How an Enhanced Geothermal System Works
The Potential
Enhanced geothermal systems (EGS), also sometimes called engineered geothermal systems, offer great potential for dramatically expanding the use of geothermal energy. Present geothermal power generation comes from hydrothermal reservoirs, and is somewhat limited in geographic application to specific ideal places in the western U.S. This represents the 'low-hanging fruit' of geothermal energy potential.
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.
The Concept
The EGS concept is to extract heat by creating a subsurface fracture system to which water can be added through injection wells. Creating an enhanced, or engineered, geothermal system requires improving the natural permeability of rock. Rocks are permeable due to minute fractures and pore spaces between mineral grains. Injected water is heated by contact with the rock and returns to the surface through production wells, as in naturally occurring hydrothermal systems. EGS are reservoirs created to improve the economics of resources without adequate water and/or permeability.
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