Increasingly popular as alternative sources of energy, wind turbine generators are a type of windmill that produces electricity by harnessing the wind. Wind turbine generators are much less harmful to the environment than burning fossil fuels, but they do require average wind speeds of at least 13 mph.

The largest of these windmills stands 150 feet tall with blades half the legend of a football field. The compartments at the top containing the generator, hub and gearbox weigh 30,000 to 45,000 pounds.