The nation’s tallest wind turbine will be mounted on a concrete tower being constructed at the site of a MidAmerican Energy Co. wind energy farm near Corning in southwest Iowa.
The company, a division of Berkshire Hathaway Inc., said Monday the prototype tower in Adams County is MidAmerican’s first concrete tower. Taller towers can raise electricity-generating turbines into higher-wind zones, opening up areas now rated as having “low to medium” wind resources to future development.
“Generally speaking, the higher the altitude, the greater the wind resource available,” said Mike Gehringer, vice president for renewable energy at MidAmerican.
The tower’s 2.3-megawatt turbine will be part of a 64-turbine, 154-megawatt wind farm to be completed by the end of this year.
The hub of the concrete tower’s turbine will be 377 feet above the ground, compared with 263 feet for most turbines at other MidAmerican wind farms in Iowa.
Each turning blade will reach as high as 554 feet, about as tall as the Washington Monument, compared with 440 feet for the top of the blades on most turbines.
Instead of fabricating three metal tower sections in a factory and trucking them to the site to be fitted together, Gehringer said, crews are pouring concrete in segments at the site and assembling the tower.
MidAmerican hired Siemens Americas Onshore Wind, a division of the German industrial company Siemens AG, to construct the tower. The concrete comes from EFCO Corp. in Des Moines, with the turbine blades from Siemens’ factory in Fort Madison, Iowa.
In Europe, some wind turbines with concrete bases can reach more than 400 feet. Precast concrete towers sway and vibrate less in the wind than steel towers, making them quieter and less subject to damaging stress, according to some companies that produce concrete towers.
Concrete towers don’t rust, don’t need painting and can be assembled in sections hauled by ordinary trucks rather than as costly oversize loads, or else built on-site.
MidAmerican spokeswoman Ruth Comer said concrete towers are somewhat more expensive than steel towers, but the extra cost will be offset by the turbine’s increased electricity production. MidAmerican will evaluate the Adams County unit to decide whether to build more.
Sri Sritharan, a civil engineering professor at Iowa State University who has studied concrete tower technology, said concrete towers may become viable alternatives as turbines must be lifted higher to reach winds that will generate electricity efficiently.
Steel turbines are more expensive to ship as they become taller, he said. The U.S. Department of Energy has supported development and testing of concrete towers, which can have longer life and lower maintenance costs than steel towers, in addition to holding turbines higher off the ground.
In a report on tower technology, the Department of Energy said transportation restrictions hinder the use of taller steel towers, while high-strength, steel-reinforced concrete can hold turbines higher but keep transportation costs down.
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