Electricity Generation and Distribution

What Is Electricity?

Electricity is a form of energy that starts with atoms. Atoms are too small to see, but they make up everything around us. All atoms are composed of subatomic particles among which are the charged particles known as electrons and protons. Protons, which are found in the nucleus of an atom, carry a positive charge (+), and electrons, which spin around the center of an atom, carry a negative charge (-). Neutrons also exist in the nucleus of a typical atom and are uncharged.

Electricity is a form of energy that is associated with the buildup and movement of electrons and protons. Electricity can be created by forcing electrons to flow from atom to atom. The force or push of electricity is measured in volts. Electrical systems of most homes and office have 120 volts.

How Electricity Is Generated

Most electricity in the U.S. is generated using coal, oil, natural gas, nuclear energy, or hydropower. Some production is done with alternative fuels like geothermal energy, wind power, biomass, solar energy, or fuel cells.

A majority of the electricity is produced at power plants with the use of steam turbines. Mechanical energy is changed into electrical energy by using various energy sources such as coal, natural gas, and oil. These fuels heat water in a boiler to produce steam. The steam, under tremendous pressure, is used to turn a series of blades mounted on a shaft turbine. The force of the steam rotates a shaft that is connected to a generator. The spinning turbine shafts turn electromagnets that are surrounded by heavy coils of copper wire inside generators. This creates a magnetic field, which causes the electrons in the copper wire to move from atom to atom, creating electricity.

The voltage produced by a generator depends upon the number of turns in its coils, the strength of the magnet, and the rate at which the magnet turns. The more turns in the coils, the more voltage is produced.

Hydropower

Hydroelectric plants use the power of falling water to push against the turbine blades, causing a rotor to spin. Water stored behind a dam is released and directed through special tubes to flow against the blades of turbines and make them turn. Hydropower provides about 10 percent of the electricity generated in the U.S. The most famous hydroelectric facility in the country is Hoover Dam.

Fossil Fuels

The majority of electricity used in the U.S. is generated from power plants that burn fossil fuels (coal, oil, and natural gas) to heat water and make steam. The highly pressurized steam is directed at the blades of turbines to make them spin.

Coal, oil, and natural gas are known as fossil fuels because they were formed from the fossilized remains of animals or plants that lived long ago. Long ago, even before the dinosaurs, these plants and animals died and settled to the bottom of lakes and oceans to be covered over by sand and mud. Over millions of years, the earth's pressure and heat converted their remains into coal, oil, and natural gas.

Coal is extracted from the ground at large mines. Coal is used to generate about half of the electricity used in the U.S.

Natural gas and oil are obtained through wells drilled deep in the earth. Natural gas is used to generate about 10 percent of the electricity used in the U.S., and oil is used to generate about two percent of electricity used in the U.S. The U.S. depends on natural gas for about 24% of its total primary energy requirements.

Nuclear Power

Nuclear power plants use the heat from splitting atoms to convert water into the steam that turns turbines. These plants rely on uranium, a type of metal that must be mined from the ground and specially processed. Fuel rods containing uranium are placed next to each other in a machine called a nuclear reactor. The reactor causes the uranium atoms to split and in so doing, they release a tremendous amount of heat. The U.S. in 2000 produced 22.3 quadrillion BTUs from nuclear electric power. (A BTU, or British thermal unit, is the amount of heat necessary to raise the temperature of one pound of water by one degree Fahrenheit.)

Geothermal Energy

Geothermal energy utilizes steam trapped in the earth. A geothermal power plant is similar to a steam power plant. A deep well is drilled and steam comes out, goes through a heat exchanger, and then spins a turbine. Electric power plants driven by geothermal energy provide over 44 billion kilowatt-hours (kWh) of electricity worldwide per year. The U.S. in 2000 produced .32 quadrillion BTUs from geothermal power.

Wind Power

The force of the wind pushes against the turbine blades, causing the rotor to spin and generate an electric current. Most wind power is produced from wind farms—large groups of turbines located in consistently windy locations. The U.S. in 2000 produced .05 quadrillion BTUs from wind power; wind energy contributed more than 3.5 billion kWh of electricity.

Biomass

Biomass is organic matter, such as agricultural wastes and wood chips and bark left over when lumber is produced. Biomass can be burned in an incinerator to heat water to make steam, which turns a turbine to make electricity. It can also be converted into a gas, which can be burned to do the same thing. Biomass provides about 3 to 4 percent of our energy in the U.S.; in 2000, 22.3 quadrillion BTUs were produced from wood, waste, and alcohol. The wood and paper products industries generate and use about two-thirds of this power. Solid wastes from cities fuel most of the remaining biopower plants, providing enough electricity to meet the needs of nearly 7 million Americans.

Solar Energy

Solar energy is generated without a turbine or electromagnet. Special panels of photovoltaic cells capture light from the sun and convert it directly into electricity. The electricity is stored in a battery. The U.S. in 2000 produced .07 quadrillion BTUs from solar power. More than 200,000 houses in the U.S. take advantage of the sun's energy.

Fuel Cells

A fuel cell is a device or an electrochemical engine that converts the energy of a fuel directly to electricity and heat without combustion. Fuel cells consist of two electrodes sandwiched around an electrolyte. When oxygen passes over one electrode and hydrogen over the other, electricity is generated. Fuel cells running on hydrogen derived from a renewable source would emit nothing but water vapor. Fuel cells are clean, quiet, and efficient.

Energy Statistics: U.S. Energy Information Administration (www.eia.doe.gov)

How Electricity Is Distributed

Power plants do not store electricity, so it is constantly being made and then distributed. Utility companies have to anticipate demand for electricity and distribute it to consumers.

Electricity can be distributed most efficiently at very high voltage. Transformers are used to “step up” or “step down” the voltage along the system of power lines that carry electricity to consumers.

First, the voltage of the electricity produced by a generator in the power plant is “stepped up” when it travels through a secondary coil of a transformer that has far more turns of wire than the primary coil. Each charge that passes through that coil then has more energy than the charges in the primary coil. The current therefore has an enormous voltage when it leaves the secondary coil and then travels through the system of cables and wires from the power plant into the transmission grid.

These transmission lines carry the electricity across long distances to substations. A substation has transformers that “step down” the high-voltage electricity into lower voltage electricity. At a substation, the current passes through a transformer with a secondary coil that has fewer turns of wire, which reduces it to only a medium-high voltage.

From the substation, distribution lines carry the electricity to other transformers on utility poles or on the ground that reduce the voltage so it can be used in homes, offices, stores, and factories. A cable then carries the electricity from the distribution wires to the house through a meter box. The meter measures how much electricity the people in the house use.

From the meter box, wires run through the walls to outlets and lights. The electricity is always waiting in the wires to be used. The amount of electricity in the lines must be kept at a constant electrical pressure to provide enough power for the appliances and equipment that will use it. A second set of wires carries the current back to the generator in the power plant. These return wires are necessary because electric current must travel in a loop, or a closed circuit.

• Next Page: Alternative Energy Sources

• Back to Menu

• Links to Go Further