Every second, the sun bathes Earth with 172,500 terawatts of energy. (A terawatt—a trillion watts—is the biggest energy unit in common use.) About a third of this prodigious flow is promptly reflected into space, mainly by clouds. The leftover—roughly 113,000 terawatts, depending on cloud cover—is available for capture. All human enterprises together now use a bit less than 18 terawatts. In other words, the sun furnishes more than six thousand times the energy produced today by all of our power plants, engines, factories, furnaces, and fires combined.
