The photo on the left shows the crane lift of the turbine nacelle for the north tower of our Cashton Greens Wind Project in Cashton, WI, during May of 2012. The photo on the right shows a technician standing on top of the nacelle of the south turbine after the lift was completed on that unit a few days later.
The two turbines that were erected in 2012 as part of the Cashton Greens Wind project are among the tallest in the state of Wisconsin, or the country for that matter. Each turbine measures 100 meters to the center of the nacelle hub at the top of the tower. That is more than a football field off the ground! Lifting very heavy objects to those heights is no simple matter. The nacelle is the heart of the turbine and holds the turbine control unit, generators, weather instrumentation, communication systems, gear box, and transmission components. The nacelle on each of these turbines weighs more than 200,000 pounds (100 tons). On a 100 meter tower, the last tower section must be lifted and secured with bolts immediately before the nacelle is lifted into place and is a process that can take several hours. This is because the harmonics of a cylindrical tower can become unstable in strong breezes at that height. The weight of the nacelle dampens that effect and stabilizes the structure. So, both the final tower section and nacelle lifts must be accomplished in a very short time period while the crane can safely lift them into place. Often, crews will pay particular attention to wind forecasts and may work well into the night to accomplish this critical step in the process before the weather changes. Rain can also create problems as the internal components of the nacelle need to be kept free of moisture and the possibility of rust. Heavy, high lifts such as these can only be accomplished on days with minimal winds. Codes are in place to regulate which lifts can be made based upon the height of the lift and the weight of the component. If these codes are exceeded, the safety of the crews could be at risk or there could be the possibility of a crane collapse. Usually, these codes and rules will be a condition specified in the construction contract on a commercial wind turbine project so as to remove any uncertainty in the decision making process.
Needless to say, management of critical lifts in the construction agreement is a critical detail. There are very few cranes in the nation that can accomplish this work and they are usually rented to the project on a daily basis at a costly rate. Proper contractual structures to manage the risk associated with construction schedule crane coordination while providing fair incentives.
Learn more about managing crane activity at our Renewable Energy Project Development Seminar.