Some visible features of geothermal energy are volcanoes, hot springs and geysers. But most geothermal energy is deep underground, often with no clues above ground as to what exists below ground. It is a clean, sustainable source of energy. Following are some ways we can make geothermal energy work for us:
Using Geothermal Energy to Generate Electricity
There are several hot spots in the USA where geothermal energy is closer to the surface, but as a general rule "for every 328 feet below ground the temperature increases 5.4 degrees Fahrenheit." Geothermal temperatures of 300 to 700 degrees Fahrenheit are required to generate electricity. Therefore geothermal wells will have to be about 3 to 7.5 miles deep in most areas of the USA in order to be used for generating electricity.
The US Department of Energy says that "engineers are developing technologies that will allow us to probe more than 10 miles below the Earth's surface in search of geothermal energy." Chevron's "Jack 2" oil well, drilled in the Gulf of Mexico about 270 miles southwest of New Orleans, was drilled to "a total depth of 28,175 feet" or about 5.3 miles. So it is theoretically possible to use geothermal energy to generate electricity nearly anywhere!
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The
dry steam power plant is the oldest type of geothermal power plant and
is still very effective. Water is pumped into the injection well.
Deep underground the water flows through rock, etc. and turns to steam.
The steam flows up through the production well and through the turbine, which is
connected to a generator to produce electricity. After the steam has gone
through the turbine it is condensed back to water and pumped back down through
the injection well.
In a flash steam power plant hot water under high pressure, instead of steam, comes up the production well, then is sprayed into a flash tank. This causes the water to vaporize. It is this vapor (steam) that drives the turbine. After the steam has gone through the turbine it is condensed back to water again and pumped back down the injection well.
In a binary-cycle power plant the hot water from the production well flows through a heat exchanger. On the other side of the heat exchanger another fluid (usually with a lower boiling point) is vaporized and drives the turbine.
A recent announcement indicates that the use of geothermal power now under development in the USA will roughly double U.S. capacity. A 2006 MIT study concluded there is potential to supply the world's energy needs for several thousand years with geothermal energy. As with any technology, there are some disadvantages to geothermal energy--including potential lawsuits based on opinions as to the cause of earthquakes in areas where geothermal energy is being utilized. If this technology is perceived as being potentially dangerous to life and property, its value maybe significantly reduced regardless how economical it is. Remember the adoption of technology is dependent on: 1) the technology itself; 2) the cost to develop and use the technology; and, 3) the value society places on the technology.
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Direct Use of Geothermal Energy
Lower temperature water (68 to 300 degrees Fahrenheit) is widely used in the USA to heat homes, offices, commercial greenhouses, fish farms, food processing facilities, gold mining operations and a wide variety of other applications. This direct use of geothermal energy can save as much as 80% over fossil fuels.
Geothermal Heat Pumps
While temperatures above ground change a lot, temperatures about 10 feet below the Earth's surface hold nearly constant between 50 and 60 degrees Fahrenheit. Geothermal heat pumps use the Earth's constant temperatures to heat and cool buildings. They transfer heat from the ground into buildings in winter and reverse the process in the summer. According to the U.S. Environmental Protection Agency (EPA), geothermal heat pumps are the most energy-efficient, environmentally clean, and cost-effective systems for temperature control.
Note: See this article online, with
hyperlinked references, at: http://www.friendlyinnovators.com/mn/20080315.htm
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Oil Shale
Al Leedahl
Engineering Design Concepts
www.leedahl.com/engineering/design/concepts.htm