Electricity Basics. Electricity Is a Secondary Energy Source

Transcription

1 Electricity Basics Electricity Is a Secondary Energy Source Electricity is the flow of electrical power or charge. It is both a basic part of nature and one of our most widely used forms of energy. Electricity is actually a secondary energy source, also referred to as an energy carrier. That means that we get electricity from the conversion of other sources of energy, such as coal, nuclear, or solar energy. These 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 nonrenewable. Electricity Use Has Dramatically Changed Our Daily Lives Before electricity became available 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. Many scientists and inventors have worked to decipher the principles of electricity since the 1600s. Some notable accomplishments were made by Benjamin Franklin, Thomas Edison, and Nikola Tesla. Benjamin Franklin demonstrated that lightning is electricity. Thomas Edison invented the first long-lasting incandescent 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 reduced the cost of transmitting electricity over long distances. 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, few of us probably stop to think what life would be like without electricity. Like air and water, we tend to take

2 electricity for granted. But we use electricity to do many jobs for us every day from lighting, heating, and cooling our homes to powering our televisions and computers. Science of Electricity Basics Everything Is Made of Atoms In order to understand electricity, 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. 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. Protons have a positive charge (+) and electrons have a negative charge (-). The positive charge of the protons is equal to the

3 negative charge of the electrons. Opposite charges attract each other. An atom is in balance when 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 consisting of one type of atom (the Periodic Table shows all the known elements), all with the same number of protons. Every atom of hydrogen, for example, has one proton, and every atom of carbon has six protons. The number of protons determines which element it is. Electricity Is the Movement of Electrons Between Atoms 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 can 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 an atom's 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. Static Electricity Exists in Nature 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.

4 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. Magnets and Electricity BACK TO TOP Magnetic Field Around a Bar Magnet Source: National Energy Education Development Project (Public Domain) The spinning of the electrons around the nucleus of an atom creates a tiny magnetic field. Most objects are not magnetic because their electrons spin in different, random directions, and cancel out each other. Magnets are different; the molecules in magnets are arranged so that their 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.

5 Magnets Have Magnetic Fields 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. Just like protons and electrons opposites attract. Magnetic Fields Can Be Used To Make Electricity Properties of magnets can be used to make electricity. Moving magnetic fields can pull and push electrons. Metals such as copper have electrons that are loosely held. So electrons in copper wires can easily be pushed from their shells by moving magnets. By using moving magnets and copper wire together, electric generators create electricity. Electric generators essentially convert kinetic energy (the energy of motion) into electrical energy. Batteries, Circuits, & Transformers Batteries Produce Electricity BACK TO TOP Source: National Energy Education Development Project (Public Domain) 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

6 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 light bulb is placed along the wire, the electricity can do work as it flows through the wire. Electrons flow from the negative end of the battery through the wire to the light bulb. The electricity flows through the wire in the light bulb and back to the positive end of the battery. Electricity Travels in Circuits Electricity travels in closed loops, or circuits. 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 an electric wire, through the light bulb, and back out another 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 TV set, producing pictures and sound. Sometimes electricity runs motors in washers or mixers. Electricity does a lot of work for us many times each day. Source: National Energy Education Development Project (Public Domain) Transformers Help To Move Electricity Efficiently Over Long Distances 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 increased delivery range made it possible to supply electricity to homes and businesses located far from the electric generating plant.

7 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. Measuring Electricity Electricity Is Measured in Watts and Kilowatts A Residential Electricity Meter BACK TO TOP 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 is the same as 1,000 watts. Electricity Use Over Time Is Measured in Kilowatthours 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 kilowatts required by the number of hours of use. For example, if you use a 40-watt light bulb for 5 hours, you have used 200 watthours, or 0.2 kilowatthours, of electrical energy. See EIA's Energy Calculator section to learn more about converting units. How Electricity is Generated BACK TO TOP

8 How Electricity Is Generated Turbine Generator Source: adapted from Energy For Keeps (Public Domain) 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, scientist Michael 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 a device that converts mechanical or chemical energy to electricity. Steam turbines, internalcombustion engines, gas combustion turbines, water turbines, and wind turbines are the most common methods to generate electricity. Steam turbine power plants powered by coal and nuclear energy produce about 70% of the electricity used in the United States. These plants are about 35% efficient. That means that for every 100 units of primary heat energy that go into a plant, only 35 units are converted to useable electrical energy.

9 Electricity in the U.S. Basics Most of the electricity in the United States is produced using steam turbines. A turbine converts the kinetic energy of a moving fluid (liquid or gas) to mechanical energy. In a steam turbine, steam is forced against a series of blades mounted on a shaft, thus rotating the shaft connected to the generator. The generator, in turn, converts its mechanical energy to electrical energy based on the relationship between magnetism and electricity. In steam turbines powered by fossil fuels, such as coal, petroleum (oil), and natural gas, the fuel is burned in a furnace to heat water in a boiler to produce steam. Fossil Fuels Generate Most U.S. Power Coal is the most common fuel for generating electricity in the United States. In 2010, 45% of the Country's nearly 4 trillion kilowatthours of electricity used coal as its source of energy. More data 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 turbine's blades to generate electricity. Gas turbines are commonly used when electricity utility usage is in high demand. In 2010, 24% of the Nation's electricity was fueled by natural gas. Petroleum can be burned to produce hot combustion gases to turn a turbine or to make steam to turn a turbine. Residual fuel oil, a product refined from crude

10 oil, is often the petroleum product used in electric plants that use petroleum to make steam. Petroleum was used to generate just over 1% of all electricity in the United States in Nuclear Power Provides About One-Fifth of U.S. Electricity 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 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, creating 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 about 20% of all the Country's electricity in Renewable Energy Sources Make Up the Rest Hydropower, the source for 6% of U.S. electricity generation in 2010, 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 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, water is diverted from a river using a relatively low dam or weir into penstocks and turbines. The dam does not store a large volume of water in a reservoir. Run-of-river power plants are more dependent on river flows than hydro plants with reservoirs for storing water which can produce electricity even when natural river flows are low. Biomass is material derived from plants or animals (i.e. biogenic) and includes lumber and paper mill wastes; food scraps, grass, leaves, paper, and wood in municipal solid waste (garbage); and forestry and agricultural residues such as wood chips, corn cobs, and wheat straw. These materials can be burned directly in steam-electric power plants, or converted to gas that can be burned in steam generators, gas turbines, or internal combustion engine-generators. Biomass accounts for about 1% of the electricity generated in the United States. Wind power is produced by converting wind energy into electricity. Electricity generation from wind has increased significantly in the United Statessince 1970, but wind power remains a small fraction of U.S. electricity generation, about 1%. Geothermal power comes from heat energy buried beneath the surface of the earth. In some areas of the United States, enough heat rises close to the

11 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 Solar power is derived from energy from the sun. There are two main types of technologies for converting solar energy to electricity: photovoltaic (PV) and solar-thermal electric. PV conversion produces electricity directly from sunlight in a photovoltaic (solar) cell. Solar-thermal electric generators concentrate solar energy to heat a fluid and produce steam to drive turbines. In 2010, less than 1% of the Nation's electricity was from solar power. How Electricity Gets to Your Home BACK TO TOP Electricity Is Delivered to Consumers Through a Complex Network Electric power is generated at power plants and then moved to substations by transmission lines large, high-voltage power lines. In the United States, the network of nearly 160,000 miles of high voltage transmission lines is known as the "grid." A local distribution system of smaller, lower-voltage distribution lines moves power from substations and transformers to customers. Electric power generation, transmission, and distribution diagram Source: National Energy Education Development Project (Public Domain) Electricity Comes from Various Sources and Kinds of

12 Providers The utility, distribution company, or retail service provider selling you power may be a not-for-profit municipal entity, an electric co-operative owned by its members, a private, for-profit company owned by stockholders (often called an investor-owned utility), or a power marketer. Some Federally-owned authorities including the Bonneville Power Administration and the Tennessee Valley Authority, among others also buy, sell, and distribute power. The origin of the electricity you consume may vary. Utilities may generate all the electricity they sell using just the power plants they own. Utilities may also purchase some of their supply on the wholesale market from other utilities, power marketers, independent power producers, or from a market based on membership in a regional transmission reliability organization. How the Grid Is Organized Most of the existing grid was built during a highly structured, highly regulated era designed to ensure that everyone in the United States had reasonable access to electricity service. Utility customers, through fees authorized and regulated by State regulatory commissions, generally paid for developing and maintaining the grid. Source: Energy Information Adminsitration. Map shows NERC (North American Electric Reliability Corporation) regions. Many local grids are interconnected for reliability and commercial purposes, forming larger, more dependable networks to maximize coordination and planning. These networks extend throughout many States. The North American Electric Reliability Corporation (NERC) was established to ensure that the grid in the United States was reliable, adequate, and secure. Some NERC members have formed regional organizations with similar missions. These organizations are referred to as Independent System Operators (ISOs) and Regional Transmission Organizations (RTOs). They are part of a national standard design advocated by the Federal Energy Regulatory Commission (FERC). Some have members who connect to lines in Canada or Mexico. Most, depending on the location and the utility, are indirectly connected to dozens and often hundreds of power plants. Some power consumed in the United States is imported from Canada and Mexico.

13 Electricity & the Environment BACK TO TOP Although electricity is a clean and relatively safe form of energy to use, there are environmental impacts associated with the production and transmission of electricity. Nearly all types of electric power plants have some impacts or effects on the environment, some more than others. The Two Coal-fired Power Plants of the Crystal River North Steam Complex in Crystal River, Florida Source: Ebyabe, Wikimedia Commons author (GNU Free Documentation License) (Public Domain) Hunter Power Plant, a Coal-Fired Power Plant South of Castle Dale, Utah Source: Tricia Simpson, Wikimedia Commons author (GNU Free Documentation License)

14 (Public Domain) The United States has laws to reduce these impacts. Perhaps the most important such law is the Clean Air Act, which established regulations for the control of air emissions from most power plants. The Environmental Protection Agency (EPA) administers the Act and sets emissions standards for power plants through various programs, such as the Acid Rain Program. The Act has resulted in a substantial reduction of emissions of some of the major types of air pollutants in the United States. The Impact of Power Plants on the Landscape All power generators or plants have a physical footprint (the area where they are placed or located). Some can be located inside, on, or next to an existing building, so the impact of their footprint is very small. Most large power plants require clearing land to locate the power plant and any necessary fuel storage areas (in the case of hydro-power dams, a reservoir forms behind the dam). Some plants may also require the construction of access roads, rail, pipelines, transmission lines, and access to cooling water supplies or reservoirs. Besides the physical footprint, many power plants are large physical structures that have impacts on the visual landscape. Some people may not like this especially where the landscape is relatively natural or pristine. In general, the larger the area disturbed, the greater the real and potential impacts on the landscape. Fossil Fuel-, Biomass-, and Waste-Burning Power Plants In the United States, fossil fuels (mainly coal, oil, and natural gas), materials that come from plants (biomass), and municipal and industrial wastes are used to generate most of the electricity we use; about 70% in Emissions that result from the combustion of these fuels include: Carbon dioxide (CO2) Carbon monoxide (CO) Sulfur dioxide (SO2) Nitrogen oxides (NOX) Particulate matter (PM) Heavy metals such as mercury Nearly all combustion byproducts have negative impacts on the environment and human health: Carbon dioxide is a greenhouse gas and a source of global warming.1

15 SO2 causes acid rain, which is harmful to plants and to animals that live in water, and it worsens or causes respiratory illnesses and heart diseases, particularly in children and the elderly. NOX contributes to ground level ozone, which irritates and damages the lungs. PM results in hazy conditions in cites and scenic areas, and, along with ozone, contributes to asthma and chronic bronchitis, especially in children and the elderly. Very small, or fine PM is also thought to cause emphysema and lung cancer. Heavy metals such as mercury can be hazardous to human and animal health. Power Plants Use Air Emission Controls Power plants are required to meet standards that limit the amounts of some of the substances that they release into the air. There are different ways that power plants meet these standards: Coal-fired plants can use coal that is low in sulfur content. Coal can also be pretreated and processed to reduce the types and amounts of undesirable compounds in combustion gases. Particulate matter emissions are controlled with devices that clean the combustion gases that exit the power plant: Bag-houses use large filters Electrostatic precipitators use charged plates Wet scrubbers use a liquid solution SO2 emissions are controlled by wet and dry scrubbers, which involves mixing lime in the fuel (coal) or by spraying a lime solution into the combustion gases. Fluidized bed combustion can also be used to control SO2. NOX emissions can be controlled by several different techniques and technologies, such as low NOX burners during the combustion phase or selective catalytic and non-catalytic converters during the post combustion phase. Some Plants Also Produce Liquid and Solid Wastes The coarse solid residue that results from the burning solid fuels is called ash. The largest particles collect at the bottom of the boiler ("bottom ash") and are removed and quenched with water. Smaller and lighter particulates ("fly ash") are collected in air emission control devices, and are usually mixed with the bottom ash. The resulting "sludge," which contains all the hazardous materials that were captured by the pollution control devices, may be stored in retention ponds, sent to landfills, or sold for use in making concrete blocks or asphalt. Many coal-fired power plants have very large sludge ponds. Several of these ponds have burst and caused extensive damage and pollution downstream of the pond. Most Power Plants Produce Greenhouse Gases

16 Greenhouse gases contribute to the greenhouse effect. Scientists know with virtual certainty that increasing greenhouse gas concentrations tend to warm the planet.2 Power plants that burn fossil fuels and materials made from fossil fuels and some geothermal power plants are the sources of about 40% of total U.S. carbon dioxide (CO2) emissions. Nuclear Power Plants Produce Different Kinds of Waste Nuclear power plants are not a source of greenhouse gases or other emissions, but they do produce two kinds of radioactive waste: Low-level radioactive waste This includes items that have become contaminated with radioactive material, such as clothing, wiping rags, mops, filters, reactor water treatment residues, and equipment and tools. Low-level waste is stored at nuclear power plants until the radioactivity in the waste decays to a level where it is allowed to be disposed of as ordinary trash or it is sent to a low-level waste disposal site. Spent (used) nuclear fuel 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 spent fuel in dry storage facilities using special outdoor concrete or steel containers with air cooling. Electric Power Lines Also Have a Footprint Power transmission and distribution lines carry electricity from power plants to customers. Most transmission lines are strung above ground on large towers. The towers and lines impact the visual landscape, especially when they pass through pristine natural areas. Trees near the wires may be disturbed and have to be managed to keep them from touching the wires and these activities can affect native plant populations and wildlife. Power lines can be placed under the ground, but this is more expensive and may result in a greater disturbance of the landscape than overhead lines.