Geothermal Energy: A Brief History of an Age Old Energy Source
Posted: Wednesday, April 06, 2005
by RKlass
Klass Photography
Quite literally, “Geo" means of the Earth, and “Thermal" comes from the Greek “Therine", meaning heat. (http://geothermal.id.doe.gov/what-is.shtml) All geothermal energy uses exploit the heat naturally contained within the Earth to perform some task. There are two basic types of geothermal energy, high temperature and low temperature. The high temperature geothermal areas have temperatures that exceed 150 degrees Centigrade. These are the most useful for electricity generation on the industrial level. (http://geothermal.id.doe.gov/what-is.shtml)
Geothermal energy is a natural part of the energy flow within the Earth’s depths. Generally speaking, the further down one drills, the hotter the temperatures. Most of the commercial-grade production geothermal energy is harvested along localized “geothermal systems", where the heat flow is near enough to the surface that hot water or steam is able to rise either to the surface, or to depths that we can reach by drilling. Many of these regions occur within the “ring of fire", a ring of geothermal sites. (http://geothermal.id.doe.gov/what-is.shtml, Ristinen, Kraushaar 158-160)
There are three basic types of geothermal electricity plants. Selection of one type or another is based mostly on the geothermal resources readily available. (http://geothermal.id.doe.gov/what-is.shtml)
In areas where steam can be directly harvested, a Dry Steam generation plant is often used. This is the simplest and most direct method of electrical generation from a geothermal resource. It uses rising steam from a well to push a turbine. The turbine in turn generates electricity. After the steam has pushed the turbine, it is then sent through a series of cooling units that allow air and water vapor to escape into the atmosphere, and return cooled water back to the geothermal reservoir. (http://geothermal.id.doe.gov/what-is.shtml)
The most common type of electrical generation is done through Flash Steam plants, where hot liquid (360+ degrees Fahrenheit) is drawn from a geothermal reservoir. The liquid is pumped at high pressure, and then allowed to suddenly drop pressure, resulting in the conversion of some of the water into steam that can generate electricity. This steam turns a turbine, much like that in a Dry Steam plant, and the remaining water and condensed vapor are returned to the well. (http://geothermal.id.doe.gov/what-is.shtml)
A third alternative for electricity generation is the Binary Cycle plant, where a working fluid is heated with the extracted hot liquid. This is useful in areas where the temperature might not be appropriate for a Flash Steam plant. By using a working liquid with a lower boiling temperature than water, more steam is produced to generate power. In addition, the hot liquid from the Earth never actually comes in contact with the turbine, as it’s heat is simply transferred through a heat exchange unit. These facilities can operate at temperatures as low as 225 degrees Fahrenheit. (http://geothermal.id.doe.gov/what-is.shtml)
Electrical generation is not the only use for geothermal energy. Heat Pump technology has brought geothermal energy into the home, as an inexpensive source of heating and cooling. These heat pumps don’t require intensely hot reservoirs, or dry steam, but rather run much like a refrigerator with pipes extending either out or down in a loop below the frost line. This technology is expandable to much of the world, and is available right in one’s backyard. (http://geothermal.marin.org/pwrheat.html#Q2)
There are several other direct uses of geothermal energy. Extracted hot water can be used in both agriculture to extend the growing season, and aquaculture, to shorten the time to grow fish and shrimp. Industrial uses like pasteurizing milk, and washing wool have been around for decades. A town in Oregon has even begun using hot geothermal water to keep their sidewalks and roads from freezing. (http://geothermal.marin.org/pwrheat.html#Q2)
Geothermal energy has enjoyed a wide array of past uses. It has been documented as an energy source for over 10,000 years. The Romans used it to heat buildings and treat eye and skin diseases. The Native Americans have used the hot waters to cook and for medical reasons, and the France has used it to heat over 200,000 homes. (http://geothermal.marin.org/pwrheat.html#Q2)
Geothermal energy uses range from localized heating and baths, to large-scale energy production. There is a varying amount of infrastructure based upon the use for geothermal energy to be efficiently harvested. According to the multi-disciplinary engineering group, Mott MacDonald, radial heating can be n efficient source of energy that is built into new homes and buildings. In terms of electrical generation, much of the distribution infrastructure exists already, the only piece remaining are the production wells and turbine used to generate the electricity. The problem is that the geothermal resources are often located in inaccessible areas, or areas that are too far from the main power grid to be efficient in electrical production. (MacDonald 5, http://geothermal.marin.org/pwrheat.html#Q2)
Worldwide energy production from geothermal reservoirs has grown to approximately 7,000 MW, with 2,700 of those being produced in the U.S. This represents a very small percentage of the overall worldwide electrical production, but geothermal energy is rapidly expanding, some predict almost 500% gains. Of course, many of the uses have nothing to do with electricity, and unlike electrical production, heating and cooling are not limited by the availability of high temperature wells. (http://geothermal.marin.org/pwrheat.html#Q2)
Geothermal energy is a 10,000 year old source that has a wide-array of uses. It will continue to be a big player in the world’s hunger for energy. As the efficiency and uses continue to grow, so too will the technology that helps provide the end user with clean reliable, and if used in a sustainable manor, renewable energy.
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Top-level comments on this article: (1 total)Awesome article! Gonna get me an A+ in science! ...
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