Geothermal is Often Referred as The Energy from The Earth
The word "geothermal" is derived from the Greek geo (earth) and therme (heat). The earth has a wide variation of temperatures and the deeper into the earth one goes, the higher the temperature as you near the core.
Geothermal Energy Locations
There are geothermal reservoirs that are naturally located in areas of the earth have heat flow that is closer to the surface. In these areas steam or hot water can actually escape from the earth's crust. One example is in Yellowstone National Park and the Yellowstone region located in Idaho, Montana and Wyoming. The hot geysers that regularly shoot into the air are huge tourist attractions.
Other areas are the Imperial Valley in Southern California and the Geysers Region in Northern California. Perhaps it's not surprising that areas where the heat trapped inside the earth can escape are also regions known for earthquake and volcanic activity. Could it be the fissures in the earth that allow heat to escape from the earth's core may be related to the same fault lines that shift on occasion to cause earthquakes?
One of the most amazing discoveries of thermal reservoir was possible only due to improved imaging equipment able to locate bodies of water trapped deep beneath the earth's surface. The Sahara Desert is known as one of the driest and hottest places on the planet.
Although we know a shift in the earth's axis every 20,000 years or so turns the Sahara into an oasis for a time, we have assumed during dry periods of history the water had disappeared. Now we understand much of the arid Sahara has underground geothermal reservoirs.
In a few areas the water naturally escapes to the surface and is responsible for the infrequent areas of oasis in the desert. This has opened new areas that could potentially use geothermal energy to irrigate and provide cropland where it did not previously exist.
The water trapped beneath the desert is at least 10,000 years old and should it be accessed and used it would not be replaced until the next distant shift of the earth's axis turns the Sahara into a green lush area for a few thousand years.
Geothermal Energy Plants
The first geothermal energy plants built were dry steam power plants. These power generation plants utilize the steam from a natural geothermal reservoir to power turbine generators and produce electricity. This type of power generation was established in Geysers region (Northern California).
Steam produced beneath the earth in the geothermal reservoir was piped directly into a turbine. The power was routed directly into a generator unit while a condenser cooled the steam and allowed the water to be collected and funneled into a cooling tower. Air and water vapor was released from the top of the cooling tower while most of the water captured from the steam was returned to the earth through a drainpipe.
Today the more common method of creating geothermal energy is through the use of flash steam power plants. Water at temperatures greater than 360 degrees is pumped from the earth's depths under pressure.
As the water reaches the generating equipment the pressure is rapidly reduced. Some of the water quickly turns into steam (flash) and used to power the turbine generator while the water that separates in the cooling process is returned to the reservoir.
Binary Cycle Plant
In dry steam and flash methods, the water or steam comes into contact with the turbine. In the binary cycle power plant the water is used to heat another fluid which is referred to as the "working fluid". The heat of the water from the geothermal reservoir vaporized the working fluid and thus powers the turbine.
The water and the working fluid have separating closed circulating systems and do not come into contact. Binary cycle plants are able to create power with waters at lower temperatures as the working fluids used have lower boiling points than water.
These binary plants do not produce emissions in the air and are considered to be environmentally responsible power plants.
Where Does Geothermal Energy Come From?
The earth's core is composed of two layers. The central core is of iron and an outer core is composed magma, which is rock so hot it has melted. The upper 10 or so feet of the earth's surface has an almost constant temperature. It is this temperature that makes an earth berm or underground dwelling inexpensive to heat and cool.
If you tour a cave at a national park you may enter the cave on a hot summer day and quickly find yourself chilled after a few minutes underground. The temperature is constant at 50-60 degrees. It's that same insulating effect that makes the basement of your home easier to heat and cool than the structure above it.
As you go miles under the earth's crust you find hot rock and warm springs. Going deeper into the earth leads us to higher temperatures and to molten lava (magma). We do not have the technology to capture the power contained in the magma but we have developed the ability to use some of the geothermal energy naturally occurring beneath our feet.
This heat escapes in some locations as steam which identifies a geothermal reservoir where extremely hot rocks are located closer to the surface. It's possible to capture that steam but also possible to pump cold water down to those hot rock beds to create hot water and steam and provide electrical power.
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