Salient White Elephant

February 24, 2009

Turbine de Saint Louis

An earlier blog – Scalable Tower for Very Large Wind Turbine – presented various ideas for improving the scalability of a horizontal axis wind turbine tower. Here’s another variation of the scalable tower:

The general idea is to first build a strong, inexpensive, and light weight tower of some kind. The diagram depicts the use of an arch for this part of the tower. (The diagram has been simplified for clarity. In reality, at least three legs would be required for the tower.) Next, a short extension is added that raises the nacelle above the highest point of the strong part of the tower and displaces it from the yaw axis in the horizontal direction. The nacelle is fixed to the extension, and does not rotate with respect to it. Instead, the leaning extension rotates with respect to the top of the strong part of the tower. The angle between the vertical yaw axis and the extension is fixed. In order to increase the structure’s ability to stand up against wind gusts and high winds, a guy wire tethers the bottom of the extension to the ground. To increase the ability to shed wind loads, the angle between the vertical yaw axis and the extension may be allowed to vary somewhat. The guy wire must be slightly stretchable to accommodate this action. Alternatively, a weight can be attached to the bottom of a guy wire that is not anchored to the ground, or the guy wire can be eliminated and a weight attached to the bottom of the extension.

Advantages of this approach include:

  • The amount of materials required to construct the tower and the weight of the tower are minimized.
  • Aerodynamic drag provides the yaw moment, so the turbine does not require a yaw system.
  • Because the greater part of each blade is far from the tower, tower shadow is much reduced. This reduces cyclic stress on a number of components, which should lead to longer life and greater reliability. It may also allow for the use of lighter, less costly components.
  • The turbine is very large, very tall, and has very long blades, and yet does not require a massive tower.

An upwind version of this idea could be designed by adding a yaw drive to control the rotational angle of the extension. If you’d like to read more about my ideas for improving the scalability of very large wind turbines, check out the Scalable Tower for Very Large Wind Turbine blog.

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