Geothermal Energy
What is Geothermal Energy
"Geothermal" comes from the Greek words geo (earth) and thermal (heat). So, geothermal means earth heat. Our earth's interior, like the sun, provides heat energy from nature. This heat, geothermal energy, yields warmth and power that we can use without polluting the environment.
Internationally, geothermal sources are prevalent in the U.S., Iceland, New Zealand, Italy, the Philippines, Indonesia, Mexico, and Central and South America.
The heat from the earth's core continuously flows outward. It conducts to the surrounding layer of rock, the mantle. When temperatures and pressure become high enough, some mantle rock melts, becoming magma. Because the magma is lighter and less dense than the surrounding rock, the magma rises, moving slowly up toward the earth's crust, carrying the heat from below.
Sometimes the hot magma reaches all the way to the surface, where it is known as lava. But most often the magma remains below earth's crust, heating nearby rock and water (rainwater that has seeped deep into the earth). Some of this hot geothermal water travels back up through faults and cracks and reaches the earth's surface as hot springs or geysers, but most of it stays deep underground, trapped in cracks and porous rock.
Geothermal energy can be harvested. We can drill wells into the geothermal reservoirs to bring the hot water to the surface. Geologists, geochemists, drillers and engineers do a lot of exploring and testing to locate underground areas that contain this geothermal water. Then, once the hot water and/or steam travels up the wells to the surface, they can be used to generate electricity in geothermal power plants or for energy saving non-electrical purposes.
In geothermal power plants steam, heat or hot water from geothermal reservoirs provides the force that spins the turbine generators and produces electricity. The used geothermal water is then returned down an injection well into the reservoir to be reheated, to maintain pressure, and to sustain the reservoir.
There are three types of power plants which harness geothermal power:
Dry Steam Power Plants
Steam plants use hydrothermal fluids that are primarily steam. The steam goes directly to a turbine, which drives a generator that produces electricity. The steam eliminates the need to burn fossil fuels to run the turbine. This is the oldest type of geothermal power plant. Steam technology is used today at The Geysers in northern California, the world's largest single source of geothermal power.
Flash Steam Power Plants
A geothermal reservoir that produces mostly hot water is called a "hot water reservoir" and is used in a "flash" power plant. Hydrothermal fluids above 182°C can be used in flash plants to make electricity. Fluid is sprayed into a tank held at a much lower pressure than the fluid, causing some of the fluid to rapidly vaporize, or "flash." The vapour then drives a turbine, which drives a generator. If any liquid remains in the tank, it can be flashed again in a second tank to extract even more energy.
Binary-Cycle Power Plants
Most geothermal areas contain moderate-temperature water. These temperatures are not hot enough to flash enough steam but can still be used to produce electricity. In a binary system the geothermal water is passed through a heat exchanger, where its heat is transferred into a second (binary) liquid. This binary liquid boils at lower temperatures than water. Heat from the geothermal fluid causes the secondary fluid to flash to vapour, which then drives the turbines. The vapour is then condensed to a liquid and is reused repeatedly. Because this is a closed-loop system, virtually nothing is emitted to the atmosphere. Moderate-temperature water is by far the more common geothermal resource, and most geothermal power plants in the future will be binary-cycle plants.
What Are The Advantages of Geothermal Energy?
- Geothermal energy is clean. Geothermal power plants do not have to burn fuels to manufacture steam to turn the turbines. Generating electricity with geothermal energy helps to conserve non-renewable fossil fuels, and by decreasing the use of these fuels, we reduce emissions that harm our atmosphere.
- Geothermal installations don't require damming of rivers or harvesting of forests and there are no mine shafts, tunnels, open pits, waste heaps or oil spills.
- Geothermal power plants are designed to run 24 hours a day, all year. A geothermal power plant sits right on top of its fuel source.
- Geothermal energy produces minimal air emissions and offsets the high air emissions of fossil fuel-fired power plants. Emissions of nitrous oxide, hydrogen sulphide, sulphur dioxide, particulate matter, and carbon dioxide are extremely low, especially when compared to fossil fuel emissions.
- Geothermal energy conserves freshwater resources. Geothermal plants use 5 gallons of freshwater per megawatt hour. This compares with 361 gallons per megawatt hour used by natural gas facilities.
How is Geothermal Power Used?
Heated water from geothermal resources can be circulated by pipes through a home or building in order to provide heat. In Iceland, for example, the entire city of Reykjavik is heated by geothermal energy. Hot water is useful in many other commercial and industrial applications. For example a dry cleaning store may use geothermal hot water for its processes if located in a geothermal area.
Geothermal sources are also used for health reasons. The warm, healing waters are used to soothe aching muscles in hot springs and health spas. One such example is the Blue Lagoon in Iceland. The temperature in the swimming area averages about 40°C (104°F), and the soothing, mineral-rich water is rumoured to have curative powers (such as curing eye and skin diseases). The lagoon is man-made. It was created by run-off from the Svartsengi power plant, which pumps up the geothermal heated water from a full mile below the surface. After being used to generate both heat and electricity, the excess (which is absolutely clean) is ejected into the lagoon.
Geothermal heat pumps (GHP)
With these heat pumps (GHP's), we take advantage of stable earth temperature - about 45 - 58°F just a few feet below the surface to help keep our indoor temperatures comfortable. GHP's circulate water through pipes buried in a continuous loop next to a building. Depending on the weather, the system is used for heating or cooling.
Aquaculture (fish farming) is an important uses of geothermal energy in the agribusiness industry.
One disadvantage is that there are not many places where you can build a geothermal power station. You need hot rocks of a suitable type, at a depth where we can drill down to them. The type of rock above is also important, it must be of a type that we can easily drill through. Hazardous gases and minerals may also come up from underground, and can be difficult to safely dispose of.
Geothermal energy is an example of how humankind are diversifying into finding different, more sustainable, and more environmentally considerate ways to meet our needs.
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[19/04/2024 12:17:47]
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