US Geothermal Industry Grew 26% in 2009 (during the Great Recession)

The areas with the highest underground temperatures are in regions with active or geologically young volcanoes. These "hot spots" occur at plate boundaries or at places where the crust is thin enough to let the heat through. The Pacific Rim, often called the Ring of Fire for its many volcanoes, has many hot spots, including some in Alaska, California, and Oregon. Nevada has hundreds of hot spots, covering much of the northern part of the state.

These regions are also seismically active. Earthquakes and magma movement break up the rock covering, allowing water to circulate. As the water rises to the surface, natural hot springs and geysers occur, such as Old Faithful at Yellowstone National Park. The water in these systems can be more than 200°C (430°F).

Seismically active hotspots are not the only places where geothermal energy can be found. There is a steady supply of milder heat—useful for direct heating purposes—at depths of anywhere from 10 to a few hundred feet below the surface virtually in any location on Earth. Even the ground below your own backyard or local school has enough heat to control the climate in your home or other buildings in the community. In addition, there is a vast amount of heat energy available from dry rock formations very deep below the surface (4–10 km). Using a set of emerging technologies known as Enhanced Geothermal Systems (EGS), we may be able to capture this heat for electricity production on a much larger scale than conventional technologies allow.

If these resources can be tapped, they offer enormous potential for electricity production capacity. In its first comprehensive assessment in more than 30 years, the U.S. Geological Survey (USGS) estimated that conventional geothermal sources on private and accessible public lands across 13 western states have the potential capacity to produce 8,000–73,000 MW, with a mean estimate of 33,000 MW.2 State and federal policies are likely to spur developers to tap some of this potential in the next few years. The Geothermal Energy Association estimates that 132 projects now under development around the country could provide up to 6,400 megawatts of new capacity.3 As EGS technologies improve and become competitive, even more of the largely untapped geothermal resource could be developed. The USGS study found that hot dry rock resources could provide another 345,100–727,900 MW of capacity, with a mean estimate of 517,800 MW. That means that this resource could one day supply nearly all of today’s U.S. electricity needs.4.

MORE: http://www.ucsusa.org/clean_energy/technology_and_impacts/energy_technologies/how-geothermal-energy-works.html