Geothermal Energy

Geothermal hot spring

Credit: Laney, Patrick (Pat) - Idaho National Engineering and Environmental Laboratory

Geothermal energy comes from reservoirs of steam and hot water beneath the earth's surface. It is among the least explored sources of renewable energy in the United States. In 2010, geothermal energy produced just over 3,000 megawatts of energy, or less than half a percent of the electricity used in this country.[1]

Today nearly 200 geothermal projects, with a total capacity of about 7,800 megawatts, are in various stages of development in 15 states, largely in the West, where most geothermal resources are concentrated.[2]

Geothermal development could have negative impacts on the environment, such as threats to local groundwater and increased seismicity from drilling activity. Geothermal development should move forward with careful siting and strong environmental protections in place.

How Geothermal Energy Works

When superhot magma from deep within the earth comes close to the surface, it heats underground water and traps it in cracks and porous rock, creating reservoirs of very hot water and steam. Deep wells can tap the high energy content of this water and steam to drive a myriad of energy services, including electricity, heating, cooling, industrial processes, and even melting snow on roads.

Drilling geothermal wells may involve hydraulic fracturing of underground formations, also known as fracking -- similar to the process used in oil and gas production. Strong protections must be in place to guard underground sources of drinking water from contamination during the fracturing process, which can also use chemical additives in addition to drilling. Hydraulic fracturing operations related to geothermal production are currently exempt from underground injection control regulations under the federal Safe Drinking Water Act.

All drilling and fracturing activities, as well as management of toxic waste, should be conducted with the highest level of environmental protection.

Another way to use geothermal energy on a smaller scale is through a geothermal heat pump, which exploits the temperature difference between the earth's surface and the air. In most places, the temperature at 10 feet below ground level remains between 50 and 60 degrees Fahrenheit year-round. In winter, a geothermal heat pump pulls heat from the relatively warmer ground and pumps it into a building. In summer, the pump cools the same building by pulling the building's warmer air into the relatively cooler ground, where the excess energy can be used in turn to heat water.

Where Geothermal Energy Is Used

The near-term development of 5,600 megawatts of geothermal energy would result in the creation of almost 100,000 jobs

Most of the United States' geothermal resources are located in the West, and in Alaska and Hawaii.

The vast majority of geothermal power is produced in California.[3] In addition to fueling power plants, geothermal energy is used to heat spas, pools, homes, greenhouses and aquaculture ponds.[4] In Klamath Falls, Oregon, geothermal heat melts snow on sidewalks during the winter.[5] In Empire, Nevada, 15 million pounds of dried onions and garlic are produced each year at a dehydration plant powered by geothermal energy.[6]

How Much Geothermal Energy Costs

At California's The Geysers, which has been operational since 1960, power is sold at $0.03 to $0.035 per kilowatt-hour. A new geothermal plant would probably charge about $0.05 per kilowatt-hour, though some plants can charge more during peak demand periods.[7] While the initial costs of drilling and installing geothermal power plants are high, operation and maintenance costs are low –- and there are no fuel costs at all, which keeps the price of the energy from fluctuating.

Industry experts agree that geothermal energy could be cost-competitive with fossil fuel energy in the short term.

Advantages of Geothermal Energy

The Department of Energy estimates that Enhanced Geothermal Systems (EGS) could produce at least 100,000 megawatts of electricity within 50 years

Geothermal energy is a clean, green, renewable resource. The earth has been emitting heat from its center for 4.5 billion years and shows no signs of slowing down. A geothermal plant in Italy has been operation since 1913, demonstrating the sustainability of this power source. However, some underground aquifers can be affected by a lack of precipitation, in which case geothermal power plants can reinject fluids underground to replenish reservoirs. For example, the city of Santa Rosa, California, pipes its treated wastewater to the Geysers power plant to be used as reinjection fluid.[8]

Geothermal power plants produce almost no global warming pollution and emit very little air pollution -- sometimes none at all. And unlike solar or wind energy, geothermal energy is available around the clock.

According to a report by the Western Governors Association (WGA), near-term development of 5,600 megawatts of geothermal energy would result in the creation of almost 100,000 jobs.

What's Around the Corner for Geothermal Energy

Enhanced Geothermal Systems, or EGS technology, is being developed to produce energy from hard-to-reach geothermal resources, such as those with less water or those in harder beds of rock. This advanced technology would expand the capabilities of geothermal power many times over. The Department of Energy estimates that EGS could produce at least 100,000 megawatts of electricity within 50 years.[9]

Google.org, the philanthropic arm of Google, is a major investor in EGS. The organization is funding research and developing informational tools to help advance the technology.[10]

Another emerging technology, known as hybridization, pairs geothermal with solar technologies to increase the efficiency of energy capture and electricity generation at a given well site. The concept could prove very valuable in the sunny, geothermal-rich western U.S. states. One such project is under construction in Turkey.[11]

Learn More


NREL Geothermal Technologies
Provides a comprehensive overview of geothermal resource potential throughout the United States.
Geothermal Energy Association
Weekly news, policy information and resources from the U.S. trade association.
An Evaluation of Enhanced Geothermal Systems Technology (PDF)
A 2008 study by the Department of Energy (DOE) on the technological requirements to commercialize Enhanced Geothermal Systems.
Protecting Americans from the Risks of Fracking
An NRDC fact sheet addresses the risks posed by hydraulic fracturing in natural gas drilling, and how to keep communities safe.

Renewable Energy Map

Energy Map

See if harvesting renewable energy makes economic sense for you with our interactive energy map.

Energy Map
Share | |
Find NRDC on
YouTube