Generating Electricity

In a closed system, the law of conservation of energy explains that energy isn't lost or created, only changed in form. In a generating plant, the energy in the fuel changes to electricity. Electricity is a more useful form of energy because it can be transmitted over distances and easily converted to heat, light, or mechanical motion.

Because electricity is expected to be available all the time and in whatever quantity required at that moment, fuel must be on hand in sufficient quantity to supply it. This requirement has led to the use of coal, natural gas, and nuclear fuels, which have been affordable and largely available in the United States in mass quantity to meet demand.

Generators and Turbines
The force of electricity used in homes and businesses comes from the collective movement of billions of electrons from atom to atom. This movement is created at power plants in a generator, a spinning device made up of copper wires and magnets. To get enough electrical force to power cities, generators are the size of locomotives and the plants that house them can be eight stories tall and wider than a football field.

In most power plants, a turbine turns the generator. The turbine has fan blades usually driven by high pressure steam. To make heat to turn water into steam, many plants burn fossil fuels, like coal or natural gas. Nuclear plants use the process of fission to make heat. Hydroelectric plants use the force of falling water to turn turbines. Wind turbines use moving air to make generators spin. For illustrations of fossil, hydro, and nuclear power plants in action, visit Learning Power.

The Grid
Electric plants are connected to a network of transmission wires that carry electricity long distances to distribution wires that connect to buildings, offices, and homes. Substations and transformers change the force in the wires at points in the journey between plant and plug, converting the electricity from high voltage, which travels best, to the lower-level voltage used by the electrical device.

Generators and the grid cannot store electric power. For the system to work reliably, electricity must be “pumped” into the wires by plants at the same rate it is removed by end-use devices or lost in transmission. Plants must convert fuel to electricity on the grid every moment in the exact amount devices need to use. Many plants work together to make enough electricity for any one moment and enough generators must be on standby to meet peak demand, like on a hot summer day. Also, intermittent sources of electricity, like wind, solar, and hydro, must be backed up by steady sources, like coal or gas, to meet demand when they aren’t available, like on calm or cloudy days.