In the power industry, energy efficiency involves getting the most usable energy out of the fuels that supply the power plants. The efficient generation of power is only one way a power plant can pursue energy efficiency. New technologies applied to the storage of energy and the transmission of energy contribute to energy efficiency. For instance, the copper wires used in typical transmission lines lose a percentage of the electricity passing through them because of resistance, which causes the wires to heat up.
Energy storage can also make an electric utility system operate more efficiently.
The most familiar way to store electricity is using batteries, but many other technologies have been developed, ranging from pumping water uphill to trapping electrical current in superconducting loops of wire. Unlike other energy sources like natural gas, fuel oil, or gasoline, which are held in large storage tanks until they are needed, most of the electricity in our country is generated at the moment it is needed. To meet changing electrical demands, some power plants must be kept idling in case they are needed. During times of high electrical demand, inefficient power plants may be brought on-line to provide extra power, and the transmission system may be stretched to near its limit, which also increases transmission energy losses. On the other hand, the inability to store excess electricity during periods of low demand can force utilities to operate power plants at less than full power, which is usually less efficient.