Tapping the Earth’s Heat: Geothermal Energy

A. Introduction

B. Origin and Nature of Geothermal Energy

C. Hydrothermal Systems

D. Geothermal Exploration and Resources

E. Low-Temperature Geothermal Resources

F. Environmental Impacts

G. Summary

Tapping the Earth’s Heat: Geothermal EnergyHOW WOULD YOU CHOOSE?

A Hot Investment

A group of investors are interested in building a geothermal power plant. Pro­ponents have argued that the low cost of such plants—including incentives available through the government because this is a renewable resource—and its low environmental impact make geothermal a strong investment. They are looking into two fast-growing metropolitan areas—Atlanta and Phoenix. How would you choose in this matter?

A. Introduction

Geothermal energy is produced from heat originating in the earth’s interior. Volca­noes, geysers, hot springs, and boiling mud pots are visible evidence of the great res­ervoirs of heat that lie within and beneath the earth’s crust. Although the amount of thermal energy within the earth is very large, useful geothermal energy is limited to

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certain sites. These resources are not infinite and can be depleted at a particular site under intensive exploitation. Nevertheless, geothermal energy is a resource that can be further developed in favorable locations. Currently 5% of the electricity generated in the United States from renewable sources comes from geothermal energy. (This is about half the contribution from wind and solar. Installed capacity for wind is almost 10 times the in­stalled capacity for geothermal in the United States.) Whereas the total energy used from geothermal resources in the United States has shown little growth in the past 10 years, globally, geothermal power has been growing steadily at a rate of about 3.5% per year.

Electricity was first produced from naturally occurring steam in Italy in 1904. Today, many geothermal power stations are operating worldwide. Table 18.1 lists the world’s geothermal generating capacity for both 1990 and 2010 for those nations with substantial geothermal facilities. The world’s total installed capacity today is more than

10,0 MWe. The Geysers in northern California, the largest such facility in the world, has a total installed capacity of about 1000 MWe—enough to power a city the size of San Francisco, located 90 miles to the south; this is about 7% of California’s electri­city needs. The big island of Hawaii provides 25% of its electricity from geothermal resources. The Philippines, Indonesia, Kenya, and Mexico have enjoyed rapid growth in generating capacity in the past decade. El Salvador generates the majority of its electri­city with steam from geothermal resources.

Nonelectric applications of geothermal energy have been developed extensively in some countries. Hot water from underground sources provides direct heating for

Table 18.1 GEOTHERMAL POWER PLANTS

Installed Capacity (MWe)

Site

1990

2010

United States

2775

3086

Philippines

890

1904

Indonesia

145

1197

Mexico

700

958

Italy

545

843

New Zealand

283

628

Iceland

45

575

Japan

215

536

El Salvador

95

204

Kenya

45

167

Costa Rica

0

166

Source: International Geothermal Association

the majority of homes in Iceland’s capital, Reykjavik, and has done so for six decades. Budapest, Hungary, has been partly heated by geothermal steam since the times of the Roman Empire. Heated greenhouses there provide vegetables and flowers the year around. Space or district heating via geothermal energy in the United States is found only on a small scale. The main developments have been for residences and businesses in the cities of Klamath Falls, Oregon; Boise, Idaho; and San Bernardino, California.

In this chapter, we will investigate the sources of geothermal energy and their po­tential yields, the use of this resource, and obstacles to its development.

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