The composite towers will stand as much as 65 ft taller than the steel towers currently used. They would be some of the largest composite structures ever built.
According to Brian Rice, Division Head for Multi-Scale Composites and Polymers at UDRI, wind turbine towers have to be strong enough to carry the weight of the turbine (which can be as much as 100 tons) but also resist buckling under the stress of the rotating machinery. Steel monopoles are pre-fabricated in sections as large as 14 ft in diameter and 70 ft long, then trucked individually to the wind site to be put together and installed on a concrete foundation. When finished, the average utility-grade wind turbine tower is about 80 m (approximately 265 ft) tall.
But the wind industry has been setting its sights on a new standard for tower height at 100 m (328 ft), Rice says. Putting larger turbines on top of taller towers facilitates access to greater wind speeds, which improves operating performance and cost. As the size of wind turbines continues to grow, however, so grow the problems and expense associated with transporting and building the towers.
“If you increase the height of the tower, you have to increase its diameter as well,” Rice explains. “Which means that next-generation wind turbines will require towers that will be too large to ship via highway, even in sections.”
The solution, he says, is to use fibre reinforced plastic (FRP) composite tower sections that would be manufactured on site at the wind farm.
“On-site fabrication eliminates the transportation problems and makes more sites accessible to wind power development,” Rice reports. “Even today there are good potential wind farm sites in remote or hilly locations, but there aren’t sufficient roads to allow for trucking in steel towers; the new design would solve that problem as well.”
In addition, the corrosion-resistant properties of composites will be far more suitable than steel for the offshore wind farms which are just starting to be developed in US waters.
The Ohio project team comprises lead partner Ershigs Inc in Manchester, UDRI and Edison Materials Technology Center in Dayton, WebCore Technologies in Miamisburg, Owens Corning in Columbus, and Ashland Performance Materials in Dublin. They have been working for more than two years to test materials and coupon samples and are now ready to move into product demonstration. The partners will design, analyse, build and test a series of progressively larger components with a goal of completing and testing a full-scale 100 m composite tower.
“In full size, these will be some of the largest composite structures ever built,” says Rice.