A (train of) parasail(s) as AWES ?

[PierreB]

Betz limit and power available in the wind

In two steps: 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…

For this parasail-based AWES mainly based on the drag force, the thrust (tension) force increases above all with the Cd. The equation (4) is applicable to a simple (not crosswind) kite: for a same Cl, the higher the Cd, the higher the tension (thrust) while, for a crosswind kite, the higher the Cl and, above all, the higher the L/D ratio, the higher force.