The most commonly explored AWES method is the Pumping or Yo-Yo kite.
Tight kite line is unspooled from a drum to turn a generator on the ground.
This generates power until the kite line reaches a length limit.
Then the kite flys back to the start while the line is spooled back onto the drum.
A passive Phugoid Mode Pumping Daisy is possible harvesting the torque waves OliverT has identified, but by wings in Phugoid oscillation. Instead of tapping torque as such, the Daisy could free-wheel, with pumping strokes tapped. Not necessarily better, except perhaps for direct pumping work, but passive Phugoid wing pumping is a novel AWES idea in itself.
I felt oscillations by using a single wing for Low radius loop, envisaging a pumping (yoyo) mode use. Can be them assimilated to phugoid waves? And what can be the benefit of the use of phugoid oscillation in pumping mode?
There are two bulk flight pitch oscillation modes commonly known, the short-period and longer phugoid. There are a handful of other flight modes, plus internal aeroelastic modes, and they all interact. That’s the sort of power motion you felt.
The reason these modes are important is because a wing wants to fly them. That’s why figure-8/Dutch-roll is so natural to fly. Ideally in AWES these modes become resonant, passively self-sustaining, with only easy tuning and on-off trim inputs needed.
Kites, or tethered wings, are promising alternatives to harvest wind energy: As shown in Fig. 1, a (rigid) kite is flown in crosswind motions like figure eights (or alternatively circles). The kite has onboard turbines and generators to generate electrical power which is sent to the ground via electric cables integrated in the tether. Due to the high speed of the kite, the relative wind speed at the kite is about a magnitude higher than the actual wind speed, so that the onboard turbines can be small. This concept is called “drag power”.
A second possibility for crosswind kite power is shown in Fig. 2: A kite (from soft materials like a paraglider or alternatively from rigid materials like a glider) is tethered to a winch on the ground which is connected to an electrical drive. The kite is flown in crosswind motions with a high lift force and pulls the tether from the winch. Energy is generated by operating the winch drive as generator (generative braking). When the maximum tether length is reached, the kite is flown to a low force position like the zenith, and/or pitched down, and reeled back in. A rigid kite can also dive towards the ground winch for minimal reel in time. During the reel-in phase, only a fraction of the generated energy is dissipated by operating the winch drive as motor. This concept is called “lift power”.