November 18, 2004

Hundreds of thousands of wind towers, you say?

A recent post casually states that it would take hundreds of thousands of wind towers to provide 5% of the electricity used in the U.S. Here are the figures that confirm that statement.

According to data from the Department of Energy, we used 38.401 quadrillion btu of electricity in 2002. That's equivalent to 11,254 terawatt-hours (TW-h). Five percent of that is 563 TW-h, or 562,711,000 megawatt-hours (MW-h).

Dividing that figure by 365 days and 24 hours shows that 5% represents an average power feed of 64,236 MW. (See the post of Oct. 21 for an explanation of power and energy units.)

The output of a well sited (for the purpose of collecting wind) aerogenerator is about 25% of its rated capacity. So to provide an average 64,236 MW would require 256,944 MW of installed capacity. Using the usual utility-size turbine of 1.5 MW, that would require 171,296 of them.

The lesson from Denmark, however, is that only about one sixth of the wind-generated power is actually used, because it so rarely corresponds with demand (David J. White, "Danish Wind: Too Good To Be True?," The Utilities Journal, July 2004). So for the U.S. to get 5% of its electricity from wind would require more than 1,000,000 turbine towers.

Existing complexes use 30-60 acres per MW capacity (the more space they have the better they work). Getting 5% of our electricity from wind would therefore require installations covering at least 72,000 and possibly (ideally) more than 144,000 square miles. That's almost the size of the entire state of Montana.