Get it? So a spinning loop produces an oscillating flux; if you graphed its values it would trace out a sine wave. That creates an oscillating voltage in the wire, causing electrons to move, and boom: you have alternating current. You just created a generator! This is called electric induction.
Now you can amp this up by replacing that single loop of wire with a wrapped coil containing many, many loops. Oh, it also works in reverse: Instead of rotating a coil in a stationary magnetic field, you can rotate magnets around a stationary coil. The relative motion is all that matters.
Putting a Spin on It
So you see, almost all methods of generating electric power come down to a magnet and a coil of wire. We just need a way to rotate one or the other. For that we have some options. If you put big blades on your rotor and expose it to the wind, the collision of air particles on the blades exerts a torque and turns a shaft. That’s a wind turbine. Or you could put turbines in a big dam and use the flowing water to turn them—that’s hydroelectric power.
You could also boil water and use steam to drive the turbines. This is what most power plants do, in fact, usually by burning fossil fuels to bring the heat. That could be coal, oil, or natural gas, it’s all the same technology. Or you could tap into underground heat and use that to produce steam—yep, that’s geothermal power.
In fact, this is how nuclear power works, too: You take a heavy element like uranium and split it into smaller atoms, which gives you energy to heat the water and drive steam turbines. Yeah, the only difference between a coal-fired power plant and a nuclear power plant is how you boil the water. You thought it was more complicated, right?
But once again, there’s a major exception, a generation technology that doesn’t use electric induction. Did you notice the omission? Ironically, it’s solar panels. Photovoltaic cells are solid-state devices—they have no moving parts—and they convert light directly into electricity.
Straight From the Source
How much juice can we get directly from the sun? Well, the intensity of solar radiation declines as it moves away from the sun, because a given amount of light is spread over a larger area. And when it reaches Earth, some of that light is absorbed or scattered in the atmosphere. (That’s why the sky is blue.) But we’re kind of at a perfect distance, one that keeps the oceans from either boiling away or freezing over.
At the equator, the solar flux—the amount of power hitting the ground—is around 1,000 watts per square meter. Of course, the Earth is curved, so that declines as you move toward the poles. But in a good spot, with a panel that has a conversion efficiency of 20 percent, you can get up to 200 W/m2. That means it takes just a few panels to provide all the electricity a home needs.
So yes, most of the energy we use comes from the sun. You might even think of fossil fuel deposits as batteries, storing solar power for future civilizations. But with the old technologies, we’re getting that energy indirectly, after multiple conversions from one form to another—and inevitable losses along the way. Why not cut out the middlemen and go direct? No carbon emissions, no air pollution, no radioactive waste, no mining or transportation costs. And the sun’s going to keep shining for five billion years.
