Geothermal Energy

Geothermal energy plant in Iceland

Geothermal Power

Geothermal power is power extracted from heat stored in the earth. This geothermal energy is generated from the original formation of the planet, from radioactive decay of minerals, and from solar energy absorbed at the surface. It has been used for space heating and bathing since ancient Roman times, but is now better known for generating electricity.

Geothermal power is cost effective, reliable, and environmentally friendly, but has historically been limited to areas near tectonic plate boundaries.

Recent technological advances have dramatically expand the range and size of viable resources, especially for applications such as home heating.

What are the benefits of using geothermal energy?

First, it's clean. Energy can be extracted without burning a fossil fuel such as coal, gas, or oil. Geothermal fields produce only about one-sixth of the carbon dioxide that a relatively clean natural-gas-fueled power plant produces, and very little if any, of the nitrous oxide or sulfur-bearing gases. Binary plants, which are closed cycle operations, release essentially no emissions.

Geothermal energy is available 24 hours a day, 365 days a year. Geothermal power plants have average availabilities of 90% or higher, compared to about 75% for coal plants.

Why is geothermal energy a renewable resource?

Answer: Because its source is the almost unlimited amount of heat generated by the Earth's core. Even in geothermal areas dependent on a reservoir of hot water, the volume taken out can be reinjected, making it a sustainable energy source.

Where is geothermal energy available?

Answer: Hydrothermal resources - reservoirs of steam or hot water - are available primarily in the western states, Alaska, and Hawaii. However, Earth energy can be tapped almost anywhere with geothermal heat pumps and direct-use applications. Other enormous and world-wide geothermal resources - hot dry rock and magma, for example - are awaiting further technology development.

What are the environmental impacts of using geothermal energy?

Answer: Geothermal technologies offer many environmental advantages over conventional power generation:

•Emissions are low. Only excess steam is emitted by geothermal flash plants. No air emissions or liquids are discharged by binary geothermal plants, which are projected to become the dominant technology in the near future.

•Salts and dissolved minerals contained in geothermal fluids are usually reinjected with excess water back into the reservoir at a depth well below groundwater aquifers. This recycles the geothermal water and replenishes the reservoir. The City of Santa Rosa, California, pipes the city's treated wastewater up to The Geysers power plants to be used for reinjection fluid. This system will prolong the life of the reservoir as it recycles the treated wastewater.

•Some geothermal plants do produce some solid materials, or sludges, that require disposal in approved sites. Some of these solids are now being extracted for sale (zinc, silica, and sulfur, for example), making the resource even more valuable and environmentally friendly.

What is the visual impact of geothermal technologies?

Answer: District heating systems and geothermal heat pumps are easily integrated into communities with almost no visual impact. Geothermal power plants use relatively small acreages, and don't require storage, transportation, or combustion of fuels. Either no emissions or just steam are visible. These qualities reduce the overall visual impact of power plants in scenic regions.

What makes a site good for geothermal electric development?

Answer: Hot geothermal fluid with low mineral and gas content, shallow aquifers for producing and reinjecting the fluid, location on private land to simplify permitting, proximity to existing transmission lines or load, and availability of make-up water for evaporative cooling. Geothermal fluid temperature should be at least 300º F, although plants are operating on fluid temperatures as low as 210º F.

Enhanced Geothermal Systems

Enhanced geothermal systems (EGS) are engineered reservoirs created to produce energy from geothermal resources.


geothermal power plant in Coso Hot Springs California

EGS technology has the potential for accessing the Earth's vast resources of heat located at depth to help meet the energy needs of the United States.

Cool Waters

Lake source cooling, also known as deep source cooling utilizes the frigid waters of lakes to cool nearby buildings.


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