Ampyx Power: Wind energy systems using tethered wings above 200 meters • Hacker News Board

Re: Ampyx Power: Wind energy systems using tethered wings above 200 meters

#21

Post by myself248 » Tue, Apr 28, 2020, 6:42 PM UTC

rwallace wrote: post #14

I think I am missing something here, because I don't quite get how the wind does continual work on the device to generate power. I mean, at the start the device goes downwind unreeling a tether, so it is pulling on the tether and doing work, so far so good. Then it reaches the maximum extent and... starts more or less staying where it is, staying aloft? Okay. But it's not systematically moving, so no longer doing wor…

I couldn't find a good explanation either, but my guess was different from some others I've seen here:

I think it doesn't generate continuously. I think the plane spends some energy to get up into the fast-moving air, while the tether pays out some of its length easily to let it climb. I think it only does this "once", or as infrequently as possible.

Once the plane is in the fast-moving air, the generators kick up their field current to extract energy from the tether being unreeled further, as the plane turns broadside to the wind to haul the tether out despite this drag. It's generating power as the tether pays out.

Then the tether runs out.

So the plane dives/glides back towards the base, while the generators run in reverse, reeling the slack back in. But it doesn't return so far as to get out of the good wind. So as soon as most of the tether is reeled back in, the plane turns to haul on it, the generators go back to generating, lather, rinse, repeat.

I think it only lands when the wind dies, or if it gets too strong to remain safely in the air.

Re: Ampyx Power: Wind energy systems using tethered wings above 200 meters

#22

Post by brandmeyer » Tue, Apr 28, 2020, 6:45 PM UTC

myself248 wrote: post #21

rwallace wrote: post #14

I think I am missing something here, because I don't quite get how the wind does continual work on the device to generate power. I mean, at the start the device goes downwind unreeling a tether, so it is pulling on the tether and doing work, so far so good. Then it reaches the maximum extent and... starts more or less staying where it is, staying aloft? Okay. But it's not systematically moving, so no longer doing wor…

I couldn't find a good explanation either, but my guess was different from some others I've seen here: I think it doesn't generate continuously. I think the plane spends some energy to get up into the fast-moving air, while the tether pays out some of its length easily to let it climb. I think it only does this "once", or as infrequently as possible. Once the plane is in the fast-moving air, the generators kick up th…

This is one scheme that runs the generator on the ground. Makani and Ampyx both run generators in the air and transmit power down to the ground on the tether.

Here's an (unkind) summary where the players are: https://cleantechnica.com/2014/03/03/airborne-wind-energy-pl...

Re: Ampyx Power: Wind energy systems using tethered wings above 200 meters

#23

Post by tekknolagi » Tue, Apr 28, 2020, 6:55 PM UTC

anotheryou wrote: post #8

Have you seen these guys (makani)? Kiting in an figure-8 with turbines instead of propellers (actually used as propellers for liftoff). https://www.youtube.com/watch?v=F6NW0QeKLZA That thing is also huuuge: https://makanipower.com/makani/images/pages/technology/cta.j... longer vid with sound: https://youtu.be/hYxeni2vVOs?t=60

Looks like Google is shutting down Makani: https://techcrunch.com/2020/02/18/alphabet-takes-the-wind-ou...

Re: Ampyx Power: Wind energy systems using tethered wings above 200 meters

#24

Post by jacquesm » Tue, Apr 28, 2020, 7:26 PM UTC

Every couple of years someone will jump out of nowhere and claim the wind energy sector has it all wrong, the list is very long. Windtree, Makani and many many others that replace simple and sturdy as well as well understood mechanisms with highly variable and fragile ones, usually without having studied the corpses of those that came before and died on the hill of unnecessary complexity. The closest that ever came to realization was the Darrieus rotor project in Canada, that consumed a ton of resources and resulted in the Aeolian (Eole?), a huge (100m, I've seen it up close before they tore it down, most impressive) VAT that ended up running for a couple of hours before its lower main bearing gave up the ghost under the vibrations.

http://www.wind-works.org/cms/typo3temp/pics/EoleCapChat045x...

Wind turbines are hard, and the standard shape that we've settled on was not due to a lack of creative ideas but simply because it is by far the simplest and most robust shape that gets the job done.

Any company pitching some complex alternative should at a minimum mention in their deck the degree to which they have researched the failures in the field of predecessors and what will set them apart.

Re: Ampyx Power: Wind energy systems using tethered wings above 200 meters

#25

Post by jacquesm » Tue, Apr 28, 2020, 7:27 PM UTC

anotheryou wrote: post #8

Have you seen these guys (makani)? Kiting in an figure-8 with turbines instead of propellers (actually used as propellers for liftoff). https://www.youtube.com/watch?v=F6NW0QeKLZA That thing is also huuuge: https://makanipower.com/makani/images/pages/technology/cta.j... longer vid with sound: https://youtu.be/hYxeni2vVOs?t=60

Another one that - forgive me the pun - failed to take off.

Re: Ampyx Power: Wind energy systems using tethered wings above 200 meters

#26

Post by jacquesm » Tue, Apr 28, 2020, 7:28 PM UTC

jillesvangurp wrote: post #5

donquichotte wrote: post #3

I briefly worked for a competitor of Ampyx. I love the idea, but given that it took decades to scale traditional wind turbines which are much simpler by design to powers in the range of MW, I can't see this happening. These systems are insanely complex, you need tethers, winches, a drone that flies 24/7 and can safely and autonomously start and land in many weather conditions. It also looks like google gave up on Mak…

True, it needs some infrastructure. But on the other hand, this may be similarly complex/expensive as installing and maintaining a wind turbine on a tower that's 100m high is. These things tend to be pretty complicated and expensive as well. It's all about operational cost vs revenue in the end (and comparing that to other solutions). IMHO wind and solar are still making great leaps currently in cost effectiveness an…

It is of an entirely different level of complexity.

Re: Ampyx Power: Wind energy systems using tethered wings above 200 meters

#27

Post by jacquesm » Tue, Apr 28, 2020, 7:30 PM UTC

brandmeyer wrote: post #19

rwallace wrote: post #14

I think I am missing something here, because I don't quite get how the wind does continual work on the device to generate power. I mean, at the start the device goes downwind unreeling a tether, so it is pulling on the tether and doing work, so far so good. Then it reaches the maximum extent and... starts more or less staying where it is, staying aloft? Okay. But it's not systematically moving, so no longer doing wor…

Imagine for a moment that you built a wind turbine generator with just one blade. Instead of two other blades, you just had a counterweight. Then replace the tower and hub with a tether, and drop the counterweight. That's effectively what these technologies are doing. In point of fact, all of the blades on a commercial wind turbine are shaped like wings, such that the reaction force of the air flowing over the wing a…

Single blade turbines approach the maximum possible under Betz' law regarding power extraction from a moving air mass but suffer from resonance and material fatigue to the point that it offsets all advantages. Twin blade rotors suffer from thump and material fatigue as well, three seems to be the optimum and is what almost all commercially available turbines use.

Kites are a complication that nobody needs.

Re: Ampyx Power: Wind energy systems using tethered wings above 200 meters

#28

Post by jacquesm » Tue, Apr 28, 2020, 7:32 PM UTC

benkarst wrote: post #16

It must be hard to get an MVP. It's been 10 years and they only have renderings?

You don't need an MVP to raise money. This is a polite way of saying that most of these are bordeline scams, they could work in theory and if the people behind them have done their homework they know full well they will never see them in large scale deployment but it is a nice way to get a bunch of cash to play around with and tinker. See also: flying cars, especially Moller.

Re: Ampyx Power: Wind energy systems using tethered wings above 200 meters

#29

Post by NohatCoder » Tue, Apr 28, 2020, 7:34 PM UTC

rwallace wrote: post #14

I think I am missing something here, because I don't quite get how the wind does continual work on the device to generate power. I mean, at the start the device goes downwind unreeling a tether, so it is pulling on the tether and doing work, so far so good. Then it reaches the maximum extent and... starts more or less staying where it is, staying aloft? Okay. But it's not systematically moving, so no longer doing wor…

The kite goes sideways relative to the wind, spooling out the tether, generating power, and speeding up. Just like a high-speed sailing boat it can reach several times the speed of the wind this way. Then when time comes the kite turns into the wind, letting the tether spool back in at no real energy cost (but not generating power during this period). The kite then turns again to repeat the process.

Note that while there are several different techniques, they all rely on the kite moving fast, this allows it to sweep a large area relative to its size, thus working around the fundamental limit that you can't extract more energy than some percentage of the directed kinetic energy contained in the air molecules moving through the swept area.

Re: Ampyx Power: Wind energy systems using tethered wings above 200 meters

#30

Post by brandmeyer » Tue, Apr 28, 2020, 7:37 PM UTC

jacquesm wrote: post #27

brandmeyer wrote: post #19

Earlier quoted context omitted.

Imagine for a moment that you built a wind turbine generator with just one blade. Instead of two other blades, you just had a counterweight. Then replace the tower and hub with a tether, and drop the counterweight. That's effectively what these technologies are doing. In point of fact, all of the blades on a commercial wind turbine are shaped like wings, such that the reaction force of the air flowing over the wing a…

Single blade turbines approach the maximum possible under Betz' law regarding power extraction from a moving air mass but suffer from resonance and material fatigue to the point that it offsets all advantages. Twin blade rotors suffer from thump and material fatigue as well, three seems to be the optimum and is what almost all commercially available turbines use. Kites are a complication that nobody needs.

The single-blade model reduction is just a rhetorical device used to guide the reader on the principle of energy generation, not on viability.

As you point out, single-blade turbines have been done but they have their own suite of mechanical problems. A more practical way to save capital cost is to under-size the electrical system relative to the blade area. You may still only get 30% capacity factor of the blades and tower, but you could get 40% or better on the electrical system for a small win.