Do Flying Wind Turbines Make Sense?

Time lapse photo of Makani’s tethered wing flying in a circle (Photo: Makani Power)

by Jonathan Koomey excerpted from his blog

I like site visits—there’s nothing like seeing a company’s innovations in person.  In the case of Makani Power, I harbored some core misconceptions about their technology, and the visit set me straight.

Corwin Hardham, CEO and one of the co-founders of Makani, invited me to visit in Fall 2011. An intern of his was taking the class I taught that semester, and he heard me mention the company’s efforts in lecture, so he put Corwin in touch with me.  Things have been so busy that I wasn’t able to arrange a visit until a few weeks ago, but I’m sure glad I stopped by.

When I drove up to Makani’s building, which formerly housed the control tower for the Alameda Naval Air Station, the first thing I saw was three rusted artillery guns.  That was a jarring sight, but the location makes sense.  Corwin explained that this site was the largest available open space in the Bay Area and was perfect for building and testing Makani’s prototypes.

Others had told me about Makani’s technology, and the words “kite” and “high altitude” always come up, but these terms are misleading.  When I think of kites, I think of Ben Franklin flying the traditional diamond-shaped kite with a tail.  The Makani turbine is a carbon fiber wing with propellers (see photo), which Ben Franklin wouldn’t have known what to do with.

And the words “high altitude” made me think of kites flying in the path of airplanes at 10,000 feet, which isn’t at all right.   Makani’s turbines fly at about 300 m (roughly 1000 feet) above the ground.

Instead, imagine building and operating just the most important part of the wind turbine, the outer part of the turbine blade (which generates most of the power) without the rest of the supporting structure.  In essence, that’s what Makani’s tethered flying wing is—the end of a turbine blade that flies in a circle and generates power.  The initial prototype generates 20 kW— the next version should generate 600 kW, assuming they get the money to build it.

The wing itself (without the generators and propellers) is incredibly light—I could easily pick it up with both hands, even though it’s about 20 feet long.  That’s the beauty of carbon fiber.  Super strong, without much weight for the wing itself.

The wing has four propellers mounted perpendicular to plane of the wing.   Each is attached to a generator that can reverse itself to serve as a motor.  This capability is needed because the wing starts from a cradle on the ground and lifts itself off to achieve the needed altitude, then switches to generator mode once the wing starts its normal circular path.  If the wing needs to come down for maintenance, the process works in reverse (and the wing can go from normal flight to sitting in its cradle in less than 5 minutes, which means that it can safely avoid adverse conditions on the ground.

The full wing in flight here showing the four generators/ propellers (Photo:  Makani Power)

Complex computer control technology is critical to the wing’s functioning.  My friend Saul Griffith, one of the cofounders of Makani, told me that the control technology was similar in complexity to found in missile guidance systems.  It’s sophisticated enough to keep the wing on a path with meter level precision, and that’s awfully good.

Power is sent down the tethers.  Better to move electrons than to worry about mechanical parts in such a complex environment.

Because the wing flies at higher altitudes than a typical wind turbine, and because it can operate at lower wind speeds, the capacity factor for a Makani turbine will be more like 50-60% (instead of 30-40% for new traditional wind turbines in good sites).  And with capital costs typically half of a traditional turbine, the Makani technology should have a significant economic advantage over traditional wind power plants (and competing fossil technologies).

Makani’s technology is yet another example of what I call substituting smarts for parts.  It’s a form of dematerialization that allows us to do more clever things using substantially fewer materials but with better performance than traditional efforts.

Makani’s technology is also a beautiful case study of the power of whole system design. Focusing on incremental changes in the design of traditional turbines can yield cost reductions, and we’ve seen that occur since the 1970s (with recent increases in the cost per kW attributable to scaling up to larger turbines with higher capacity factors, among other things). But to create game changing innovation, it takes a comprehensive rethinking of the problem starting with a clean sheet redesign, and that’s exactly what Makani’s innovations represent.

I started out as a skeptic about this technology, but my visit, and conversations with Saul and others convinced me that it holds the real promise of revolutionizing the production of electricity from the wind.  My friend Gil Masters, emeritus professor at Stanford and one of the giants in the renewable energy world, wholeheartedly agrees (we just had lunch this week).

– Dr. Jonathan Koomey was a researcher and scientist at Lawrence Berkeley National Laboratory (LBNL) for more than two decades. This was excerpted from his blog with permission.

25 Responses to Do Flying Wind Turbines Make Sense?

  1. Michelle M says:

    How high do migrating birds fly? If this can be put higher than the flight of birds, I’d be okay with it. The poor animals have enough trouble with our habitat encroachment and poisoning of the waterways. And what happens during windstorms? Can we look forward to having one of these crash through the windshields of our cars?

  2. Mike Roddy says:

    This is fascinating, keep us posted, Jonathan. As for cost, I’d be interested in a spreadsheet, since claims are not always verified in the market, as you know.

  3. Richard D says:

    Don’t know if this is right or not, but the Makani Website says:

    “Contrary to popular belief, conventional wind turbines harm relatively few birds or bats when compared with buildings, radio tower guy wires and cats. Compared with conventional wind turbines, the Makani Airborne Wind Turbine (AWT) has three key advantages for sharing airspace with avian life. First and foremost, it flies at an altitude well above that of most birds. Secondly, the absence of a tower makes the Makani system much less prone to nesting or perching. Finally, the wing travels at the same speed as the tip of a modern, utility scale wind turbine, and studies suggest that birds, including the higher-flying migratory birds such as cranes, safely navigate the blades of these turbines.When sited correctly, turbines have very low impact on birds (early turbines were sited along ridgelines and places preferred by raptors and other birds). The AWT offers greater siting flexibility because the Makani system need not be positioned on ridges and can happily fly above valleys or low places in the terrain. This flexibility enables AWTs to be placed outside of migratory paths and further from large bird populations.”

  4. Robert Hudson says:

    I suspect that getting the wing to fly higher than birds would be difficult. But, I would speculate that since the wing is so much smaller than a turbine blade that it would greatly reduce the risk of striking birds as long as the speed at which it moves is not too great.

  5. Andy750 says:

    The wind is not stronger at the outside edge of an imaginary horozontal-axis turbine. Or is any movement beneficial here, and a circle – by coincidence – is the best path to follow?
    Other than that curious point, it’s good to see someone take advantage of microcontroller & other recent technologies in our search for less harmful energy.
    It would be even better if it was open-source!

  6. Andy750 says:

    OK, after visiting their site it became more clear how this works. It has to fly in circles… But it has nothing to do with conventional turbine behavior.

  7. Leif says:

    I would think that the outer circumference of the wing course is over 100 mph and could just climb to a flatter circle to address higher wind loads.

    The bird “strike area” would be greatly reduced over conventional wind turbines as well, which is also far less than the unaddressed bird deaths of ecocidal fossil fuels in and of itself.

    As for the FAA, there are any number of radio towers that equal or exceed that height and footprint as well as bird deaths. Even the top tips of conventional turbines can approach that altitude.

    All in all, it looks very promising and I am looking forward to continued simplification and deployment. Of course deployment in remote locations will be much simplified as well, not requiring large trucks and mega-crane access.

  8. fj says:

    The intrinsic sense of elegance and beauty gives clear indication what’s in store as we learn to integrate more intimately with the natural world.

  9. fj says:

    This is a wonderful post and the design concept “substituting smarts for parts” likely covers net zero mobility solutions as well.

  10. hebintn says:

    I like this concept better… would love to see a prototype actually working.
    This is some cool out of the box thinking. Maybe would be more bird friendly.

  11. Brooks Bridges says:

    Taller towers kill more birds

    “Overall, avian mortality increased with tower height,” they observe. In some instances, observations of birds being killed by towers dramatically increases for structures over 300 meters in height. ”

    Found above at:

    Also, guy wires and lights have big impacts.

    But habitat loss, cats and building windows are biggest killers by far.

  12. If a hurricane or tornado were coming, the wing can land in about 5 minutes. You clearly wouldn’t want the wing flying over a highway in case something goes wrong, but flying over an isolated field would be fine. In terms of avian mortality, the amount of swept area is far lower than a standard turbine, so bird issues should be less of a problem than for conventional wind plants.

    All energy sources have some unintended impacts, so we have to balance incommensurables against each other with any choice we make. Not easy to do, but we can’t escape that fundamental truth.

  13. Makani’s FAQ page answers all of these questions and more:

  14. Paul Klinkman says:

    I look at the device as a long-range wind power solution. The device will fail until it has a surprisingly sophisticated computer system.

    Right now, the device is an aviation hazard. Some dummy will stray into its test area, and then the giant high speed boomerang will frustrate the poor pilot’s attempts to avoid hitting it. I see the same problems with bird strikes. We also need a device that can spot dust devils, rain updrafts and other hazards coming.

    The device might have a future over water where birds and planes are few, but it would still need a landing spot when bad weather approaches.

  15. Joan Savage says:

    I’m all for improvements, and this looks like a cool way to be relatively mobile in power generation – but they may want to re-consider that assertion about birds and altitude. If the Makani is “well above that of most birds” it would have to be above 2000 feet.

    Sidebar – some of the problems with birds and fixed turbines have nothing to do with altitude, but with a sort of food chain. If the turbine color or vibrational frequency attracts insects, those can attract insectivore birds, and in turn those can attract raptors that hunt insectivore birds.

    As for altitude — From The Zoological Society of Milwaukee:

    Some geese and ducks fly at incredible heights. Bar-headed geese have been recorded as high as 29,000 feet when they migrate over the Himalayas! That’s five miles above our heads, even higher than Mount Everest!

    Most night-migrating songbirds fly below 2000 feet (600 m) when flying over land. Some will fly as high as 6,500 feet (1,980 m). Occasionally, they may fly higher to reach favorable winds.

    The wind sometimes causes birds to fly at certain heights. When the bird is flying into the wind (called a headwind), it flies very low. When the wind is blowing the same direction as the bird, pushing it along (called a tailwind), it will fly high, where the wind is the fastest.”

  16. Michelle M says:

    Cats and building windows are a hazard for smaller birds. Geese, ducks, eagles and hawks are more endangered by these devices. They may make up most of the birds that are killed by them. This might be a small percentage of birds overall, but quite a significant percentage of large birds.

  17. Michelle M says:

    Nice of him to answer FAQs without actually field-testing the device in these circumstances. At this point his answers are speculation.

  18. fj says:

    It shouldn’t be a big deal to cordon-off air spaces with inexpensive less lethal lighted and lighter-than-air fencing, etc.; including virtual signs “Naysayers Beware.”

  19. Paul Klinkman says:

    At 100 mph the wing is still lethal to geese. So are commercial jets, but the airlines have more political clout. Avoidance systems for both flying hazards are in their infancy.

  20. Joan Savage says:

    The optional down-time might be helpful if a locale has the issue of bird flock migration, too.

  21. fj says:

    Another great part the design is that it is agile technology, put up, take down, even modify on demand; most likely another important part of designing for the future.

  22. I say keep it simple.
    Blatantly I have a design too… here it is.
    Prototype 2 near completion.
    Really like the photos. nice article.

  23. Joe Faust says:

    A spectrum of alternative kite energy methods is being explored. Survey them through EnergyKiteSystems web of open-resource files. Over 800 stakeholders have been identified.

  24. dr2chase says:

    Lightning? I would think running a conductor up to 1000 feet might be an issue whenever a storm is nearby.

  25. Eric says:

    We already have alternative energy waiting for us to harness it: thorium-based nuclear reactors. Far and away much safer than traditional nuclear (half-life measured in decades, not centuries); plentiful (it’s found everywhere on the planet); difficult & costly to make weapons-grade; cannot self-sustain, so no meltdown possibility; a little goes a long way (small amounts can yield massive power output); ready to go, no refining needed. It’s almost as if this stuff was placed here on purpose.