As I’ve always said about AWE concepts, rather than starting out chasing megaWatts, try powering a single home first. Or even just a system useful for any purpose. (Charging a phone?)
Maybe the parachute idea could be useful for something - who knows, while not very “efficient”, at least it is relatively simple.
Seems to me it makes more sense to verify a concept at an achievable scale before even worrying about megaWatt versions. I guess it’s easier to dream about giant scale than build at miniature scale. Or for people with misappropriated, unsuitably-large budgets, they can waste money, manpower, and resources, building large models before they have verified the usefulness of the basic concept at a smaller scale.
Betz limit 16/27 is 4 times the limit in pumping mode which is given for 4/27. The paper details the reasons. I see a simple reason: the swept area, in pumping mode, is dragging at 1/3 wind speed which is reel-out speed, keeping 2/3 wind speed. So the force (measured by the square of wind speed) becomes 2²/3² = 4/9. Power is force x reel-out speed: 4/9 x 1/3 = 4/27.
The parachute takes the whole area of power available in the wind, if we do not take into account wind deflections around the parachute, which remains to be seen (but it can be the same for the swept area of a conventional wind turbine). Now if we increase the drag coefficient Cd of the parachute, the drag force will increase. And said drag force will affect the swept area as well as the flying body (in this case the parachute), both being merging. If the Cd is 3, the AWE parachute system could harvest up to 12/27 of the power available in the wind.
I am wondering if drag coefficient is meaningless if a large enough cloth is put in the sky. The Reynolds number maybe converges to something? Seems the cloth would be the ultimate collection of energy in the wind. The wind bending around the edges is not something the Betz limit accounts for?
Probably the answer to your question is yes for a farm of parachutes. But in practice, the deflected wind around a single parachute is not so important, although being possibly a non visible part of the swept area which is subject to the Betz limit.
The Betz limit takes account of energy extraction slowing the wind, whereby a lot of the wind goes around the rotor disc, just as we avoid going into a store if the prices are too high. And even the air that has had energy extracted must still be left with some energy in order to leave the volumetric region of energy extraction, to allow more wind to enter.
I realize the real world is complicated. But I believe the premise of the Betz limit calculation only accounts for the energy of the air passing through the swept area. So if you start talking about the air outside the swept area, you need to calculate in a more sophisticated way.
Also I am suggesting, without much in terms of analysis, that given a big enough swept area, the drag coefficient may converge to a fixed value for any object covering the skies completely, like a parachute. Suggesting the idea, not suggesting that it is true
