Geothermal Energy Shows Promise, Though Cost Limits Potential

Published November 10, 2016

Geothermal energy is a renewable source of power that receives relatively little media attention, and even though it does not suffer from the intermittency problems plaguing wind and solar power and is cheaper than those sources, geothermal receives relatively little support from the government.

Even if it were to receive government support, it still wouldn’t be economically competitive compared to the electric power generated from fossil fuels—except in those regions with ample geothermal activity but a relatively limited supply of fossil fuels.

Geothermal energy is heat that has been emitted from Earth. We can recover this heat in the form of steam or hot water and use it to heat buildings or generate electricity. Heat is continuously generated inside Earth by the decay of isotopes of various radioactive elements located deep beneath the ground that keep magma in a liquid state and result involcanic heat near Earth’s surface. Archaeological evidence shows early humans probably used geothermally heated water from natural pools and hot springs for cooking, bathing, keeping warm, and in religious ceremonies.

Earth’s Heat-Generating Power

There are two common types of geothermal power plants: dry steam plants and flash steam plants.

Dry steam plants use steam piped directly from a geothermal reservoir to turn turbines that generate electricity. Dry steam was first used in a power plant at Lardello near Tuscany, Italy in 1904. The first commercial-scale geothermal development in the United States was a small 10 megawatt (MW) dry steam plant at The Geysers in California, constructed by Pacific Gas & Electric in 1960. It remains in operation and has been expanded to include 29 separate units, which are owned by multiple companies. They have the potential to generate more than 1,500 MW of electric power (nameplate capacity), making it the largest dry steam plant in the world.

Globally, flash steam plants provide the vast majority of geothermal energy used by humans. These plants take high-pressure hot water from great depths and convert it to steam to drive turbines. When the steam cools, it condenses into water and is injected back into the ground to be used again. A hot water field is usually considered to have possible economic value if the reservoir is found at a depth of less than two kilometers, with a salt content lower than 60 grams per kilogram of water. Above the latter, the corrosiveness of the water makes mechanical operation difficult.

U.S. Is Geothermal Power Leader

Most of the geothermal development in the United States has occurred in Western states. Regions of higher-than-normal heat flow are usually associated with tectonic plate boundaries and areas of relatively recent volcanic events.

The United States leads the world in geothermal electric power generation, with more than 3,700 MW of installed capacity, which make up less than 0.5 percent of the country’s total electric power. California is the U.S. leader in geothermal power production; it produces 80 percent of the national total. Sixteen percent is produced in Nevada, and the rest is produced, in descending order of production, in Utah, Hawaii, Oregon, Idaho, and New Mexico. Also, very small amounts of geothermal electricity are generated in Alaska and Wyoming.

In total, the world produces more than 13,000 MW of geothermal electric power in 24 countries, with the Philippines producing the second-highest amount: nearly 2,000 MW of generating capacity, which make up almost 16 percent of the country’s electric power. With 665 MW of nameplate capacity, Iceland produces the seventh-most geothermal power, constituting 26 percent of the nation’s total electric power and making Iceland the nation most dependent on geothermal-generated electricity.

Other relatively new or experimental geothermal power systems produce less than 1 percent of global geothermal electric power.

An additional source of geothermal power and heat comes from distributed geothermal groundwater heat pumps and shallow closed-loop Earth heat pumps, which are used in individual homes and businesses. Temperatures 10 feet below Earth’s surface are nearly constant, ranging 50–60 degrees Fahrenheit. Because these temperatures are normally warmer than surface temperatures in winter and cooler than surface temperatures in the summer, heat pumps can be used to exchange heat from Earth to a building in winter and from a building to Earth in summer. They provide many homes in the United States and in countries such as Iceland with a considerable amount of energy, reducing dependence on other sources of electric power and heat.

Costs Limit Geothermal Development

In locations in which geothermal resources exist but are untapped, cost is the prime limiting factor. Although geothermal power is considerably cheaper than solar and several other power sources, it is still much more expensive to produce than power from conventional fossil-fuel and nuclear power plants.

Only a small fraction of Earth’s available geothermal energy has been utilized, and only in areas where geologic conditions permit relatively easy access. The Geothermal Energy Association’s (GEA) 2016 annual report says only 6–7 percent of the world’s global geothermal electric power potential of more than 200,000 MW has been tapped. GEA reports in 2016, 12,500 MW of geothermal capacity, spread across 82 countries, was under construction.

Jay Lehr, Ph.D. ([email protected]) is science director for The Heartland Institute. This article was adapted from the “Geothermal” energy section of the Alternative Energy and Shale Gas Encyclopedia, published in 2016by John Wiley & Sons and edited by Jay Lehr and Jack Keeley.