Geothermal Energy
Geothermal energy is a renewable and sustainable power source that comes from the heat generated by the earth. "Geo" means earth and "thermal" means heat. The Earth has four main layers, as is shown in the first picture below (Geothermal Education Office). Each layer has different compositions, functions and temperatures, as is illustrated in the second figure below (Geothermal Education office). The heat of the earth radiates outward and sometimes melts the mantle at temperatures of 300° F- 700°F. When the mantle becomes melted magma is created. Sometimes magma reaches the surface of the crust and is then called lava. The magma reaches the crust and heats nearby rocks and water. The heated water can reach the surface and form hot springs and geysers.
Geothermal energy creates less environmental pollution, is renewable and sustainable, avoids importing energy resources, benefits remote areas, adds to energy source diversity, creates less waste disposal and has a long life span.
Geothermal energy is produced by drilling a well into the ground where thermal activity is occuring. Once a well has been identified and a well head attached, the steam is separated from the water, the water is diverted through a turbine engine which turns a generator. Usually the water is injected back into the ground to resupply the geothermal source. The pictures below illustrate how the set-up of a geothermal site collecting energy looks like (EIA kids site) and (Geothermal Education Office).
Locations of Geothermal Energy Use
Geothermal energy is generally harnessed in areas of volcanic activity. The Pacific Ring is a prime spot for the harnessing of geothermal activity because it is an area where the tectonic processes are always taking place. The picture below shows the general location of the Ring of Fire (EIA kids site).
The USGS defines tectonic processes as a series of actions and changes relating to, causing, or resulting from structural deformation of the earth's crust. [Adapted from American Heritage Dic. of the English Language, 4th ed.] This picture illustrates the term tectonic processes (Geothermal Education Office).
Geothermal power plants are used all over the world, but can not be located just anywhere. They are located where tectonic plates collide and generate volcanic activity. The map below shows where plate boundaries are located and the following map illustrates the general location of geothermal power plants being used around the world.
The table below shows MW of Geothermal Energy in different countries around the world. For more information on the countries below, click on the name. For further information on other geothermal plants throughout the world visit this website, Selected Geothermal Power Plants (ORMAT GreEnergy Power).
Zunil, Guatemala 24 MW
São Miguel, Açores Islands, Portugal 14 MW
Leyte, The Philippines 125 MW
Olkaria, Kenya 100 MW
Nagqu, Tibet, P.R. of China 1.0 MW
Reykjanes Peninsula, Iceland 9.1 MW
The table below shows the countries that are using Geothermal Energy and the number of Megawatts that their power plants produce.
Producing countries in 1999 Megawatts
United States
2,850
Philippines 1,848
Italy 768.5
Mexico 743
Indonesia 589.5
Japan 530
New Zealand 345
Costa Rica 120
Iceland 140
El Salvador 105
Nicaragua 70
Kenya 45
China 32
Turkey 21
Russia 11
Portugal (Azores) 11
Guatemala 5
French West Indies (Guadeloupe) 4
Taiwan 3
Thailand 0.3
Zambia 0.2
Within the United States, the West (and specifically California) are major producers of Geothermal Energy. Each state has different regulations on geothermal energy. According to the Bureau of Land Management in California, , "The Geothermal Steam Act of 1970, as amended, (84 Stat, 1566; 30 U.S.C. 1001-1025) provides the Secretary of the Interior with the authority to lease public lands and other federal lands, including National Forest lands, for geothermal exploration and development in an environmentally sound manner. This authority has been delegated to the Bureau of Land Management (BLM). BLM implements the Act through the regulations contained in 43 Code of Federal Regulations (CFR) Part 3200." The table below shows the amount of money, leases and megawatts produced in California during the Fiscal Year 2000 (October 1, 1999-September 30, 2000).
Types of Geothermal Power Plants
Geothermal technology has three varied ways of taking geothermal energy and turning it in to useable energy for humans to use. The most common systems are steam and binary power plants. There are two different types of steam power plants: dry steam and flash steam. The following definitions and pictures are from Geothermal Technologies Program or Godfrey Boyle in Renewable Energy: Power for a Sustainable Future.
Dry Steam Power Plants or Hot Dry Rock Power Plants
Vapor dominated resources where steam production is not contaminated
Steam is 1050°F - 1220° F
Steam passes through turbine
Steam expands
Blades and shaft rotate and generate power
Cooling towers generate waste heat
Most common and most commercially attractive (Godfrey Boyle)
Used in areas where geysers do not exist
Need water to inject down into rock
Well is deep
Takes more time to inject water in well
Binary cycle power plant
Uses lower-temperatures, but much more common, hot water resources (100° F – 300° F).
Hot water is passed through a heat exchanger in conjunction with a secondary (hence, "binary plant") fluid with a lower boiling point (usually a hydrocarbon such as isobutane or isopentane).
Secondary fluid vaporizes, which turns the turbines, which drive the generators.
Remaining secondary fluid is simply recycled through the heat exchanger.
Geothermal fluid is condensed and returned to the reservoir.
Binary plants use a self-contained cycle, nothing is emitted.
Energy produced by binary plants currently costs about 5 to 8 cents per kWh.
Lower-temperature reservoirs are far more common, which makes binary plants more prevalent.
Flash or Steam plants
Use very hot (more than 300° F) steam and hot water resources (as found at The Geysers plants in northern California)
Steam either comes directly from the resource, or the very hot, high-pressure water is depressurized ("flashed") to produce steam.
Steam then turns turbines, which drive generators that generate electricity.
Only significant emission from these plants is steam (water vapor).
Minute amounts of carbon dioxide, nitric oxide, and sulfur are emitted, but almost 50 times less than at traditional, fossil-fuel power plants.
Energy produced this way currently costs about 4-6 cents per kWh.
Introduction
ReplyDeleteDeep inside the Earth lies the top layer of the mantle consisting of hot liquid rock called magma. Underground, water can be heated up to boiling temperatures and turn into steam through the heat emitted by these rocks. Harnessing the thermal energy fomr hot water and steam, we can produce electricity through environmentally-friendly means.
What is Geothermal Energy?
The word "geothermal" means "Earth" plus "heat". Most of the geothermal energy inside the Earth that we use is in the form of subterranean reservoirs of water. A number of technologies have developed that has allowed us to take advantage of this heat.
How Geothermal Plants Work
All geothermal plants work by producing steam to turn a turbine and generator. However, several modifications have improved the technology, making it more suitable for mainstream usage.
Dry Steam Power Plants: Dry steam power plants were the first type of geothermal plants. They rely on steam pumped directly from underground wells to turn a turbine which drives a generator to produce electricity. These plants only emit excess steam and minor amounts of gases.
Flash Steam Power Plants: The most common type of geothermal plants. Flash steam power plants use water with temperatures greater than 200°C pumped at high pressures to the surface, where the pressure is suddenly dropped, causing the hot water to "flash" into steam. The steam is then used to power a turbine and generator. Any leftover water is pumped back into the reservoir, or into a second tank where it can be flashed again to generate more steam. The only by-products of this process are excess steam and trace gases.
Binary-Cycle Power Plants: Binary-cycle power plants operate at lower temperatures than flash steam power plants. Binary-cycle power plants use the heat of the hot water to boil a secondary fluid with a low boiling point. The heat from the water thus causes the secondary fluid to flash to steam, which will drive the turbines. After a cooling process, the water is then injected back into the reservoir to be reused again later. Because the two fluids are separated during the whole process, almost nothing is emitted to the atmosphere. Since water in underground reservoirs usually have moderate temperatures, binary-cycle power plants will likely be the main geothermal technology in the future. The disadvantage of this system is that it tends to be less efficient.
Geothermal Energy Advantages and Disadvantages Advantages Disadvantages
•Reliable
•Low emissions
•Plentiful resource
•Sustainable as water can be injected back into hot rock to pick up more heat
•Cost effective (on par with hydrocarbons)
•Takes up little space compared to oil and gas production
•Naturally occurring vents are not widely available (accessible in only select locations)
•Potential artificial vents are often too far and deep in the ground to be effective
•Occasionally limited due to heat and water depletion
Summary
Geothermal has many environmental and economic advantages. In countries where hydrocarbon resources are limited, geothermal power can be cost competitive. As a plentiful and low emission energy source, research continues into geothermal energy to make it more widely available.