Do regulations in the United States limit the size of aerial wind turbines?

Question

What with all the work done by the FAA recently on regulating drone usage, I thought it would be nice to turn my eyes to the sky for another, less-known type of aerial denizen: the aerial wind turbine.

Wikipedia has all the relevant information, so I won't rehash it here. The most important thing here is that aerial wind turbines - and I'm mostly interested in aerostat-based designs - are free-floating, just like certain types of tethered drones, which have given the FAA headaches because they're not like most aircraft.

I did find this article, which says

Regulations and technological restrictions suggest it may not happen very soon, or at all, but some researchers believe aerial turbines will be tapping high-altitude winds for power generation sometime in our future and perhaps within the decade.

and

That said, companies currently working on the project seem very loosely formed. They are in the development phase and are aware of federal airspace restrictions.

Here's the relevant FAA page.

I suspect that FAA regulatory measures on drones cover aerial wind turbines, but I'm not positive, and I'd like to see some specific mention of them in regulations, if possible. I assume they're treated as (tethered) drones, but I haven't been able to find any direct mention.

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Getting to the point: Aerial wind turbines are, in general, much smaller than typical wind turbines. There are obviously some factors that make it easier for wind turbines built on the ground to be larger (support, for instance). But larger turbine blades, while a source of trade-offs, can be much more helpful.

What regulations (in the United States), if any, limit the size of aerial wind turbines?

Answer 1

I think you may be misinterpreting aerial wind turbines as a type of aircraft. The FAA section of the Code of Federal Regulations defines an aircraft as a device that is used or intended to be used for flight in the air. I suppose the real debate comes down to what you define as "flight," which the CFR does not deal with. While an aerial wind turbine certainly is supporting itself in the air through aerodynamics, it's still tethered to the ground and I wouldn't exactly call that "flight" in the same sense as it's being applied to the aircraft being regulated in these codes.

This question is really more complex than anyone can answer right now, because I have a feeling that in the not-so-distant future (<10 years?) a company manufacturing aerial wind turbines will submit some sort of request for a ruling to the FAA on whether or not they're aircraft, and if they disagree, they'll file a suit and go to court over the definition of "flight." But for now, let's assume they aren't aircraft.

Traditional wind turbines are regulated by Title 14, Part 77 of the CFR, and I think the aerial wind turbines would be regulated with the same code. They're merely an obstruction that is fairly high and has some capacity to move around with the wind, depending on how tightly they're tethered.

Section 17 describes an obstruction as anything higher than 499 feet above ground level, with lower height restrictions near airports, for obvious reasons. However, Section 9 states that the FAA must be notified of any construction going higher than 200 feet. The key here is that the regulations say absolutely nothing about whether or not you are legally allowed to build something over 200 feet. It simply says that you should notify the FAA, and they will make a determination.

If you are below 500 feet, the code doesn't appear to be explicit on this fact, but it seems you'd find little argument with your request. Over 500 feet, they'll look into it a little more deeply, because that is officially an obstruction. But they're still free to say "We don't think this will be an issue, go ahead."

So do the regulations explicitly limit the size? No. They make no limitations on what you can build, just that you have to get approval once you pass certain restrictions, dependent on your location and proximity to airports.