Geothermal energy
Geothermal energy is produced by the heat of the earth and is often associated with volcanic and seismically active regions. It originates from the original formation of the planet, from radioactive decay of minerals, and from solar energy absorbed at the surface.
Was then used for bathing since Paleolithic times and for space heating since ancient Roman times, but is now better known for generating electricity.
Worldwide, about 10,715 megawatts (MW) of geothermal power is running in 24 countries. An additional 28 gigawatts of direct geothermal heating capacity is installed for district heating, space heating, spas, industrial processes, desalination and agricultural applications
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[edit] Understanding Geothermal Energy
Geothermal energy means energy or power extracted from beneath the earth. The energy inside the earth was formed by the decay of minerals and forests several years ago. Traditionally, it was used for bathing and heating purposes but today it is also used for generating electricity. Geothermal energy is called renewable source of energy because heat is continuously produced inside the earth.
This heat is brought to the near-surface by thermal conduction and by intrusion into the earth's crust of molten magma originating from great depth. As groundwater is heated, geothermal energy is produced in the form of hot water and steam.
Geothermal energy is produced inside the earth's surface. The earth's layer consists of innermost layer called Iron Core which itself has two layers: solid iron core and an outer core made of hard rock, called magma, mantle which surrounds the core and the outermost layer called crust which forms oceans and continents. When magma comes close to the earth's surface i.e. crust it heats up the ground water which gets trapped in porous rocks. They may also flow along faults and fractured rock surfaces. Now these hydrothermal resources have 2 ingredients: water (Hydro) and heat (thermal). When these hydrothermal resources occur naturally these are called Geothermal reservoirs. Various tools and techniques are used nowadays to detect geothermal reservoirs.
[edit] Geothermal Energy Existence
Geothermal energy exists in the form of:
- Volcanoes
- Hot Springs
- Geysers
[edit] About Geothermal Energy
Geothermal energy is clean and sustainable and environment friendly. That is, it is a domestic energy resource with cost, reliability and environmental advantages over conventional energy sources. It contributes both to energy supply, with electrical power generation and direct-heat uses.
- It may be noted that the so called 'ring of fire' of the Earth envelopes the Pacific rim.
- Though there are over 300 hot springs sites in India, this form of energy is yet to be tapped.
- In USA, California generates highest amount of electricity through Geothermal energy.
[edit] Tapping Geothermal energy
There are different methods to using Nature's Geothermal energy productively.
- Geothermal Electricity Production
- Geothermal Direct Use
- Geothermal heat pump
[edit] Geothermal Electricity Production
Most power plants need steam to generate electricity. The steam rotates a turbine that activates a generator, which produces electricity. Many power plants still use fossil fuels to boil water for steam. Geothermal power plants, however, use steam produced from reservoirs of hot water found a couple of miles or more below the Earth's surface. There are three types of geothermal power plants: dry steam, flash steam, and binary cycle.
Dry steam power plants draw from underground resources of steam. The steam is piped directly from underground wells to the power plant, where it is directed into a turbine/generator unit. There are only two known underground resources of steam in the United States: The Geysers in northern California and Yellowstone National Park in Wyoming, where there's a well-known geyser called Old Faithful. Since Yellowstone is protected from development, the only dry steam plants in the country are at The Geysers.
Flash steam power plants are the most common. They use geothermal reservoirs of water with temperatures greater than 360°F (182°C). This 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 is then separated from the water and used to power a turbine/generator. Any leftover water and condensed steam are injected back into the reservoir, making this a sustainable resource.
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 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.
Small-scale geothermal power plants (under 5 megawatts) have the potential for widespread application in rural areas, possibly even as distributed energy resources. Distributed energy resources refer to a variety of small, modular power-generating technologies that can be combined to improve the operation of the electricity delivery system.
In the United States, most geothermal reservoirs are located in the western states, Alaska, and Hawaii.
[edit] Geothermal Direct Use
When a person takes a hot bath, the heat from the water will usually warm up the entire bathroom. 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.
Geothermal direct use dates back thousands of years, when people began using hot springs for bathing, cooking food, and loosening feathers and skin from game. Today, hot springs are still used as spas. But there are now more sophisticated ways of using this geothermal resource.
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.
Geothermal hot water can be used for many applications that require 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. With some applications, researchers are exploring ways to effectively use the geothermal fluid for generating electricity as well.
In the United States, most geothermal reservoirs are located in the western states, Alaska, and Hawaii.
[edit] Geothermal Heat Pumps
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.
The West Philadelphia Enterprise Center uses a geothermal heat pump system for more than 31,000 square feet of space. Credit: Geothermal Heat Pump Consortium
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.
All areas of the United States have nearly constant shallow-ground temperatures, which are suitable for geothermal heat pumps.
[edit] Advantages Of Geothermal Energy
- For generation of electricity, hot water is brought from the underground reservoir to the surface through production wells, and is flashed to steam in special vessels by release of pressure. The steam is separated from the liquid and fed to a turbine engine, which turns a generator. Spent geothermal fluid is injected back into peripheral parts of the reservoir to help maintain reservoir pressure. In the absence of steam, heat from hot water is extracted through a secondary fluid and the high pressure vapour from the secondary fluid is utilized to run the turbine.
- If the reservoir is to be used for direct-heat application, the geothermal water is usually fed to a heat exchanger and the heat thus extracted is used for home heating, greenhouse, vegetable drying and a wide variety of other small scale industries. Hot water at temperatures less than 120 o C can be used for this purpose. Further, the spent hot water, after generating electricity can also be used for direct application.
- As a result of today's geothermal production, consumption of exhaustible fossil fuels is offset, along with the release of acid Rain and greenhouse gases that are caused by fossil-fuel use. Systems for use of geothermal energy have proven to be extremely reliable and flexible. Geothermal electric power plants are on line 97% of the time, whereas nuclear plants average only 65% and coal plants only 75% on-line time. Geothermal plants are modular, and can be installed in increments as needed. Because they are modular, then can be transported conveniently to any site. Both baseline and peaking power can be generated. Construction time can be as little as 6 months for plants in the range 0.5 to 10 MW and as little as 2 years for clusters of plants totalling 250 MW or more.
- The competing goals of increased energy production for worldwide social development and of mitigating release of atmosphere-polluting gases are not compatible using today's fuel mix, which relies heavily on coal and petroleum. Development of geothermal energy has a large net positive impact on the environment compared with development of conventional energy sources. Geothermal power plants have sulphur-emissions rates that average only a few percent of those from fossil-fuel alternatives. The newest generation of geothermal power plants emits only ~135 gm of carbon (as carbon dioxide) per megawatt-hour (MW-hr) of electricity generated. This figure compares with 128 kg /MW-hr of carbon for a plant operating on natural gas (methane) and 225 kg/MW-hr of carbon for a plant using bituminous coal. Nitrogen oxide emissions are much lower in geothermal power plants than in fossil power plants. Nitrogen-oxides combine with hydrocarbon vapours in the atmosphere to produce ground-level ozone, a gas that causes adverse health effects and crop losses as well as smog. There are other environmental advantages to geothermal energy. Geothermal power plants require very little land, taking up only a fraction of that needed by other energy sources. Thus emission of CO2 and SO2 by geothermal power plants is far less compared with conventional fossil fuel based power plants
[edit] Future Of Geothermal Energy
The future of Geothermal energy depends on three factors: it's demand, supply and it's competitiveness among other renewable resources in terms of cost, availability, reliability etc.. Demand for geothermal energy is going to increase and increase with the increase in the population and extinction of other non-renewable sources. Moreover, today government also support the resources which are cleaner and do not spoil the environment. Supply of geothermal energy is limited and confined to certain areas only. The entire resource of geothermal energy is fairly bigger than that of coal, oil and gas. Geothermal energy can be made more widely available if the methods and technologies used to extract it are improved. Geothermal energy is still not explored fully. Several miles below the earth surface is hot, dry rock being heated by the molten magma directly below it.
