Whoa, they're big

Those wind turbines popping up across the U.S., sometimes singly and but more often in “wind farms,” are larger than one might first think. Seen from a passing vehicle, headed south on I-65 toward Purdue near Wolcott, Ind., for example, the slowly and gracefully turning rotors bely the true size of these power producers.
A little investigation turned up some interesting information about this technology. Commercial scale wind turbines only operate at wind speeds of 11 mph or greater. Typically they are mounted 100 ft or more above the ground, which lets them take advantage of the faster and less turbulent wind at that height. Taller towers sometimes use rotors having a diameter of more than 300 feet.
Each typically generates a megawatt or more of electrical energy. Where wind farms can be connected to the electrical grid, they can contribute significantly to our electrical power needs.

We came across this Department of Energy photo that shows one completed tower, another where the rotor is being lifted into place, and a few people, a big crane, and a pickup truck to help show the scale. Each of the blades is 118 ft long. It's at the Red Hills Wind Farm in Oklahoma. Just in case the photo's missing, here's the link: http://www.nrel.gov/data/pix/Jpegs/16483.jpg (Photo by Todd Spink, courtesy of DOE/NREL.)
Refreshed URL for the image (with explanation), Oct 30, 2015: http://images.nrel.gov/viewphoto.php?imageId=6311868