Alan Marcus
Geothermal energy is a superior source of energy because it is constantly being produced. Radioactive decay of nuclei with long half lives that were imbedded in the Earth’s interior during its genesis accounts for seventy percent of the globe’s internal energy. The remainder of this energy is derived from either the residual heat left over form the Earth’s formation, gravitational forces, or meteorite impacts.
Geothermal energy is available anywhere on the planet. On average the Earth emits one sixteenth of a watt per meter squared, however this number can dramatically increase in regions near volcanoes, hot springs and fumaroles. Therefore, the uniqueness ofeach location around the world causes the Earth’s internal heat to be stored underground in many different natural structures. In some areas, the globe’s heat is stored in the rocks that form the Earth. There is a normal temperature increase, called the Normal Geothermal Gradient, of 30 degrees Celsius for every kilometer dug below the Earth’s surface. However, the precise amount of temperature increase that occurs as one’s depth increases is not a constant over the entire surface, it depends on the rock’s temperature. Therefore, in hotter sections of the planet there is Hot Dry Rock which produces an increase in temperature of forty degrees for every kilometer dug below the surface. In addition, a reserve of geothermal heat even hotter than the solid rock type is molten magma, which is melted rock.
Also, some regions of the planet house underground aquifers that use water to store large quantitiesof heat. Some areas contain vast hot water pools deep below the surface called Hot Water Reservoirs. In other places the conditions are right to produce Natural Stem Reservoirs of water vapor that is trapped under tons of earth. In addition, there are Geopressured Reservoirs that house brine saturated with natural gas that is under large amounts of pressure from the extreme weight of the overlying rocks.
People, seeing this vast supply of energy, a supply so large that about 30 megawatts of energy can be produced over 30 years by cooling one kilometer cubed of hot rock, have developed methods of extracting the Earth internal warmth. People in any location on the planet can directly use the geothermal heat for warmth. They accomplish this feat by first injecting cool water into a well to be heated by the Earth. Then, if necessary,a heat pump is used to heat the water to a high enough temperature to be usable in space heating. After the heat has been removed from it, the water is then injected back into the hot ground, and the cycle continues. This sequence of event can either be carried out in ground heat collectors or in a borehole heat exchange system. Ground heat collectors circulate water in horizontal loops at a depth of 80 to 160 centimeters. Then a heat pump raises the temperature up to a level high enough for space heating. Borehole heat exchange systems use one or two vertical loops that extend 150 meters below the surface to heat water. This system does not require a heat pump because the water temperature is high enough to use it directly for space heating. Direct use of geothermal energy is used for many applications such as space heating, air conditioning, industrial processes, drying, melting snow, and heating greenhouses, aguaculture, pools, and water.
Areas that are near volcanoes have enough geothermal warmth to be used for more than just direct heating because thesesourcestemperatures exceed the 150 degrees Celsius minimum required to produce electricity. Since several different locations produce electricityand different types of geothermal sourcesare used to produce electricity, the amount that each plant can generate varies between 100 kilowatts to 100 megawatts of electricity per year, andthere are many kinds of geothermal electric plant. Dry steam power plants are designed to harness the power stored innatural steam reserves because steam that rises directly from the geothermal sourcedrives the turbines. Also, after the steam is used and cooled it condenses into water, and it is sequentially injected back into the underground source.
Hot water reserves are appropriate for flash steam power plants. These power plantsdraw high pressured hot water that is over 360 degrees Fahrenheit from a deep underground source and transport it into a low pressure chamber. In this compartment the hot water vaporizes into steam, and this steam spins the turbines. Once the steam has served its purpose, it is cooled, it condenses back into water and then it is injected back into the water reservoir that it came from.
Binary cycle plants are ideal for hot water sources that contain water between 250 and 360 degrees Fahrenheit. In these geothermal plants once the underground water reaches the surface it is passed close to an organic fuel, such as butane, that has a lower boiling point than water. The organic fuel then transforms into the gas that turns the turbines. After it has been used and has been condensed, the organic substance is then heated by water again. Also, the cooled geothermal water is injected directly back into the source it came from.
In regions with hot dry rocks, a hot dry rock power plant is suitable. This type of electricity generating system sends pressurized water down an injection well to be heated by hot rocks deep under the ground. Then the heated pressurized water, which reaches temperatures of 200 degrees Fahrenheit or more, is brought to the surface and passed near an organic liquid, such as butane. The water is now cooled and subsequently injected back down the well to continue the cycle. The butane vaporizes, and the gas is used to turn a turbine. After the organic gas has been used to produce electricity, it condenses and is subsequently passed adjacent to more hot water in order to continue the process.
Geothermal sources of energy are heating homes and generating electricity because besides being readily available, their use has many positive side effects. Geothermal energy can enhance a country’s as well as an individual’s positionmonetarily. A nation would benefit form the extra valuable minerals, such as zinc and silica, that can be extracted from the geothermal water before it is injected back into the ground. Also, the Earth’s energy is “homegrown,” which means creating new jobs, creating a better global trading position and creating less dependence on oil producing countries. In addition, geothermal power plants would be useful to a country because they can be online for 100 percent to 90 percent of the time, while coal can only be online for 75 percent of the time and nuclear can only be online for 65 percent of the time.Geothermal energy is also especial lucrative for the United States because United States companies have signed six billion dollars worth of contracts to build plants in foreign nations in the last few years.
Geothermal energy is also the consumer’s ally because its price is either comparable or cheaper than conventional energy sources. When a costumer’s receives electricity from a large geothermal power plant their rates, which are four to eight cents per kilowatt hour, are almost competitive with conventional plants. In addition, people who heat their homes with geothermal heat save money in the long run even though installing a geothermal heating system is pricier than installing a conventional unit. Vertical loops do not require any extra capital after installation becauseit does not require energy to raise the temperature of the water to temperatures suitable for space heating. In addition, horizontal loops, which need heat pumps to raise the temperature of the circulating water up to temperatures appropriate for space heating, costs a consumer less money than conventional methods of heating. A geothermal heat pump uses four times less energy to heat a home than a conventional system, and this translates into lower energy bills.
In addition to monetary practicality, geothermal energy also produces abundant environmental benefits. A big environmental concern is the emission from fossil fuels because the increasing amount of carbon dioxide in the atmosphere causes the green house effect to reach dangerously high levels of potency, and sulfur dioxide and nitrogen oxides are causing acid rain. Geothermal power plants do not add to this problem because they release far less emissions than conventional power plants. The dirtier geothermal plants, flash and dry steam plants, produce 1,000 to 2,000 times less carbon dioxide than fossil fuel ran generators, little sulfur dioxide and no nitrogen oxides. The cleaner geothermal plants, binary and hot dry rock, release no emissions at all. The decrease in emissions translates into annually saving83.3 million barrels of fossil fuel from being burned for electricity, which would have produced 40.2 million tons of carbon dioxide, and 103.6 million barrels of fuel from being burned for direct heating uses, which would have released 49.6 million tons of carbon dioxide. Geothermal plants are also environmentally sound because they require an extremely small amount of space,400 meters squared can produce a gigawatt of energy over thirty years.
Even thoughthe Earth’s heat is readily available and there are many reasons to use it for energy, the process of obtaining this energy must not be haphazard because there are potential dangers lurking within the use of it. The brine from the geopressured reservoirs can salinate the soil, which will kill plant life. Injecting used geothermal water back into the source will solve this problem because the salt never reaches the soil. In addition, extracting large amounts of water can change the pressure of the water on the rock surrounding, and this can lead to land subsidence and increased seismic activity. To solve this dilemma the water must be injected back into the source so that the water pressure against the rock remains relatively stable. In addition, the presence of hydrogen sulfide in geothermal water can also be a problem because high dose of this gas can be lethal and after a few inhalations of this gas at a high concentration its smell, which is like rotten eggs, disappears. This drawback can also be remedied by injecting the geothermal water back into the reservoir because this process does not allow the lethal gas to escape the water. In addition, there is consternation about the noise pollution created while drilling wells, however this noise’s duration is finite.
With all of geothermal energy’s potential and availability it will surely be developed much more extensively in the near future. This source of energy will also be able to be used for a long time into the future because geothermal energy’s sources will continue to replace the energy used. In addition, it is estimated that the Earth can produce 600,000 exajoules of energy over five million years. This rate is believed to be enough energy to fulfill human energy requirements for the rest of the biosphere.
Sources
For my sources, I used the text book, Energy and the Environment and the following websites.