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The structural efficiencies, modularity, and tailored damping of land based Space Frame towers also benefits deep water, off-shore sites. With an adaptation of the steel and damped struts of the land based tower, the larger turbines are able to withstand the increased dynamic and fatigue loads associated with deeper water wave forces that become economically challenging with conventional tower and foundation methods. Connected directly to a pile, gravity, or suction bucket seabed foundation, the tower rises as a continuous structure up to 71m hub height. Thus the 100m tower is suitable for mid range depths to 29m while the 125m tower can be installed in depths up to 54m, opening up vast areas of developable waters.
Waves produce large, wide ranging frequency forces that present significant cost challenges to conventional off-shore wind turbine towers. As the water deepens or plunging waves become more prevalent, the cost problem rapidly becomes worse as conventional foundations require exponentially increasing stiffness to withstand structural “ringing” and the associated large fatigue loads. Thus, the under water structure comprises one of the largest cost components and typically limits projects to monopiles at less than 16 m depth. Several methods have been explored to achieve greater stiffness in deeper water but each has significant limitations with associated cost traps …….The Space Frame Wind Tower™ uses a better approach.
Instead of increasing the tower stiffness, the tower uses structural damping and remains light and cost effective. As with the baseline land product, damped struts are placed in strategic locations to reduce the harmonics from the winds. Other damped struts are also tailored to reduce the ringing and structural fatigue from the waves. This combination damping reduces the underwater weight of the tower by 50% or more than the best known methods today. Since most of this weight savings is steel, economics are enhanced and potentially much more off-shore development can occur. The increasing need for damping in the dynamic environment of water, waves, and wind enables the Space Frame towers in many untold, soon to be discovered ways in many challenging conditions.
Tower oscillations tend to become greater for larger rotors in extreme wind events. Conventional towers reduce these harmonics by adding steel weight to increase tower stiffness. This places economic limits on rotor size. In contrast, by adding damping instead of weight into the lighter space frame tower, resonance vibrations are suppressed; fatigue levels are lowered, and stress levels are reduced creating more options for turbine blade designers. For example, turbines designed for a 90m rotor can be implemented at 100m diameters by adding additional damping to the struts. The combination of lower cost towers and foundations plus the ability to accommodate even lower wind speed rotors presently under development is of significant dual benefit for marginal class 3 and 4 wind off-shore sites.
The modular, on site construction of Space Frame Towers eliminations significant transportation logistics. In addition, the lightweight structurally robust design, can be dropped into the sea as a complete unit installed in segments or lifted into place. This leverages additional deployment and foundation methods not presently being considered, especially for deep water and 5 MW or greater installations. Because the scalability and portability of the tower frame removes the barriers to all turbine sizes, even 10 MW machines are more readily achievable.
From 5nm to 50nm off the coast of the United States about 907 GW of wind potential is ready for harvest; an amount greater than the entire U.S. electrical capacity. Twenty percent or 181 GW is in water up to 60m deep. This is equivalent to 51,000 turbines in the 3.5 MW class; each that could be potentially installed on a Space Frame Wind Tower™. In consideration of this large opportunity both domestically and internationally, partners are being sought to develop the next generation Space Frame tower up to 5 MW.
Click here to learn about how Wasatch Wind can expand your offshore wind development possibilities with an in-depth brochure. |
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