Rant: Why is AWE maybe better than HAWT

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So I see two possible benefits for utility scale AWE

  • Access to high altitude winds
  • Less material use

I think only the second one makes much sense, the first one I consider a perk.

The power output of a wind power plant is very dependent on \frac{C_L^3}{C_D^2} (lift coefficient times glide ratio squared). For a HAWT, the same can be expressed by tip speed ratio TSR. But for windmills there is a max TSR possible because you will eventually be hitting the Betz limit (or in other words the wake of the blade in front).

This I believe is the biggest «break» for AWE, considering all added complications AWE entails. There is no max limit to glide ratio for AWE in terms of swept area diameter. because you can so easily just expand the diameter to accomodate a higher TSR/glide number.

This, if you are with me so far, means that utility scale AWE should focus on higher glide numbers. This is already quite difficult as HAWT have laid the bare really high. But maybe

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2

Yes. A high number can be achieved in two ways, possibly by combining them:

  • The “usual” way, being a high lift-to-drag ratio

  • A very high lift coefficient as for Flettner (until 8 at a spin ratio of 3 or 4) or Sharp (until 3) rotors, or as for High lift coefficient and biplane kite, the last being able to be combined with the previous (high lift-to-drag ratio).

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How about steadier and more consistent winds?

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It is a perk, but the cost of tether drag kills your performance. So you would always want the minimum tether. The minimum tether would normally be decided by ground clearance, turning abilities, path shape, reel out length in a cycle etc

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The minimum length tether moving with the kite. You could have a central tether with multiple quick moving tethers branching off from it.

And if tether drag kills your performance with single kite designs so you can’t access the higher altitude, more consistent winds and there is therefore also less opportunity for dual use of the land you’re on, certainly much less than with HAWTs, that kind of kills your hope of staying on land if you want to go bigger - which is the entire point of the exercise -, so you have no option but to go offshore, which is the opposite of de-risking or cheap.

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Any multiple kites on a single tether or something not moving cross-tether of course is another story. Though my definition seems to cover the most popular options these days.