Validation of Segmented Flanges for Large Diameter Wind Turbine Towers

At sites ranging from Texas to Iowa, utility scale wind has become the lowest cost electricity source available, with recent prices well below 3cents/kWhr, lower than the cost of both coal and shale gas. This not only provides these communities with clean, low cost energy, it also provides a valuable "second crop" to the land owners in these areas. However, this opportunity is currently limited to a relatively small percentage of the country - while the 8 Plains states generate nearly 20% of their electricity from wind, the nationwide average is less than 5%.Keystone Tower Systems has developed a new technology that makes low cost wind energy accessible in all 50 states, and also ensures that a greater percentage of the value stays with the local communities where the turbines are installed. Today, wind energy is only economical in regions where strong winds can reach close to the ground, because current tower technologies cannot cost effectively lift turbines higher than ~80m. This height limitation is the byproduct of transportation limits between the tower factory and the project site - taller towers would ideally be larger in diameter at the base, but this results in structures that are simply too large to transport by road or rail. Keystone's technology bypasses the tower transport constraint by enabling steel to be shipped as flat sheets that are rolled and welded to form a tower at the project site. By fabricating at the wind plant, Keystone's system enables towers to cost effectively scale to any size. It also enables the tower, the most expensive component in a turbine, to be produced in the local community, rather than at a distant factory.During Phase I of this SBIR program, Keystone worked with the top turbine manufacturer in the world to design a field fabricated tower that is more than 70% taller than standard models, and with a leading wind farm developer on the initial design of a mobile tower fabrication facility that could be setup on a wind project during the construction phase. Also during Phase I, commercially available technologies were identified for almost all of the steps in tower fabrication, such as in-field painting from the bridge industry. However, large diameter flanges were identified as a critical gap. Because of the large size of these flanges (some as large as 7m in diameter), they are too large to ship and must be delivered in multiple segments. Large diameter towers also become very flexible, which, along with segmentation, presents unique challenges during the installation process. These challenges must be overcome while meeting the very tight tolerances that are required to ensure good load distribution and strong fatigue resistance. Keystone has developed a flange manufacturing and installation process that we believe will meet all of the necessary requirements, but it requires extensive validation in order to ensure that the flange will survive the 10s of millions of fatigue cycles that it will experience over its 20 year lifetime, as well as convince the conservative wind industry to accept this new technology. Keystone will carry out this validation program in the current project.