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Conductive Tether Blues

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  • dave santos
    Several companies seek to put flygens at high altitude. Expert opinion sees Sky Windpower as the most promising of this bunch. They have the best
    Message 1 of 3 , Oct 25, 2009
      Several companies seek to put flygens at high altitude. Expert opinion sees Sky Windpower as the most promising of this bunch. They have the best engineers, the longest trackrecord, the best studies, the safest design, & have been by far the most generous & open with public information.
       
      But the flygen approach has daunting challenges, particularly the safety-critical issues of placing high mass at high altitude & practical concerns of managing a long conductive tether. Remote unobstructed siting mitigates the risks & is still a vast opportunity. Vigorous research is justified. This note addresses conductive tether issues in particular; problems & possible solutions.
       
      Mcnaughten & associates calculated years ago that a conductive tether flygen would often leave miles of cable laying on the ground, nevermind runaway. This would be terrible around populations, especially across powerlines or highways. KiteLab's tether experiments support these concerns. 
       
      When tether force slacks a heavy cable sags very quickly to the ground, often faster than a normal reel or motoring aloft can react. Thicker conductive lines don't just add drag, but negative lift by negative AoA. Imagine how much 20km of downforce amounts to on top of the high weight of a flygen. Aluminum is the lightest conductor for its electrical capacity, but fatigues rapidly in high flexural cycling like reeling-unreeling. Copper is quite heavy & the limited supply is needed for global generation capacity, as Brooks pointed out.
       
      Possible Solutions-
      Use a light polymer tether & don't bother sending power down at all. High altitude electricity could be used in many ways. Regional scale radio & cellular transmission are killer apps. Onboard use for actuation & electric propulsion in transient calm is attractive.
       
      Treat the tether as a flying object in itself. Add lifter kites all along it. A polymer multi tether upwind can allow a high downforce cable to run downwind, generating some of its own lift.
       
      Reduce weight by every trick available. Separate two wire conductors as multi-lines to reduce insulation required. Aluminized polymer fibers based on surface conduction might help.
       
      Wait for it. A vast array of flygens might beam power to a common microwave receiver. Ambient temperature superconducters will someday make flygens & conductor cables ultralight. 
       
      Keep generators on the ground. Many of the AWE teams have shown that ground based generators work well. High altitudes seem practical. More research & actual fly-offs are needed to fully resolve the flygen v. groundgen contest. Both approaches may find niche superiority.
       
      Very small low altitude systems can be useful & safe. Such gadgets are especially useful for light mobile use. KiteLab's little flygen is handy & pretty harmless. DanF is right that a tower is the solution for a small fixed installation.

    • Joe Faust
      I am voting to use a instead of the for small fixed location solution. ... The alternative would read: DanF is right that a tower is a solution for a
      Message 2 of 3 , Oct 25, 2009
        I am voting to use "a" instead of "the" for small fixed location solution.

        The statement:
        >> ""DanF is right that a tower is the solution for a small fixed installation.""

        The alternative would read:
        "DanF is right that a tower is a solution for a small fixed installation."

        What tickles this tension?
        I am assuming that by "tower" was meant the hard-structured tower with compressional members with or without cable stays for holding rotors of various number of blades (1, 2, 3, 4, etc.). I am not ready to quit on searching and finding neat ever-up AWECS (EU-AWECS) for the sector that might be covered by "small fixed installation." For one, I sense we are yet in the infancy of putting on the choice table the possibilities.

        Your two-line tether tension-only tower and your three-line tension-only tether tower are yet incubating; out of those may come something strong for small fixed installations. Also, the kytoon continues to be improved and make intrusions into AWECS designing that may be fit for small fixed installations. And there will be the wrestle with just what "small" and "fixed" means per site and need. And I keep open that the three mentioned avenues for tension-only towering may be a beginning part of a short-list of AWE solutions for small fixed installations.

        It will be interesting to see total system cost per kWh that may come out of competing solutions for small fixed installations. Total system cost will include operator's time, average casualty, replacement smoothing, property value changes from installation fact, repair, maintenance, etc.

        The hard towered evolving is also not finished for small fixed installations. AWE infancy will grow up. Then we will see wider choices.

        JoeF
      • dave santos
        JoeF,   Re: small tower solution, i was speaking for gentiles who are not tako kichi (kite crazy). Flying kites from towers is a good compromise, no?
        Message 3 of 3 , Oct 25, 2009
          JoeF,
           
          Re: small tower solution, i was speaking for gentiles who are not "tako kichi" (kite crazy). Flying kites from towers is a good compromise, no?
           
          Here is a fix for sudden conductive tether sag-
           
          Neat Volcano Application
           
          A tall volcanic cone with a top crater is ideal terrain for anchoring large scale AWE. Simply bore anchors thru the thin crater wall & bring the cables together in the center. An AWE array can launch & land suspended from this center. Several great volcanoes reach to around 15000 ft not far from large populations, For example, Popocatepetl volcano could serve as a high altitude base to tap the subtropic jet stream within sight of Mexico City.
           
          -------------------------------------
           Whoops. last post failed to mention problem of high conductive losses of long flygen tethers.
           

          --- On Sun, 10/25/09, Joe Faust <joefaust333@...> wrote:

          From: Joe Faust <joefaust333@...>
          Subject: [AirborneWindEnergy] Re: Conductive Tether Blues
          To: AirborneWindEnergy@yahoogroups.com
          Date: Sunday, October 25, 2009, 4:39 PM

           
          I am voting to use "a" instead of "the" for small fixed location solution.

          The statement:
          >> ""DanF is right that a tower is the solution for a small fixed installation. ""

          The alternative would read:
          "DanF is right that a tower is a solution for a small fixed installation. "

          What tickles this tension?
          I am assuming that by "tower" was meant the hard-structured tower with compressional members with or without cable stays for holding rotors of various number of blades (1, 2, 3, 4, etc.). I am not ready to quit on searching and finding neat ever-up AWECS (EU-AWECS) for the sector that might be covered by "small fixed installation. " For one, I sense we are yet in the infancy of putting on the choice table the possibilities.

          Your two-line tether tension-only tower and your three-line tension-only tether tower are yet incubating; out of those may come something strong for small fixed installations. Also, the kytoon continues to be improved and make intrusions into AWECS designing that may be fit for small fixed installations. And there will be the wrestle with just what "small" and "fixed" means per site and need. And I keep open that the three mentioned avenues for tension-only towering may be a beginning part of a short-list of AWE solutions for small fixed installations.

          It will be interesting to see total system cost per kWh that may come out of competing solutions for small fixed installations. Total system cost will include operator's time, average casualty, replacement smoothing, property value changes from installation fact, repair, maintenance, etc.

          The hard towered evolving is also not finished for small fixed installations. AWE infancy will grow up. Then we will see wider choices.

          JoeF


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