Energy - põhjalik referaat energiast (1)

SISUKORD
1.ENERGY STORY 4
2.USES OF ENERGY 4
2.1 Uses of energy in homes 5
2.2 Types of energy used in homes 6
2.3 Energy use in different types of homes 6
2.4 Commercial Energy Use 8
2.5 Industrial and Manufacturing Energy Use 10
2.6 Transportation Energy Use 12
3.RENEWABLE ENERGY 14
3.1 What Role Does Renewable Energy Play in the United States ? 14
3.2 Why Don’t We Use More Renewable Energy? 15
4.NONRENEWABLE ENERGY 15
5.SIGNFICANT EVENTS IN THE HISTORY OF ENERGY BY FUEL 16
5.1 Signficant Events in the History of Energy Uses 18
6. SAVING ENERGY 19
7.ELECTRICITY 20
7.1 The science of electricity 21
7.2 Static electricity 22
7.3 Magnets and electricity 22
7.4 Batteries produce electricity 23
7.5 Electricity travels in circuits 23
7.6 How electricity is generated 24
7.7 The transformer - moving electricity 26
7.8 Measuring electricity 27
8. SOLAR ENERGY 27
8.1 Photovoltaic energy 28
8.2 Solar thermal heat 29
8.3 Solar thermal power plants 30
8.4 Solar energy and the environment 30
9.WIND ENERGY 30
9.1 The History of Wind 31
9.2 How wind machines work 31
9.3 Types of wind machines 32
9.4 Wind power plants 33
9.5 Wind production 33
9.6 Wind and the environment 34
10. TIDAL ENERGY 34
10.1 Wave Energy 35
10.2 Ocean Thermal Energy Conversion (OTEC) 36
10.3 Solar 36
10.4 Wind 36
37
Picture 10.3. Wind turbine 37
11. HYDROPOWER 37
11.1 How hydropower works 37
11.2 Where hydropower is generated 38
11.3 Hydropower and the environment 39
12. NUCLEAR ENERGY 39
12.1 Nuclear fuel – uranium 39
12.2 Nuclear power plants generate electricity 40
12.3 Types of reactors 40
12.4 Nuclear power and the environment 41
13. GEOTHERMAL ENERGY 41
13.1 Energy inside the earth 42
13.2 Where is geothermal energy found ? 42
13.3 Uses of geothermal energy 43
13. 4 Direct use of geothermal energy 44
13.5 Geothermal power plants 44
13.6 Geothermal heat pumps 45
13.7 Geothermal energy and the environment 45
14. BIOMASS 45
14.1 Wood and wood waste 46
14.2 Municipal solid waste, landfill gas, and biogas 47
14.3 Biofuels - ethanol and biodiesel 47
14.4 Biomass and the environment 47
15. COAL 49
15.1 How we get coal 49
15.2 Transporting coal 50
15.3 Types of coal 51
15.3 Where we get coal 51
15.4 How coal is used 53
15.4.1 For electric power 53
15.4.2 For industry 53
15.4.3 For making steel 53
15.4.4 For export 53
15.5 Coal and the environment 53
16.NATURAL GAS 54
54
16.1 How Do We Get Natural Gas? 55
16.2 How Is Natural Gas Stored and Delivered ? 55
16.3 How is Natural Gas Measured? 56
16.4 How Is Natural Gas Used? 56
57
16.5 How Does Natural Gas Impact the Environment? 57
17. PETROLEUM (OIL) 58
17.1 Where Do We Get Our Oil? 58
17.2 What Fuels Are Made From Crude Oil? 58
17.3 How Does Oil Impact The Environment? 59

ENERGY STORY
Once upon a time, in a town not far away , there was an 8th grader who was afraid of the dark . Her name was Jules . She was also afraid of the quiet , and of the cold . So she always left on the lights , the TV, and stereo even when she had her I-Pod earbuds on. She took lots of very long, hot showers. She never walked anywhere, but got rides from her mom in a big SUV. She couldn't be happy unless she was using all the energy she possibly could for all the stuff around her.
Her friend , Les, didn't like to use any energy at all. He walked to school, read books instead of watching TV, played the trumpet instead of Guitar Hero, and turned off the lights anytime he left a room .
Then one evening , there was a power outage. The lights went out, the TV turned off, and everything became very quiet. Jules became very upset, and quite scared. She couldn't do anything that she wanted to do. She didn't think she could survive. Meanwhile , Les didn't seem to mind at all. He was able to light a few candles and he could still read his books, practice his trumpet, and hang out and play cards with his family.
The two friends then realized that there was a big difference in their lifestyles and the amount of energy they used. So Jules decided she should figure out how much energy Les used and then compare her energy consumption to how much she really needed. To do this, they figured out how much energy Jules was using for entertainment, light, heating and cooling, cleaning, preparing food, transportation, and communication devices . They discovered that the amount of energy used for any purpose could be measured in different ways . Light bulbs are measured in watts . Air conditioners and hot water heaters are measured in BTUs, while energy used by cars is measured in gallons of fuel.
They used a spreadsheet to figure out how much energy they consumed for each of their activities . Each of the lights, car miles , games, and other appliances was converted to a common unit of power consumption called kilowatt - hours . The spreadsheet was used to determine how many kilowatt-hours were used during each day, each week, and each year for each energy consumption activity. The spreadsheet converted their energy consumption to show them the amount of money it costs for each energy consumption activity. In the end, they were shocked to see how much money Jules' energy using habits cost compared to Les' habits.

USES OF ENERGY
The United States is a highly developed and industrialized society. We use a lot of energy - in our homes, in businesses, inindustry, and for traveling between all these different places .
The industrial sector uses almost one-third of the total energy. The residential and commercial sectors combined use 39 percent of all energy. These two sectors include all types of buildings, such as houses , offices, stores, restaurants, and places of worship. Energy used for transportation accounts for more than a quarter of all energy.
Picture 2.1. Share of energy consumed by major selectors of the economy (2007)
2.1 Uses of energy in homes
The ability to maintain desired temperatures is one of the most important accomplishments of modern technology . Our ovens, freezers, and homes can be kept at any temperature we choose, a luxury that wasn't possible 100 years ago. Keeping our homes comfortable uses a lot of energy. Over 40 percent of the average home's energy consumption is used for heating. Another 20 percent is used for water heating, 8 percent for cooling rooms , and 5 percent for refrigeration. Almost one- fourth of the energy used in homes is used for lighting and appliances. Lighting is essential to a modern society. Lights have revolutionized the way we live , work, and play.
Picture 2.2. How energy is used in homes (2005)
Most homes still use the traditional incandescent bulbs invented by Thomas Edison . These bulbs convert only about ten percent of the electricity they use to produce light, the other 90 percent is converted into heat. In 1879 , the average bulb produced only 14 lumens per watt , compared to about 17 lumens per watt today . By adding halogen gases, the efficiency can be increased to 20 lumens per watt.
Compact fluorescent bulbs, or "CFLs", have made inroads into home lighting systems in the last few years. These bulbs last much longer and use much less energy, producing significant savings over the life of the bulb.
Appliances such as refrigerators, washing machines and dryers are also more energy efficient than they used to be. In 1990 Congress passed the National Appliance Energy Conservation Act, which requires new appliances to meet strict energy efficiency standards. Learn more about energy efficient light bulbs and appliances, and other ways to save energy at home.
2.2 Types of energy used in homes
Natural gas is the most widely consumed energy source in American homes, followed by electricity, heating oil and propane. Natural gas and heating oil (fuel oil) are used mainly for home heating. Electricity may also be used for heating and cooling, plus it lights our homes and runs almost all of our appliances including refrigerators, toasters, and computers . Many homes in rural areas use propane for heating, while others use it to fuel their barbecue grills.
Picture 2.3. Types of energy consumed in homes (2005)
2.3 Energy use in different types of homes
About 80 percent of residential energy use is consumed in single family homes, while 15 percent is consumed in multi -family dwellings such as apartments, and 5 percent is consumed in mobile homes.
Picture 2.4. Energy use in different types of homes
More than half of the energy used for heating in single-family homes (either attached or detached ) is natural gas, about one-fourth is electricity, and one- tenth is fuel oil (heating oil). Over three-fourths of single-family homes have some type of air conditioning. Most single-family homes have a washing machine and a dryer.
Among Single-Family Dwellings:
In 2005, for the Main Heating Fuel and Equipment :

• 56% use Natural Gas
  
• 26% use Electricity
  
• 7% use Fuel Oil
  
• 6% use LPG
  
• 1% use Kerosene
  

84% of single family homes have air conditioning (central system, wall/ window units – or both ).
For Appliances:

• 95% have a clothes washer
  
• 92% have a clothes dryer
  
• 74% have a personal computer
  

Multi-family dwellings such as apartments use about equal amounts of natural gas and electricity for heating. More than 80 percent of multi-family homes have air conditioning and more than one-third contain washers and dryers.
Among Multi-Family Dwellings:
In 2005, for the Main Heating Fuel and Equipment:

• 47% use Natural Gas
  
• 41% use Electricity
  
• 7% use Fuel Oil
  

82% of multi-family homes have air conditioning (a central system,wall/window units - or both).
For Appliances:

• 40% have a clothes washer
  
• 35% have a clothes dryer
  
• 55% have a personal computer
  

Mobile homes are more likely than the other types of homes to heat with propane(LPG). More than one-third of mobile homes use electricity and about one-third use natural gas for heating. Most mobile homes contain washing machines and dryers.
Among Mobile Homes:
In 2005, for the Main Heating Fuel and Equipment:

• 27% use Natural Gas
  
• 42% use Electricity
  
• 3% use Fuel Oil
  
• 19% use LPG
  
• 4% use Kerosene
  

84% of mobile homes have air conditioning(central system, wall/window units - or both.
For Appliances:

• 87% have a clothes washer
  
• 78% have a clothes dryer
  
• 49% have a personal computer
  

2.4 Commercial Energy Use
Commercial buildings include a wide variety of building types—offices, hospitals, schools , police stations, places of worship, warehouses, hotels, barber shops, libraries , shopping malls—and that’s just the beginning of the list. These different commercial activities all have unique energy needs but, as a whole , commercial buildings use more than half their energy for heating and lighting.
Picture 2.5. How energy is used in commercial buildings
Electricity and natural gas are the most common energy sources used in commercial buildings. Commercial buildings also use another source that you don’t usually find used in residential buildings— district energy. When there are many buildings close together, like on a college campus or in a big city, it is sometimes more efficient to have a central heating and cooling plant that distributes steam, hot water, or chilled water to all of the different buildings. A district system can reduce equipment and maintenance costs, as well as save energy.
Picture 2.6. Types of energy used in commercial buildings
Retail and service buildings use the most total energy of all the commercial building types. This isn’t too surprising when you think of all the stores and service businesses in most towns. Offices use a large share of energy, too. Education buildings, like your school, use 13 percent of all total energy, which is even more than all hospitals and other medical buildings combined! Lodging buildings (like hotels or dormitories) use 8 percent of all energy. Warehouses and food service (like restaurants) each use 7 percent. Public assembly buildings, which can be anything from libraries to sports arenas, use 6 percent; food sales buildings (like grocery stores and conveniencestores) use 4 percent. All other types of buildings, like places of worship, fire stations, police stations, and laboratories, account for the remaining 10 percent of commercial building energy.
Picture 2.7 Energy use by type of building
2.5 Industrial and Manufacturing Energy Use
The United States is highly industrialized. Industry accounts for about one-third of the energy used in the country .
There are many different uses and a variety of different energy sources in the manufacturing sector. One main use is as boiler fuel, which means producing heat that is transferred to the boiler vessel to generate steam or hot water. Another use is as process heating, which is when energy is used directly to raise the temperature of products in the manufacturing process; examples are separating components of crude oil in petroleum refining, drying paint in automobile manufacturing, and cooking packaged foods .
Picture 2.8. Major end uses of some common energy sources
In the manufacturing sector, the predominant energy sources are natural gas and electricity (a secondary source). Manufacturers also use other energy sources for heat, power, and electricity generation. Many uncommon energy sources are also used by manufacturers as a feedstock(a raw material used to make other products).
Picture 2.9. Sources of used for industry and manufacturing
Every industry uses energy, but there are a handful of energy- intensive industries that use the bulk of the energy consumed by the industrial sector.
The chemical industry is the largest industrial consumer of energy, followed closely by petroleum refining. The refining, chemical, paper and metal industries together use:

• 94% of the feedstock
  
• 92% of the byproduct energy
  
• 70% of total inputs of energy for heat, power, and electricity generation
  

Picture 2.10. Energy use by type of industry
2.6 Transportation Energy Use
America is a nation on the move . About 28 percent of the energy we use goes to transporting people and goods from one place to another.
Cars, vans, and buses are commonly used to carry people. Trucks, airplanes, and railroads can be used to carry people and freight. Barges and pipelines only carry freight. In 2005, there were almost 239 million vehicles (cars, buses, and trucks) in the United States. That’s more than three motor vehicles for every four people!
Automobiles, motorcycles, trucks, and buses drove nearly 3.0 trillion miles in 2005. That’s almost one-twelfth the distance to the nearest star beyond the solar system. It’s like driving to the sun and back 13,440 times .
Picture 2.11. Energy use for transportation
Gasoline is used mainly by cars, motorcycles, and light trucks; diesel is used mainly by heavier trucks, buses, and trains . Together, gasoline and diesel make up 86 percent of all the energy used in transportation.
There is currently a push to develop vehicles that run on fuels other than petroleum products, or on blended fuels. Today, there are some vehicles that run on electricity, natural gas, propane, and ethanol. Hybrid -electric vehicles combine the benefits of gasoline engines and electric motors, reducing the amount of fuel required for moving a vehicle. This is why hybrid-electric vehicles can get more miles per gallon of gasoline compared to vehicles that run on gasoline alone.
Picture 2.12. Fuels used for transportation
The people in the United States have always had a love affair with the automobile. Personal vehicles (like cars and light trucks) consume 63 percent of the total energy used for transportation, while commercial vehicles (like large trucks and construction vehicles), mass transit (like airplanes, trains, and buses), and pipelines account for the rest .
Picture 2.13. Energy use by type of vehicle

RENEWABLE ENERGY
Renewable energy sources can be replenished in a short period of time. The five renewable sources used most often are:

• biomass - including wood and wood waste, municipal solid waste, landfill and biogas, ethanol, and biodiesel;
  
• water (hydropower);
  
• geothermal;
  
• wind;
  
• solar.
  

3.1 What Role Does Renewable Energy Play in the United States?
The use of renewable energy is not new. More than 150 years ago, wood, which is one form of biomass, supplied up to 90 percent of our energy needs. As the use of coal, petroleum, and natural gas expanded , the United States became less reliant on wood as an energy source. Today, we are looking again at renewable resources to find new ways to use them to help meet our energy needs. Overall consumption from renewable sources in the United States totaled 6.8 quads (quadrillion Btu) in 2007, or about 7 percent of all energy used nationally. Consumption from renewable sources was at its highest point in 1997, at about 7.2 quads.
Picture 3.1. The Role of Renewable Energy Consumption in the Nation's Energy Supply , 2007
Over half of renewable energy goes to producing electricity. The next largest use is the production of heat and steam for industrial purposes . Renewable fuels, such as ethanol, are also used for transportation and to provide heat for homes and businesses. Renewable energy plays an important role in the supply of energy. When renewable energy sources are used, the demand for fossil fuels is reduced. Unlike fossil fuels, non-biomass renewable sources of energy (hydropower, geothermal, wind, and solar) do not directly emit greenhouse gases.
3.2 Why Don’t We Use More Renewable Energy?
In the past, renewable energy has generally been more expensive to use than fossil fuels. Plus, renewable resources are often located remote areas and it is expensive to build powerlines to the cities where they are needed. The use of renewable sources is also limited by the fact that they are not always available (for example, cloudy days reduce solar energy, calm days mean no wind blows to drive wind turbines , droughts reduce water availability to produce hydroelectricity).
The production and use of renewable fuels has grown more quickly in recent years due to higher prices for oil and natural gas, and a number of State and Federal Government incentives, including the Energy Policy Acts of 2002 and 2005. The use of renewable fuels is expected to continue to grow over the next 30 years, although we will still rely on non-renewable fuels to meet most of our energy needs.
3.3 How Do We Measure Renewable Energy?
Each of the energy sources we use is measured, purchased, and sold in a different form. Many units of measurement are used to measure the energy we use. Learn more about converting energy units in the Units of Measurement section .

NONRENEWABLE ENERGY
Nonrenewable energy sources come out of the ground as liquids, gases and solids. Right now, crude oil (petroleum) is the only naturally liquid commercial fossil fuel. Natural gas and propane are normally gases, and coal is a solid. Coal, petroleum, natural gas, and propane are all considered fossil fuels because they formed from the buried remains of plants and animals that lived millions of years ago. Uranium ore, a solid, is mined and converted to a fuel. Uranium is not a fossil fuel. These energy sources are considered nonrenewable because they can not be replenished (made again) in a short period of time. Renewable energy sources can be replenished naturally in a short period of time.
Picture 4.1. Non-renewable energy

SIGNFICANT EVENTS IN THE HISTORY OF ENERGY BY FUEL
Pre-1885
Wood was the primary source for cooking, warmth, light, trains and steamboats. Cutting wood was time consuming, hard work.
1700's
After eons of superstitious imaginations about electricity, Ben Franklin figured out that static electricity and lightening were the same . His correct understanding of the nature of electricity paved the way for the future.
1830-1839
Michael Faraday built an induction dynamo based on principles of electromagnetism, induction, generation and transmission.
1860’s
Mathematical theory of electromagnetic fields was published. Maxwell created a new era of physics when he unified magnetism , electricity and light. One of the most significant events, possibly the very most significant event, of the 19th century was Maxwell's discovery of the four laws of electrodynamics ("Maxwell's Equations"). This led to electric power, radios, and television .
1763- 1774
Pumping water from coal mines was a most difficult and expensive problem. The steam engine developed by James Watt during these years provided the solution . Watt's steam engine remained basically unchanged for the next century and its uses expanded to change the whole nature of industry and transportation.
1885-1950
Coal was the most important fuel. One half ton of coal produced as much energy as 2 tons of wood and at half the cost. But it was hard to stay clean in houses heated with coal.
Late 1860’s The steel industry gave coal a big boost .
1982
Coal accounted for more than half of the supply of electricity but little was used in homes. In terms of national electricity generation, hydropower, natural gas, and nuclear energy contributed between 10 and 15 percent each.
By 1870 Oil had become the country’s second biggest export after the industry was started by Edwin Drake .
1890
Mass production of automobiles began,creating demand for gasoline. Prior to this, kerosene used for lighting had been the main oil product.
1951- present Oil has given us most of our energy. Automobiles increased the demand for oil.
1960
The Organization of Petroleum Exporting Countries ( OPEC ) was formed by Iran, Iraq , Kuwait, Saudi Arabia, and Venezuela . The group has since grown to include 11 member countries.
1970
U.S. production of petroleum (crude oil and natural gas plant liquids) reached its highest level at 11.7 million barrels per day. Production in the Lower -48 States has been generally declining
since 1970. Some of this decline has been offset by increased
Alaskan production after 1978.
1993
forward For the first time the U.S. imported more oil and refined products from other countries than it produced. More and more imports have been needed because of growing petroleum demand and declining U.S. production
1906
Special theory of relativity written. Albert Einstein created a new era of physics when he unified mass, energy, magnetism, electricity, and light. One of the most significant events, if not the very most significant event, of the 20th century was Einstein's writing the formula of E=mc2: energy = mass times the square of the speed of light. This led to nuclear medicine - and a much longer life span, astrophysics, and commercial nuclear electric power
1942 Scientists produced nuclear energy in a sustained nuclear reaction.
1957 The first commercial nuclear power plant began operating .
1995 Nuclear power contributed about 20 percent of the nation's electricity.
5.1 Signficant Events in the History of Energy Uses
1781 The stagecoach was the worldwide standard for passenger travel .
1800
Transportation as we know today was almost non-existent. Railroads covered far less territory. Trains were much smaller. Horse -drawn carts moved food and all other items on land , and barges moved them on rivers .
1881 The steam-powered railway train had become the worldwide standard for passenger travel.
1908
Henry Ford produced the Model T car ( Note that the Model T had been designed to use ethanol, gasoline, or any combination of the two fuels).
1920
The Ford Motor Company manufactured the Model T in large numbers .
1949-2000
In transportation, use of energy is overwhelmingly petroleum. Energy for this use more than tripled from 1949 to 2000, with motor gasoline accounting for about two-thirds of it. Distillate fuel oil and jet fuel are other important petroleum products used in transportation.
1950-present The National Highway Defense System opened interstate highways for fast trucks.
1800 The residential sector consumed most of America's energy.
1850-1980 The average energy that each person used increased steadily.
1979-1982
Energy consumption decreased ten percent. The industrial sector cut its consumption by 20 percent. The residential and commercial sectors energy consumption stayed about the same.
1950
Distillate fuel oil heated about 22 percent of U.S. households. Over a third of all U.S. housing units were warmed by coal. Natural gas was used to warm about 25 percent of U.S. households. Electricity was used to warm only 0.6 percent of U.S. households.
1978 Microwave ovens were located in 8 percent of U.S. households.
1990 16 percent of households owned one or more personal computers.
1997

• Only about 11 percent of all U.S. housing units were warmed by distillate fuel oil.
  
• Only 0.2 percent of all U.S. housing units were warmed by coal.
  
• More than 50 percent of all U.S. households used natural gas for warmth.
  
• Electricity was used as the main heating fuel in 29 percent of U.S. households.
  
• 35 percent of U.S. households had personal computers.
  
• 83 percent of U.S. households had microwaves.
  
• 99 percent of U.S. households had a color television.
  
• 47 percent of U.S. households had central air conditioning.
  
• 85 percent of of U.S. households had one refrigerator
  
• 15 percent of U.S. households had two or more refridgerators.
  

SAVING ENERGY
All of us use energy every day—for transportation, cooking, heating and cooling rooms, manufacturing, lighting, and entertainment. The choices we make about how we use energy— turning machines off when we’re not using them or choosing to buy energy efficient appliances—impact our environment and our lives .
There are many things we can do to use less energy and use it more wisely. Two main ways to save energy are energy conservation and energy efficiency. Many people think these terms mean the same thing, but they are different.
Energy conservation is any behavior that results in the use of less energy. Turning the lights off when you leave the room and recycling aluminum cans are both ways of conserving energy.
Energy efficiency is the use of technology that requires less energy to perform the same function. A compact fluorescent light bulb that uses less energy than an incandescent bulb to produce the same amount of light is an example of energy efficiency. The decision to replace an incandescent light bulb with a compact fluorescent is an example of energy conservation.
Recycling means to use something again. Newspapers can be used to make new newspapers. Aluminum cans can be used to make new aluminum cans. Glass jars can be used to make new glass jars.
Recycling often saves energy and natural resources through conservation.
It almost always takes less energy to make a product from recycled materials than it does to make it from new materials. Using recycled aluminum scrap to make new aluminum cans, for example, uses 95 percent less energy than making aluminum cans from bauxite ore, the raw material used to make aluminum. Natural resources are riches provided courtesy of Mother Nature. Natural resources include land, plants, minerals, and water. By using materials more than once, we conserve natural resources. In the case of paper, recycling saves trees and water. Making a ton of paper from recycled stock saves up to 17 trees and uses 50 percent less water.

ELECTRICITY
Electricity is the flow of electrical power or charge . It is a secondary energy source which means that we get it from the conversion of other sources of energy, like coal, natural gas,
oil, nuclear power and other natural sources, which are called primary sources. The energy sources we use to make electricity can be renewable or non-renewable, but electricity itself is neither renewable or non-renewable.
Electricity is a basic part of nature and it is one of our most widely used forms of energy. Many cities and towns were built alongside waterfalls (a primary source of mechanical energy) that turned water wheels to perform work. Before electricity generation began over 100 years ago, houses were lit with kerosene lamps, food was cooled in iceboxes, and rooms were warmed by wood- burning or coal-burning stoves. Beginning with Benjamin Franklin's experiment with a kite one stormy night in Philadelphia, the principles of electricity gradually became understood . Thomas Edison helped change everyone's life -- he perfected his invention -- the electric light bulb. Prior to 1879, direct current (DC) electricity had been used in arc lights for outdoor lighting. In the late-1800s, Nikola Tesla pioneered the generation, transmission, and use of alternating current (AC) electricity, which can be transmitted over much greater distances than direct current. Tesla's inventions used electricity to bring indoor lighting to our homes and to power industrial machines.
Despite its great importance in our daily lives, most of us rarely stop to think what life would be like without electricity. Yet like air and water, we tend to take electricity for granted . Everyday, we use electricity to do many jobs for us -- from lighting and heating/cooling our homes, to powering our televisions and computers. Electricity is a controllable and convenient form of energy used in the applications of heat, light and power.
7.1 The science of electricity
In order to understand how electric charge moves from one atom to another, we need to know something about atoms. Everything in the universe is made of atoms—every star, every tree, every animal . The human body is made of atoms. Air and water are, too. Atoms are the building blocks of the universe. Atoms are so small that millions of them would fit on the head of a pin.
Atoms are made of even smaller particles . The center of an atom is called the nucleus . It is made of particles called protons and neutrons. The protons and neutrons are very small, but electrons are much, much smaller. Electrons spin around the nucleus in shells a great distance from the nucleus. If the nucleus were the size of a tennis ball, the atom would be the size of the Empire State Building. Atoms are mostly empty space .
Picture 7.1. Nucleaus and electrons
If you could see an atom, it would look a little like a tiny center of balls surrounded by giant invisible bubbles (or shells). The electrons would be on the surface of the bubbles, constantly spinning and moving to stay as far away from each other as possible. Electrons are held in their shells by an electrical force .
The protons and electrons of an atom are attracted to each other. They both carry an electrical charge. An electrical charge is a force within the particle . Protons have a positive charge (+) and electrons have a negative charge (-). The positive charge of the protons is equal to the negative charge of the electrons. Opposite charges attract each other. When an atom is in balance , it has an equal number of protons and electrons. The neutrons carry no charge and their number can vary .
The number of protons in an atom determines the kind of atom, or element, it is. An element is a substance in which all of the atoms are identical (the Periodic Table shows all the known elements). Every atom of hydrogen , for example, has one proton and one electron , with no neutrons. Every atom of carbon has six protons, six electrons, and six neutrons. The number of protons determines which element it is.
Electrons usually remain a constant distance from the nucleus in precise shells. The shell closest to the nucleus can hold two electrons. The next shell can hold up to eight. The outer shells cans hold even more. Some atoms with many protons can have as many as seven shells with electrons in them.
The electrons in the shells closest to the nucleus have a strong force of attraction to the protons. Sometimes, the electrons in the outermost shells do not. These electrons can be pushed out of their orbits. Applying a force can make them move from one atom to another. These moving electrons are electricity.
7.2 Static electricity
Electricity has been moving in the world forever. Lightning is a form of electricity. It is electrons moving from one cloud to another or jumping from a cloud to the ground. Have you ever felt a shock when you touched an object after walking across a carpet? A stream of electrons jumped to you from that object. This is called static electricity.
Have you ever made your hair stand straight up by rubbing a balloon on it? If so, you rubbed some electrons off the balloon. The electrons moved into your hair from the balloon. They tried to get far away from each other by moving to the ends of your hair. They pushed against each other and made your hair move—they repelled each other. Just as opposite charges attract each other, like charges repel each other.
7.3 Magnets and electricity
The spinning of the electrons around the nucleus of an atom creates a tiny magnetic field . Most objects are not magnetic because the atoms are arranged so that the electrons spin in different, random directions, and cancel out each other. Magnets are different; the molecules in magnets are arranged so that the electrons spin in the same direction. This arrangement of atoms creates two poles in a magnet, a North - seeking pole and a South -seeking pole.
Picture 7.2. Bar magnet
A magnet is labeled with North (N) and South (S) poles. The magnetic force in a magnet flows from the North pole to the South pole. This creates a magnetic field around a magnet.
Have you ever held two magnets close to each other? They don’t act like most objects. If you try to push the South poles together, they repel each other. Two North poles also repel each other.
Turn one magnet around and the North (N) and the South (S) poles are attracted to each other. The magnets come together with a strong force. Just like protons and electrons, opposites attract.
These special properties of magnets can be used to make electricity. Moving magnetic fields can pull and push electrons. Some metals , like copper have electrons that are loosely held. They can be pushed from their shells by moving magnets. Magnets and wire are used together in electric generators.
7.4 Batteries produce electricity
A battery produces electricity using two different metals in a chemical solution. A chemical reaction between the metals and the chemicals frees more electrons in one metal than in the other. One end of the battery is attached to one of the metals; the other end is attached to the other metal. The end that frees more electrons develops a positive charge and the other end develops a negative charge. If a wire is attached from one end of the battery to the other, electrons flow through the wire to balance the electrical charge. A load is a device that does work or performs a job. If a load––such as a lightbulb––is placed along the wire, the electricity can do work as it flows through the wire. In the picture above , electrons flow from the negative end of the battery through the wire to the lightbulb. The electricity flows through the wire in the lightbulb and back to the battery.
Picture 7.3. Batteries produce electricity
7.5 Electricity travels in circuits
Electricity travels in closed loops, or circuits (from the word circle ). It must have a complete path before the electrons can move. If a circuit is open , the electrons cannot flow. When we flip on a light switch , we close a circuit. The electricity flows from the electric wire through the light and back into the wire. When we flip the switch off, we open the circuit. No electricity flows to the light. When we turn a light switch on, electricity flows through a tiny wire in the bulb. The wire gets very hot. It makes the gas in the bulb glow. When the bulb burns out, the tiny wire has broken . The path through the bulb is gone . When we turn on the TV, electricity flows through wires inside the set, producing pictures and sound . Sometimes electricity runs motors—in washers or mixers. Electricity does a lot of work for us. We use it many times each day.
7.6 How electricity is generated
A generator is a device that converts mechanical energy into electrical energy. The process is based on the relationship between magnetism and electricity. In 1831, Faraday discovered that when a magnet is moved inside a coil of wire, electrical current flows in the wire.
A typical generator at a power plant uses an electromagnet—a magnet produced by electricity—not a traditional magnet. The generator has a series of insulated coils of wire that form a stationary cylinder. This cylinder surrounds a rotary electromagnetic shaft. When the electromagnetic shaft rotates, it induces a small electric current in each section of the wire coil. Each section of the wire becomes a small, separate electric conductor. The small currents of individual sections are added together to form one large current. This current is the electric power that is transmitted from the power company to the consumer.
An electric utility power station uses either a turbine, engine, water wheel , or other similar machine to drive an electric generator or a device that converts mechanical or chemical energy to generate electricity. Steam turbines, internal- combustion engines, gas combustion turbines, water turbines, and wind turbines are the most common methods to generate electricity. Most power plants are about 35 percent efficient. That means that for every 100 units of energy that go into a plant, only 35 units are converted to usable electrical energy.
Most of the electricity in the United States is produced in steam turbines. A turbine converts the kinetic energy of a moving fluid (liquid or gas) to mechanical energy. Steam turbines have a series of blades mounted on a shaft against which steam is forced, thus rotating the shaft connected to the generator. In a fossil-fueled steam turbine, the fuel is burned in a furnace to heat water in a boiler to produce steam. Coal, petroleum (oil), and natural gas are burned in large furnaces to heat water to make steam that in turn pushes on the blades of a turbine.
Did you know that most electricity generated in the United State comes from burning coal? In 2007, nearly half (48.5%) of the country's 4.1 trillion kilowatthours of electricity used coal as its source of energy.
Natural gas, in addition to being burned to heat water for steam, can also be burned to produce hot combustion gases that pass directly through a turbine, spinning the blades of the turbine to generate electricity. Gas turbines are commonly used when electricity utility usage is in high demand. In 2007, 21.6% of the nation's electricity was fueled by natural gas.
Petroleum can also be used to make steam to turn a turbine. Residual fuel oil, a product refined from crude oil, is often the petroleum product used in electric plants that use petroleum to make steam. Petroleum was used to generate about two percent (2%) of all electricity generated in U.S. electricity plants in 2007. Nuclear power is a method in which steam is produced by heating water through a process called nuclear fission. In a nuclear power plant, a reactor contains a core of nuclear fuel, primarily enriched uranium. When atoms of uranium fuel are hit by neutrons they fission ( split ), releasing heat and more neutrons. Under controlled conditions , these other neutrons can strike more uranium atoms, splitting more atoms, and so on. Thereby, continuous fission can take place, forming a chain reaction releasing heat. The heat is used to turn water into steam, that, in turn, spins a turbine that generates electricity. Nuclear power was used to generate 19.4% of all the country's electricity in 2007.
Hydropower, the source for 5.8% of U.S. electricity generation in 2007, is a process in which flowing water is used to spin a turbine connected to a generator. There are two basic types of hydroelectric systems that produce electricity. In the first system, flowing water accumulates in reservoirs created by the use of dams . The water falls through a pipe called a penstock and applies pressure against the turbine blades to drive the generator to produce electricity. In the second system, called run-of- river , the force of the river current ( rather than falling water) applies pressure to the turbine blades to produce electricity.
Geothermal power comes from heat energy buried beneath the surface of the earth. In some areas of the country, enough heat rises close to the surface of the earth to heat underground water into steam, which can be tapped for use at steam-turbine plants. This energy source generated less than 1% of the electricity in the country in 2007.
Solar power is derived from the energy of the sun. However , the sun's energy is not available full-time and it is widely scattered. The processes used to produce electricity using the sun's energy have historically been more expensive than using conventional fossil fuels. Photovoltaic conversion generates electric power directly from the light of the sun in a photovoltaic (solar) cell. Solar-thermal electric generators use the radiant energy from the sun to produce steam to drive turbines. In 2007, less than 1% of the nation's electricity was based on solar power.
Picture 7.4. Turbine generator
Wind power is derived from the conversion of the energy contained in wind into electricity. Wind power, less than 1% of the nation's electricity in 2007, is a rapidly growing source of electricity. A wind turbine is similar to a typical wind mill.
Biomass includes wood, municipal solid waste (garbage), and agricultural waste, such as corn cobs and wheat straw. These are some other energy sources for producing electricity. These sources replace fossil fuels in the boiler. The combustion of wood and waste creates steam that is typically used in conventional steam-electric plants. Biomass accounts for about 1% of the electricity generated in the United States.
7.7 The transformer - moving electricity
To solve the problem of sending electricity over long distances, William Stanley developed a device called a transformer. The transformer allowed electricity to be efficiently transmitted over long distances. This made it possible to supply electricity to homes and businesses located far from the electric generating plant.
The electricity produced by a generator travels along cables to a transformer, which changes electricity from low voltage to high voltage. Electricity can be moved long distances more efficiently using high voltage. Transmission lines are used to carry the electricity to a substation. Substations have transformers that change the high voltage electricity into lower voltage electricity. From the substation, distribution lines carry the electricity to homes, offices and factories, which require low voltage electricity.
7.8 Measuring electricity
Electricity is measured in units of power called watts. It was named to honor James Watt, the inventor of the steam engine. One watt is a very small amount of power. It would require nearly 750 watts to equal one horsepower. A kilowatt represents 1,000 watts. A kilowatthour (kWh) is equal to the energy of 1,000 watts working for one hour . The amount of electricity a power plant generates or a customer uses over a period of time is measured in kilowatthours (kWh). Kilowatthours are determined by multiplying the number of kW's required by the number of hours of use. For example, if you use a 40-watt light bulb 5 hours a day, you have used 200 watthours, or 0.2 kilowatthours, of electrical energy. See our Energy Calculator section to learn more about converting units.

SOLAR ENERGY
The sun has produced energy for billions of years. Solar energy is the sun’s rays (solar
radiation ) that reach the earth.Solar energy can be converted into other forms of energy, such as heat and electricity. In the 1830s, the British astronomer John Herschel used a solar thermal collector box (a device that absorbs sunlight to collect heat) to cook food during an expedition to Africa . Today, people use the sun's energy for lots of things.
Solar energy can be converted to thermal (or heat) energy and used to:

• Heat water – for use in homes, buildings, or swimming pools.
  
• Heat spaces – inside greenhouses, homes, and other buildings.
  

Solar energy can be converted to electricity in two ways:

• Photovoltaic (PV devices) or “solar cells” – change sunlight directly into electricity. PV systems are often used in remote locations that are not connected to the electric grid. They are also used to power watches, calculators, and lighted road signs.
  
• Solar Power Plants - indirectly generate electricity when the heat from solar thermal collectors is used to heat a fluid which produces steam that is used to power generator. Out of the 15 known solar electric generating units operating in the United States at the end of 2006, 10 of these are in California , and 5 in Arizona . No statistics are being collected on solar plants that produce less than 1 megawatt of electricity, so there may be smaller solar plants in a number of other states.
  

The major disadvantages of solar energy are:

• The amount of sunlight that arrives at the earth's surface is not constant. It depends on location , time of day, time of year, and weather conditions.
  
• Because the sun doesn't deliver that much energy to any one place at any one time, a large surface area is required to collect the energy at a useful rate .
  

8.1 Photovoltaic energy
Photovoltaic energy is the conversion of sunlight into electricity. A photovoltaic cell, commonly called a solar cell or PV, is the technology used to convert solar energy directly into electrical power. A photovoltaic cell is a nonmechanical device usually made from
silicon alloys.
Sunlight is composed of photons, or particles of solar energy. These photons contain various amounts of energy corresponding to the different wavelengths of the solar spectrum. When photons strike a photovoltaic cell, they may be reflected , pass right through, or be absorbed. Only the absorbed photons provide energy to generate electricity. When enough sunlight (energy) is absorbed by the material (a semiconductor),
electrons are dislodged from the material's atoms. Special treatment of the material surface during manufacturing makes the front surface of the cell more receptive to free electrons, so the electrons naturally migrate to the surface.
When the electrons leave their position, holes are formed. When many electrons, each carrying a negative charge, travel toward the front surface of the cell, the resulting imbalance of charge between the cell's front and back surfaces creates a voltage potential like the negative and positive terminals of a battery. When the two surfaces are connected through an external load, electricity flows.
The photovoltaic cell is the basic building block of a photovoltaic system. Individual cells can vary in size from about 1 centimeter (1/2 inch) to about 10 centimeter (4 inches) across. However, one cell only produces 1 or 2 watts, which isn't enough power for most applications. To increase power output, cells are electrically connected into a packaged weather-tight module . Modules can be further connected to form an array . The term array refers to the entire generating plant, whether it is made up of one or several thousand modules. The number of modules connected together in an array depends on the amount of power output needed.
The performance of a photovoltaic array is dependent upon sunlight. Climate conditions (e.g., clouds, fog) have a significant effect on the amount of solar energy received by a photovoltaic array and, in turn, its performance. Most current technology photovoltaic modules are about 10 percent efficient in converting sunlight. Further research is being conducted to raise this efficiency to 20 percent.
The photovoltaic cell was discovered in 1954 by Bell Telephone researchers examining the sensitivity of a properly prepared silicon wafer to sunlight. Beginning in the late 1950s, photovoltaic cells were used to power U.S. space satellites (learn more about the history of photovaltaic cells). The success of PV in space generated commercial applications for this technology. The simplest photovoltaic systems power many of the small calculators and wrist watches used everyday. More complicated systems provide electricity to pump water, power communications equipment, and even provide electricity to our homes.
Some advantages of photovoltaic systems are:

• Conversion from sunlight to electricity is direct, so that bulky mechanical generator systems are unnecessary.
  
• PV arrays can be installed quickly and in any size required or allowed.
  
• The environmental impact is minimal , requiring no water for system cooling and generating no by-products.
  

8.2 Solar thermal heat
Solar thermal(heat) energy is often used for heating swimming pools, heating water used in homes, and space heating of buildings. Solar space heating systems can be classified as passive or active .
Passive space heating is what happens to your car on a hot summer day. In buildings, the air is circulated past a solar heat surface(s) and through the building by convection (i.e. less dense warm air tends to rise while more dense cooler air moves downward) . No mechanical equipment is needed for passive solar heating.
Active heating systems require a collector to absorb and collect solar radiation. Fans or pumps are used to circulate the heated air or heat absorbing fluid. Active systems often include some type of energy storage system.
Picture 8.1. Solar cells
Solar collectors can be either nonconcentrating or concentrating.
1) Nonconcentrating collectors – have a collector area (i.e. the area that intercepts the solar radiation) that is the same as the absorber area (i.e., the area absorbing the radiation). Flat-plate collectors are the most common and are used when temperatures below about 200o degrees F are sufficient, such as for space heating.
2) Concentrating collectors – where the area intercepting the solar radiation is greater, sometimes hundreds of times greater, than the absorber area.
8.3 Solar thermal power plants
Solar thermal power plants use the sun's rays to heat a fluid, from which heat transfer systems may be used to produce steam. The steam, in turn, is converted into mechanical energy in a turbine and into electricity from a conventional generator coupled to the turbine. Solar thermal power generation works essentially the same as generation from fossil fuels except that instead of using steam produced from the combustion of fossil fuels, the steam is produced by the heat collected from sunlight. Solar thermal technologies use concentrator systems due to the high temperatures needed to heat the fluid. The three main types of solar-thermal power systems are:

• Parabolic trough – the most common type of plant.
  
• Solar dish
  
• Solar power tower
  

8.4 Solar energy and the environment
Solar energy is free, and its supplies are unlimited. Using solar energy produces no air or water pollution but does have some indirect impacts on the environment. For example, manufacturing the photovoltaic cells used to convert sunlight into electricity, consumes silicon and produces some waste products. In addition, large solar thermal farms can also harm desert ecosystems if not properly managed.

WIND ENERGY
Wind is simple air in motion . It is caused by the uneven heating of the earth’s surface by the sun. Since the earth’s surface is made of very different types of land and water, it absorbs the sun’s heat at different rates.
During the day, the air above the land heats up more quickly than the air over water. The warm air over the land expands and rises, and the heavier, cooler air rushes in to take its place, creating winds. At night, the winds are reversed because the air cools more rapidly over land than over water.
In the same way, the large atmospheric winds that circle the earth are created because the land near the earth's equator is heated more by the sun than the land near the North and South Poles.
Picture 9.1. Wind energy
Today, wind energy is mainly used to generate electricity. Wind is called a renewable energy source because the wind will blow as long as the sun shines.
9.1 The History of Wind
Since ancient times, people have harnessed the winds energy. Over 5,000 years ago, the ancient Egyptians used wind to sail ships on the Nile River. Later , people built windmills to grind wheat and other grains . The earliest known windmills were in Persia (Iran). These early windmills looked like large paddle wheels. Centuries later, the people of Holland improved the basic design of the windmill. They gave it propeller-type blades, still made with sails. Holland is famous for its windmills.
American colonists used windmills to grind wheat and corn, to pump water, and to cut wood at sawmills. As late as the 1920s , Americans used small windmills to generate electricity in rural areas without electric service. When power lines began to transport electricity to rural areas in the 1930s , local windmills were used less and less, though they can still be seen on some Western ranches.
The oil shortages of the 1970s changed the energy picture for the country and the world. It created an interest in alternative energy sources, paving the way for the re- entry of the windmill to generate electricity. In the early 1980s wind energy really took off in California, partly because of state policies that encouraged renewable energy sources. Support for wind development has since spread to other states, but California still produces more than twice as much wind energy as any other state.
The first offshore wind park in the United States is planned for an area off the coast of Cape Cod, Massachusetts (read an article about the Cape Cod Wind Project).
9.2 How wind machines work
Like old fashioned windmills, today’s wind machines use blades to collect the wind’s kinetic energy. Windmills work because they slow down the speed of the wind. The wind flows over the airfoil shaped blades causing lift , like the effect on airplane wings , causing them to turn. The blades are connected to a drive shaft that turns an electric generator to produce electricity.
With the new wind machines, there is still the problem of what to do when the wind isn’t blowing. At those times, other types of power plants must be used to make electricity.
9.3 Types of wind machines
There are two types of wind machines (turbines) used today based on the direction of the rotating shaft ( axis ): horizontal–axis wind machines and vertical -axis wind machines. The size of wind machines varies widely. Small turbines used to power a single home or business may have a capacity of less than 100 kilowatts. Some large commercial sized turbines may have a capacity of 5 million watts, or 5 megawatts. Larger turbines are often grouped together into wind farms that provide power to the electrical grid.
Horizontal-axis
Most wind machines being used today are the horizontal-axis type. Horizontal-axis wind machines have blades like airplane propellers. A typical horizontal wind machine stands as tall as a 20-story building and has three blades that span 200 feet across. The largest wind machines in the world have blades longer than a football field! Wind machines stand tall and wide to capture more wind.
Picture 9.1. Horizontal wind machine
Vertical-axis
Vertical–axis wind machines have blades that go from top to bottom and the most common type (Darrieus wind turbine) looks like a giant two-bladed egg beaters. The type of vertical wind machine typically stands 100 feet tall and 50 feet wide. Vertical-axis wind machines make up only a very small percent of the wind machines used today.
The Wind Amplified Rotor Platform (WARP) is a different kind of wind system that is designed to be more efficient and use less land than wind machines in use today. The WARP does not use large blades; instead, it looks like a stack of wheel rims. Each module has a pair of small, high capacity turbines mounted to both of its concave wind amplifier module channel surfaces. The concave surfaces channel wind toward the turbines, amplifying wind speeds by 50 percent or more. Eneco, the company that designed WARP, plans to market the technology to power offshore oil platforms and wireless telecommunications systems.
9.4 Wind power plants
Wind power plants, or wind farms as they are sometimes called, are clusters of wind machines used to produce electricity. A wind farm usually has dozens of wind machines scattered over a large area. The world's largest wind farm, the Horse Hollow Wind Energy Center in Texas , has 421 wind turbines that generate enough electricity to power 220,000 homes per year.
Unlike power plants, many wind plants are not owned by public utility companies . Instead they are owned and operated by business people who sell the electricity produced on the wind farm to electric utilities . These private companies are known as Independent Power Producers.
Operating a wind power plant is not as simple as just building a windmill in a windy place. Wind plant owners must carefully plan where to locate their machines. One important thing to consider is how fast and how much the wind blows.
As a rule , wind speed increases with altitude and over open areas with no windbreaks. Good sites for wind plants are the tops of smooth, rounded hills, open plains or shorelines, and mountain gaps that produce wind funneling. Wind speed varies throughout the country. It also varies from season to season. In Tehachapi, California, the wind blows more from April through October than it does in the winter . This is because of the extreme heating of the Mojave Desert during the summer months. The hot air over the desert rises, and the cooler, denser air above the Pacific Ocean rushes through the Tehachapi mountain pass to take its place. In a state like Montana, on the other hand, the wind blows more during the winter. Fortunately, these seasonal variations are a good match for the electricity demands of the regions . In California, people use more electricity during the summer for air conditioners. In Montana, people use more electricity during the winter months for heating.
9.5 Wind production
In 2006, wind machines in the United States generated a total of 26.6 billion kWh per year of electricity, enough to serve more than 2.4 million households. This is enough electricity to power a city larger than Los Angeles , but it is only a small fraction of the nation's total electricity production, about 0.4 percent. The amount of electricity generated from wind has been growing fast in recent years. In 2006, electricity generated from wind was 2 ½ times more than wind generation in 2002.
New technologies have decreased the cost of producing electricity from wind, and growth in wind power has been encouraged by tax breaks for renewable energy and green pricing programs. Many utilities around the country offer green pricing options that allow customers the choice to pay more for electricity that comes from renewable sources.
Wind machines generate electricity in 28 different states in 2006. The states with the most wind production are Texas, California, Iowa , Minnesota, and Oklahoma .
Most of the wind power plants in the world are located in Europe and in the United States where government programs have helped support wind power development. The United States ranks second in the world in wind power capacity, behind Germany and ahead of Spain and India. Denmark ranks number six in the world in wind power capacity but generates 20 percent of its electricity from wind.
9.6 Wind and the environment
In the 1970s, oil shortages pushed the development of alternative energy sources. In the 1990s , the push came from a renewed concern for the environment in response to scientific studies indicating potential changes to the global climate if the use of fossil fuels continues to increase. Wind energy is an economical power resource in many areas of the country. Wind is a clean fuel; wind farms produce no air or water pollution because no fuel is burned. Growing concern about emissions from fossil fuel generation, increased government support, and higher costs for fossil fuels (especially natural gas and coal) have helped wind power capacity in the United States grow substantially over the last 10 years.
The most serious environmental drawbacks to wind machines may be their negative effect on wild bird populations and the visual impact on the landscape . To some, the glistening blades of windmills on the horizon are an eyesore; to others, they’re a beautiful alternative to conventional power plants.

TIDAL ENERGY
Tides are caused by the gravitational pull of the moon and sun, and the rotation of the earth. Near shore , water levels can vary up to 40 feet. Only about 20 locations have good inlets and a large enough tidal range- about 10 feet- to produce energy economically. The simplest generation system for tidal plants involves a dam, known as a barrage, across an inlet. Sluice gates on the barrage allow the tidal basin to fill on the incoming high tides and to empty through the turbine system on the outgoing tide, also known as the ebb tide. There are two-way systems that generate electricity on both the incoming and outgoing tides.
Tidal barrages can change the tidal level in the basin and increase turbidity in the water. They can also affect navigation and recreation. Potentially the largest disadvantage of tidal power is the effect a tidal station can have on plants and animals in the estuaries.
There are currently two commercial sized barrages in operations. One is located in La Rance, France ; the other is in Annapolis Royal , Nova Scotia, Canada. The US has no tidal plants and only a few sites where tidal energy could be produced economically. France, England , Canada, and Russia have much more potential.
Picture 10.1. Tidal turbine
Tidal fences can also harness the energy of tides. A tidal fence has vertical axis turbines mounted in a fence. All the water that passes is forced through the turbines. They can be used in areas such as channels between two landmasses. Tidal fences have less impact on the environment than tidal barrages although they can disrupt the movement of large marine animals. They are cheaper to install than tidal barrages too. A tidal fence is planned for the San Bernardino Strait in the Philippines .
Tidal turbines are a new technology that can be used in many tidal areas. They are basically wind turbines that can be located anywhere there is strong tidal flow. Because water is about 800 times denser than air, tidal turbines will have to be much sturdier than wind turbines. They will be heavier and more expensive to build but will be able to capture more energy.
10.1 Wave Energy
Waves are caused by the wind blowing over the surface of the ocean. There is tremendous energy in the ocean waves. The total power of waves breaking around the world’s coastlines is estimated at 2-3 million megawatts. The west coasts of the US and Europe and the coasts of Japan and New Zealand are good sites for harnessing wave energy.
One way to harness wave energy is to bend or focus the waves into a narrow channel, increasing their power and size. The waves can then be channeled into a catch basin or used directly to spin turbines. There are no big commercial wave energy plants, but there are a few small ones. Small, on-shore sites have the best potential for the immediate future; they could produce enough energy to power local communities. Japan, which imports almost all of its fuel, has an active wave-energy program.
Picture 10.2. Wave Energy
10.2 Ocean Thermal Energy Conversion (OTEC)
The energy from the sun heats the surface water of the ocean. In tropical regions, the surface water can be 40 or more degrees warmer than the deep water. This temperature difference can be used to produce electricity. The OTEC system must have a temperature difference of at least 25 degrees Celsius to operate, limiting use to tropical regions. Hawaii has experimented with OTEC since the 1970’s. There is no large-scale operation of OTEC today. There are many challenges. First, the OTEC systems are not very energy efficient. Pumping water is a giant engineering challenge. Electricity must also be transported to land. It will probably be 10 to 20 years before the technology is available to produce and transmit electricity economically from OTEC systems.
10.3 Solar
Research is being done to place solar farms over the ocean. With oceans making up 70 percent of the earth’s surface, some people believe near the coasts would be a perfect place for solar farms. Currently, solar energy is used on offshore platforms and to operate remotely located equipment at sea. Solar energy is a renewable energy source, is free and does not pollute. Visit the solar section of the site for more on solar.
10.4 Wind
Wind energy, like solar energy is already used on land. Wind turbines, and wind farms can only be placed where the wind constantly blows. Along the coast of much of the US , conditions are well suited to use wind energy. There are people who are opposed to putting turbines just offshore. People think the turbines will spoil the view of the ocean. Right now, there is a plan to build an offshore wind plant off the coast of Cape Cod , MA. Wind is a renewable energy source that does not pollute so some people see it as a good alternative to fossil fuels. To learn more about wind, visit the wind section of the site.
Picture 10.3. Wind turbine

HYDROPOWER
Of the renewable energy sources that generate electricity, hydropower is the most often used. It accounted for 6 percent of total U.S. electricity generation and 71 percent of generation from renewables in 2007.
It is one of the oldest sources of energy and was used thousands of years ago to turn a paddle wheel for purposes such as grinding grain. Our nation’s first industrial use of hydropower to generate electricity occurred in 1880, when 16 brush -arc lamps were powered using a water turbine at the Wolverine Chair Factory in Grand Rapids, Michigan. The first U.S. hydroelectric power plant opened on the Fox River near Appleton, Wisconsin, on September 30, 1882. Until that time, coal was the only fuel used to produce electricity. Because the source of hydropower is water, hydroelectric power plants must be located on a water source. Therefore , it wasn’t until the technology to transmit electricity over long distances was developed that hydropower became widely used.
11.1 How hydropower works
Understanding the water cycle is important to understanding hydropower. In the water cycle:

• Solar energy heats water on the surface, causing it to evaporate.
  
• This water vapor condenses into clouds and falls back onto the surface as precipitation.
  
• The water flows through rivers back into the oceans, where it can evaporate and begin the cycle over again.
  

Mechanical energy is derived by directing , harnessing, or channeling moving water. The amount of available energy in moving water is determined by its flow or fall.Swiftly flowing water in a big river, like the Columbia River along the border between Oregon and Washington, carries a great deal of energy in its flow. So, too,with water descending rapidly from a very high point, like Niagara Falls in New York . In either instance , the water flows through a pipe, or penstock,then pushes against and turns blades in a turbine to spin a generator to produce electricity. In a run-of-the-river system, the force of the current applies the needed pressure, while in a storage system, water is accumulated in reservoirs created by dams, then released when the demand for electricity is high. Meanwhile, the reservoirs or lakes are used for boating and fishing , and often the rivers beyond the dams provide opportunities for whitewater rafting and kayaking. Hoover Dam, a hydroelectric facility completed in 1936 on the Colorado River between Arizona and Nevada , created Lake Mead, a 110-mile-long national recreational area that offers water sports and fishing in a desert setting .
Picture 11. 1. The water cycle
11.2 Where hydropower is generated
Over one-half of the total U.S. hydroelectric capacity for electricity generation is concentrated in three States (Washington, California and Oregon) with approximately 27 percent in Washington, the location of the Nation’s largest hydroelectric facility – the Grand Coulee Dam.
Picture 11.2. Top hydropower producting states 2007
It is important to note that only a small percentage of all dams in the United States produce electricity. Most dams were constructed solely to provide irrigation and flood control .
11.3 Hydropower and the environment
Some people regard hydropower as the ideal fuel for electricity generation because, unlike the nonrenewable fuels used to generate electricity, it is almost free, there are no waste products, and hydropower does not pollute the water or the air. However, it is criticized because it does change the environment by affecting natural habitats . For instance, in the Columbia River, salmon must swim upstream to their spawning grounds to reproduce, but the series of dams gets in their way. Different approaches to fixing this problem have been used, including the construction of " fish ladders" which help the salmon "step up" the damv to the spawning grounds upstream.

NUCLEAR ENERGY

Nuclear energy is energy in the nucleus (core) of an atom. Atoms are tiny particles that make up every object in the universe. There is enormous energy in the bonds that hold atoms together. Nuclear energy can be used to make electricity. But first the energy must be released. It can be released from atoms in two ways: nuclear fusion and nuclear fission.
In nuclear fusion, energy is released when atoms are combined or fused together to form a larger atom. This is how the sun produces energy.
In nuclear fission, atoms are split apart to form smaller atoms, releasing energy. Nuclear power plants use nuclear fission to produce electricity.
12.1 Nuclear fuel – uranium
The fuel most widely used by nuclear plants for nuclear fission is uranium. Uranium is nonrenewable, though it is a common metal found in rocks all over the world. Nuclear plants use a certain kind of uranium, U-235, as fuel because its atoms are easily split apart. Though uranium is quite common, about 100 times more common than silver , U-235 is relatively rare . Most U.S. uranium is mined, in the Western United States. Once uranium is mined the U-235 must be extracted and processed before it can be used as a fuel.
Picture 12.1. Fission
During nuclear fission, a small particle called a neutron hits the uranium atom and splits it, releasing a great amount of energy as heat and radiation. More neutrons are also released. These neutrons go on to bombard other uranium atoms, and the process repeats itself over and over again. This is called a chain reaction.
12.2 Nuclear power plants generate electricity
Nuclear power accounts for about 19 percent of the total net electricity generated in the United States, about as much as the electricity used in California,Texas and New York, the three states with the most people. In 2007, there were 66 nuclear power plants (composed of 104 licensed nuclear reactors) throughout the United States.
Most power plants burn fuel to produce electricity, but not nuclear power plants. Instead, nuclear plants use the heat given off during fission as fuel. Fission takes place inside the reactor of a nuclear power plant. At the center of the reactor is the core, which contains the uranium fuel.
The uranium fuel is formed into ceramic pellets. The pellets are about the size of your fingertip , but each one produces the same amount of energy as 150 gallons of oil. These energy- rich pellets are stacked end-to-end in 12- foot metal fuel rods. A bundle of fuel rods is called a fuel assembly. Fission generates heat in a reactor just as coal generates heat in a boiler. The heat is used to boil water into steam. The steam turns huge turbine blades. As they turn, they drive generators that make electricity. Afterward, the steam is changed back into water and cooled in a separate structure at the power plant called a cooling tower. The water can be used again and again.
12.3 Types of reactors
Just as there are different approaches to designing and building airplanes and automobiles, engineers have developed different types of nuclear power plants. Two types are used in the United States: boiling-water reactors (BWRs), and pressurized-water reactors (PWRs). In the BWR, the water heated by the reactor core turns directly into steam in the reactor vessel and is then used to power the turbine-generator. In a PWR, the water passing through the reactor core is kept under pressure so that it does not turn to steam at all – it remains liquid. Steam to drive the turbine is generated in a separate piece of equipment called a steam generator. A steam generator is a giant cylinder with thousands of tubes in it through which the hot radioactive water can flow. Outside the tubes in the steam generator, nonradioactive water (or clean water) boils and eventually turns to steam. The clean water may come from one of several sources: oceans, lakes or rivers. The radioactive water flows back to the reactor core, where it is reheated, only to flow back to the steam generator. Roughly seventy percent of the reactors operating in the U.S. are PWR.
Nuclear reactors are basically machines that contain and control chain reactions, while releasing heat at a controlled rate. In electric power plants, the reactors supply the heat to turn water into steam, which drives the turbine-generators. The electricity travels through high voltage transmission lines and low voltage distribution lines to homes, schools, hospitals, factories, office buildings, rail systems and other users.
12.4 Nuclear power and the environment
Compared to electricity generated by burning fossil fuels, nuclear energy is clean. Nuclear power plants produce no air pollution or carbon dioxide but a small amount of emissions result from processing the uranium that is used in nuclear reactors.
Like all industrial processes, nuclear power generation has by-product wastes: spent (used) fuels, other radioactive waste, and heat. Spent fuels and other radioactive wastes are the principal environmental concern for nuclear power. Most nuclear waste is low-levelradioactive waste. It consists of ordinary tools , protective clothing , wiping cloths and disposable items that have been contaminated with small amounts of radioactive dust or particles. These materials are subject to special regulation that govern their disposal so they will not come in contact with the outside environment.
On the other hand, the spent fuel assemblies are highly radioactive and must initially be stored in specially designed pools resembling large swimming pools (water cools the fuel and acts as a radiation shield ) or in specially designed dry storage containers. An increasing number of reactor operators now store their older and less spent fuel in dry storage facilities using special outdoor concrete or steel containers with air cooling. The United States Department of Energy's long range plan is for this spent fuel to be stored deep in the earth in a geologic repository, at Yucca Mountain, Nevada.

GEOTHERMAL ENERGY
The word geothermal comes from the Greek words geo (earth) and therme (heat). So, geothermal energy is heat from within the earth. We can use the steam and hot water produced inside the earth to heat buildings or generate electricity. Geothermal energy is a renewable energy source because the water is replenished by rainfall and the heat is continuously produced inside the earth.
13.1 Energy inside the earth
Geothermal energy is generated in the earth's core, about 4,000 miles below the surface. Temperatures hotter than the sun's surface are continuously produced inside the earth by the slow decay of radioactive particles, a process that happens in all rocks. The earth has a number of different layers:

• The core itself has two layers: a solid iron core and an outer core made of very hot melted rock, called magma .
  
• The mantle which surrounds the core and is about 1,800 miles thick. It is made up of magma and rock.
  
• The crust is the outermost layer of the earth, the land that forms the continents and ocean floors. It can be three to five miles thick under the oceans and 15 to 35 miles thick on the continents.
  

Picture 13.1. The earth’s interior
The earth's crust is broken into pieces called plates . Magma comes close to the earth's surface near the edges of these plates. This is where volcanoes occur . The lava that erupts from volcanoes is partly magma. Deep underground, the rocks and water absorb the heat from this magma. The temperature of the rocks and water get hotter and hotter as you go deeper underground.
People around the world use geothermal energy to heat their homes and to produce electricity by digging deep wells and pumping the heated underground water or steam to the surface. Or, we can make use of the stable temperatures near the surface of the earth to heat and cool buildings.
13.2 Where is geothermal energy found?
Most geothermal reservoirs are deep underground with no visible clues showing above ground.
Geothermal energy can sometimes find its way to the surface in the form of:

• volcanoes and fumaroles (holes where volcanic gases are released)
  
• hot springs and
  
• geysers.
  

Picture 13.2. Ring of fire
The most active geothermal resources are usually found along major plate boundaries where earthquakes and volcanoes are concentrated. Most of the geothermal activity in the world occurs in an area called the Ring of Fire. This area rims the Pacific Ocean.
When magma comes close to the surface it heats ground water found trapped in porous rock or water running along fractured rock surfaces and faults. Such hydrothermal resources have two common ingredients: water (hydro) and heat (thermal). Naturally occurring large areas of hydrothermal resources are called geothermal reservoirs. Geologists use different methods to look for geothermal reservoirs. Drilling a well and testing the temperature deep underground is the only way to be sure a geothermal reservoir really exists.
Most of the geothermal reservoirs in the United States are located in the western states, Alaska , and Hawaii. California is the state that generates the most electricity from geothermal energy. The Geysers dry steam reservoir in northern California is the largest known dry steam field in the world. The field has been producing electricity since 1960.
13.3 Uses of geothermal energy
Some applications of geothermal energy use the earth's temperatures near the surface, while others require drilling miles into the earth. The three main uses of geothermal energy are:
1) Direct Use and District Heating Systems which use hot water from springs or reservoirs near the surface.
2) Electricity generation in a power plant requires water or steam at very high temperature (300 to 700 degrees Fahrenheit). Geothermal power plants are generally built where geothermal reservoirs are located within a mile or two of the surface.
3) Geothermal heat pumps use stable ground or water temperatures near the earth's surface to control building temperatures above ground.
13. 4 Direct use of geothermal energy
The direct use of hot water as an energy source has been happening since ancient times. The Romans , Chinese, and Native Americans used hot mineral springs for bathing, cooking and heating. Today, many hot springs are still used for bathing, and many people believe the hot, mineral-rich waters have natural healing powers.
After bathing, the most common direct use of geothermal energy is for heating buildings through district heating systems. Hot water near the earth's surface can be piped directly into buildings and industries for heat. A district heating system provides heat for 95 percent of the buildings in Reykjavik, Iceland . Examples of other direct uses include: growing crops, and drying lumber, fruits , and vegetables.
13.5 Geothermal power plants
Geothermal power plants use hydrothermal resources which have two common ingredients: water (hydro) and heat (thermal). Geothermal plants require high temperature (300 to 700 degrees Fahrenheit) hydrothermal resources that may come from either dry steam wells or hot water wells. We can use these resources by drilling wells into the earth and piping the steam or hot water to the surface. Geothermal wells are one to two miles deep.
The United States generates more geothermal electricity than any other country but the amount of electricity it produces is less than one-half of a percent of electricity produced in United States. Only four states have geothermal power plants:

• California - has 33 geothermal power plants that produce almost 90 percent of the nation's geothermal electricity.
  
• Nevada - has 14 geothermal power plants.
  
• Hawaii and Utah - each have one geothermal plant.
  

There are three basic types of geothermal power plants:

• Dry steam plants - use steam piped directly from a geothermal reservoir to turn the generator turbines. The first geothermal power plant was built in 1904 in Tuscany, Italy at a place where natural steam was erupting from the earth.
  
• Flash steam plants - take high-pressure hot water from deep inside the earth and convert it to steam to drive the generator turbines. When the steam cools, it condenses to water and is injected back into the ground to be used over and over again. Most geothermal power plants are flash plants.
  
• Binary power plants - transfer the heat from geothermal hot water to another liquid. The heat causes the second liquid to turn to steam which is used to drive a generator turbine.
  

13.6 Geothermal heat pumps
While temperatures above ground change a lot from day to day and season to season, temperatures in the upper 10 feet of the Earth's surface hold nearly constant between 50 and 60 degrees Fahrenheit. For most areas, this means that soil temperatures are usually warmer than the air in winter and cooler than the air in summer. Geothermal heat pumps use the Earth's constant temperatures to heat and cool buildings. They transfer heat from the ground (or water) into buildings in winter and reverse the process in the summer.
According to the U.S. Environmental Protection Agency (EPA), geothermal heat pumps are the most energy-efficient, environmentally clean, and cost-effective systems for temperature control. Although, most homes still use traditional furnaces and air conditioners, geothermal heat pumps are becoming more popular . In recent years, the U.S. Department of Energy along with the EPA have partnered with industry to promote the use of geothermal heat pumps.
13.7 Geothermal energy and the environment
The environmental impact of geothermal energy depends on how it is being used.

• Direct use and heating applications have almost no negative impact on the environment.
  
• Geothermal power plants do not burn fuel to generate electricity, so their emission levels are very low. They release less than 1 percent of the carbon dioxide emissions of a fossil fuel plant. Geothermal plants use scrubber systems to clean the air of hydrogen sulfide that is naturally found in the steam and hot water. Geothermal plants emit 97 percent less acid rain - causing sulfur compounds than are emitted by fossil fuel plants. After the steam and water from a geothermal reservoir have been used, they are injected back into the earth.
  
• Geothermal features in national parks , such as geysers and fumaroles in Yellowstone National Park, are protected by law, to prevent the land from being disturbed.
  

BIOMASS
Biomass is organic material made from plants and animals. Biomass contains stored energy from the sun. Plants absorb the sun's energy in a process called photosynthesis. The chemical energy in plants gets passed on to animals and people that eat them. Biomass is a renewable energy source because we can always grow more trees and crops, and waste will always exist. Some examples of biomass fuels are wood, crops, manure, and some garbage.
When burned, the chemical energy in biomass is released as heat. If you have a fireplace, the wood you burn in it is a biomass fuel. Wood waste or garbage can be burned to produce steam for making electricity, or to provide heat to industries and homes.
Pictures 14.1. Types of biomass
Burning biomass is not the only way to release its energy. Biomass can be converted to other usable forms of energy like methane gas or transportation fuels like ethanol and biodiesel. Methane gas is the main ingredient of natural gas. Smelly stuff, like rotting garbage, and agricultural and human waste, release methane gas - also called "landfill gas" or "biogas." Crops like corn and sugar cane can be fermented to produce the transportation fuel, ethanol. Biodiesel, another transportation fuel, can be produced from left-over food products like vegetable oils and animal fats .
Biomass fuels provide about 3 percent of the energy used in the United States. People in the USA are trying to develop ways to burn more biomass and less fossil fuels. Using biomass for energy can cut back on waste and support agricultural products grown in the United States. Biomass fuels also have a number of environmental benefits.
14.1 Wood and wood waste
The most common form of biomass is wood. For thousands of years people have burned wood for heating and cooking. Wood was the main source of energy in the U.S. and the rest of the world until the mid-1800s. Biomass continues to be a major source of energy in much of the developing world. In the United States wood and waste (bark, sawdust, wood chips , and wood scrap) provide only about 2 percent of the energy we use today.
About 84 percent of the wood and wood waste fuel used in the United States is consumed by the industry, electric power producers, and commercial businesses. The rest, mainly wood, is used in homes for heating and cooking.
Many manufacturing plants in the wood and paper products industry use wood waste to produce their own steam and electricity. This saves these companies money because they don't have to dispose of their waste products and they don't have to buy as much electricity. The photograph to the right is of biomass fuel, probably wood chips, being stored and dried for later use in a boiler.
14.2 Municipal solid waste, landfill gas, and biogas
Another source of biomass is our garbage, also called municipal solid waste (MSW). Trash that comes from plant or animal products is biomass. Food scraps, lawn clippings, and leaves are all examples of biomass trash. Materials that are made out of glass, plastic, and metals are not biomass because they are made out of non-renewable materials. MSW can be a source of energy by either burning MSW in waste-to-energy plants, or by capturing biogas. In waste-to-energy plants, trash is burned to produce steam that can be used either to heat buildings or to generate electricity.
In landfills, biomass rots and releases methane gas, also called biogas or landfill gas. Some landfills have a system that collects the methane gas so that it can be used as a fuel source. Some dairy farmers collect biogas from tanks called "digesters" where they put all of the muck and manure from their barns. Read about a field trip to a real waste-to-energy plant or learn about the history of MSW.
14.3 Biofuels - ethanol and biodiesel
"Biofuels" are transportation fuels like ethanol and biodiesel that are made from biomass materials. These fuels are usually blended with the petroleum fuels - gasoline and diesel fuel, but they can also be used on their own. Using ethanol or biodiesel means we don't burn quite as much fossil fuel. Ethanol and biodiesel are usually more expensive than the fossil fuels that they replace but they are also cleaner burning fuels, producing fewer air pollutants.
Ethanol is an alcohol fuel made from the sugars found in grains, such as corn, sorghum, and wheat, as well as potato skins, rice , sugar cane, sugar beets, and yard clippings. Scientists are working on cheaper ways to make ethanol by using all parts of plants and trees. Farmers are experimenting with " woody crops", mostly small poplar trees and switchgrass, to see if they can grow them cheaply and abundantly. Most of the ethanol used in the United States today is distilled from corn. About 99 percent of the ethanol produced in the United States is used to make "E10" or "gasohol" a mixture of 10 percent ethanol and 90 percent gasoline. Any gasoline powered engine can use E10 but only specially made vehicles can run on E85, a fuel that is 85 percent ethanol and 15 percent gasoline.
Biodiesel is a fuel made with vegetable oils, fats, or greases - such as recycled restaurant grease. Biodiesel fuels can be used in diesel engines without changing them. It is the fastest growing alternative fuel in the United States. Biodiesel, a renewable fuel, is safe, biodegradable, and reduces the emissions of most air pollutants.
14.4 Biomass and the environment
Biomass can pollute the air when it is burned, though not as much as fossil fuels. Burning biomass fuels does not produce pollutants like sulfur, that can cause acid rain. When burned, biomass does release carbon dioxide, a greenhouse gas. But when biomass crops are grown, a nearly equivalent amount of carbon dioxide is captured through photosynthesis. Each of the different forms and uses of biomass impact the environment in a different way:
Burning wood - Because the smoke from burning wood contains pollutants like carbon monoxide and particulate matter , some areas of the country won't allow the use of wood burning fireplaces or stoves on high pollution days. A special clean-burning technology can be added to wood burning fireplaces and stoves so that they can be used even on days with the worst pollution.
Burning Municipal Solid Waste (MSW) or Wood Waste - Burning municipal solid waste (MSW or garbage) and wood waste to produce energy, means that less of it has to get buried in landfills. Plants that burn waste to make electricity must use technology to prevent harmful gases and particles from coming out of their smoke stacks. The particles that are filtered out are added to the ash that is removed from the bottom of the furnace. Because the ash may contain harmful chemicals and metals, it must be disposed of carefully. Sometimes the ash can be used for road work or building purposes. Learn more about MSW or waste-to-energy plants.
Collecting landfill gas or biogas - Collecting and using landfill and biogas reduces the amount of methane that is released into the air. Methane is one of the greenhouse gases associated with global climate change. Many landfills find it cheaper to just burn-off the gas that they collect because the gas needs to be processed before it can be put into natural gas pipelines. Learn more about landfills.
Ethanol- Since the early 1990s ethanol has been blended into gasoline to reduce harmful carbon monoxide emissions. Blending ethanol into gasoline also reduces toxic pollutants found in gasoline but causes more "evaporative emissions" to escape . In order to reduce evaporative emissions, the gasoline requires extra processing before it can be blended with ethanol. When burned, ethanol does release carbon dioxide, a green house gas. But growing plants for ethanol may reduce greenhouse gases, since plants use carbon dioxide and produce oxygen as they grow.
Picture 14.2. The carbon cycle
Biodiesel- Biodiesel is much less polluting than petroleum diesel. It results in much lower emissions of almost every pollutant: carbon dioxide, sulfur oxide, particulates, carbon monoxide, air toxics and unburned hydrocarbons. Biodiesel does have nitrogen oxide emissions that are about 10 percent higher though. Blending biodiesel into petroleum diesel can help reduce emissions. Biodiesel contains almost no sulfur and can help reduce sulfur in diesel fuel used throughout the country.

COAL
Coal is a combustible black or brownish-black sedimentary rock composed mostly of carbon and hydrocarbons. It is the most abundant fossil fuel produced in the United States.
Coal is a nonrenewable energy source because it takes millions of years to create. The energy in coal comes from the energy stored by plants that lived hundreds of millions of years ago, when the earth was partly covered with swampy forests . For millions of years, a layer of dead plants at the bottom of the swamps was covered by layers of water and dirt, trapping the energy of the dead plants. The heat and pressure from the top layers helped the plant remains turn into what we today call coal.
Picture 15.1. How coal was formed
15.1 How we get coal
Mining the Coal Coal miners use giant machines to remove coal from the ground. They use two methods: surface or underground mining. Many U.S. coal beds are very near the ground's surface, and about two-thirds of coal production comes from surface mines. Modern mining methods allow us to easily reach most of our coal reserves. Due to growth in surface mining and improved mining technology, the amount of coal produced by one miner in one hour has more than tripled since 1978. Surface mining is used to produce most of the coal in the U.S. because it is less expensive than underground mining.
Surface mining can be used when the coal is buried less than 200 feet underground. In surface mining, giant machines remove the top-soil and layers of rock to expose large beds of coal. Once the mining is finished , the dirt and rock are returned to the pit, the topsoil is replaced, and the area is replanted. The land can then be used for croplands, wildlife habitats, recreation, or offices or stores.
Picture 15.2. Surface mining
Underground mining, sometimes called deep mining, is used when the coal is buried several hundred feet below the surface. Some underground mines are 1,000 feet deep. To remove coal in these underground mines, miners ride elevators down deep mine shafts where they run machines that dig out the coal. Read about a visit to a real underground coal mine.
Picture 15.3. Deep mining
Processing the Coal.
After coal comes out of the ground, it typically goes on a conveyor belt to a preparation plant that is located at the mining site. The plant cleans and processes coal to remove dirt, rock, ash, sulfur, and other unwanted materials, increasing the heating value of the coal.
15.2 Transporting coal
After coal is mined and processed, it is ready to be shipped to market. The cost of shipping coal can cost more than the cost of mining it. Most coal is transported by train, but coal can also be transported by barge, ship , truck , and even pipeline . About 68 percent of coal in the U.S. is transported, for at least part of its trip to market, by train. It is cheaper to transport coal on river barges, but barges cannot take coal everywhere that it needs to go. If the coal will be used near the coal mine, it can be moved by trucks and conveyors. Coal can also be crushed, mixed with water, and sent through a "slurry" pipeline. Sometimes, coal- fired electric power plants are built near coal mines to lower transportation costs.
15.3 Types of coal
Coal is classified into four main types, or ranks (lignite, subbituminous, bituminous, anthracite), depending on the amounts and types of carbon it contains and on the amount of heat energy it can produce. The rank of a deposit of coal depends on the pressure and heat acting on the plant debris as it sank deeper and deeper over millions of years. For the most part, the higher ranks of coal contain more heat-producing energy.
Lignite is the lowest rank of coal with the lowest energy content. Lignite coal deposits tend to be relatively young coal deposits that were not subjected to extreme heat or pressure. Lignite is crumbly and has high moisture content. There are 20 lignite mines in the United States, producing about seven percent of U.S. coal. Most lignite is mined in Texas and North Dakota. Lignite is mainly burned at power plants to generate electricity.
Subbituminous coal has a higher heating value than lignite. Subbituminous coal typically contains 35-45 percent carbon, compared to 25-35 percent for lignite. Most subbituminous coal in the U.S. is at least 100 million years old. About 44 percent of the coal produced in the United States is subbituminous. Wyoming is the leading source of subbituminous coal.
Bituminous coal contains 45-86 percent carbon, and has two to three times the heating value of lignite. Bituminous coal was formed under high heat and pressure. Bituminous coal in the United States is between 100 to 300 million years old. It is the most abundant rank of coal found in the United States, accounting for about half of U.S. coal production. Bituminous coal is used to generate electricity and is an important fuel and raw material for the steel and iron industries. West Virginia , Kentucky , and Pennsylvania are the largest producers of bituminous coal.
Anthracite contains 86-97 percent carbon, and has a heating value slightly lower than bituminous coal. It is very rare in the United States, accounting for less than one-half of a percent of the coal mined in the U.S. All of the anthracite mines in the United States are located in northeastern Pennsylvania.
15.3 Where we get coal
Coal reserves are beds of coal still in the ground waiting to be mined. The United States has the world's largest known coal reserves, about 263.8 billion short tons. This is enough coal to last approximately 225 years at today's level of use.
Coal production is the amount of coal that is mined and sent to market. In 2006, the amount of coal produced at U.S. coal mines reached an all time high of 1,162.5 million short tons. Coal is mined in 27 states. Wyoming mines the most coal, followed by West Virginia, Kentucky, Pennsylvania, and Texas.Coal is mainly found in three large regions, the Appalachian Coal Region , the Interior Coal Region, and Western Coal Region (includes the Powder River Basin).
Picture 15.4. Coal production in three regions, 2006, millions of short tons 1,162.8 millon short tons
Appalachian Coal Region:

• More than one-third of the coal produced in the U.S. is produced in the Appalachian Coal Region.
  
• West Virginia is the largest coal-producing state in the region, and the second largest coal-producing state in the U.S.
  
• Large underground mines and small surface mines.
  
• Coal mined in the Appalachian coal region is primarily used for steam generation for electricity, metal production, and for export.
  

Interior Coal Region:

• Texas is the largest coal producer in the Interior Coal Region, accounting for almost one-third of the region’s coal production.
  
• Mid-sized surface mines.
  
• Mid- to large-sized companies.
  

Western Coal Region:

• Over half of the coal produced in the U.S. is produced in the Western Coal Region.
  
• Wyoming is the largest regional coal producer, as well as the largest coal-producing state in the nation.
  
• Large surface mines.
  
• Some of the largest coal mines in the world.
  

15.4 How coal is used
About 92 percent of the coal used in the United States, is for generating electricity. Except for a small amount of net exports, the rest of the coal is used, as a basic energy source in many industries, including, steel, cement and paper. The four major uses of coal are:
15.4.1 For electric power
Coal is used to generate almost half of all electricity produced in the United States. Besides electric utility companies, industries and businesses with their own power plants use coal to generate electricity. Power plants burn coal to make steam. The steam turns turbines which generate electricity.
15.4.2 For industry
A variety of industries use coal's heat and by-products. Separated ingredients of coal (such as methanol and ethylene) are used in making plastics , tar, synthetic fibers, fertilizers, and medicines. The concrete and paper industries also burn large amounts of coal.
15.4.3 For making steel
Coal is baked in hot furnaces to make coke, which is used to smelt iron ore into iron needed for making steel. It is the very high temperatures created from the use of coke that gives steel the strength and flexibility for products such as bridges, buildings, and automobiles.
15.4.4 For export
In 2006, 49.6 million short tons, or about four percent of the coal mined, was exported to other countries from the United States. Coal is exported to many different countries, but most trade is with Canada, Brazil , the Netherlands , and Italy. More than half of coal exports are used for making steel. Coal exports have been generally shrinking in the past 10 years, while the amount of coal imported from other countries has been growing. In 2006, about 36.2 million short tons of coal were imported from other countries. Most of these imports (from Colombia, Venezuela, and Indonesia ) were shipped to electric power producers along the U.S. coastlines.
15.5 Coal and the environment
Environmental laws and modern technologies have greatly reduced coal's impact on the environment. Without proper care, mining can destroy land and pollute water. Today, restoring the land damaged by surface mining is an important part of the mining process. Because mining activities often come into contact with water resources, coal producers must also go to great efforts to prevent damage to ground and surface waters.
When coal is burned as fuel, it gives off carbon dioxide, the main greenhouse gas that is linked with global warming . Burning coal also produces emissions, such as sulfur, nitrogen oxide (NOx), and mercury , that can pollute the air and water. Sulfur mixes with oxygen to form sulfur dioxide (SO2), a chemical that can affect trees and water when it combines with moisture to produce acid rain. Emissions of nitrogen oxide help create smog, and also contribute to acid rain. Mercury that is released into the air eventually settles in water. The mercury in the water can build up in fish and shellfish , and can be harmful to animals and people who eat them. The Clean Air Act and the Clean Water Act require industries to reduce pollutants released into the air and the water.
The coal industry has found several ways to reduce sulfur, nitrogen oxides, and other impurities from coal. They have found more effective ways of cleaning coal before it leaves the mine, and coal companies look for low-sulfur coal to mine. Power plants use "scrubbers" to clean sulfur from the smoke before it leaves their smokestacks. In addition, industry and government have cooperated to develop "clean coal technologies" that either remove sulfur and nitrogen oxides from coal, or convert coal to a gas or liquid fuel. The scrubbers and NOx removal equipment are also able to reduce mercury emissions from some types of coal. Scientists are working on new ways to reduce mercury emissions from coal-burning power plants, since the Environmental Protection Agency (EPA) has set tighter mercury limits for the future.

NATURAL GAS
Millions of years ago, the remains of plants and animals decayed and built up in thick layers. This decayed matter from plants and animals is called organic material -- it was once alive. Over time, the mud and soil changed to rock, covered the organic material and trapped it beneath the rock. Pressure and heat changed some of this organic material into coal, some into oil (petroleum), and some into natural gas -- tiny bubbles of odorless gas. The main ingredient in natural gas is methane, a gas (or compound) composed of one carbon atom and four hydrogen atoms.
Picture 16.1. Petroleum and natural gas formation
In some places, gas escapes from small gaps in the rocks into the air; then, if there is enough activation energy from lightning or a fire, it burns. When people first saw the flames, they experimented with them and learned they could use them for heat and light.
16.1 How Do We Get Natural Gas?
The search for natural gas begins with geologists (people who study the structure and processes of the earth). They locate the types of rock that are known to contain gas and oil deposits.
Today their tools include seismic surveys that are used to find the right places to drill wells. Seismic surveys use echoes from a vibration source at the earth’s surface (usually a vibrating pad under a truck built for this purpose) to collect information about the rocks beneath. Sometimes it is necessary to use small amounts of dynamite to provide the vibration that is needed.
Scientists and engineers explore a chosen area by studying rock samples from the earth and taking measurements. If the site seems promising, drilling begins. Some of these areas are on land but many are offshore, deep in the ocean. Once the gas is found, it flows up through the well to the surface of the ground and into large pipelines. Some of the gases that are produced along with methane, such as butane and propane (also known as 'by-products'), are separated and cleaned at a gas processing plant. The by-products, once removed, are used in a number of ways. For example, propane can be used for cooking on gas grills.
Because natural gas is colorless, odorless and tasteless, mercaptan (a chemical that has a sulfur like odor) is added before distribution, to give it a distinct unpleasant odor ( smells like rotten eggs). This serves as a safety device by allowing it to be detected in the atmosphere, in cases where leaks occur.
Most of the natural gas consumed in the United States is produced in the United States. Some is imported from Canada and shipped to the United States in pipelines. Increasingly
natural gas is also being shipped to the United States as liquefied natural gas(LNG).
We can also use machines called "digesters" that turn today's organic material (plants, animal wastes, etc.) into natural gas. This replaces waiting for thousands of years for the gas to form naturally.
16.2 How Is Natural Gas Stored and Delivered?
The gas companies collect it in huge storage tanks, or underground, in old gas wells. The gas remains there until it is added back into the pipeline when people begin to use more gas, such as in the winter to heat homes.
Natural gas is moved by pipelines from the producing fields to consumers. Since natural gas demand is greater in the winter, gas is stored along the way in large underground storage systems, such as old oil and gas wells or caverns formed in old salt beds. The gas remains there until it is added back into the pipeline when people begin to use more gas, such as in the winter to heat homes.
When chilled to very cold temperatures, approximately -260 degrees Fahrenheit, natural gas changes into a liquid and can be stored in this form. Because it takes up only 1/600th of the space that it would in its gaseous state, Liquefied natural gas (LNG) can be loaded onto tankers (large ships with several domed tanks) and moved across the ocean to deliver gas to other countries. When this LNG is received in the United States, it can be shipped by truck to be held in large chilled tanks close to users or turned back into gas to add to
pipelines. When the gas gets to the communities where it will be used(usually through large pipelines), the gas is measured as it flows into smaller pipelines called " mains ". Very small lines, called "services", connect to the mains and go directly to homes or buildings where it will be used.
16.3 How is Natural Gas Measured?
We measure and sell natural gas in cubic feet ( volume ) or in British Thermal Units (heat content). Heat from all energy sources can be measured and converted back and forth between British thermal units (Btu) and metric units. See the Energy Calculator for help with converting natural gas units.
One Btu is the heat required to raise the temperature of one pound of water one degree Fahrenheit. Ten burning kitchen matches release 10 Btu. A candy bar has about 1000 Btu. One cubic foot of natural gas has about 1031 Btu. A box 10 feet deep, 10 feet long, and 10 feet wide would hold one thousand cubic feet of natural gas.
16.4 How Is Natural Gas Used?
Approximately 23 percent of the energy consumption of the U.S. comes from natural gas. Slightly more than half of the homes in the U.S. use natural gas as their main heating fuel. Natural gas is also an essential raw material for many common products, such as: paints ,
fertilizer, plastics, antifreeze, dyes, photographic film , medicines, and explosives. We also get propane when we process natural gas. Propane is the fuel many of us use in our barbecue grills.
Picture 16.2. Natural gas use 2007
Natural gas has thousands of uses and industry depends on it. It's used to produce steel, glass, paper, clothing, brick , electricity and much more!
Homes use it too. More than 62 percent of homes use natural gas to fuel stoves, furnaces, water heaters, clothes dryers and other household appliances. It is also used to roast coffee , smoke meats, bake bread and much more.
16.5 How Does Natural Gas Impact the Environment?
Natural gas burns more cleanly than other fossil fuels. It has fewer emissions of sulfur, carbon, and nitrogen than coal or oil, and when it is burned, it leaves almost no ash particles. Being a clean fuel is one reason that the use of natural gas, especially for electricity generation, has grown so much and is expected to grow even more in the future.
Of course, there are environmental concerns with the use of any fuel. As with other fossil fuels, burning natural gas produces carbon dioxide which is a very important greenhouse gas. Many scientists believe that increasing levels of carbon dioxide and other greenhouse gases in the earth’s atmosphere are changing the global climate.
Also, as with other fuels, natural gas also affects the environment when it is produced, stored and transported. Because natural gas is made up mostly of methane (another greenhouse gas), small amounts of methane can sometimes leak into the atmosphere from wells, storage tanks and pipelines. The natural gas industry is working to prevent any methane from escaping . Exploring and drilling for natural gas will always have some impact on land and marine habitats. But new technologies have greatly reduced the number and size of areas disturbed by drilling, sometimes called "footprints." Satellites, global positioning systems, remote sensing devices, and 3-D and 4-D seismic technologies, make it possible to discover natural gas reserves while drilling fewer wells. Plus, the use of horizontal and directional drilling make it possible for a single well to produce gas from much bigger areas than in the past.
Natural gas pipelines and storage facilities have a very good safety record . This is very important because when natural gas leaks it can cause explosions. Since raw natural gas has no odor, natural gas companies add a smelly substance to it so that people will know if there is a leak. If you have a natural gas stove, you may have smelled this “rotten egg” smell of natural gas when the pilot light has gone out.

PETROLEUM (OIL)
Oil was formed from the remains of animals and plants that lived millions of years ago in a marine (water) environment before the dinosaurs. Over the years, the remains were covered by layers of mud. Heat and pressure from these layers helped the remains turn into what we today call crude oil . The word "petroleum" means "rock oil" or "oil from the earth."
17.1 Where Do We Get Our Oil?
Crude oil is a smelly, yellow-to-black liquid and is usually found in underground areas called reservoirs. Scientists and engineers explore a chosen area by studying rock samples from the earth. Measurements are taken, and, if the site seems promising, drilling begins. Above the hole, a structure called a 'derrick' is built to house the tools and pipes going into the well. When finished, the drilled well will bring a steady flow of oil to the surface.
The world's top five crude oil-producing countries are:

• Saudi Arabia
  
• Russia
  
• United States
  
• Iran
  
• China
  

Over one-fourth of the crude oil produced in the United States is produced offshore in the Gulf of Mexico. The top crude oil-producing states are:

• Texas
  
• Alaska
  
• California
  
• Louisiana
  
• Oklahoma
  

The amount of crude oil produced (domestically) in the United States has been getting smaller each year. However, the use of products made from crude oil has been growing, making it necessary to bring more oil from other countries. About 58 percent of the crude oil and petroleum products used in the United States comes from other countries.
17.2 What Fuels Are Made From Crude Oil?
After crude oil is removed from the ground, it is sent to a refinery by pipeline, ship or barge. At a refinery, different parts of the crude oil are separated into useable petroleum products. Crude oil is measured in barrels ( abbreviated "bbls"). A 42-U.S. gallon barrel of crude oil provides slightly more than 44 gallons of petroleum products. This gain from processing the crude oil is similar to what happens to popcorn, it gets bigger after it is popped.
One barrel of crude oil, when refined, produces about 19 gallons of finished motor gasoline, and 9 gallons of diesel, as well as other petroleum products. Most of the petroleum products are used to produce energy. For instance, many people across the United States use propane to heat their homes and fuel their cars. Other products made from petroleum include: ink, crayons, bubble gum, dishwashing liquids, deodorant, eyeglasses, records, tires, ammonia, and heart valves.
17.3 How Does Oil Impact The Environment?
Products from oil (petroleum products) help us do many things. We use them to fuel our airplanes, cars, and trucks, to heat our homes, and to make products like medicines and plastics. Even though petroleum products make life easier - finding , producing, moving, and using them can cause problems for our environment like air and water pollution. Over the years, new technologies and laws have helped to reduce problems related to petroleum products. As with any industry, the government monitors how oil is produced, refined, stored, and sent to market to reduce the impact on the environment. Since 1990, fuels like gasoline and diesel fuel have also been improved so that they produce less pollution when we use them.
Exploring and drilling for oil may disturb land and ocean habitats. New technologies have greatly reduced the number and size of areas disturbed by drilling, sometimes called "footprints." Satellites, global positioning systems, remote sensing devices, and 3-D and 4-D seismic technologies, make it possible to discover oil reserves while drilling fewer wells. Plus, the use of horizontal and directional drilling make it possible for a single well to produce oil from much bigger areas. Today's production footprints are only about one-fourth the size of those 30 years ago, due to the development of movable drilling rigs and smaller "slimhole" drilling rigs. When the oil in a well is gone, the well must be plugged below ground, making it hard to tell that it was ever there. As part of the "rig-to-reefs" program, some old offshore rigs are toppled and left on the sea floor to become artificial reefs that attract fish and other marine life. Within six months to a year after a rig is toppled, it becomes covered with barnacles, coral, sponges, clams, and other sea creatures.
If oil is spilled into rivers or oceans it can harm wildlife.When we talk about "oil spills" people usually think about oil that leaks from ships when they crash. Although this type of spill can cause the biggest shock to wildlife because so much oil is released at one time, only 2 percent of all oil in the sea comes from ship or barge spills. The amount of oil spilled from ships dropped a lot during the 1990's partly because new ships were required to have a " double -hull" lining to protect against spills. While oil spills from ships are the most well-known problem with oil, more oil actually gets into water from natural oil seeps coming from the ocean floor. Or, from leaks that happen when we use petroleum products on land. For example, gasoline that sometimes drips onto the ground when people are filling their gas tanks, motor oil that gets thrown away after an oil change, or fuel that escapes from a leaky storage tank . When it rains, the spilled products get washed into the gutter and eventually go to rivers and the ocean. Another way that oil sometimes gets into water is when fuel is leaked from motorboats and jet skis .
A refinery is a factory where crude oil is processed into petroleum products. Because many different pollutants can escape from refineries into the air, the government monitors refineries and other factories to make sure that they meet environmental standards.
When a leak in a storage tank or pipeline occurs, petroleum products can also get into the ground, and the ground must be cleaned up. To prevent leaks from underground storage tanks, all buried tanks are supposed to be replaced by tanks with a double-lining. This hasn't happened everywhere yet. In some places where gasoline leaked from storage tanks, one of the gasoline ingredients called methyl tertiary butyl ether ( MTBE ) made its way into local water supplies. Since MTBE made water taste bad and many people were worried about drinking it, a number of states banned the use of MTBE in gasoline, and the refining industry voluntarily moved away from using it when blending reformulated gasoline.
Gasoline is used in cars, diesel fuel is used in trucks, and heating oil is used to heat our homes. When petroleum products are burned as fuel, they give off carbon dioxide, a greenhouse gas that is linked with global warming. The use of petroleum products also gives off pollutants - carbon monoxide, nitrogen oxides, particulate matter, and unburned hydrocarbons - that help form air pollution. Since a lot of air pollution comes from cars and trucks, many environmental laws have been aimed at changing the make-up of gasoline and diesel fuel so that they produce fewer emissions. These "reformulated fuels" are much cleaner-burning than gasoline and diesel fuel were in 1990. In the next few years, the amount of sulfur contained in gasoline and diesel fuel will be reduced dramatically so that they can be used with new, less-polluting engine technology.
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