How electricity is generated

Electric generator Diagram of an electricity generator - Spinning rotor turning coiled copper wire inside stationary magnets to generate electricity.

Source: Adapted from Energy for Keeps (public domain)

In 1831, scientist Michael Faraday discovered that when a magnet is moved inside a coil of wire, an electric current flows in the wire. An electricity generator is a device that converts a form of energy into electricity. Generators operate because of the relationship between magnetism and electricity. Generators that convert kinetic (mechanical) energy into electrical energy produce nearly all of the electricity that consumers use.

A common method of producing electricity is from generators with 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 coil becomes a small, separate electric conductor. The small currents of the individual sections combine to form one large current. This current is the electricity that moves through power lines from generators to consumers.

Most of U.S. electricity generation is from electric power plants that use a turbine or similar machine to drive electricity generators.

A turbine converts the potential and kinetic energy of a moving fluid (liquid or gas) to mechanical energy. In a turbine generator, a moving fluid—such as water, steam, combustion gases, or air—pushes a series of blades mounted on a shaft, which rotates the shaft connected to a generator. The generator, in turn, converts the mechanical energy to electrical energy based on the relationship between magnetism and electricity.

Different types of turbines include steam turbines, combustion (gas) turbines, water (hydroelectric) turbines, and wind turbines. In steam turbines, hot water and steam are produced by burning a fuel in a boiler or by using a heat exchanger to capture heat from a fluid heated with, for example, solar or geothermal energy. The steam drives a turbine, which powers a generator. The fuels or energy sources used for steam turbines include biomass, coal, geothermal energy, petroleum fuels, natural gas, nuclear energy, and solar thermal energy. Most of the largest electric power plants in the United States have steam turbines.

Combustion gas turbines, which are similar to jet engines, burn gaseous or liquid fuels to produce hot gases to turn the blades in the turbine.

Internal combustion engines, such as diesel engines, are also used to produce mechanical energy to operate electricity generators. Diesel-engine generators are used in many remote villages in Alaska and are widely used for power supply at construction sites and for emergency or backup power supply for buildings and power plants. Diesel-engine generators can use a variety of fuels including petroleum diesel, biodiesel, natural gas, biogas, and propane. Small internal combustion engine generators fueled with gasoline, natural gas, or propane are commonly used by construction crews and tradespeople and for emergency power supply for homes.

Combined-heat-and-power (CHP) plants, sometimes called cogenerators, use the heat that is not directly converted to electricity in a steam turbine, combustion turbine, or an internal combustion engine generator for other purposes, such as space heating or industrial process heat. Some power plants use the unused heat or combustion gases from one turbine, such as a gas turbine, to generate more electricity in another turbine, such as a steam turbine. This system of two separate generators using a single fuel source is called a combined cycle. CHP and combined-cycle power plants are some of the most efficient ways to convert a fuel into useful energy.

Hydroelectric turbines use water to spin turbine blades, and wind turbines use the wind.

Electricity generators that do not use turbines include solar photovoltaic cells, which convert sunlight directly into electricity, and fuel cells, which convert fuels, such as hydrogen, into electricity through a chemical process.

The share of total U.S. utility-scale electricity generation in 2017 by major types of electricity generators

  • Steam turbines–64%
  • Combustion turbines–21%
  • Hydroelectric turbines–7%
  • Wind turbines–6%
  • Solar photovoltaic systems–1%
  • Internal combustion engines–less than 1%