According to the Department of Energy, Enhanced Geothermal Systems or EGS, “offers the chance to extend use of geothermal resources to larger areas of the western U.S., as well as into new geographic areas of the entire U.S. More than 100,000 MWe of economically viable capacity may be available in the continental United States, representing a 40-fold increase over present geothermal power generating capacity. This potential is about 10% of the overall U.S. electric capacity today, and represents a domestic energy source that is clean, reliable, and proven.”
EGS technology creates a subsurface fracture system in “hot, dry rock” into which water can be added through injection wells. Injected water is then heated by contact with the rock and can be returned to the surface via production wells. An animation describing the process can be found here and a two-page fact sheet from the Department of Energy (pdf) is also available.
The SMU Geothermal Laboratory, with support from Google.org, recently completed a heat flow map showing the potential for EGS in the continental U.S. using Google Earth. A 3 minute video and animation describing EGS is also available.