Institute for Energy Research

Geothermal

Geothermal energy is harnessed from the natural heat of the Earth. In some cases, this means tapping extremely hot temperatures via steam at great depths. In others, it involves the use of moderate temperatures at shallow depths. These are known as "heat sinks" and are valuable for their use in creating energy.

Geothermal energy is gaining support as a potential contributor to meeting the growing energy needs of our nation. Today, however, geothermal energy only provides about one-third of 1% of all the energy consumed in the United States.

Courtesy DOE/NREL Pacific Gas & Electric

To produce electricity, hot water or steam extracted from high temperature geothermal reservoirs in the Earth’s crust is piped to steam turbines at electric utilities that drive generators. Moderate-to-low temperature geothermal resources are used for direct-use applications such as space heating or “district” heating, where a sole source of geothermal energy is used to heat multiple buildings or in some cases, a whole community.

Lower-temperature, shallow-ground geothermal resources are used by geothermal heat pumps to heat and cool individual buildings. Such uses of geothermal energy are becoming increasingly popular as an option for new home construction by those who seek long-term energy savings, as heating and cooling via a geothermal heat pump is very cost-effective.

Extraction of geothermal energy involves drilling holes with rigs like those used in the oil and gas industry and drawing water and steam from within the Earth. In the US, only four states have geothermal power plants: California (with 33), Nevada (15), Hawaii (1), and Utah (1).

Geothermal power plants do not burn fuel to produce electricity, so their emission levels are very low. They typically release about 1 to 3 percent of the carbon dioxide emissions of a fossil fuel plant. They can, however, adversely affect the stability of the surrounding land.

Power from geothermal sources can be price competitive in some locations, and its power works continually, providing a steady source of electricity. Geothermal plants have traditionally been small, and it takes many of them to produce significant amounts of electricity. Also, steam from geothermal plants cannot be transported over long distances because the heat dissipates, so energy transmission is typically by wire, and plants tend be located on or very near the site of the geothermal activity.

The US is the biggest producer of geothermal power, but geothermal energy accounts for only about three-quarters of 1% of net US electricity. This figure could rise to one percent in a few years if all 74 currently planned geothermal projects, most of which are in the Western states, are built. Federal law was changed in 2005 to encourage the use of geothermal energy on government lands by removing impediments to siting facilities there. Because of its proven success, its ability to produce large amounts of energy if built to scale, and its economic attractiveness, geothermal energy looks ready to assume a growing role in providing for the needs of the nation.

Printable Geothermal Energy Charts:

• Geothermal 1: Historic US Consumption

• Geothermal 2: Percent of Total US Energy Consumption

• Geothermal 3: Percent of US Electric Energy Consumption.pdf