Geothermal Energy Information
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What is Geothermal Energy?
The United States leads the world when it comes to geothermal energy production, and has more than 77 power plants that are capable of producing a combined 3086 megawatts of power. These plants are concentrated around hot spots in the Western states, and they combine to make geothermal energy the 4th largest renewable energy source.
The typical geothermal energy plant functions in a manner similar to what is shown in the image above. Water trapped beneath the surface of the Earth is superheated by magma. It can't evaporate because there is nowhere for it to go. Wells are drilled through the top layer of impermeable rock and down through the permeable rock that sits above the water. Wells that are a mile or so deep tap into reservoirs of steam and extremely hot water and bring it to the surface.
Once it reaches the surface, it can be processed in three main types of power plants:
Binary cycle plants use hot geothermal water to heat a secondary fluid by passing it close to fluid. The secondary fluid vaporizes, and the vapor is used to push turbines.
Flash steam plants typically pull superheated water from deep within the Earth into low-pressure tanks, where the water vaporizes into steam. The steam is then used to drive turbines that create geothermal energy.
Dry steam plants are the simplest of the three. They capture geothermal steam and use to drive the turbines.
United States Geothermal Energy Map
As you can see, geothermal activity is most pronounced in the western United States, so it's no surprise most of the geothermal poer plants are located there. Geothermal energy production is concentrated in California and Nevada, with plants either on the way or in use in a number of other states.
The Geysers
No discussion of geothermal energy would be complete without mention of the Geysers. The Geysers are a group of 22 geothermal energy plants located just 72 miles north of San Francisco, California. It is the largest geothermal power complex in the world, producing an average of 955 MW of power. It is capable of producing up to 1517 MW at peak production. Calpine Corporation owns the lion's share of the plants at the Geysers location, as they currently own and operate 19 out of 22 functional plants.
The Geysers development spans 30 square miles across Lake, Sonoma and Mendocino county. It provides power to these three counties, as well as Marin and Napa counties. It fulfills close to 60% of the power needs of the Northern California coastal region running from the Oregon state line down to the Golden Gate Bridge.
It is a dry steam field, powered by superheated steam that is used to turn turbines that generate electricity. The complex is refueled with sewage effluent that comes from Lake County and Santa Rosa treatment plants.
Other Uses of Geothermal Energy
District heating systems pump heated water through buildings to heat them during the winter. Geothermal heat pumps are used to control building temperatures during both the winter and the summer in some areas. Another novel use for geothermal energy sees heated water being pumped through pipes close to the surface of roads in order to melt snow off of the roadway.
While above-ground temperatures can fluctuate wildly from day to day and even from hour to hour, temperatures below the Earth's surface stay a constant 50 to 60 degrees Fahrenheit. Geothermal heat pumps can be used to transfer warmth in the winter and heat in the summer. According to the EPA, geothermal heat pumps are the most energy-efficient and cost-effective means of heating and cooling our homes.
The Downside to Geothermal Energy
Disseminators of geothermal energy information often fail to admit that there is a downside. While pollutants released during the production of this green energy are kept to a minimum, there is an environmental downside. Hydrogen sulfide can be released, which is foul-smelling and can be toxic in high concentrations.
The geothermal fluid may contain elevated levels of toxic material like boron and sulfur, and it will either need to be disposed of or pumped back into the Earth. Another concern is the amount of superheated water being pulled from a location. Once the water has been depleted, it will either need to be replaced or new locations will need to be found, as subterranean water is a finite resource.
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