In the late 19th century, when Nicola Tesla and George Westinghouse demonstrated that alternating current (AC) was cheaper to produce and easier to distribute to houses and factories than direct current (DC), the AC generation industry took off as hundreds of power plants began to spring up throughout the United States. But what is essentially needed to generate alternating current and why it is called "alternating"? Basically three things are needed: a magnet (or electromagnet), enameled wire, and a rotatory axle.
The electromagnet and the enameled wire is installed on the rotatory axle (or shaft) of a generator. This rotating part is called "rotor", which induces alternating current on the static part of the generator, which is called "stator" and consists of a multi-grooved round steel casing in which enameled copper wire is wound along these inner grooves. But why is it called "alternating"? Because the rotating magnet of the generator rotor constantly alternates or changes polarity, going form positive to negative to positive to negative, and so forth; this induces a flow of electrons along the enameled copper wire on the stator that alternates the flow direction as the magnet changes polarity, going in one way, then in the other as in waves.
But, what makes a generator shaft rotates, so that it can generate AC electricity? For that we need either an internal combustion engine or a turbine, coupling its shaft to the generator's. We know that the engine is powered by gasoline or diesel, but when these flammable fluids are expensive or absent, we have to put the engine aside and use a turbine. What powers the turbine? Different alternative sources, such as steam, gas, falling water, or wind. Steam is the most widely used source of energy to power turbines in AC generation in power plants in the United States and Europe. But steam has to be obtained and pressurized from boiling water in a boiler and, for this, we also need fuel, such as coal, wood, gas, and nuclear uranium rods in a controled fission nuclear power plant. Is there any other way to produce the needed heat to get steam from water? Fusion.