Minesto Underwater AWE News

News
26

I’m placing this in “News coverage”, as opposed to “News” - a subtle distinction, but here it is:
By now, you must all be getting used to these “news” “stories”:
Winged ‘Sea Dragons’ Can Generate Electricity For 25,000 Homes

Let’s examine this “story” more closely:
“25,000 homes”. There it is again: pulling some large number of homes out of thin air, and creating a definitive statement of “fact” that some ongoing effort that has made similar claims for years, is suddenly some new news that we haven’t heard before.

Minesto, with their “Deep Green” underwater version of Makani, was supposed to have been powering many homes for years now, except they always seem to be “getting ready to get ready”, and the grid-feed that is supposed to have been taking place for years now, is mysteriously still in its original “holding pattern” of merely “contributing to the Faroe Islands’ national grid as part of a trial run over the past year.”

The stated output seems to have dropped drastically for the 5-meter size, which now::
“allows each of them to glide through the water in a figure-of-eight pattern and generate enough electricity to power approximately four or five homes.”

This implies sporadic and intermittent, low-power grid-tie generation, producing much less electricity than we’ve been led to believe, on a “testing” basis, not what we’ve been told for years now that they had a product that was going to be routinely powering many homes.

Now, suddenly, we’re told that these 5-meter underwater kites can each power only 4 to 5 homes!
But don’t worry, they are about to increase the kite wingspan from 5 meters to 12 meters, and this 1.4 x increase in wingspan is supposed to result in a phenomenal increase in power:

“According to Minesto, the firm is currently working on new kites with a wingspan of 39 feet (12 meters) rather than 16 feet (five meters). These will be able to generate 1.2 megawatts of power, meaning that an underwater fleet would be enough to power half of the Faroe Islands’ 50,000 households.”

OK so a 140% increase in size is predicted to result in a 1000-fold increase in output???

To me, the first thing to notice is the false claim of the headline:
“Winged ‘Sea Dragons’ Can Generate Electricity For 25,000 Homes”
Really? 25,000 Homes?

Really? They CAN? They don’t exist yet, but they already “can” power 25,000 homes? Well I guess they DID say the 25,000 homes would be powered by a “fleet” of turbines, not just one, but how many are in a fleet? No mention. Can you identify the probable falsehoods being conveyed here? They’re not even saying how much power the existing “Deep Green” underwater-aircraft have been making. “Four to five homes”. That could mean anywhere from 4-5 kW, up to 40-50 kW, depending on how they define “powering four to five homes”, but it is a far cry from powering 25,000 homes. I would have to say, I do not believe increasing wingspan from 5 meters to 12 meters could increase output by ~5000 times. Do you? Should we take this effort seriously after reading this? I’m thinking this article purports to be an announcement of great success, but if read carefully, reads more like a last desperate gasp of hopeful public-relations hype translating loosely to: “If you have stock in this company, sell it now while you still can!” :slight_smile:

1 Like
27

Media has all sorts of weird agendas not necessarily related to those of the company.
I’ve been edited, misrepresented etc.
They mostly want positive spin on a story not many people will understand.
I reckon Minesto will be improving their tech with each attempt.
Just hope they have some good seals on those shaft bearings

28

Yes just about everyone who has ever been “in the news” knows they get many details wrong. This, however, seems like a recitation of the typical, ongoing public relations statements coming from Minesto. OK so you are placing your bet on steady improvement, leading to success for Minesto? I’m seeing the same sort of impaired improvement we’ve become used to seeing as companies slowly deplete their resources and credibility until suddenly one day you read about the upcoming “auction”.

29

In the linked article:

According to Minesto, the firm is currently working on new kites with a wingspan of 39 feet (12 meters) rather than 16 feet (five meters). These will be able to generate 1.2 megawatts of power, meaning that an underwater fleet would be enough to power half of the Faroe Islands’ 50,000 households.

1.2 MW for a 12 m kite, and 25,000 homes with “an underwater fleet” of 12 m kites. What is wrong?

30

The Dragon 12 wing - YouTube

https://www.youtube.com/@minesto4054/videos

2 Likes
31

Super fascinating! ……

1 Like
32

Indeed, it is impressive. If a crosswind kite can generate this much power underwater, some hopes could also be realized at high altitudes.

2 Likes
33

More impressive “news of the future”. Look! They delivered our new part! Wow, amazing they were able to deliver a part - after all these years… I gave up on these guys a long time ago.

34

Bloody awesome Minesto.
Continuing steady progress.
That’s really impressive.
I can hear Doug burning with jealousy all the way across the Atlantic

1 Like
35

Its also a matter of a thousand flies that could not be wrong here. They would be unsensible to build at this scale (very costly) unless they had data that this may succeed. So maybe one of:

  • The concept is proven to produce power at smaller scale, and this would be cost effective for the site
  • They are hoping that power is easier to generate at larger scale
  • They are hoping they figure out the remaining issues before its too late

I think the first one is more likely. If they are at the other two, maybe a new Makani type of failure is imminent. But seeing that the first one seems most likely, there is some reason maybe not to celebrate, but at least to cheer up

36

The Dragon 12 – main design properties:

  • 1.2 MW rated capacity generator
  • Dry weight (excl. tether): approx. 28 tonnes
  • Turbine diameter: 3,5 m
  • Overall Kite dimensions: LxWxH: 9.8 x 12 x 5.2 m
  • Tether length: 55-100m

The first Dragon 12 unit is being manufactured and is planned to be commissioned in 2023.

The Dragon 4 – main design properties:

  • 100 kW rated capacity generator
  • Dry weight (excl. tether): approx. 2.7 tonnes
  • Turbine diameter: 1,3 m
  • Overall Kite dimensions: LxWxH: 4 x 4.9 x 2.8 m
  • Tether length: 40-100m

37

Some interesting aspects of the design;

Tether to wingspan ratio 8.16 - 20.4 for D4 and 4.6 - 8.3 for D12 which is quite small. At Kitemill we are looking at 33 - 80. [This is just a rough number subject to change]. This means short tether with less drag relatively. The ratio bears more similarity to «The Pyramid» than traditional airborne Jojo style designs.

The vertical wing sections; it seems weird to me that the design would need so large vertical wing sections. For sure this kite will not side slip much. This means no dihedral action for roll control. Or, it could mean dihedral action that is very stiff. I would question how much drag these add. My guess is that they are used for maintaining a tight loop radius. Another guess is a need to provide lots of aileron control authority without adding wingspan. But these wing sections dont seem to have actuators. To be honest this part of the design does not appeal much to me, though maybe they have their reasons.

On actuators in general I see rudder and elevators providing control of yaw and pitch.

1 Like
38

For tidal energy, the stronger current is found closer to the surface. It is not necessary and even not desirable to install machines in deep water.

For AWE the issue is reversed, since one of the purposes is harnessing high altitude winds. That said “The Pyramid” ratio (which is closer to Minesto’s ratio) seems preferable to me: Unlock the market by shortening the tether. The main thing is to be able to increase the dimensions of the wing or wing arrays when the tether lengthens. But it may not be the priority yet.

1 Like
39

Yeah sure, I’m jealous looking at an ongoing, slow-motion trainwreck.
I think this old saying applies to so many items brought up here:
“It’s far easier to fool someone than to convince them that they’ve been fooled”
:slight_smile:

2 Likes
40

I think tether length to wingspan ratio is interesting because the physics involved subsea and airborne is quite similar. I did not check in detail if everything is kind of the same wrt lift and drag of the kite vs drag of tether at the same scale. But I wouldnt be surprised if there are many similarities.

The one difference you could spot right away though is subsea tethers should be much thicker than flying ones. The lift of a certain wingspan wing will be enormous subsea due to the high density of water vs air. And the area of the tether «cut» must match those realities.

As density of water is ~1000 times that of air, the tether would maybe be \sqrt{1000} times larger diameter. But then the apparent flow over the kite would probably be much less. So that again makes the tension much lower and tether thinner. Still, for a given kite, if designed to pull as much as possible, would have 31x larger tether drag in water compared to in air, if you look at tether vs kite drag.

Hence their ultra short tether I guess.

I would actually think Minesto may not make much sense without fairings on their tether.

42

The figure I normally see is 800 times the density of air, for H2O.
I’m a bit skeptical of Minesto because they’ve been around for many years now, and never seem to make their milestones, with most stated “progress” seemingly perpetually set in future-tense. :slight_smile:

1 Like
43

I was rounding off a bit eagerly. You are of course correct here, at least more correct.

I was thinking more about the tether. The same dimensioned wing and tether under water vs air would give the relative same drag if the flying speed is reduced so that the tether doesnt break. So if you think like that, everything is more or less the same.

The question is really are Minesto producing at the flying speed that would match Kitemill/Makani/whatever or are they flying relatively faster so that the tether must be thicker to accomodate more pulling force. My gut feeling says yes… but the difference is probably not very extreme. Tidal currents are slow, perhaps 2 m/s while wind is 12 m/s.

Anyway, another observation is that maybe bounding [eg. yoyo] would not work well underwater because the slow current speed does not really lend itself to 1/3 current speed reel out. That would mean a gigantic tether force to make any sense. Which again means really thick and draggy tether. So the hovering [eg. flygen] makes more sense subsea.

44

Well, I’ve only heard it a hundred times or so. I’m all for doing quick estimates in my head though, without getting too hung up on unnecessarily precise numbers. But it’s easy to adjust to another round number and not be off by 20%. Maybe just for the benefit of the other kids in the class.
Beyond that, I’d say over-analyzing Minesto is like rearranging the deck chairs on the Titanic (as the band plays on!) They’ve been going on like this for many years now, and never seem to get out ahead of the curve. Not sure what their problem is, but I think maybe it starts with using a “kite” in the first place. :slight_smile:

45

It’s a bit like AWES, for which in addition blimps wouldn’t be valid, would they, Doug?

So here is a tidal turbine that could work, following a principle close to that of a regular wind turbine.

46

Well Windy, AWE people are too dumb to try an aerostat, cuz, see, it’s such old news, so grimy and industrial, so… well. proven. Proven to reach high altitudes, proven to carry a payload, proven to withstand high winds. Nah, way way way too boring. And no patent coverage! Not so easy to soak investors! Far better to, say, break out some highly-impressive Ivy-League credentials and make your own blimp - with a tunnel going through the center to use more envelope material to take up all that space that could hold more helium! Then finally use an off-the-shelf 2.7 kW downwind turbine with a heavy inverter in the nacelle. i wonder if they took it out and moved it to the ground?. Seems like they could have saved a lot of effort just buying a blimp and hanging a windmill from it. But, as I explained, that would be too simple, too, well… logical!

Yup, Orbital is my all-time favorite hydrokinetic energy player. In fact I was close to investing in it, but it wasn’t like just buying stock, it was a bit complicated. Anyway. I think they have a good design, for a reasonable concept. It has many elements that I’ve always wondered why others haven’t used. It’s something I would come up with myself. I’d rather be able to service it on the surface, then have to dive or bring it up, and as Pierre said, currents are faster at the surface, so, ding ding, WAAAHHHH get out of the way!