Study on The Design Methods of Tall Wind Turbine Foundation (A Case of Adama I Wind Farm)

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Date

2019-04

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Addis Ababa University

Abstract

Wind energy has been deemed an appropriate means of diversifying Ethiopia’s energy mix while simultaneously addressing the deficit in electricity supply which the country faces. The first wind farm in Ethiopia is Adama I wind farm, which generates a 51MW of energy using 34 sets of wind turbine generators. The foundation supporting the wind turbine generators is designed assuming the load encountered to be static; however, wind turbine structures are inherently dynamic structures, and the design of foundations for resistance of dynamic loading requires a different design approach other than static approach. Both the static and dynamic foundation design approach for wind turbine structure are studied in this project. When designing the foundation taking into account the dynamic nature of the structure, the final design resulted in the circular gravity base foundation with a bottom diameter of 13.2 m, and depth of 3m. The reduction in dimensions of one particular foundation is interpreted by the change in volume of concrete, which showed a decrement of 124 m 3 when compared with the existing typical foundation in Adama I wind farm. Moreover, the foundation design to support all the 31 turbines is identical across 5km stretch of wind farm land, and didn’t cater to the local soil or rock condition. In reality, the ground condition is different across the wind farm land; as result, the effect of using different bearing capacity values on foundation dimension is also explored. The final design resulted in the circular gravity base foundation with a bottom diameter of 14 m, and depth of 2.5 m for all the bearing capacity used in the study. The reduction in dimensions of one particular foundation is interpreted by the volume of concrete, volume of backfill. The volume of the concrete showed 115 m 3 decrement; the backfill material decreased by 1,137 m 3 when compared with the existing foundation in Adama I wind farm. The results of this part of study show that the increasing the bearing capacity had negligible contribution in reducing the dimensions of the foundation. This project concludes that the bearing capacity is not the major limiting factor when designing a foundation for the Adama I wind farm. The stability against overturning is the most critical criteria for both the static and dynamic approaches. Furthermore, when designing wind turbine foundation taking into consideration the soil structure interaction and dynamic nature of the wind turbine generators, the foundation dimension showed a decrement, which emphasizes the static approach to foundation design is conservative.

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Keywords

Tall Wind Turbine, Adama, Wind Farm, Foundation

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