One Way or Another, Most of Our Electricity Comes From Solar Power | WIRED

CommentLoader-

Save StorySave this story

CommentLoader-

Save StorySave this story

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 Images

Wind 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 elec