As construction nears completion at the 6-MW Pioneer Grove Wind Farm in Cedar County, Iowa, Acciona Windpower has completed fabrication of the first section of a 100-meter-high concrete tower, the first of its kind for the company in North America.

Chicago-based Acciona North America, a subsidiary of the Madrid-based conglomerate that owns Acciona Windpower, has used concrete towers to support more than 80 wind turbines, the company states. But this is the first such tower to be built in North America and the first from any supplier to support a 3-MW turbine at 100 m.

The concrete tower is being fabricated in sections at Acciona Windpower's West Branch, Iowa, facility, says an Acciona North America spokesman. It will be erected along with a 92-m-high steel tower, both designed to support 3-MW wind turbines.

"The AW-3000 turbines at Pioneer Grove will produce more power more efficiently than anything we've installed before," says Joe Baker, chief executive officer of Acciona Windpower.

Charles Hanskat, civil engineering consultant in Northbrook, Ill., says concrete is advantageous for building higher towers for larger, more efficient generators. "Concrete can carry higher lateral and dynamic forces than steel," he says.

Steel fatigue can occur when large generators are mounted on slender steel tubes, he says, "since steel is more flexible under dynamic loads of wind turbines," he says. "Once you reach 100 meters, you are pushing past the limit where steel is cost- and design-effective."

Pioneer Grove expects to sell power to the Central Iowa Power Cooperative via a 20-year power purchase agreement by the year's end, the spokesman says.