CHAPTER ONEThe History of Solar Energy
About 4.5 billion years ago, Earth's Sun was born. It sits at the center of our solar system, 93 million miles away from Earth. It's also about 30,000 light years away from the center of the Milky Way galaxy. Our solar system is located in one of the Milky Way's spiral arms. Just as all of our planets rotate around the Sun, our solar system rotates around the center of the galaxy. It takes a mere 250 million years to do so.
Unlike the earth, the sun is entirely gaseous. It's approximately 74 percent hydrogen, 25 percent helium, and 1 percent other. A constant nuclear chain reaction produces the light and heat given off by the sun's layers. The sun's luminosity, or brightness, is the same as that produced by four trillion-trillion (4,000,000,000,000,000,000,000,000) 100-watt lightbulbs. The sun will continue to get brighter and larger for another five billion years.
In the meantime, humanity benefits from the solar energy that reaches the earth. We receive just one-billionth of the total energy generated by the sun. About 174,000 terawatts (TW) of radiation hits the earth's upper atmosphere. It reflects roughly 30 percent back into space. Oceans, landmasses, and clouds absorb the rest. The wavelengths of the solar radiation we receive are in the visible, ultraviolet, and near infrared spectrums. To put the amount of solar energy the earth gets into perspective, we receive more energy from the sun in one hour than the world uses in an entire ...