By Deston Nokes

As wind turbine generators increase in size, some tower manufacturers are gearing up to accommodate developers' requests for towers that rise above 100 meters [328 feet] in height. ...

Today, with so many of the "lower" level resources being harvested, companies are seeking ways to maximize domestic wind generation. WindKraft Nord (WKN) USA was the first in the U.S. to vault higher to take advantage of wind resources at higher altitudes. However, all signs indicate that more developments will include taller towers. ...

"The challenges of hauling the new towers are obvious," Jess Collins, group president at Broadwind Energy, says. "Most 80-meter towers already are 14 feet in diameter at the base, and increasing it will be an even bigger challenge when it comes to bridge clearance. A larger-diameter structure means a taller load once it becomes horizontal on a truck. Finding routes through many states already is a challenge, and it will continue to get tougher.

Collins notes that trains have been helpful in transporting components to wind sites but that any increase in tower diameter will limit rail['s] ability to serve the wind industry.

As turbines and rotor diameters grow, the physical demands on the towers will continue to increase.

"To build 105-meter towers, the foundation has to be redesigned larger," Florian Zerhusen, president of WKN USA, says. "Plus, it also depends on the soil condition."

According to Peder Hansen, executive vice president of Northstar Wind Towers in Nebraska, there are two options for managing the loads of these massive turbines: The first is to increase the structure's wall thickness, and the second is to increase the bottom diameter of the tower, thus enabling a continuous or increasing taper towards the foundation.

"Thicker walls are the number-one option today, because transportation restrictions dictate the maximum diameter allowed," Hansen says.