What is solar power? The primary source of all energy on planet Earth is from the sun. Solar power is power generated directly from sunlight. Solar power can be used for heat energyor converted into electric energy. Renewable Energy When we use solar power, we don't use any of the Earth's resources like coal or oil. This makes solar power a renewable energy source. Solar power is also clean power that doesn't generate a lot of pollution. Solar Power for Heat Solar power can be used for heating up homes and other buildings. Sometimes solar power for heating can be passive. This is when there are no mechanical components used to move the heat around. Passive heating helps to keep houses warm in the winter, to heat up swimming pools, and even makes our car warm when we park it outside (which is nice in the winter, but not so much on a hot summer day). Active heating is when there are mechanical components to help move the heat around. The sun could be used to heat up water or air that is then pumped around a building to provide even heat in all the rooms. Solar Power for Electricity When most of us think of solar power, we think of the solar cells that turn rays of sunshine into electricity. Solar cells are also called photovoltaic cells. The word "photovoltaic" comes from the word "photons", which are particles that make up sunlight, as well as the word "volts", which is a measurement of electricity. Today solar cells are commonly used in small handheld devices like calculators and wrist watches. They are becoming more popular for buildings and homes as they become more efficient. One nice thing about solar cells is that they can be placed on the roof of a building or home, not taking up any extra space. Solar cells on a house used for making electricity How do solar cells work? Solar cells convert the energy of photons from the sun into electricity. When the photon hits the top of the cell, electrons will be attracted to the surface of the cell. This causes a voltage to form between the top and the bottom layers of the cell. When an electric circuit is formed across the top and the bottom of the cell, current will flow, powering electrical equipment. It takes a lot of solar cells to power a building or a home. In this case, a number of solar cells are connected into a large array of cells that can produce more total energy. History of Solar Power The photovoltaic cell was invented in 1954 by researchers at Bell Labs. Since then, solar cells have been used on small items such as calculators. They have also been an important power source for spaceships and satellites. Starting in the 1990s the government has funded research and offered tax incentives to people using clean and renewable power such as solar energy. Scientists have made advances in the efficiency of the solar cell. Today solar cells are around 5 to 15% efficient, meaning a lot of the energy of the sunlight is wasted. They hope to achieve 30% or better in the future. This will make solar energy a much more economical and viable energy alternative. Are there any drawbacks to solar power? Solar power has two major drawbacks. One drawback is that the amount of sunshine in a specific place changes due to the time of day, the weather, and the time of the year. The other drawback is that with current technology it takes a lot of expensive photovoltaic cells to produce a decent amount of electricity. Fun Facts about Solar Power The world's largest solar thermal plants are located in the state of California. Many large photovoltaic plants are being built around the world. Some of the largest are located in China, Canada, and the United States (Nevada). If only 4% of the world's deserts were covered in photovoltaic cells, they could supply all of the world's electricity. Many people think that as solar panels become more efficient and less expensive they will become a standard feature of new homes and buildings. In 1990 a solar powered aircraft flew across the United States using no fuel. Albert Einstein won a Nobel Prize in 1921 for his research into photovoltaic power. What is wind power? Wind power is energy, such as electricity, that is generated directly from the wind. It is considered a renewable energy source because there is always wind on the Earth and we aren't "using up" the wind when we make energy from it. Wind power also does not cause pollution. Wind Turbines and Wind Farms In order to make electricity from wind, energy companies use large windmills called wind turbines. They are called this because they use turbine generators to generate the electricity. In order to create a lot of energy capable of powering thousands of homes, energy companies build large wind farms with lots of wind turbines. They usually build these in consistently windy places. Some companies build wind farms out in the ocean. These are called offshore wind farms. How tall are wind turbines? Wind turbines are really big structures. The tower itself is typically between 200 and 300 feet tall. When you add in the height of the blades, some turbines tower 400 feet high! The blades are quite big, too. There are typically three wind blades on a wind turbine. Each blade is usually between 115 and 148 feet long. How does a wind turbine work? A wind turbine works the opposite of a fan. Instead of using electricity to turn the blades to make wind, it uses the wind to turn the blades to make electricity. When the wind turns the blades, the blades turn a shaft inside the turbine. This shaft is big, but turns slowly. The shaft, however, is connected to a number of gears which causes a smaller shaft to turn much faster. This smaller shaft drives the electrical generator which generates the electricity that can be used by homes and businesses. The parts inside a wind turbine help to generate electricity What if there isn't any wind? If there isn't any wind, then no energy will be generated by the wind turbine. However, engineers do a lot of measurements and calculations to figure out the best areas to place the wind turbines. The wind won't be blowing all the time, but the important thing is how much the wind blows on average. History of Windmills Windmills have been used since the Middle Ages in order to harness the energy of the wind. They were initially used to pump water or to grind flour. They are still used in many places of the world today to pump water. It was in the late 1800s and early 1900s that windmills were first used to generate electricity. Are there any drawbacks to wind power? One major issue some people have with wind power is how the wind turbines mess up the view or landscape. Other drawbacks include the large blades killing birds and noise pollution from the turbine. Most people agree that the positives of a fully renewable and clean energy resource far outweigh the negatives. Fun Facts about Wind Power For a wind turbine to make money it must be placed in a spot with an average annual wind speed of 15 miles per hour. In 2011, the top wind power producing state in the United States was Texas. Texas was followed by Iowa, California, Minnesota, and Illinois. Around 3% of the electricity in the United States in 2011 was provided by wind power. This was enough to power around 10 million homes. Tax breaks and new technologies have helped the output from wind power to grow significantly in the last 10 years. The largest wind farm in the United States is the Horse Hollow Wind Energy Center in Texas. It has 421 wind turbines. What is hydropower? Hydropower is power that is generated from moving water such as rivers. Renewable Energy Hydropower is a renewable energy source. This means that using a dam or a river to generate electricity doesn't use up any limited resources like coal or gasoline. How do we get power from water? Falling or flowing water from a big river has a lot of energy. We can harness this by forcing the water through a pipe called a penstock. As the water flows through the pipe it turns the blades of a turbine which spins an electric generator. As long as the water is flowing, the generator will be able to provide electricity. Electricity can be generated by water moving through a dam There are three main ways that engineers design hydroelectric power plants: Storage System - The storage system uses a dam. The dam slows the flow of a river and stores up water in a lake. A portion of the water is released into the river at the bottom of the dam. The fall of the water, and the water pressure from the lake, forces the water through the dam and spins turbine generators. Dams are expensive to build, but they also help control flooding, can create a large recreational lake, and can provide fresh water for surrounding towns. Run-of-the-river System - In a run-of-the-river system the turbines are spun by the natural flow of the river. These systems have the advantage of not creating a huge lake and flooding the area above the dam. As a result, they have less overall impact on the environment. However, in order to provide continuous electricity, the river they use must stay full throughout the year, as the flow is not regulated by a dam. Pumped Storage System - This system is like the storage system except it uses pumps to pump used water back up into the reservoir. The way this works is that during the night, when electricity use is much less, it uses the extra electricity to pump the water back up to the top of the dam and refill the reservoir. This improves the overall efficiency of the hydropower plant. Go here to read about the ocean power technologies tidal and wave power. Advertisement | Report Ad History of Hydropower Using rivers to power mechanical devices is not a new concept. As far back as ancient times, thousands of years ago, people used hydropower to perform tasks such as grinding grain into flour. In the late 1800s scientists first figured out how to use hydropower to generate electricity. The first hydroelectric power plant was built in Wisconsin in 1882. Since then, many more power plants have been built in the United States including the Hoover Dam in 1936 and the Grand Coulee Dam in 1942. Are there any drawbacks to hydropower? Like any power source there are some drawbacks to hydropower. One drawback is the loss of land and the damage to the local ecosystem caused when a lake is created by a dam. This can also cause people to have to relocate and leave their homes. Another disadvantage is methane emissions generated by the reservoirs. Dams and turbines can also hurt fish and disrupt their migration to spawning grounds. Fun Facts about Hydropower There are over 2,000 hydroelectric power plants in the United States. Many countries, such as Norway and Brazil, get a significant portion of their electricity (as much as 85%) from hydropower. The largest dam and hydroelectric power plant in the world is the Three Gorges Dam in China. It provides 22,500 Megawatts of electricity! Most of the dams in the United States were not built to supply power. They were built for flood control and to provide local irrigation. A large portion of the hydropower generated in the United States occurs in the western states. The number one producer of hydropower is Washington state which produced 29% of the nations hydropower in 2011. What is biomass energy? Biomass sounds like a complicated word, but it really isn't. Biomass is just any material made by plants and animals that we can covert into energy. Biomass has energy stored in it from the sun. Plants get energy from the sun through a process called photosynthesis. Animals get their energy indirectly from the sun by eating plants. Renewable Energy Biomass energy is considered a renewable energy source because we can always grow more plants and trees. It is not an infinite resource, however, as there is only so much land and water to grow plants. Main Types of Biomass Energy Biomass Energy comes in many shapes and forms. The majority of biomass energy in the United States comes from wood. Other popular forms of biomass include crops such as corn, manure, and even garbage. How do we get power from biomass? Burning - One way to release the energy from biomass is to burn it. The heat from burning biomass can be used to heat homes or to create steam which can then generate electricity. One example of this is burning a fire in your home. You burn the wood, which is the biomass, and it releases energy which heats your home. Methane gas - When biomass rots it produces methane gas. Methane gas can be used to make natural gas which is a common source of energy. This means that when garbage rots in landfills, that stinky gas can be used for energy! Biofuels - Some crops, like corn and sugar cane, can be converted into a biofuel called ethanol. Ethanol can be used instead of gasoline in many cars. Another type of biofuel is biodiesel. Biodiesel can be made from vegetable oils and animal fats. Biodiesel can be used as heating oil and also to power cars and busses. Methane gas from landfills can be used to generate electricity History of biomass Energy Biomass has been used as a source of heat energy since man first discovered fire. Many people around the world still burn wood as their primary source of heat during the winter. The use of biofuels such as ethanol has been around for some time as well. It was used as lamp fuel in the United States in the 1800s. The first Model-T Fords used ethanol for fuel until 1908. Recently, biomass and biofuels have become popular as an alternative to fossil fuels such as gasoline. Are there any drawbacks to biomass energy? Some of the negatives to using biomass energy include: Air pollution from burning Releasing green house gasses such as carbon dioxide into the atmosphere Burning trash and waste can release harmful chemicals and gasses into the environment The land cleared for growing corn and sugar cane can reduce habitats and destroy ecosystems The land used for growing biomass could be used to grow other crops for food Growing biomass can use fertilizers and other chemicals that can cause water pollution Despite all the negatives associated with biomass energy, many people believe that it is a better and cleaner alternative to burning fossil fuels such as oil and coal. Fun Facts about biomass Energy The methane gas from cow manure can be used to create energy. Most of the gasoline sold in the United States contains some ethanol. Garbage is burned for energy as well. This not only makes use of trash for energy, but reduces the amount of trash that goes into landfills. This process is called Waste-toEnergy. Farmers create energy from animal manure using tanks called digesters. The digesters produce biogas, which can be used to generate electricity. The main ingredient needed for ethanol is sugars. These sugars are found in plants such as corn, rice, sugar cane, barley, switch grass, and even grass clippings. Biodiesel is the fastest growing alternative fuel in the United States. What is geothermal energy? The inside, or core, of the Earth is very hot. This heat sometimes breaks through to the surface of the Earth through volcanoes or geysers. When we use heat from the Earth to generate energy it's called geothermal energy. The name geothermal is a combination of the word "geo", which means earth, and "thermal", which means heat. Sustainable Energy The Earth is constantly being warmed by its core. When we use geothermal energy we don't use up resources like we do when we burn gas or coal. Although we do use up a tiny bit of the Earth's heat, it is a very little amount in comparison to the overall heat of the Earth. This makes geothermal energy a type of sustainable energy. Geothermal power plants are very clean and have little negative impact on the environment. Geothermal heat pumps can keep homes warm How do we get power from the Earth? There are three main ways that we harness and use geothermal energy: Geothermal heat pumps - About 10 feet below the surface of the Earth, the ground is a consistent temperature between 50 and 60° F throughout the year. Geothermal heat pumps take advantage of this constant temperature to heat or cool water. By moving water through the Earth it can be heated in the winter or cooled in the summer. This water can then be used by a heat exchanger to heat or cool the air in a home. This can be a very efficient and inexpensive way to heat or cool buildings. Direct use - Another way to take advantage of the Earth's heat is to directly use hot water from hot springs. This water can be used with heat exchangers to heat up homes and buildings. It also can be used to heat pools. Generating electricity - Finally, geothermal energy can be used by power plants to create electricity. Power plants take advantage of extremely hot water that is between one and two miles deep in the Earth. Some power plants pipe the steam directly up to the generator. They are called dry steam power plants. Other power plants, called flash steam plants, use high pressure from deep in the Earth to create steam to drive the generator. Generating electricity using a geothermal power plant History of Geothermal Energy The use of geothermal energy is nothing new. People used hot springs as far back as Ancient China. The Ancient Romans took the concept a step further and used hot springs as a way to heat flooring and public baths. The first use of geothermal energy for electricity was in 1904 when the geothermal electric generator was invented. A few years later, in 1911, the first geothermal electric plant was built. In the 1940s, the heat pump began to be used for heating buildings, but it didn't become popular until the 1970s oil crisis. Are there any drawbacks to geothermal energy? Probably the main disadvantage to geothermal energy is the cost. It can be very expensive to build a geothermal plant. Building a plant can also be risky for a power company as the steam can potentially run out at a given site. The main environmental disadvantage is the possibility of releasing toxic gasses when the well is drilled into the ground. Fun Facts about Geothermal Energy The majority of geothermal electric plants in the United States are found in the western portion of the country. California is the number one producer, followed by Nevada, Utah, Hawaii, and Idaho. The United States is the largest producer of geothermal electricity. In 2011, the Philippines generated around 16% of their total electricity using geothermal electric plants. Iceland produced 26% of their total electricity using geothermal energy. It is possible for geothermal electric plants to cause earthquakes. The best place to find geothermal resources is along plate boundaries. This is also where you find the most volcanoes and get the most earthquakes. Wave and Tidal Energy Turning the energy of the ocean's waves and tides into power that we can use is a new and unproven technology. However, the potential is there for a significant renewable and environmentally clean energy source. What is wave energy? Wave energy is energy harnessed from the waves of the ocean. Waves are formed by wind moving across the surface of the ocean. A large amount of energy is stored in waves. A wave power device What is tidal energy? Tidal energy is energy produced by the tides of the ocean. Tides are produced by the pull of gravityfrom the Moon as well as the spin of the Earth. There is a lot of energy in the movement of that much water. Renewable Energy Wave and tidal power is considered renewable energy because we don't "use up" anything when we convert their energy to something usable like electricity. How do we get power from waves? There are three main ways that scientists think we can capture the power of waves: Surface devices - These devices gain power from the waves moving them up and down on the surface of the ocean. Underwater devices - These devices range from balloon type objects attached to the ocean floor to long tubes that stretch over a long distance. When the waves cause them to oscillate, they move a turbine and create electricity. Reservoir - These devices take advantage of the waves moving water into a reservoir on the coastline. As water moves back out into the ocean it is forced down a tube and turns the blades of turbine. The turbine then converts the energy into electricity. How do we get power from the tides? There are also three main ways that tidal energy is harnessed: Tidal Barrages - A tidal barrage works like a dam. When the tide goes high, the reservoir fills up. When the tide drops, the dam lets the water out. In both directions the moving water can spin the blades of turbines to create electricity. Tidal Fences - These are smaller structures than a barrage. A number of vertical turbines form a fence between two land masses. When the tide moves in or out, the turbines spin and generate electricity. Tidal Turbines - These are individual turbines placed anywhere there is a strong tidal flow. History of Wave and Tidal Energy Concepts for wave energy have existed since the 1800s, however modern wave technology began in the 1940s with the experiments of scientist Yoshio Masuda. Funding into wave energy technology has recently increased due to the need for renewable energy sources. The first wave power plant in the world opened in 2008 at the Agucadoura Wave Farm in Portugal. Tidal power to turn water wheels and grind grains was used as far back as Roman times and the Middle Ages. The idea of using tidal power for electricity is fairly recent, but the costs have been too high to make it a major energy source. Recent technological advances have shown that it could become a competitive and viable source. Are there any drawbacks to wave and tidal energy? The main disadvantage to these technologies today is cost. The cost of installing and maintaining a large wave or tidal power plant is too expensive versus other alternatives such as wind farms. Another drawback is the limited number of locations where current technologies can be economically installed. Both wave and tidal energy can also have some effect on the environment. Large tidal barrages can make it difficult for migrating fish. Also, spinning turbines can injure animals and fish. Fun Facts about Wave and Tidal Energy Tidal turbines are more expensive to build and maintain than wind turbines, but produce more energy. They also produce energy more consistently as the tide is continuous while the wind doesn't always blow. Wave and tidal energy converters are located near the coastline. It is easier to install, maintain, capture the energy, and retrieve the energy when they are located close to the coast. The United States has no tidal power plants. There are two existing large tidal barrages in the world today. One is in France and the other in Canada. Oil (Petroleum) 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." Where does Oil come from? 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. 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." How we get 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 Coal How coal was formed? 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. 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. 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. Surface mining: Underground 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. Natural Gas Where does Natural Gas come from? 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. 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. How we get Natural Gas? The search for natural gas begins with geologists (people who study the structure of the earth) locating the types of rock that are usually found near 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. How 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. 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. Once in this form, it takes up only 1/600th of the space that it would in its gaseous state. 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. Uranium (nuclear) 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. Nuclear Fuel Atoms are made up of three major particles: protons, neutrons and electrons. The most common fissionable atom is an isotope (the specific member of the atom's family) of uranium known as uranium235 (U-235 or U 235 ), which is the fuel used in most types of nuclear reactors today. Although uranium is quite common, about 100 times more common than silver, U-235 is relatively rare. Nuclear power plants generate electricity 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. 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. Most popular of them are: 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. 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 is shipped or distributed through transmission lines to homes, schools, hospitals, factories, office buildings, rail systems and other customers. Nuclear Steam Supply System: The reactor core is composed of four main elements: THE FUEL. Nuclear fuel consists of pellets of enriched uranium dioxide encased in 12-foot long pencil-thick metal tubes, called fuel rods. These fuel rods are bundled to form fuel assemblies. A nuclear plant can operate continuously for up to 2 years. To run this long, a reactor must have as many as 100 to 300 fuel assemblies. THE CONTROL RODS. The control rods contain material that regulates the rate of the chain reaction. If they are pulled out of the core, the reaction speeds up. If they are inserted, the reaction slows down. THE COOLANT. A coolant, usually water, is pumped through the reactor to carry away the heat produced by the fissioning of the fuel. This is comparable to the water in the cooling system of a car, which carries away the heat built up in the engine. In a reactor, as much as 330,000 gallons of water flow through the reactor core every minute to carry away the heat. THE MODERATOR. A moderator, water, slows down the speed at which atoms travel. This reduction in speed actually increases the opportunity to split, thereby releasing energy. Although engineering designs are quite complex, these four elements -- the fuel, the control rods, the coolant and the moderator -- are the basic components of a nuclear reactor. Nuclear power and the environment Like all industrial processes, nuclear power generation has by-product wastes: radioactive waste and heat. Nuclear generated electricity does not emit carbon dioxide into the atmosphere. Radioactive wastes are the principal environmental concern for nuclear power. Most nuclear waste is low-level nuclear waste. It is ordinary trash, 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 storage so they will not come in contact with the outside environment. On the other hand the irradiated fuel assemblies are highly radioactive and must 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. Most nuclear fuel is stored under water. A few reactors store their older and less radioactive fuel in dry storage facilities outside using special concrete or steel containers with air cooling. Hydrogen Hydrogen is the chemical element with atomic number 1. It is represented by the symbol H. At standard temperature and pressure, hydrogen is a colorless, odorless, nonmetallic, tasteless, highly flammable diatomic gas with the molecular formula H2. With an atomic weight of 1.00794 u, hydrogen is the lightest element. Hydrogen is the simplest element known to man. Each atom of hydrogen has only one proton. It is also the most plentiful gas in the universe. Stars are made primarily of hydrogen. The sun is basically a giant ball of hydrogen and helium gases. In the sun's core, hydrogen atoms combine to form helium atoms. This process—called fusion gives off radiant energy. This radiant energy sustains life on earth. It gives us light and makes plants grow. It makes the wind blow and rain fall. It is stored as chemical energy in fossil fuels. Most of the energy we use today came from the sun's radiant energy. Hydrogen gas is lighter than air and, as a result, it rises in the atmosphere. This is why hydrogen as a gas (H2) is not found by itself on earth. It is found only in compound form with other elements. Hydrogen combined with oxygen, is water (H2O). Hydrogen combined with carbon, forms different compounds such as methane (CH4), coal, and petroleum. Hydrogen is also found in all growing things— biomass. It is also an abundant element in the earth's crust. Hydrogen has the highest energy content of any common fuel by weight(about three times more than gasoline), but the lowest energy content by volume (about four times less than gasoline). It is the lightest element, and it is a gas at normal temperature and pressure. Hydrogen gas, H2, was first artificially produced and formally described by T. Von Hohenheim (also known as Paracelsus, 1493–1541) via the mixing of metals with strong acids. He was unaware that the flammable gas produced by this chemical reaction was a new chemical element. In 1671, Robert Boyle rediscovered and described the reaction between iron filings and dilute acids, which results in the production of hydrogen gas. In 1766, Henry Cavendish was the first to recognize hydrogen gas as a discrete substance, by identifying the gas from a metal-acid reaction as "inflammable air" and further finding in 1781 that the gas produces water when burned. He is usually given credit for its discovery as an element. In 1783, Antoine Lavoisier gave the element the name hydrogen (from the Greek hydro meaning water and genes meaning creator) when he and Laplace reproduced Cavendish's finding that water is produced when hydrogen is burned Hydrogen and energy carrier Energy carriers move energy in a usable form from one place to another. Electricity is the most wellknown energy carrier. We use electricity to move the energy in coal, uranium, and other energy sources from power plants to homes and businesses. We also use electricity to move the energy in flowing water from hydropower dams to consumers. It is much easier to use electricity than the energy sources themselves. Like electricity, hydrogen is an energy carrier and must be produced from another substance. Hydrogen is not widely used today but it has great potential as an energy carrier in the future. Hydrogen can be produced from a variety of resources (water, fossil fuels, biomass) and is a byproduct of other chemical processes. Unlike electricity, large quantities of hydrogen can be easily stored to be used in the future. Hydrogen can also be used in places where it’s hard to use electricity. Hydrogen can store the energy until it’s needed and can be moved to where it’s needed. How is hydrogen made Since hydrogen doesn't exist on earth as a gas, we must separate it from other elements. We can separate hydrogen atoms from water, biomass, or natural gas molecules. The two most common methods for producing hydrogen are steam reforming and electrolysis (water splitting). Scientists have even discovered that some algae and bacteria give off hydrogen. Steam reforming is currently the least expensive method of producing hydrogen and accounts for about 95 percent of the hydrogen produced in the United States. It is used in industries to separate hydrogen atoms from carbon atoms in methane(CH4). Because methane is a fossil fuel, the process of steam reforming results in greenhouse gas emissions that are linked with global warming. Electrolysis is a process that splits hydrogen from water. It results in no emissions but it is currently a very expensive process. New technologies are being developed all the time. Hydrogen can be produced at large central facilities or at small plants for local use. Every region of the country (and the world) has some resource that can be used to make hydrogen. Its flexibility is one of its main advantages. USES OF HYDROGEN About 9 million metric tonnes of hydrogen are produced in the United States today, enough to power 20-30 million cars or 5-8 million homes. Nearly all of this hydrogen is used by industry in refining, treating metals, and processing foods. Most of this hydrogen is produced in just three states: California, Louisiana, and Texas. The National Aeronautics and Space Administration (NASA) is the primary user of hydrogen as an energy fuel; it has used hydrogen for years in the space program. Liquid hydrogen fuel lifts the space shuttle into orbit. Hydrogen batteries—called fuel cells—power the shuttle’s electrical systems. The only by-product is pure water, which the crew uses as drinking water. Hydrogen Fuel CellHydrogen fuel cells (batteries) make electricity. They are very efficient, but expensive to build. Small fuel cells can power electric cars. Large fuel cells can provide electricity in out of the way places with no power lines. Because of the high cost to build fuel cells, large hydrogen power plants won't be built for a while. However, fuel cells are being used in some places as a source of emergency power to hospitals and to wilderness locations. Portable fuel cells are being sold to provide longer power for laptop computers, cell phones, and military applications.