Monday, May 21, 2007

All About Geothermal Energy - Basics

All About Geothermal Energy - Basics

***What is geothermal energy?
***What are the different ways in which geothermal energy can be used?
***What more can you tell me about geothermal electric power plants?
***What is a baseload resource?
***What is “availability factor” and “capacity factor”?
***Where can I find more detailed information about geothermal energy?

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 ... .

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 ... .

***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 ... .

***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 ... .

What more can you tell me about geothermal electric power plants?
There are four widely used types of geothermal power plants, and three types that are more experimental at this time.

*** Flash Power Plant
Geothermal steam is separated in a surface vessel (steam separator) and delivered to the turbine, and the turbine powers a generator.

***Dry Steam Power Plant
Steam directly from the geothermal reservoir runs the turbines that power the generator, and no separation is necessary because wells only produce steam. The image below is a more simplified version than the image above.

***Binary Power Plant
Recent advances in geothermal technology have made possible the economic production of electricity from lower temperature geothermal resources, at 100o C (212o F) to 150o C (302 o F). Known as binary geothermal plants, these facilities reduce geothermal energy’s already low emission rate to near zero.

In the binary process, the geothermal water heats another liquid, such as isobutane, that boils at a lower temperature than water. The two liquids are kept completely separate through the use of a heat exchanger used to transfer the heat energy from the geothermal water to the “working-fluid." The secondary fluid vaporizes into gaseous vapor and (like steam) the force of the expanding vapor turns the turbines that power the generators.

***Flash/Binary Combined Cycle
This type of plant, which uses a combination of flash and binary technology, has been used effectively to take advantage of the benefits of both technologies. In this type of plant, the flashed steam is first converted to electricity with a backpressure steam turbine, and the low-pressure steam exiting the backpressure turbine is condensed in a binary system


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