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Most of the coal used in the U.S. is for electricity (almost 93%); the rest is used as a basic energy source in industries such as steel, cement, and paper. Almost half of the electricity generated in the U.S. is fueled by coal. Power plants burn coal to produce steam. The steam turns turbines that generate electricity. The ingredients in coal can also be separated. Industries can then use the heat and byproducts of coal. Methanol and ethylene are some of the ingredients in coal that can be separated. These ingredients can be used to make plastics, tar, synthetic fibers, fertilizers, and medicines. Coal can also be baked in hot furnaces to make coke. Coke can be used to make steel.
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Mining and burning coal can have several adverse effects on ecosystems, water quality, landscapes, and the environment. The combustion of coal produces five principle byproducts which can be harmful to the environment: sulfur dioxide (linked to acid rain and respiratory illness), nitrogen oxides (linked to the formation of acid rain and photochemical smog), carbon dioxide (primary greenhouse gas emission from energy use), and mercury (linked to neurological and developmental damage in humans and animals of most concern when it enters water).
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The Clean Air Act and Clean Water Act have forced industries to reduce the pollutants that are released into the air and water from the combustion of coal. Industry has worked with the government to find ways to reduce emissions such as sulfur and nitrogen oxides from coal burning and to find ways to make it more energy-efficient so less needs to be burned. Power plants clean coal with "scrubbers" before it leaves the smokestack. Other equipment such as catalytic converters (to remove nitrogen oxides) and electrostatic precipitators and baghouses (to remove particulate matter) also reduce mercury emissions from some types of coal. Scientists are still working on new ways to reduce mercury emissions and to address the carbon dioxide emissions from coal burning power plants. Sometimes carbon dioxide is captured and sequestered underground.
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Natural Gas
Natural gas is the source of 24% of the U.S. energy consumption.
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Natural gas lies many feet beneath the ground and is made of mostly methane. It is often found alongside other fossil fuels and is created by organisms in wetlands and landfills. Geologists today use tools such as seismic surveys to find natural gas and drill wells. Some areas are on land and some are in the ocean. Gas is then brought up through a well and transported through pipelines. Byproducts such as butane and propane are separated, cleaned, and removed for other uses. The U.S. produces most of the gas that it consumes and some is imported from Canada.
Natural gas is stored in underground storage systems and transported when needed through pipelines. Once in the communities, gas flows into smaller pipelines called "mains" which connect to very small lines called "services", which go directly to homes or buildings where it will be used. Natural gas can also be cooled to about --260 °F and turned into a compact form of liquid gas, which is ideal for storage and shipment.
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Natural gas is used to produce steel, glass, paper, clothing, brick, electricity and it is used as an essential raw material for many common products such as paints, fertilizer, plastics, antifreeze, dyes, photographic film, medicines, and explosives. In the U.S., more than half the homes use natural gas as their main heat source. It is also used for stoves, water heaters, and other household appliances.
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Burning natural gas produces carbon dioxide, but it is the cleanest of all fossil fuels. It has fewer emissions and leaves no ash particles when burned. Natural gas does affect the environment as it is produced, stored, and transported. Small amounts of methane can sometimes leak into the atmosphere. This is something the natural gas companies are trying to prevent. Also, exploring and drilling for gas disrupts land and marine habitats. New technology and horizontal and directional drilling help lessen the impact by being able to access a larger area by a single well. Natural gas pipelines and storage facilities have a good safety record, although natural gas leaks can lead to explosions.
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Nuclear
Nuclear energy from uranium is the source of 8.5% of the U.S. energy consumption.
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Nuclear energy comes from the core of an atom (a tiny particle that makes up every object.) The energy is released through nuclear fusion (atoms are combined) or nuclear fission (atoms are split.) Nuclear power plants use this energy to make electricity. The most common fuel that nuclear plants use to produce nuclear energy is a kind of uranium called U-235, because its atoms are easily split. Uranium is a nonrenewable metal found in rocks all over the world, but this specific kind is rare. Most of the uranium produced in the U.S. in mined in the Western United States. Deposits of uranium are also found in Australia, Canada, Africa, and South America. 86% of the uranium used in the U.S. is imported. 42% comes from Australasia and Canada; 33% comes from Kazakhstan, Russia, and Uzbekistan; and 11% comes from Brazil, Czech Republic, Namibia, Niger, South Africa, and the United Kingdom.
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Nuclear power plants do not produce air pollution or carbon dioxide, but mining and refining the uranium requires large amounts of energy which may be from fossil fuels. A major environmental concern for nuclear power is its radioactive waste. When atoms are split, they produce radiation and radioactive materials that are dangerous to living organisms. Low-level radioactive waste is stored temporarily to reduce the level of radioactivity and then disposed of usually by burying it and covering it with clay, soil, and rocks. High-level radioactive waste may be stored permanently. The Nuclear Regulatory Commission governs all aspects of producing, handling, and disposing of nuclear energy. An uncontrolled nuclear reaction could be devastating, and could result in a widespread contamination of air and water for hundreds of miles around a reactor, but because of the strict rules and regulations, the risk of this happening is thought to be very small.
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Renewables
Renewable energy sources include biomass, geothermal energy, hydropower, solar energy, and wind energy. These sources can be replenished quickly and are mainly used as sources of electricity. In 2008, renewables represented less than 8% of the total U.S. energy consumption.
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Hydroelectric
Hydroelectric, is the source of 2.5% of the U.S. energy consumption.
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Hydroelectric power is inexpensive, safe, and available around the world. Our future energy needs cannot be met solely by hydroelectric power, but we should continue to use water power wherever possible. It is feasible that 1.5 TW of energy can be produced by hydroelectric power.
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Hydropower produces the most electricity of all renewable sources in the U.S. In 2008, 67% of electricity generation from renewables was from hydropower (6% of total electricity generation). Hydropower relies on the water cycle. In the water cycle, solar energy heats the surface of the water and causes it to evaporate. Next the water vapor condenses into clouds and turns into precipitation. The water flows through rivers and back into the oceans and evaporated again.
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Hydropower is one of the oldest sources of energy, being used thousands of years ago for grinding grain. The U.S. first began to use it for industry in 1800, but because hydroelectric power plants must be located on a water source, it wasn't widely used until it became possible to transmit electricity over long distances.
Today hydropower is produced at large facilities in the West. Most dams are used to provide irrigation and flood control and a small percentage are used for electricity. The amount of energy that is produced depends on the flow and fall. Swiftly flowing water or water descending rapidly from a very high point will produce the most energy.
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Hydropower generators do not produce any emissions of air pollutants, but can have environmental impacts. Hydropower dams, reservoirs, and the operation of generators can obstruct migration of fish and change the natural water temperature, chemistry, flow characteristics, and silt loads. This can change the ecology and rock and land forms of the river, impacting the animal and plant life in and around the river. Greenhouse gases can also form in reservoirs and be emitted into the atmosphere. The U.S. Department of Energy is also researching ways to decrease the percentage of fish that are killed by the turbines. They hope to bring the percentage down from the current 5-10% to less than 2%. Dams can also interfere with reproduction of salmon.
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Tidal barrages are dams that are built across inlets. They work by filling up on the high tides and emptying through the turbine system on the outgoing tide. There are two commercial-sized barrages operating in the world, one in France and one in Nova Scotia, Canada. There is a third experimental barrage in Russia. France, England, Canada, and Russia have much more potential to use this type of energy.
Tidal fences can also harness the energy of tides, and can be used in channels between two landmasses. They are made of vertical axis turbines mounted on a fence. Tidal fences are cheaper and have less of an impact on the environment than barrages, but they can disrupt the movement of large marine animals. There are plans to build a tidal fence in the Philippines.
Tidal turbines are similar to wind turbines and can be located anywhere where there is a strong tidal flow. They need to be sturdy because water is dense, so they are more expensive to build but also capture more energy.
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Ocean waves have the potential to produce a tremendous amount of energy. It is estimated that the total coast of the U.S. could have produced 7% of the electricity consumed by the U.S. in 2008. The best sources of this energy are the west coasts of the United States and Europe and the coasts of Japan and New Zealand. There are many ways to harness wave energy, with devices that are placed underwater, on the ocean floor, or that ride on top of waves. The world's first commercial wave farm opened in Portugal in 2008. The U.S. Department of Energy's Office of Energy Efficiency and Renewable Energy is funding research and development on the Ocean Thermal Energy Conversion (OTEC) system which may be used to produce and transmit electricity in 10-20 years. This system uses the difference in temperature of surface water (heated by the sun) and deeper water (cooler) to produce electricity.
Geothermal
Geothermal, is the source of 0.4% of the U.S. energy consumption.
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Geothermal energy is heat from within the earth, recovered as steam or hot water, and used for heat or electricity. Earth's hot core heats underground water and rocks. There are three main uses for geothermal energy. People can use hot water from springs or reservoirs near the surface, they can drill deep wells (1-2 miles deep) into the ground and pump the hot water or steam to the surface, or they can use the stable temperatures near Earth's surface to control building temperatures above ground.
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Geothermal reservoirs are places where large areas of naturally occurring hydrothermal resources exist. Hydrothermal resources are a combination of water and heat, most often found near plate boundaries. For example, when magma comes close to the surface, it could heat water that is trapped in fractured rock surfaces and faults. Sometimes there are no noticeable clues that an area has geothermal activity underneath it, but sometimes you will find volcanoes, hot springs, or geysers there. Geologists can drill wells and check the temperature to test for geothermal reservoirs.
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The U.S. is the leader in geothermal power generation. Most geothermal reservoirs in the U.S. are located in the western states and Hawaii. California has 34 geothermal power plants, producing 90% of the U.S. geothermal electricity. Nevada has 16 and Hawaii, Idaho, Montana, and Utah each have one. There are three types of geothermal plants: dry steam plants, flash steam plants, and binary cycle power plants. Ten feet below the earth's surface, the temperature remains nearly constant between 50-60 degrees F. Geothermal heat pumps use the earth's constant temperatures to heat and cool buildings. According to the U.S. Environmental Protection Agency (EPA), geothermal heat pumps are "the most efficient, environmentally clean, and cost effective systems for temperature control." They are becoming more popular in the U.S. and industry has partnered with the EPA to promote further use.
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Geothermal power plants release less than 1% of the carbon dioxide emissions of a fossil fuel plant and 97% less sulfur compounds (acid rain causing). Geothermal plants also use a scrubber system to clean the air of hydrogen sulfide, naturally found in the steam and hot water.
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Wind
Wind, is the source of 0.5% of the U.S. energy consumption.
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We could potentially get 2 TW of energy from wind power from land and we could get even more from offshore power. This of course could not meet all of our energy needs for the future either. Also, the location is an obstacle because much energy would be lost in transmission, considering that the source would be far away from where the need is.
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Wind is the motion of the air due to the uneven heating of the Earth's surface by the sun. In the daily wind cycle, the warm air (over land during the day and water at night) expands and rises and cooler air (over water during the day and land at night) rushes in to take its place, causing wind. Atmospheric winds are created because the land near the equator is heated more than the land at the North and South Poles.
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Today's wind machines (turbines) use blades to collect wind's kinetic energy to turn an electric generator to produce electricity. Wind turbines are best placed in areas with high wind speed. This can be high altitude areas or open areas with no windbreaks such as smooth, rounded hills, open plains, shorelines, and mountain gaps. Wind turbines can be small enough to power a single home or business and produce 100 kilowatts of energy or large enough to produce 5 million watts (megawatts). They can also be grouped together to form a wind farm and supply power to the electric grid. The world's largest wind farm is in Texas and has 421 wind turbines. Most turbines have a horizontal axis and typically stand as tall as a 20-story building, with three blades that span 200 feet across. Vertical-axis turbines typically stand 100 feet tall and 50 feet wide.
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In 2008, 34 states in the U.S. operated large wind turbines to generate electricity. The U.S. ranked first in the world for wind power capacity. The U.S. is followed by Germany, Spain, and China. Denmark is also notable because although it is ranked ninth in the world, it generates about 20% of its electricity from wind. The top wind producing states are Texas, California, Minnesota, Iowa, and Washington. Government programs have helped support wind power development in the U.S. and Europe, where most of the wind power plants in the world are located. There is potential to use wind energy along the coasts of the U.S., but some people think it will spoil the view. There are plans to build an offshore wind plant off the coast of Cape Cod, Massachusetts.
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Wind is a clean fuel that produces no air or water pollution. The only environmental drawback is the negative impact on wild bird populations. Some people also feel that windmills are an eyesore.
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Biomass
Biomass, is the source of 3.9% of the U.S. energy consumption.
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Biomass is not very efficient because plants only store ~1% of the solar energy they absorb. In order to meet our future need of 20 TW, we would need to cover 31% of the Earth's surface with biomass.
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Biomass is a renewable energy source made from plants and animals. Some examples of biomass are wood, crops, manure, and some garbage. Through photosynthesis, plants absorb the sun's energy. Chemical energy in biomass is released as heat when it is burned. Biomass can be burned to produce steam for electricity generation or to provide heat. The most common form of biomass is burning wood, which people have done for thousands of years. Wood was the main source of energy in the world until the mid-1800s. The United States burns about 14% of its trash and some of that is used to produce steam for heat or electricity, while reducing the amount of garbage placed in landfills.
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Biomass does not always have to be burned to release the energy inside; it can also be converted to other forms of energy. Rotting garbage and agricultural and human waste release methane gas which can be used to produce electricity. Landfills can collect the methane gas that it produces and treat it to be sold commercially. There are almost 400 operating landfill gas energy projects in the United States, mostly in California, Illinois, and Michigan. Some crops such as corn and sugar cane can be fermented to produce ethanol. Leftover food products like vegetable oil and animal fats can produce biodiesel. Ethanol and biodiesel are transportation fuels. Ethanol is added to all gasoline in the United States. The Federal Government has mandated that we increase the amount of biofuel used (most likely ethanol) in fuel by 2022. Some farmers collect the manure, dirt, and waste from their barns and put them in a tank called a digester. The methane gas inside the tank is separated and can be used to generate electricity for the farm or sold to the electric company.
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The different types of biomass fuels and the ways they are used can impact the environment in different ways. Biomass crops release carbon dioxide (and a small amount of sulfur) when burned, but as the crops are grown, they capture nearly the same amount of carbon dioxide through photosynthesis.
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Power plants that burn solid waste must use special technology to prevent harmful gases and particles from entering the atmosphere. The environmental Protection Agency (EPA) has strict rules in place to monitor these industries and requires anti-pollution devices such as scrubbers, fabric filters, and electrostatic precipitators. Leftover ash is contaminated if the waste was not properly separated before being burned to remove items such as batteries, which should never be burned. Ash is tested for contamination and, if it is safe, it can be used to cover landfills, build roads, make cement, or to make artificial reefs for marine animals.
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Ethanol and gasoline fuel mixtures burn cleaner but have more evaporative emissions from fuel tanks and dispensers, which can lead to the formation of harmful, ground-level ozone and smog. Carbon dioxide also forms when ethanol is burned, but can be offset by growing plants like corn and sugarcane, which absorb carbon dioxide as they grow, to make ethanol.
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Biodiesel combustion produces less sulfur oxides, particulate matter, carbon monoxide, and hydrocarbons, but more nitrogen oxide. Again, if oils from plants are used in biodiesel the carbon dioxide emissions will be off-set.
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Solar
Solar, is the source of 0.1% of the U.S. energy consumption.
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Solar energy is the only renewable resource that can alone meet our future energy needs. It is estimated that we can obtain between 50 and 1,500 TW of energy from solar energy. We would need to use a lot of land (comparable to the nation's interstate highways) to produce this amount of energy.
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Another source estimates that covering 4% of the world's desert area with PV cells could supply all of the world's energy. The Gobi desert alone could meet almost meet the world's demand.
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Solar energy is the sun's rays that reach the earth. Solar radiation can be converted into other forms of energy, such as heat and electricity. Thermal (heat) energy can be used to heat water or spaces. Solar energy can be converted to electricity through photovoltaic (PV) "solar cells" or through concentrating solar power plants.
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PV cells change sunlight directly into electricity. PV cells are made of semiconductors such as crystalline silicon or various thin-film materials, and can be grouped into panels and arrays of panels to power items such as small calculators to large power plants. Two large photovoltaic plants were completed in Europe in 2008. One was built in Portugal and one in Germany.
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Concentrating solar power plants generate electricity by using solar energy to heat a fluid that produces steam to power a generator. There were 11 solar power generating units operating in the United States at the end of 2008: 9 in California, 1 in Arizona, and 1 in Nevada. California has nine solar power plants in three locations. Concentrating solar power technologies there use mirrors to reflect and concentrate the sunlight onto receivers and convert it into heat.
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Solar energy is everywhere the sun shines and it is the Earth's most available energy source, but there are some disadvantages of using solar energy. First, the amount of sunlight hitting the Earth's surface is not constant and it is dependent upon many factors: location, time of day, time of year, and weather conditions. Second, a large surface area is required to collect the amount of solar energy we need. Also, collecting solar energy is very expensive. There are some advantages of using PV systems: sunlight is converted directly to electricity and does not require bulky generator systems, any size PV array can be installed quickly, and there is minimal environmental impact no water is required and there are no by-products.
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