I highly recommend watching the documentary they produced, https://t.co/y70yeZ3ZjY?amp=1 . My takeaway is that it took 14 years to produce a working kite and in that time conventional wind turbines became much more economical and efficient. After realizing this, they pivoted to doing off-shore wind generation because the cost for competitor products was higher. They had one somewhat successful test but were out of money and couldn't find any other investors.
What was somewhat surprising to me though was that, for all their technical ability, nobody at Makani foresaw the future of conventional wind turbine efficiency?
It just kinda seems like all of a sudden (in the documentary), they lifted their heads up, and 10 years had passed and conventional wind energy was dramatically improved. Case closed, that's it.
Well, I think the main TLDR is that it would require significant additional investment to reach MVP. Also- the energy sector lacks the huge margins of the tech sector. Renewables have long been subject to a boom-bust cycle driven by the prevailing price of energy.
Our released technical report "The Energy Kite" is intended to help answer this question, and to explain what we would do if we had the opportunity to continue our work. Check it out here:
https://storage.googleapis.com/x-prod.appspot.com/files/Maka...
One major learning is that it ultimately appeared to us that crosswind kite power currently offers little benefit over traditional horizontal axis wind turbines for onshore applications, except perhaps niche applications such as small-scale generation allowing rapid deployment. There may still be a viable opportunity for large-scale crosswind kite power in the deepwater offshore environment. In that environment, conventional wind requires huge floating platforms to deal with the overturning moment arising from the turbine drag acting at the top of the tower. In crosswind kite power, only a small buoy is required to support the tether tension.
Finally, the M600 failed to meet its performance specification (the "power curve" which shows how power generation scales with wind speed). The reasons for this are detailed in the technical report (starting on page 231 of the above link). (We designed a follow-on system called MX2 which we believe would meet its performance objectives but the project was cancelled before it was built.)
Not an insider but isn't it obvious? Too expensive and it can only crash once. Regular wind turbines are probably cheaper and failsafe. Should have pivoted but it is a make it work at all costs kind of vanity project. Once you go big pivoting is not an option. Investors don't want to hear that. They just want a delivery date.
I was on one of these multi-billion boondoggle projects. Basically people keep it going even though it is not viable. Telltale sign is the project is spun off or 'cut loose' to die.
The product can be totally amazing though and parts of it could be a viable company on its own. Maybe these projects should be structured in a way that each component is a business entity.
The tether replaces one set of problems with a different set of problems. Some of the new problems had promising solutions, but others were more marginal.
1) Land use. The small props are loud, and the setbacks relative to populated areas are pretty high for tether and crash safety. Solution: offshore. Now you have two problems :)
2) The tether's weight is a factor. Its hard to build in much margin on this component before it gets too heavy to fly. What happens if a gust temporarily reduces tension on the tether? Can it handle a shock load from the kite hits the end again if it comes off its sphere? How many conductors can you run down the tether? IIRC, they were running DC+ and DC-... with no ground. Now, what exactly happens during lightning strike? At the time they believed that they were just barely on the "feasible" side for this component on a feasible-infeasible axis, but it was pretty darned close.
3) The power system was complex. Tether weight biases you strongly towards a medium voltage power system (a few kV pole-to-pole) to cut down on the weight of the conductors. However, the size of the turbine was smaller than any medium voltage application I had ever heard of. Maybe the ground side could be COTS, but the flight side almost certainly couldn't. So now you are also in the business of building bespoke medium-voltage switching power converters and motor/generators. There's nothing fundamentally infeasable about this, its just a bunch of hard work that detracts somewhat from the main mission. A startup would much rather buy this tech, but they were forced to build it instead.
I mention the power system explicitly because that's particularly in my bailiwick, but I think it was really a microcosm of the project as a whole. They were building an airplane for the purpose of energy production. So they had to solve all of the problems that an airplane company has to solve. Also, since electricity is so cheap, you can't afford to pay human operators for all of the generators, so you also must solve many of the problems that an autonomous airplane company has to solve. In salty air to boot.
Overall, there's just a staggering amount of NRE that must be spent chasing a market that is already commoditized. 50 USD/MW-hr is a typical benchmark for wholesale electricity. Meanwhile, solar panels are iterating and getting cheaper and traditional wind turbines are iterating and getting cheaper. Eventually, the bean-counters start to notice.
There's an alternative explanation: Makani (and Wing, and Titan, and the robotics initiative, and other things) were initiated when Larry was still young and excited about the technology itself. We used to morbidly joke that Ruth Porat (hired CFO) was going around the company asking questions like, "Airplanes, Larry? Really?" (taps clipboard, raises eyebrow). Eventually the long years of almost-but-not-quite-success wore them down past the point of endurance, and the projects started dying off when the leadership got bored of them.
Having worked in the industry a bit, yes, likely both are true. There are very complex engineering problems to solve and Makani was taking one of the more complicated approaches to the problem. Some other kite power companies (including the one I worked at) have the generator on the ground and use an ascending figure 8 pattern of flight to pull the tether thus generating power (at the top of the cycle the kite goes into a sort of controlled stall to lose altitude, the tether is rewound and the cycle continues) - that approach certainly has issues as well.
I often think that maybe most of us were taking a much more complicated approach than is actually needed. Perhaps (thinking out loud) something much simpler like a soft kite with a sort of trap-door which closes as it ascends and opens to let it fall to a lower altitude would be a much simpler approach - essentially a bag kite with an end that can be opened and closed - obviously it would be smaller scale, but most of the kite power companies are working at a much smaller scale than Makani was.
The tether was indeed medium voltage, but the motors and controllers were not, through use of a fairly novel stacked architecture.
There were still hard problems to solve there, but ultimately the power system worked well, and out performed it's original design targets. It was not responsible for the projects demise.
From what I hear the robotics initiative is still going. I left in early 2019 and the project has its challenges (robotics is hard), but from what I could tell they still had support of leadership.