There’s a whole menu of different energy sources to choose from in generating electric power—coal, gas, wind, and so on—and some are worse for the planet than others. But regardless of where we gather it, the energy itself almost always comes from the sun. Don’t believe me? Let’s think about it:
When you burn coal, it reacts with oxygen and releases energy. But where did that energy come from? Prehistoric vegetation. Ancient ferns and weird swamp trees captured energy from sunlight using photosynthesis. Over eons, all that greenstuff got buried, where heat and pressure turned it into coal. That’s right, coal-based power is solar power. You could even call it a renewable resource, if you don’t mind waiting 100 million years.
Same with oil and natural gas. These fuels come from ancient marine microorganisms like phytoplankton and algae, which again used photosynthesis. (Sorry, oil isn’t from dinosaurs; there’s no fossils in fossil fuels.) Gazillions of these organisms died and settled to the bottom of the sea over time, getting buried in sediment and turning into the sludge we call petroleum. If you see an oil well on land, that spot was probably once underwater.
OK, but hydroelectric? That’s based on the gravitational potential energy of water at high elevations. As it runs downhill in rivers, it can do work, like spinning turbines. Well, how did the water get up there? It was deposited by snow and rain, which came from evaporation of seawater, which is driven by the sun’s heat. Yep, solar power.
Photograph: Getty ImagesWind energy? Well, the sun heats the Earth’s surface, but it does so unevenly. Its rays hit low latitudes more directly than high latitudes, and continents heat up faster than oceans. Result: Warm air rises, creating low-pressure areas that cooler air rushes in to fill. We call that wind. So, light energy is converted to thermal energy, and then to kinetic energy in air molecules. Solar.
What about human power, like you’d use to charge those hand-crank batteries in emergency kits? You get your energy from eating, and where does food come from? Plants. Even if you eat meat or fish, every food chain begins with plants that fix the sun’s light energy. (Kind of gives new meaning to the term “power plant,” right?)
Bottom line: Pretty much everything on Earth runs on sunshine. All the different energy “sources” that people debate are just conduits. Energy can’t be created or destroyed, only converted from one form to another. By the way, that means we’ll never run out of energy. Heck, the sun releases far more energy in a second than humans have consumed in their entire existence.
Oh, there is one major power source that doesn’t channel the sun’s energy. Can you guess? It’s nuclear. That’s because nuclear reactors are engaged in something similar to the sun: converting mass into energy. It’s fission versus fusion, but either way, E = mc2.
How Does It Become Electricity?
So how do we turn that energy into electric power so we can watch TV? Because, you know, if you set up your sofa and TV in the yard so the sun shines on it, nothing happens. Once again, the answer is simpler than you’d think. Almost all power stations use the same basic trick: rotating a coil of wire in a magnetic field.
This works because electric and magnetic forces are really just two sides of the same coin. As James Maxwell showed in 1865, an oscillating electric field creates a magnetic field, and an oscillating magnetic field creates an electric field. This, in fact, is what allows electromagnetic waves (i.e., light energy) from the sun to propagate through empty space and reach Earth.
But we want to go back to an earlier discovery by Michael Faraday in the 1830s. He showed that with a changing magnetic flux, you can create electric potential (voltage) in a wire that is not connected to any power supply, causing a current to flow through it if the circuit is closed. Voilà! You just made electricity.
Great! uh … what the heck is magnetic flux? OK, imagine rain falling on a piece of paper. The amount of rain that hits the paper would be the rain flux, which depends on (1) how hard it’s raining (the intensity) and (2) the size and angle of the paper. Lying flat it’ll be soaked; held vertically, it’ll stay dry. Between those extremes, you get varying amounts of flux.
Now replace the rain with a magnetic field pointing in a certain direction, represented by the red arrows in the diagram below. The flux is the amount of magnetic field passing through a loop of wire. When it’s parallel, as on the left, there’s zero flux. If we turn it, thus increasing the area exposed, the flux grows until the loop is perpendicular. Beyond that point it starts declining again.
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 5 billion years.
