Wind turbines are an increasingly popular source of energy in the United States and Europe and in many other countries around the globe. In order to realize scale efficiencies in capturing energy from the wind, developers are erecting wind turbine farms having increasing numbers of wind turbines with larger turbines positioned at greater heights. In large wind turbine farm projects, for example, developers typically utilize twenty-five or more wind turbines having turbines on the order of 1.2 MW positioned at fifty meters or higher. These numbers provide scale efficiencies that reduce the cost of energy while making the project profitable to the developer. Placing larger turbines at greater heights enables each turbine to operate substantially free of boundary layer effects created through wind shear and interaction with near-ground irregularities in surface contours—e.g., rocks and trees. Greater turbine heights also lead to more steady operating conditions at higher sustained wind velocities, thereby producing, on average, more energy per unit time. Accordingly, there are economic and engineering incentives to positioning larger turbines at greater heights.
Positioning larger turbines at greater heights comes, however, with a cost. The cost is associated with the larger and more massive towers that are required to withstand the additional weight of the larger turbines and withstand the wind loads generated by placing structures at the greater heights where wind velocities are also greater and more sustained. An additional cost concerns the equipment that is required to erect the wind turbine. For example, the weight of conventional tube towers for wind turbines—e.g., towers having sectioned tube-like configurations constructed using steel or concrete—increases in proportion to the tower height raised to the 5/3 power. Thus, a 1.5 MW tower typically weighing 176,000 lbs at a standard 65 meter height will weigh approximately 275,000 lbs at an 85 meter height, an increase of about 56 percent. Towers in excess of 250,000 lbs, or higher than 100 meters, however, generally require specialized and expensive cranes to assemble the tower sections and to mount the turbine and blades on the assembled tower. Just the cost to transport and assemble one of these cranes can exceed $250,000 for a typical 1.5 MW turbine. In order to amortize the expense associated with such large cranes, wind turbine farm developers desire to pack as many wind turbines as possible onto the project footprint, thereby spreading the crane costs over many wind turbines. However, with sites having limited footprints, developers are forced to amortize transport and assembly costs of the crane using fewer turbines, which may be economically unfeasible. Further, projects installed on rough ground require cranes to be repeatedly assembled and disassembled, which may also be economically unfeasible. Projects located on mountain top ridges or other logistically difficult sites may, likewise, be all but eliminated due to unfeasible economics, in addition to engineering difficulties associated with locating a crane at such sites.
It is thus advantageous to be able to assemble high-elevation structural towers and to mount heavy wind turbines on the top of such towers without relying on relatively large and prohibitively expensive crane equipment. A principle object of the present invention is therefore to provide an apparatus and method for assembling high elevation structural towers and mounting wind turbines on top of such assembled towers without the need for large and prohibitively expensive crane equipment. This and other objects, features and advantages of the present invention will become more apparent with reference to the below description.