Reply #23: From my admittedly limited knowledge, two of the biggest are GE and Vestas

[A HERETIC I AM]

http://www.vestas.com/

Vestas has a plant north of Denver in Brighton, CO. I know this because I picked up one of the cars onboard right across the street from it! They had blades on rail cars, as well as hubs, housings and tower sections.

I was curious if the blades were perhaps carbon fiber so I banged on it and it sounded and felt like aluminum. It was hollow but the hub end was very stout and solid, for at least 15 feet from the end. It had welds that would lead me to believe the hub end had several bulkheads inside before the blade proper began as well as thicker wall material. That would make sense, as it has to bear all the stress when the blade is spinning not to mention carry the weight of the entire blade itself.