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| Use of Geothermal Energy |
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The three main uses of geothermal energy are:
- Direct Use
- Electricity Generation
- Heat Pumps
Direct Use
Geothermal reservoirs of hot water, which are found a couple of miles or more beneath the Earth's surface, can also be used to provide heat directly. This is called the direct use of geothermal energy. The direct use of hot water as an energy source has been happening since ancient times, when people began using hot springs for bathing, cooking food, and loosening feathers and skin from game. Today, many hot springs are still used for bathing, and many people believe the hot, mineral-rich waters have natural healing powers.
After bathing, the most common direct use of geothermal energy is for heating buildings through district heating systems. Hot water near the earth's surface can be piped directly into buildings and industries for heat. Its current uses include heating buildings (either individually or whole towns), raising plants in greenhouses, drying crops, heating water at fish farms, and several industrial processes, such as pasteurizing milk.
In modern direct-use systems, a well is drilled into a geothermal reservoir to provide a steady stream of hot water. The water is brought up through the well, and a mechanical system - piping, a heat exchanger, and controls - delivers the heat directly for its intended use. A disposal system then either injects the cooled water underground or disposes of it on the surface.
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Geothermal Power Plant:
Geothermal power plants use hydrothermal resources which have two common ingredients: water (hydro) and heat (thermal). Geothermal plants require high temperature (300 to 700 degrees Fahrenheit) hydrothermal resources that may come from either dry steam wells or hot water wells. We can use these resources by drilling wells into the earth and piping the steam or hot water to the surface. Geothermal wells are one to two miles deep. Most power plants need steam to generate electricity. The steam rotates a turbine that activates a generator, which produces electricity. Geothermal power plants, use steam produced from reservoirs of hot water found a couple of miles or more below the Earth's surface.
There are three basic types of geothermal power plants:
- Dry steam plants - use steam piped directly from a geothermal reservoir to turn the generator turbines.
- Flash steam plants - take high-pressure hot water from deep inside the earth and convert it to steam to drive the generator turbines. When the steam cools, it condenses to water and is injected back into the ground to be used over and over again, making this a sustainable resource. Most geothermal power plants are flash plants.
- Binary power plants - Binary cycle power plants operate on water at lower temperatures of about 225°–360°F (107°–182°C). These plants use the heat from the hot water to boil a working fluid, usually an organic compound with a low boiling point. The heat causes the second liquid to turn to steam which is used to drive a generator turbine.
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Geothermal Heat Pump
The shallow ground, the upper 10 feet of the Earth, maintains a nearly constant temperature between 50° and 60°F (10°–16°C). Like a cave, this ground temperature is warmer than the air above it in the winter and cooler than the air in the summer. Geothermal heat pumps take advantage of this resource to heat and cool buildings.
Geothermal heat pump systems consist of basically three parts: the ground heat exchanger, the heat pump unit, and the air delivery system (ductwork). The heat exchanger is basically a system of pipes called a loop, which is buried in the shallow ground near the building. A fluid (usually water or a mixture of water and antifreeze) circulates through the pipes to absorb or relinquish heat within the ground.
In the winter, the heat pump removes heat from the heat exchanger and pumps it into the indoor air delivery system. In the summer, the process is reversed, and the heat pump moves heat from the indoor air into the heat exchanger. The heat removed from the indoor air during the summer can also be used to heat water, providing a free source of hot water.
Geothermal heat pumps use much less energy than conventional heating systems, since they draw heat from the ground. They are also more efficient when cooling your home. Not only does this save energy and money, it reduces air pollution.
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