Could We Get All Our Power From Solar Energy When the World Runs Out of Oil and Coal?

Probably not, if you mean making electricity from solar panels.

There certainly is lots of sunshine, but capturing it and converting it efficiently is the problem. Let’s do the arithmetic.

Every day, the sun shines down upon the surface of Earth an amount of energy equal to three times the world’s annual energy consumption. That means that to keep up with consumption we would have to capture and convert all the sunlight falling on about one-tenth of a percent of Earth’s surface. That may not sound like much, but it’s about 180,000 square miles (470,000 square kilometers) of solar panels, or about the size of Spain.

Double that to take care of the inescapable fact that it’s always nighttime in half the world. And oh, yes: There are clouds.

But if you think about it, all of our energy sources today come from the sun, with only one exception: nuclear energy, which we discovered how to make about sixty years ago. Nuclear energy, in the form of nuclear fusion, is where the sun gets its energy in the first place. So speaking cosmically, there is really only one source of energy in the universe, and it’s nuclear. Even Earth’s internal heat, the source of volcanos and hot springs, is fed by nuclear energy from radioactive minerals.

But until we learned how to make some of our own nuclear energy down here on Earth, we had to procure our share of cosmic nuclear energy through a go-between: Old Sol. The sun converts its own nuclear energy into heat and light for us, and all of our current energy sources come from that heat and light. They are therefore solar energy in a real sense.

Let’s look at our “solar energy” sources one at a time. Fossil fuels: Coal, natural gas and petroleum are the remnants of plants and animals that lived millions of years ago. But what created those plants and animals? The sun. Plants used the energy of sunlight to grow by photosynthesis and the animals came along and ate the plants (and, alas, one another). All life on Earth owes its existence to the sun and so, therefore, does the energy we get today from fossil fuels.

Water power: Hydroelectric power plants suck the gravitational energy out of falling water by enticing it into plummeting down onto the blades of turbines, our modern version of the waterwheel. Instead of your having to have a waterwheel or turbine in the kitchen to grind your coffee beans, the turbine-driven generators convert the water’s gravitational energy into electrical energy, which is then piped to your wall outlet through copper wires.

The water cascades down Niagara Falls or spills over Hoover Dam because in deference to Sir Isaac Newton (the falling-apple guy), it is trying to get closer to the center of Earth. Then isn’t water power really the power of gravitational attraction? Isn’t it Earth-provoked, rather than sun-provoked?

Yes, but hold your horsepower. How did that water get so high in the first place that it can then fall down under the influence of gravity?

It’s the sun again. The sun beats down on the oceans, evaporating water into the air, where it is blown around by the winds, forms clouds and eventually rains or snows back down. So without the sun’s water-lifting power, we wouldn’t have water-falling power. We wouldn’t have waterfalls or rivers, because without being replenished from above by sun-raised rain and snow, they’d all run dry.

Wind power: Windmills capture energy from moving air. But what makes the air move? You guessed it: the sun.

The sun’s rays shine down upon Earth’s surface, a little stronger here and a little weaker there, depending on the seasons, the latitudes, cloud cover and a number of other things. But the land is warmed up by the sun’s rays much more than the oceans are, and that creates unevenly heated air masses around the globe. As the warmer masses rise and the cooler masses rush in at ground level to replace them, the air flows, producing everything from balmy breezes to monsoons. Because all of these winds are ultimately traceable back to the sun’s heat, wind power is truly sun-provoked.

All right, so all of our winds aren’t caused by the sun. Some of them are caused by Earth, without any outside help.

Earth is rotating, and as it rotates it carries along a thin surface layer of gas, the atmosphere. Now gases and liquids are what we call fluids, substances that flow easily, unlike solids. (Most people use the word “fluid” to mean only liquids, but gases also flow, and are therefore fluids.) Any fluid will have a tough time staying in place when the solid body it’s trying to hang on to is moving. In an airplane, for example, the coffee in your cup slops around when the plane hits bumpy air the moment after the flight attendant pours it.

In the same way, the rotational movement of Earth makes the air slop around to a certain extent, like the coffee in the cup. And what is air that’s slopping around? Wind. So some of our winds are Earth-provoked, rather than sun-provoked.

One way in which Earth’s rotation affects air movements is quite interesting. It’s called the Coriolis effect.