The earth is constantly generating naturally occurring heat. This heat is known as geothermal heat and can be used to produce electricity. Electricity produced from geothermal energy is environmentally friendly and renewable.
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How is Geothermal Energy Generated
The slow decay of radioactive elements such as uranium, thorium, and potassium produces heat deep within the earth’s core. The heat is transferred or conducted to surrounding rocks (called the mantle) causing a proportion of these to melt and become magma.
Convection within the mantle enables magma to move upwards to the earth’s surface. The resulting volcanic areas are targeted by those generating electricity from Conventional Engineered Geothermal Systems.
The temperature on the upper thin layer of the earth’s surface is nearly constant (between 10-16°C). Buildings can be heated and cooled by connecting them to this resource. A geothermal heat pump system consists of a heat pump, an air delivery system (ductwork), and a heat exchanger system of pipes buried in the thin ground near the building.
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 provide a free source of hot water. Electricity can be generated by drilling Wells into reservoirs.
Some geothermal power plants use the steam from a reservoir to power a turbine/generator, while others use the hot water to boil a working fluid that vaporizes and then turns a turbine. Hot water near the surface of the earth can be used directly for heat.
Direct use applications include heating buildings, drying crops, growing plants in greenhouses, heating water at fish farms, and several industrial processes such as pasteurizing milk.
Hot dry rock resources occur at depth of 3 to 5 miles everywhere beneath the Earth’s surface and at lesser depths in certain areas. Access to these resources involves injecting cold water down one well, circulating it through hot fractured rock, and drawing off the heated water from another well.
Many technologies have been developed to take advantage of geothermal energy.
Geothermal Electricity Generation
Generating electricity from the Geothermal (Earth’s heat).
Geothermal power plants, use steam produced from vegetables of hot water found a few miles or more below the Earth’s surface. There are three types of geothermal power plants.
- Dry steam
- Flash steam
- Binary cycle
Dry Steam Power Plant
Dry steam power plants draw hot water from underground resources of steam. The steam is directly from underground wells to the power plant, where it is directed into a turbine/generator unit.
Flash Steam Power Plant
Flash steam power plants are very common. They use geothermal reservoirs of water with temperatures greater than 182°C. In these plants, very hot water flows up, through wells in the ground under its own pressure.
As it flows upward, the pressure decreases, and some of the hot water boils into steam. The steam and liquid are separated in a surface vessel, called a steam separator.
The steam is then fed to the turbine and the turbine powers a generator. Any leftover water and condensed steam are injected back into the reservoir, making this a sustainable resource.
Binary Cycle Power Plant
Binary cycle Power Plants operate on the water at a lower temperature of about 107°C
to 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 working fluid is vaporized in a heat exchanger and used to turn a turbine. The water is then injected back into the ground to be reheated. The water And the working fluid are kept separated during the whole process so there are little or no air emissions.
Geothermal Direct Use
Producing heat directly from hot water within the earth.
Geothermal sources have been used for thousands of years, when people began using hot springs for bathing, cooking food, and loosening feathers and skin from the game.
Hot springs are still used as spas. But there are now more ways of using this geothermal resource. Present-day, in direct use systems, a well is drilled into a geothermal reservoir which provides a steady stream of hot water.
The water is brought up through the wall, and a mechanical system piping, a heat exchanger, and control Deliver the heat directly. A disposal system then either insects the cooled water underground or disposes of it on the surface.
Modern geothermal heat systems are used directly, without involving a power plant or a heat pump for a variety of applications such as space heating and cooling, food preparation, hot spring bathing and spas, agriculture, aquaculture, greenhouses, snow melting, and industrial processes.
Geothermal Heat Pumps
Using the shallow (thin) ground to heat and cool buildings.
Animals usually make underground holes for shelter which provides warmth in the winter and escapes the heat of the summer. The principle of geothermal heat pumps provides both heating and cooling solutions.
The geothermal heat pump’s heating system circulates water or other liquid to pull heat from the interior of the earth through pipes in a continuous loop.
Electricity is used to boost or cool the temperature and distribute it through a heat pump and conventional duct system. For cooling, the process has reversed the system extracts heat from the building and moves It back into the earth loop.
The loop system can be used almost everywhere in the world taking advantage of the earth’s relatively constant temperature at depths below about 10 feet to 300 feet, and can be buried conveniently on a property such as under a landscaped area, parking lot, or pond, either horizontally or vertically.
A geothermal heat pump system can also direct the heat to a water heater and unit for hot water use.