Sometimes, you read something on the web that just sounds so intriguing yet unlikely that you have to prove that it’s incorrect. From a discussion in Metafilter I ran into a site that claimed that all of the U.S.’s power needs could be met with a 50 square mile solar array in Texas.
Just on the face of this, it’s a cool idea, but it’s one of those things that didn’t even seem possible within a magnitude, so of course a few minutes of Googling was in order. Given the ecologically destructive effects of oil and coal burning, there would be no way that we would be doing it if solar were a reasonable option.
For the year 2000, the U.S. consumed about 3.8 trillion kilowatt-hours (kWh) of energy. You need about a 100 square feet of solar panel to provide 1 kWh. The amount of energy generated over the year depends heavily, of course, on where the panels are installed, but let’s assume that we’re going to put them in Texas, which means that we’ll get 1,800 kWh a year.
So, working this out means that we get:
3.8×10^12 kWh / 1800 kWh * 100 ft^2 / 5280^2 ft
… which is about 87 square miles on a side. Still enormously huge and enormously expensive, but just in checking the facts I’ve gone from “Oh, right, there’s no way” to something that is within a magnitude of reasonability. A magnitude, really, is just an engineering problem. There is no doubt that it would be totally unreasonable to make this many solar panels, there would be shortages in gallium arsenide and other components used for solar panels today. On the other hand, these figures are predicated on 10% efficiency, whereas we have experimental technologies that are getting in the range of 30%.