Generous Geothermals

Geothermal (heat energy) is the most abundant source of available energy on Earth. In fact, Earth's crust, which is about 6 miles thick, contains 50,000 times as much thermal energy as it does energy stored in coal and gas.

Humans have used geothermal energy for thousands of years. Ten thousand years ago, Native Americans used hot springs for cooking. The Romans built reservoirs around springs to create heated bathing complexes. But not until the turn of the 20th century did we realize how to extract Earth's heat energy.

Here's how it works: In conventional geothermal tapping, a drill bores 1,000 to 10,000 feet deep into Earth's crust—into a subterranean water source whose surrounding rocks are heated by molten lava below. (The temperature of the rocks found in association with these regions can run from several hundred degrees Fahrenheit to several thousand.) Once the hole is drilled, there are several ways to tap the heat energy.

The simplest—and oldest—way is to tap steam right from the source and run it directly into a turbine, which, as it spins, creates a constant flow of electricity.

Another way is to draw hot water (about 400 degrees F)—which is also under high pressure—from deep within Earth and pump it into low-pressure tanks. In the process, some of the water instantly vaporizes. This residual steam can be used to run turbines. If the subterranean water source is cooler (in the 300 degrees F range), the water can be piped through a heat exchanger, where it is used to vaporize a second fluid that boils at a lower temperature. This is called a “binary process.”

Today, geothermal energy is a mainstay in many nations around the world. There are more than 40 power plants producing electricity from geothermal energy in the United States alone. In the Philippines, 16 percent of the power used on the island of Luzon, which is home to more than 40 million people, comes from geothermal power plants. And Reykjavik, Iceland, receives almost all its heat energy from geothermal sources. (Iceland, overall, receives 49.5 percent of its energy from geothermal sources.)

Using geothermal power plants to generate electricity produces less than one one-thousandth of the air pollution of equivalent coal plants. But conventional methods (especially the hot water ones) have some drawbacks. Geothermal plants can produce much more wastewater than a coal-fired or atomic power plant. Without proper management, extremely hot wastewater can be discharged into local streams, lakes, or salt water and disrupt the local ecology. The wastewater can also contain toxic chemicals (such as arsenic, lead, and mercury).

Scientists and engineers are working to develop new methods of tapping this energy reserve that would minimize some of these problems.


Characterized by or consisting of two parts or components; twofold.

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  1. The article states that geothermal power plants can produce more wastewater than coal-fired or atomic power plants. Why is the wastewater dangerous to ecosystems? What is contained in the wastewater? Why do you think the wastewater sometimes contains toxic chemicals? Do you think geothermal energy is a good source or a bad source of energy? Why? Write a paragraph about geothermal energy. Explain why wastewater from a geothermal plant can be dangerous. Include details about why you think wastewater contains toxic chemicals. State whether you think geothermal energy is a good or a bad energy source, and tell why you have this opinion.
    Answer: The wastewater from geothermal plants is dangerous to ecosystems because the temperature of the water is higher than the lakes, streams, and salt water into which it is released. This can disrupt the temperature of the ecosystem and kill plants and animals. Wastewater contains toxic chemicals, such as arsenic, lead, and mercury. Since geothermal energy is sometimes harvested from water found deep within Earth, the chemicals probably come from rocks next to this water. Students' opinions about geothermal energy being a good energy source or a bad energy source may vary. Some students may believe it is a good energy source because geothermal energy production causes little air pollution and does not deplete fossil fuel resources. Other students may believe geothermal energy is not a good energy source because it can pollute lakes, streams, and oceans.