In power generation, the generator is a device that converts the original power (mechanical energy) into the electrical energy for external circuits. Sources of mechanical energy include steam turbines, gas turbines, water turbines, internal combustion engines and even cranks. The first electromagnetic generator Faraday disk was built by British scientist Michael Faraday in 1831. Generators supply almost all the electricity to the grid.

The electric energy is conversed into mechanical energy by electric motor, and the motor and generator have many similarities. Many motors can be driven mechanically to generate electricity, and acceptable manual generators are often manufactured.