Geothermal Energy 101
Geothermal energy primarily comes from the volcanic heat stored beneath the earth's surface. Underground reservoirs of water heated by volcanic activity can be tapped for steam to generate electricity.
Almost everywhere, the shallow ground or the upper 10 feet of the Earth's surface maintains a nearly constant temperature between 50° and 60°F (10° and 16°C). Geothermal heat pumps can tap into this resource to heat and cool buildings. A geothermal heat pump system consists of a heat pump, an air delivery system , and a heat exchanger - a system of pipes buried in the shallow ground near the building.
In the winter, the heat pump removes heat from the heat exchanger and pumps it into the indoor air delivery system. In the summer, the process is reversed, and the heat pump moves heat from the indoor air into the heat exchanger. The heat removed from the indoor air during the summer can also be used to provide a free source of hot water. This allows the system to reach fairly high efficiencies (300% to 600%) on the coldest winter nights, compared to 175% to 250% for air-source heat pumps on cool days.
Almost everywhere, the shallow ground or the upper 10 feet of the Earth's surface maintains a nearly constant temperature between 50° and 60°F (10° and 16°C). Geothermal heat pumps can tap into this resource to heat and cool buildings. A geothermal heat pump system consists of a heat pump, an air delivery system , and a heat exchanger - a system of pipes buried in the shallow ground near the building.
In the winter, the heat pump removes heat from the heat exchanger and pumps it into the indoor air delivery system. In the summer, the process is reversed, and the heat pump moves heat from the indoor air into the heat exchanger. The heat removed from the indoor air during the summer can also be used to provide a free source of hot water. This allows the system to reach fairly high efficiencies (300% to 600%) on the coldest winter nights, compared to 175% to 250% for air-source heat pumps on cool days.
Where are they currently found in the US?
The US Geological Survey published the three charts below illustrating the current distribution of geothermal energy in the United States.
The US Geological Survey published the three charts below illustrating the current distribution of geothermal energy in the United States.
Identified Geothermal Resources
As of 2005, the United States has an installed and utilized power production capacity of more than 2500 Megawatts electric (MWe) from geothermal plants located in Alaska, California, Hawaii, Idaho, Nevada and Utah. |
Undiscovered Resources
Undiscovered geothermal resources were assessed in same states in which the identified moderate and high temperature geothermal systems are located. They reflect the limited degree of exploration and development in states other than California and Nevada. The undiscovered resources results indicate that additional exploration could add substantially to the total of identified geothermal resources and further expand geothermal power production. Regions with significant geothermal potential but few identified geothermal systems include northeastern Nevada, western Utah, southern Idaho, eastern Oregon, and parts of New Mexico and Colorado. |
Enhanced Geothermal Systems
Require some form of engineering to develop the permeability necessary for the circulation of hot water or steam and the recovery of heat for electrical power generation. Because exploitation of this resource incorporates the augmentation or creation of permeability in place, the presence of elevated temperatures at drillable depths is the dominant factor controlling the quality of the resource. |
Economic Benefits
- Low operating costs : Homeowners with Geothermal units typically enjoy energy savings of 25 to 50% over the conventional gas, oil, or heat pump systems. In fact, the typical 2000-sq.-ft. home can be heated and cooled for as little as $1 a day. In addition, Geothermal systems can supplement the home's conventional water heater, saving up to 30% of hot water costs every year. Geothermal systems use small amounts of electricity to transfer heat to and from the ground to your home. Homeowners typically experience an annual savings of 30% to 70% when compared to ordinary systems.
- Quiet: Geothermal systems use the same principles that operate a refrigerator or freezer, and the units are just as quiet. There is no unsightly outdoor unit to disturb you or your neighbors.
- Life cycle cost: Ordinary systems require expensive regular maintenance for each unit - the furnace, the air conditioner, and the water heater. When properly installed, a geothermal system requires little or no maintenance beyond periodic checks and filter changes. Equipment life is prolonged since geothermal are located indoors and out of the varying climate and weather. Geothermal systems typically last more than 20 years if properly maintained.
- Improved Comfort: Geothermal systems heat and cool homes evenly, eliminating the hot and cold blasts of air found with conventional systems. Geothermal also dehumidifies the air during the hot summer months.
Considerations:
As of now, geothermal is a minnow among power sources. America has the world’s highest installed capacity of geothermal generating plants—3.4 gigawatts’ worth at last count (see first chart)—but they generate only 0.4% of its electricity (see second chart). New “enhanced geothermal systems” (EGS), however, look set to make geothermal a bigger contributor.
As of now, geothermal is a minnow among power sources. America has the world’s highest installed capacity of geothermal generating plants—3.4 gigawatts’ worth at last count (see first chart)—but they generate only 0.4% of its electricity (see second chart). New “enhanced geothermal systems” (EGS), however, look set to make geothermal a bigger contributor.