Solar Power

September 16, 2009
  • Physics
  • Politics
  • Technology

If you read enough Thomas Friedman, you should already be indoctrinated with the mantra that green jobs and renewable energy are the future. And you should already be well aware that America is starting to lag behind other major industrial countries in that front, including Germany and China. Friedman's latest column focuses on the United States' shortcomings in implementation of solar power, even while much of the technology and industry is made in America (his columns are always interesting, and only sometimes bombastic and awkwardly written). Friedman's correct, we should certainly increase funding to solar research, and the government should take a bigger role in encouraging green industry (the stimulus was a nice start). After all, the Sun has been powering this planet for billions of years, and it's pretty good at what it does.

The sun produces a lot of energy. It's the biggest nuclear power planet in our solar system, and it sends its power to Earth in the form of light. To be specific, the Sun produces 3.8 * 10 ^ 26 Watts of power that it shoots out into the universe in all directions. That's a lot of energy released every second. To get some feel for that magnitude, worldwide energy consumption in a year is about 510^20 Joules, which amounts to about 1.5 * 10^13 Watts. That's about one 10^13th of the sun's power (as in 1/10000000000000). Of course, not all of this reaches the Earth, and most of it is sent out into deep space for people in other solar systems to see as a far away star. Because we are so far from the Sun, we only get about 10^17 Watts of power. But that's still way more than we need.

So, solar power is incredibly abundant and is a remarkable source of energy. Friedman says that we don't use enough solar energy, but I have to disagree with him. In fact, the VAST majority of the energy that we consume comes from the sun (though most of it very indirectly). What do I mean? Well, let's follow the energy cycle backwards a bit.

Imagine I start a fire in the fireplace in my room (okay, the fireplace in my room is fake and is only there for decoration, but ignore that for now). I burn a few logs, sit in front of the mantle, hold out my hands, and feel the heat warming me up. What I'm really feeling is stored solar energy, the direct result of nuclear reactions in the sun. Trees are giant solar batteries. They collect light energy directly from the sun using efficient solar panels called leaves. The leaves absorb the sun's rays (the only absorb some of the rays, the most abundant ones, and relfect the rest, which is what makes them green) and use that energy to make wood. As everyone knows, plants breathe carbon dioxide and release oxygen. Wood is made mostly of carbon. This is no coincidence. Plants take in CO2 and use the energy of the sun to break that apart into C and O2. The plant doesn't care about the oxygen and it just gets rid of it (thankfully for us). But it takes all the carbon, sticks it together, and turns it into wood.

It takes energy to break apart the carbon and oxygen. Carbon and oxygen like to be together, so the plant requires the power of the sun to pull them apart. Thus, the carbon in the wood wants to reunite with the oxygen and has a lot of potential energy to do this (meaning, there's a net release of energy when the carbon breaks apart and gets back together with oxygen). When I burn wood in my fireplace, I'm just allowing carbon and oxygen to once again join hands, and the heat I feel is the energy that the plant put into the CO2 in the first place to turn it into wood and oxygen. So, in a sense, the heat I feel is the sun's rays that the plant absorbed via it's leaves, which were stored within the wood, and then released when I burn the wood.

If you didn't already know, people also like to burn oil for fuel. But that's really the same thing as the wood. Oil is just very dense plant remains (it's mostly prehisoric algae. It's not actually made of dinosaurs as people sometimes joke). It's basically fermented wood soup. When we burn oil, we're just burning highly dense, liquid plant batteries (because it's so dense, it releases a lot of carbon into the atmosphere and also releases a lot of energy in the process). But it still comes from plants, meaning the energy originally came from the sun. The same goes for coal, gas, and pretty much anything that is burned to make power. It's just indirect solar power.

(Not all of our power is solar. Hydroelectric power is just absorbing gravity indirectly. Nuclear power uses the strong force to turn neutrons into protons. Wind power comes from the spinning of the Earth, meaning that every time we use wind turbines, we slow the rotation of the Earth just a little bit. Geothermal power comes from the hotness at the center of the Earth, which is produced by gravity. Again, every time we use that, we cool down the Earth a little bit).

So where does the Sun get so much energy? Well, solar energy really is just gravity. The sun is a lot of hydrogen that is pulled together by its mutual gravitational force. Eventually, it becomes extremely dense and the hydrogen atoms are pulled close enough together to fuse into helium, and a lot of energy in the form of photons are released. So really, the solar energy of the sun is the result of gravity and nuclear QCD effects.

At some point, gravity will continue to pull the sun together, but the sun will be unable to keep producing enough energy via fusion to keep itself from collapsing. The sun will swell and eventually fizzle out, leaving our solar system dark. Hopefully we will have fixed our energy dependence issues by then.