[tinco]

Thank you so much for that document it's so interesting. Interesting lesson from the exec summary: The real world kite underperformed the model by nearly half, and from the numericals it seems like the main reasons we're that the turning radius was about double that what you were trying to get, and that the tether drag was a significant loss that was not accounted for. The next gen model would be the same span but with a larger area and with a shorter tether, the turning radius would be a lot smaller and it would effectively halve the drag and increase performance by 30% but it would still underperform the initial model by about 20%.

The general big conclusion as I get it is that because of these losses even though the kites are capable of getting more wind per kite, when area is constrained a conventional turbine seems to have better density.

The idea that the kites have lower installation cost offshore does seem interesting to me, but I only skimmed it so maybe that's offset by something else.

[ntucker86]

The Airborne Wind Energy section is general, and discusses energy kite performance in a broad way - the tether drag was well predicted and wasn't a surprise for our prototype.

The inability to turn the necessary tight paths and some degraded aero performance are responsible for most of the performance miss. Also hugely concerning was the struggle to saturate power at high winds.

It is important to separate and highlight tether drag in the context of the purported big benefit of airborne wind turbines accessing higher, faster winds. While they do indeed access higher winds, they do so via tether length and elevation angle, both of which carry losses. The net effect in almost all scenarios isn't a win.

[yourapostasy]

> ...tether drag was a significant loss that was not accounted for...

I wonder if some of the losses to tether drag could be made up for by re-purposing some of the wave energy tech to capture energy from the base of the tether as the kite pulls and slackens on the base, or if the tether could be made rigid on demand with some tech in the future.

[ntucker86]

There isn't a large amount of energy stored in the tether catenary or elasticity. Any hardware to recoup it probably wouldn't pay for itself.

Offshore, there can be a lot of energy stored in buoy motion, and utilizing this can help, but probably in a resonant way that doesn't require additional hardware.

"Rigid" is a relative term. The tether already utilized a carbon fiber core. It doesn't get much stiffer, short of going to exotic fibers or more of them, both of which degrade performance in other ways.

The optimum is going to be closer to a strength limited tether than an overly stiff one.