Geothermal Alternative Energy - A Primer

What is geothermal energy? Geothermal energy is defined as heat from the Earth. It is a clean, renewable resource that provides energy in the United States and around the world. It is considered a renewable resource because the heat emanating from the interior of the Earth is essentially limitless. The heat continuously flowing from the Earth’s interior is estimated to be equivalent to 42 million megawatts of power.(1) The interior of the Earth is expected to remain extremely hot for billions of year to come, ensuring an inexhaustible flow of heat.
What are the different ways in which geothermal energy can be used?Geothermal energy can be used for electricity production, for direct use purposes, and for home heating efficiency (through geothermal heat pumps).

Geothermal electricity: To develop electricity from geothermal resources, wells are drilled into the natural hot water or steam, known as a geothermal reservoir. The reservoir collects many meters below the groundwater table. Wells bring the geothermal liquid to the surface, where it is converted at a power plant into electricity (see below for more information about the different types of geothermal electricity production).

Direct Use: Direct use applications utilize geothermal heat without first converting it to electricity, such as for space heating and cooling, food preparation, industrial processes, etc. People have been taking advantage of direct use applications for centuries, with documentation of early uses tracing back to ancient Roman times.

Geothermal Heat Pumps (GHPs): Geothermal heat pumps are devices that take advantage of the relatively constant temperature of the Earth's interior, using it as a source and sink of heat for both heating and cooling. When cooling, heat is extracted from the space and dissipated into the Earth; when heating, heat is extracted from the Earth and pumped into the space. Geothermal heat pumps can be used anywhere on Earth, and are considered by the EPA to be one of the most efficient heating and cooling systems available.

How much energy is geothermal electricity capable of supplying to the U.S. right now? The USGS assessment (cited above), found 20,000 - 26,000 megawatts of known geothermal sites that exist throughout the United States. Of this, a recent report for the Western Governors’ Association (WGA) estimates that 13,000MW of identified resources are expected to be developable within the next 10-20- years of which 5,600 megawatts can be developed within the next five to ten years at competitive prices with the production tax credit (for details about the WGA estimate, please click the Excel file here).

That report notes: "This is a commercially achievable capacity for new generation and does not include the much larger potential of unknown, undiscovered resources." It also notes that its market and cost assumptions "do not consider advances in technology or any learning curve effects that could reduce costs or expand available production." (WGA Geothermal Task Force Report, pages 4 and 7 respectively, January 2006, available at www.westgov.org).
The total US geothermal resource is estimated to be much larger. The Energy and Geosciences Institute of the University of Utah estimates just the thermal aquifers contain 55 x 1018 Joules of energy, which would be roughly equivalent to the energy needed to provide 15.3 Billion kilowatt hours of electric power, or five times the total US electrical production in 1990. Other geothermal systems -- magmatic systems, geopressurized basins and resources available only with enhanced geothermal techniques -- are estimated to contain significantly even more energy.