Nearly all the electricity on the planet, with the exception of batteries and photovoltaic solar cells, is generated by taking advantage of a single physical law: magnetic fields produce a force on moving charges. So how can we produce an electrical current? Make a loop of conducting copper wire. Place that loop in between two magnets. Rotate the loop. As you rotate the loop, you give the free electrons in the copper some velocity. The magnetic field then causes a force on them that causes them to flow around the loop. Voila, electricity.
Of course, we would gain nothing as a civilization if all our electricity was produced by men who spent their days turning loops of wire. What we need is something to turn the coil for us. So we steal some energy from somewhere else in nature.
Any power plant will have inside it many turbines. The turbines are generally connected via a shaft to what is basically a coil of wire. The coil of wire sits between two magnets. What makes the turbine spin depends on the source of energy of the power plant. In a hydroelectric dam, it will be water running over the turbine. Steam, created from water that has been heated by burning coal, or by a nuclear reaction, or by focused sunlight, is another popular choice. When the turbine spins, it produces an electrical current, just as we have already discussed. And that’s basically the whole story. Although the public commonly thinks of hydroelectric power as different than coal power as different than nuclear power, they are really all operating on the same principle.
If you’re also interested in how batteries provide electricity, read on.
ELECTRICITY FROM BATTERIES
Batteries are dependent upon chemical reactions for their function. You have likely noticed that all batteries have two terminals, or “electrodes,” one positive and one negative. Inside the battery, chemical reactions essentially carry electrons “uphill” from the positive terminal to the negative terminal, raising their energy as they do so. When you connect something to the battery like a light bulb, the electrons then flow “downhill” through the light bulb, losing energy as they do so, until they end up back where they started, on the positive electrode.
From what I’ve written, you might think that batteries should last forever, but of course that isn’t so. Nature never gives you something for nothing, so the battery must stop working eventually. What I didn’t mention is that these chemical reactions that move the electrons around also cause other changes to the battery electrodes that aren’t easily reversible. In a nickel-cadmium battery, for example, the cadmium electrode reacts to yield two electrons, but also turns from cadmium into cadmium hydroxide, which can be of no further use.