What Is Electricity? - Information Resource Center

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Power is a form of energy. It is the flow of electrons. All matter is made up of atoms, and an atom has a center, called a nucleus. The nucleus contains positively charged particles called protons and uncharged particles called neutrons. The nucleus of an atom is surrounded by negatively charged particles called electrons. The negative charge of an electron is equal to the positive charge of a proton, and the number of electrons in an atom is usually equal to the number of protons. When the balancing force between protons and electrons is upset by an outside force, an atom may gain or lose an electron. When electrons are "lost" from an atom, the free movement of these electrons constitutes an electric current. 

Power is a basic part of nature and it is one of our most widely used forms of energy.  We get power, which is a secondary energy source, from the conversion of other sources of energy, like coal, natural gas, oil, nuclear power and other natural sources, which are called primary sources. Many cities and towns were built alongside waterfalls (a primary source of mechanical energy) that turned water wheels to perform work. Before power generation began slightly 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 power gradually became understood. In the mid-1800s, Thomas Edison changed everyone's life -- he perfected his invention -- the electric light bulb. Prior to 1879, power had been used in arc lights for outdoor lighting. Edison's invention used power to bring indoor lighting to our homes.


To solve the problem of sending power over long distances, George Westinghouse developed a device called a transformer. The transformer allowed power to be efficiently transmitted over long distances. This made it possible to supply power to homes and businesses located far from the electric generating plant. 

Despite its great importance in our daily lives, most of us rarely stop to think how life would be like without power. Yet like air and water, we tend to take power for granted. Everyday, we use power to do many functions for us -- from lighting and heating/cooling our homes, to being the power source for televisions and computers.  power is a controllable and convenient form of energy used in the applications of heat, light and power. 

Today, the United States (U.S.) electric power industry is organized to ensure that an adequate supply of power is available to meet all demand requirements at any given instant.


An electric generator is a device for converting mechanical energy into electrical energy.  The process is based on the relationship between magnetism and power. When a wire or any other electrically conductive material moves across a magnetic field, an electric current occurs in the wire. The large generators used by the electric utility industry have a stationary conductor. A magnet attached to the end of a rotating shaft is positioned inside a stationary conducting ring that is wrapped with a long, continuous piece of wire. When the magnet rotates, it induces a small electric current in each section of wire as it passes. Each section of wire constitutes a small, separate electric conductor. All the small currents of individual sections add up to one current of considerable size. This current is used for electric power.


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 power. Steam turbines, internal-combustion engines, gas combustion turbines, water turbines, and wind turbines are the most common methods to generate power. 

Most of the power in the United States is produced through the use of steam turbines in power plants. 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 power in the United States? In 2000, more than half (52%) of the county's 3.8 trillion kilowatthours used coal as its primary source of themal generated energy in power stations.

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 power. Gas turbines are commonly used when power utility usage is in high demand. In 2000, 16% of the nation's power 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 less than three percent (3%) of all power generated in U.S. power plants in 2000.

Nuclear power is a method in which steam is produced by heating water through a process called nuclear fission. In nuclear power plants, 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 power. Nuclear power is used to generate 20% of all the country's power.

Hydropower, the source for 7% of U.S. power generation, 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 power. 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 power. 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 power.


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 generates less than 1% of the power in the country.

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 power 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. Less than 1% of the nation's generation is based on solar power.

Wind power is derived from the conversion of the energy contained in wind into power. Wind power, like the sun, is rapidly growing source of power, and is used for less than 1% of the nation's power. 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 power. 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 less than 1% of the power generated in the United States.

The power produced by a generator travels along cables to a transformer, which changes power from low voltage to high voltage. Power can be moved long distances more efficiently using high voltage. Transmission lines are used to carry the power to a substation. Substations have transformers that change the high voltage power into lower voltage power. From the substation, distribution lines carry the power to homes, offices and factories, which require low voltage power.


Power 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 kilowatt-hour (kWh) is equal to the energy of 1,000 watts working for one hour. The amount of power 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 watts of power, or .2 kilowatthours of electrical energy..

Electric Power in General

Traditional electric utilities in the United States are responsible for ensuring an adequate and reliable source of power to all consumers in their service territories at a reasonable cost. Electric utilities include investor-owned, publicly owned, cooperatives, and Federal utilities. Power marketers are also considered electric utilities--these entities buy and sell power, but usually do not own or operate generation, transmission, or distribution facilities. Utilities are regulated by local, State, and Federal authorities.

The electric power industry is evolving from a highly regulated, monopolistic industry with traditionally structured electric utilities to a less regulated, competitive industry. The Public Utility Regulatory Policies Act of 1978 (PURPA) opened up competition in the generation market with the creation of qualifying facilities. The Energy Policy Act of 1992 (EPACT) removed some constraints on ownership of electric generation facilities and encouraged increased competition in the wholesale electric power business.

Nonutility Power Producers

Qualifying Facilities: PURPA facilitated the emergence of a group of nonutility power-generating companies called qualifying facilities or QFs. Under PURPA, small power producers and cogenerators receive status as a QF by meeting certain requirements for ownership, operating methods, and efficiency. Those requirements were established by the Federal Energy Regulatory Commission (FERC).

Cogenerators: Facilities which produce power and another form of useful thermal energy through the sequential use of energy (usually heat or steam for industrial processes or heating/cooling purposes) are called cogenerators--many of which have status as QFs. Cogenerators are primarily engaged in business activities (such as, agriculture, mining, manufacturing, transportation, education). The power that they do generate is mainly for their own use, but any excess is sold to the host utility.

Independent Power Producers: These facilities (known as IPPs) must use renewable energy as a primary source for generation of power. IPPs operate within the franchised territories of host utilities. They do not possess transmission facilities or sell power on the retail market (that is, all their sales are wholesale or sales for resale). By definition, a facility that has QF status is not an IPP.

Exempt Wholesale Generators: EPACT modified the Public Utility Holding Company Act (PUHCA) and created another class of nonutility power producers: exempt wholesale generators (EWGs). EPACT exempted EWGs from the corporate and geographic restrictions imposed by PUCHA. With this modification, public utility holding companies are allowed to develop and operate independent power projects anywhere in the world.

Total electric power generating capability as of year-end 2000 totaled 811,625 megawatts of which 74.2 percent was attributed to utilities and 25.8 percent to nonutilities.

Coal accounted for 38.8 percent of generating capability and 51.8 percent of the 3,800 billion kilowatthours of electric industry net generation.

The average price of power in the United States increased in 1999, for the first year since 1992, to 6.68 cents per kilowatthour. The three states with the highest average price of power were Hawaii (14.0 cents per kilowatthour), New Hampshire (11.6 cents per kilowatthour), and New York (11.2 cents per kilowatthour). The three lowest were Kentucky (4.1 cents per kilowatthour), Idaho (4.2 cents per kilowatthour), and Wyoming (4.4 cents per kilowatthour).

Energy Information Administration
1000 Independence Avenue, SW
Washington, DC 20585



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