Challenges and Opportunities for Airborne Wind Energy in the United States Report to US Congress November 2021

A US Dept of Energy Report on
Challenges and Opportunities for Airborne Wind Energy in the United States
Report to Congress November 2021

Holds a much more open view of the state of AWES evolution.

Unlike the recent decided and settled AWES viewpoint article from @Lorenzo Fagiano

The DoE report reads…
AWE system designs to date are diverse and largely experimental. There is little
convergence, so far, as to a preferred technology or approach, and no megawatt-scale
AWE systems have been commercially deployed. Several AWE designs under
development show promise. The overall design space has not yet been fully explored.

That noncommittal statement would have served a decade ago.
I wonder how much they spent to figure it out.

Page 12: concerning yo-yo systems, the challenges outlined below are often underestimated.

A session on electrical system requirements noted that AWE electrical systems (generators,
power electronics) are challenging for ground-gen systems due to the extremes of operation—
slow, high torque, reeling-out and fast, low-torque reeling in. The unique oscillating power
generation profiles and the energy required to launch and recover fly-gen systems also pose

As I’ve mentioned in the past, wind energy, as an art, is thousands of years old, and it can be instructive for AWE efforts to compare against an equivalent ground-based or tower-based system. For the “yo-yo” (inaccurate term since the reel stops, then reverses direction, at the end of travel, unlike a yo-yo) kite-reeling systems, a comparable ground-based system might include a sailing land-yacht with wheels, first tacking downwind pulling a tether against a reeling drum to produce power, then being reeled back upwind, dragging a tether along the ground the whole time. Seems a bit unlikely when you think about it. Sure it could technically produce power, but geez, really? You’re gonna run something like that for 20 years? OK how about a tower-mounted version: A wind turbine on a tower, with no generator, spins unloaded, maybe mounted on a track aligned with the wind direction, pulling a tether wrapped around a drum downwind by its thrust force alone (not using the rotation at all), then, at the end of its travel, adjusting its blade pitch or rotor orientation to produce less thrust force, and being reeled back upwind, with all the power generated and used by the reel coming from rotor thrust only, never the rotation. My take is such a contraption would be absurd - reminiscent of a humorous Rube Goldberg cartoon from a century ago, visibly ridiculous to even a casual reader.
That is why I have, on the one hand, admired the determination and effort of the kite-reeling teams, and been impressed with the numbers they cite, but on the other hand, forced to be skeptical of their ultimate success, due to this Rube Goldberg nature of their operational paradigm. At one point, now many years ago, I was momentarily convinced kite-reeling had “cracked the code”, based on their own numbers and statements, but the consistent lack of any such system in regular operation in the intervening years has thrown a wet blanket on that, and I’m now unconvinced that kite-reeling is leading anywhere but the auction block or the well-populated scrapheap/junkyard/museum of disproven, wannabe wind energy solutions.

Intermittent operation for an intermittent energy, that makes a lot of intermittence …
That said SkySails appears to be a leader with its measured average power of 92 kW for its yo-yo AWES.