Electricity Generation

Georgia Perimeter College

Objectives

  1. List some of the ways in which electricity can be generated.

  2. State the dominant way in which electricity is generated in the U.S.
  3. Demonstrate an understanding of how electricity is generated from fossil fuels like coal, oil, and natural gas.
  4. Describe how nuclear power can be used to generate electricity.
  5. Describe the function of an electrical transformer.
  6. Demonstrate an understanding of how electricity is transported from the power plant to your house, and the changes it undergoes.
This section addresses, in whole or in part, the following Georgia GPS standard(s):
  • S8P2. Students will be familiar with the forms and transformations of energy.
    c. Compare and contrast the different forms of energy (heat, light, electricity, mechanical motion, sound) and their characteristics.
  • S8P5. Students will recognize characteristics of gravity, electricity, and magnetism as major kinds of forces acting in nature.
    b. Demonstrate the advantages and disadvantages of series and parallel circuits and how they transfer energy.
    c. Investigate and explain that electric currents and magnets can exert force on each other.

This section addresses, in whole or in part, the following Benchmarks for Science Literacy:
  • Magnetic forces are very closely related to electric forces and can be thought of as different aspects of a single electromagnetic force. Moving electric charges produce magnetic forces and moving magnets produce electric forces. The interplay of electric and magnetic forces is the basis for electric motors, generators, and many other modern technologies, including the production of electromagnetic waves.

  • Electrical energy can be produced from a variety of energy sources and can be transformed into almost any other form of energy. Moreover, electricity is used to distribute energy quickly and conveniently to distant locations.
  • Energy can change from one form to another, although in the process some energy is always converted to heat. Some systems transform energy with less loss of heat than others.

This section addresses, in whole or in part, the following National Science Education Standards:
  • Energy is a property of many substances and is associated with heat, light, electricity, mechanical motion, sound, nuclei, and the nature of a chemical. Energy is transferred in many ways.
  • Electrical circuits provide a means of transferring electrical energy when heat, light, sound, and chemical changes are produced.
  • In most chemical and nuclear reactions, energy is transferred into or out of a system. Heat, light, mechanical motion, or electricity might all be involved in such transfers.
  • Electricity in circuits can produce light, heat, sound, and magnetic effects. Electrical circuits require a complete loop through which an electrical current can pass.
  • Resources are things that we get from the living and nonliving environment to meet the needs and wants of a population.
  • Some resources are basic materials, such as air, water, and soil; some are produced from basic resources, such as food, fuel, and building materials; and some resources are nonmaterial, such as quiet places, beauty, security, and safety.
  • The supply of many resources is limited. If used, resources can be extended through recycling and decreased use.
     

How Electricity is Generated

(From the Energy Information Administration)

Electricity is form of energy characterized by the presence and motion of elementary charged particles generated by friction, induction, or chemical change. Electricity 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.

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 coal is the largest single primary source of energy used to generate electricity in the United States? In 2005, more than half (51%) of the country's 3.9 trillion kilowatthours of electricity used coal as its source of energy.

            Chart of Electric Power Generation by Fuel Type (2005)

Image from the Energy Information Administration

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 2005, 17% 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 three percent (3%) of all electricity generated in U.S. electricity plants in 2005.

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 20% of all the country's electricity in 2005.

Hydropower, the source for almost 7% of U.S. electricity generation in 2005, 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 2005.

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 2005, less than 1% of the nation's electricity was based on solar power.

 

A light powered by a solar cell

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 2005, 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.

U.S. Electric Power Industry Net Summer Generating Capacity 2005

Image from the Energy Information Administration

 

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.

 

Electrical substation

 

Figure 1 is a graphic depicting power generation, transmission and distribution. For more information, contact the National Energy Information Center at 202-586-8800

Image from the Energy Information Administration

http://www.eia.doe.gov/neic/brochure/electricity/images/transmission.gif

http://www.eia.doe.gov/kids/energyfacts/sources/images/TRANSPORTELECTRICITY1.jpg

Utility pole with cylindrical electrical transformer

Home electric meter

 

Georgia Power truck


 


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Content provided by the Energy Information Administration.

Page created by Pamela J.W. Gore
Georgia Perimeter College,
Clarkston, GA

Page created March 13, 2007
Modified May 19, 2007
Web link updated December 4, 2007