kinds of surveys (electrical, magnetic, chemical, and seismic) must be gathered and studied in various ways.

Drilling is crucial for determining the suitability of the region for geothermal energy power production. It must be determined whether the geothermal reservoir will be hot enough to support commercial electrical production. Small-diameter

temperature

(or thermal)

gradient holes (TGH)

are drilled to various depths to determine the temperature gradient in the region. Thermal characteristics of the material brought up from drilling are quickly examined to determine the geothermal characteristics and the extent of the resource. The TGH may be drilled in steps, and at first may only go to a depth of a few hundred meters. Sometimes the TGH may be drilled deeper in an attempt to penetrate the geothermal reservoir. But the depth is dependent on the geologic and hydrologic conditions.

Quiz Which of the following is the closest to the maximum temperature at 6 km depth in the United States (do not consider volcanoes, etc.)?

A) 25 0 C B) 250 0 C C) 2500 0 C D) 25,000 0 C E) 250,000 0 C

Quiz Which of the following is the closest to the maximum temperature at 6 km depth in the United States (do not consider volcanoes, etc.)?

A) 25 0 C

B) 250 0 C - actually 325 0 C

C) 2500 0 C D) 25,000 0 C E) 250,000 0 C

Divide into groups and discuss: Flash geothermal power plant Dry steam geothermal power plant Binary geothermal power plant Flash/binary combined geothermal power plant Enhanced geothermal systems

Co-Production with Oil and Gas Wells

Oil and gas fields already in production may be another potential source of geothermal energy, because a significant amount of hot water or suitable high-pressure conditions are present. This could possibly allow for the production of geothermal produced electricity at the same time that oil and gas is extracted. In many cases, the extraction of oil and gas may even be enhanced. The 2007 MIT mentioned earlier estimated that the United States may even be able to produce 44 GWe of electricity by 2050 by co producing electricity, oil, and natural gas. The study went so far as to suggest that such advanced geothermal systems could supply 10% of US baseload electricity by 2050, given sufficient research and development over the next 10 years.

As part of the American Recovery and Investment Act of 2009, $400 million of new funding was allocated to the US DOE’s Geothermal Technologies Program. Of these funds, $90 million may go to up to 10 demonstration projects to develop and test EGS technology. Another $50 million will fund up to 20 other demonstration projects, which includes co-production.

The Southern Methodist University Geothermal Energy Program has identified many GW of possible energy by co-production. There are currently two geothermal co production demonstrations sites underway in the United States: at the Rocky Mountain Oil Test Center in Wyoming and the Jay oil field in Florida.

Electrical Production Today Most geothermal power plants use flash technology (New Zealand). Most new growth is in binary plants that can utilize low and moderate temperatures.

Potential in Asia and Pacific Islands is immense. Philippines is heavily involved.

Central America and Caribbean have large potential and need.

5 GW under development in USA.

Europe is involved, especially Italy, Turkey and Iceland.

Environmental Impact Some gases.

Subsidence, motion & sinking of Earth. Germany, New Zealand, Switzerland (near Basel, 10,000 seismic events in 6 days of water injection), Australia, almost none in the Geysers (best monitored in world).

Quiz Which of the following processes has the most geothermal power plants currently installed?

A) Flash B) Dry steam C) Binary D) Flash/binary combined E) Enhanced geothermal systems

Quiz Which of the following processes has the most geothermal power plants currently installed?

A) Flash

B) Dry steam C) Binary D) Flash/binary combined E) Enhanced geothermal systems

The future is not clear.

• • Costs for producing electricity are high.

Good for heating source and ground based heat pumps.

• • • Small-scale plants (< 5 MW) in rural areas.

Need Enhanced Geothermal Systems.

Need co-production with oil and gas wells.

Lots of pros and cons. Look at them. Pros outweigh cons. Need tax incentives, subsidies, research and development.