Topic: Tower-Supported AWES

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May 3, 2020, post by  Gordon Spilkin   
Tower-Supported AWES

Hello Dave,
Glad to be back with you guys. I hope email format will enable me to publish sketches and pictures and not just links.  [Ed answers: yes, send all in email or links! We will process items and host them.]

While analyzing the effects of turbine orientation and cosine-cubed effects, I came to the conclusion that if you can’t reorient the turbines to face the wind then the best performance is at low tether angle. This is because cosine-cubed losses are always more than gains from higher wind speed. This phenomenon applies to Daisy, Sky Serpent, MAR1, yo-yo parachutes, and even your looping foil. At a low tether angle we might as well substitute a lightweight tower (or mountain) for a lifter kite. I know this is not HAWE but maybe this is the low cost system that we must compete against.

Here are the reasons that I think tower support is advantageous:
Since the best performance will be obtained with a low tether angle, the support will ensure that the low angle is maintained.
Since tether angle is fixed, the PTO and generator design is simplified.
  • Since the best performance will be obtained with a low tether angle, the support will ensure that the low angle is maintained.

  • Since tether angle is fixed, the PTO and generator design is simplified.

  • Tether length can be substantially increased to accommodate many more turbines.

  • The natural curve of the catenary will reduce shadowing effects.

  • Launch and land operations are not required except perhaps for high wind conditions and maintenance.

  • If the wind dies and starts again, the turbines will automatically start turning without assistance.

  • The whole length of the tether can be elevated so that the land below can be used for other purposes such as farming or recreation.

  • In the case of Daisy and MAR1, turbines or rings can be spaced further apart since hockling is unlikely to occur with constant tether tension. Further spacing reduces masking effects.

  • In the case of Sky Serpent, the system is more scalable since the weight of heavier torsion tubes and larger turbines will be borne by the tower.
A major problem with this system is accommodating changes in wind direction. Rather than relocating the tower, we can rotate the PTO generator stand around the tower.

Rod’s tower test gave us important information. The static tension in the tether is less than 12 kg whereas the tension on the PTO/generator is 100 kg while operating at 8 m/s . The load on the tower is therefore minimal. How about rocking the top of the tower from side to side with the guide wires to create crosswind action?
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