Seems like the EU also favours Orbital O2
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Only it uses multiples of the material for only twice the power generated.
Underwater, flygen seems to make much more sense. I think tidal currents are stronger in shallower water, so a shorter and constant tether length makes more sense. Minesto’s design is basically a submarine connected to a tether, where only the shape of the submarine and the control are unknowns. And it can’t fall out of the sky.
I think it even makes more sense than static towers, as you can tow them back to land for servicing, and installation should be easier. And you’d have all the other promised benefits of AWE over traditional wind.
The unknowns are I think mostly economical, not technical. Can they reduce the cost of the kite enough, and is there enough tidal energy available to justify making hundreds of kites and with that benefit from economies of scale?
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It is like the “two simplest AWE ideas” described on Using an aerostat or a kite as a lifter of a regular wind turbine, by juxtaposing proven technologies?.
Minesto uses crosswind motion in the water in the same way that most AWE companies operate crosswind kites. Both crosswind kites have a far better power to mass ratio, but need sophisticated control.
For tidal turbines the question still remains unanswered. For AWES I think we have had the answer for a long time, taking into account that “crosswind flight” mode could also be extended to some rotary devices like Daisy or The Pyramid.
Steel is cheap. Reliable operation is paramount. Orbital is 100% crosswind (crosscurrent).
At equal mass, a crosswind or crosscurrent kite with its turbine sweeps an area larger than said turbine (whose blades operate by definition crosswind or crosscurrent) alone.
I agree.
Yeah, that’s the whole idea, right? But it goes from simple to complicated, with lots more stuff to go wrong. What you need is “set it and forget it” simplicity and reliability, not endless problems to contend with. 
Steel is cheaper than composites, though more steel is surely more expensive than less steel. Coming from drilling ships with large derricks, I have heard steel is most certainly not free
Well my dad, who graduated in the top 10% of his engineering class at Yale, told me “steel is cheap”.
And that there is so much oil out there you wouldn’t believe it. That was back when “they” said we had run out. Anyway, sure steel isn’t free and less is better than more if you want to save money, but they make ships out of it, so I think Orbital Marine is on solid ground - er um liquid water - choosing a steel hull.
I am sure steel [if that is what they have] is an excellent choice. I am just pointing out that future is not clear cut. If both Minesto and Orbital succed in making power, both with steel, Minesto seems to use less steel. This would be a competitive advantage. And needs to be seen together with other advantages to either system.
I’m seeing using steel just acknowledging it is the standard for ship hulls, so why reinvent that material choice? And if it uses a bit more steel, that may a low cost compared to having to service an underwater base station and a possibly rogue submarine on a cable, as a start.
But, after watching their videos again, I’m seeing some “issues” with Orbital:
They mentioned and showed two (2) tethers, one each, toward the bow and stern.
They seem to be going for permanent aim.
Their blades have no camber, and have “pitch-control”. Pitch control adds one more expense and one more thing to go wrong.
Just as when I had not noticed that a flettner rotor would need to reverse rotation depending on relative wind direction, the Orbital machine has to reverse pitch as the tide reverses.
I had assumed the whole craft would change direction 180 degrees, pivoting around a single, upstream tether.
Their blades also have no twist, so as to work in both directions equally well.
Hmmmm…
I will say the 10 kW WIND turbine here has pultruded blades with constant chord and no twist. Except they can sort of twist a bit due to centrifugal forces in high winds. But at least they have camber. (And the manufacturer has finally moved on to using “real blades” for their new, larger, 15 kW machine, because they could not keep cheating the known laws of wind energy at the larger diameter.)
The Orbital promotional material shows a “farm” (array) of their machines in line with each other (why, to block the current?) and I guess they do not pivot to aim into the current, but are permanently aimed. That means they go from “upstream” of the supporting arms to “downstream” of the supporting arms. That will cause issues with the blades hitting the “wake” of the supporting arms.
So I do see problems with the Orbital system. Doesn’t mean it’s not going to work out, but those are definite “Professor Crackpot-esque” symptoms (known-non-optimal characteristics), in my humble opinion.
A blade with no camber and no twist is not going to perform as well as one with pitch-twist and camber.
I’d say the basic design might be refined with time, maybe using less steel too. Maybe Orbital’s contribution will be just getting the base station up out of the deep water and onto the surface where things can be serviced easier.
It’s also necessary, with the variable current velocity. Your idea would be more hassle anyway. And since it’s necessary, it’s a good idea to use it to its full potential. Here is a tidal current chart: NOAA Current Predictions - Current Predictions
I’m not following why the blades would have to have no camber or twist, unless they don’t actually rotate 180 degrees when the current direction changes?
An older video with some info: Turning The Tide
Orbital also uses composite blades.
Hello windy:
Thanks for some good info on the decommissioning of their old unit, and the comparative newness of the O2. I had thought they only had one prototype operating. It is interesting to compare their statements of HOW MUCH energy they put to the grid over time, as contrasted with Minesto’s far weaker and less specific claims.
I’m not sure where you get the idea that pitch control is “necessary” to handle a variance in stream velocity, unless you think they are powering an induction generator directly coupled to the 50 Hz grid over there. Even then, pitch control would not be strictly necessary. Look up “The Danish Concept” of wind turbine design from the 1980’s. The blades were just bolted to the hub - no pitch control whatsoever, in varying windspeeds, yet within a tight rpm range. Your assertion that pitch control is needed for varying current speeds sounds like stuff armchair-inventors come up with when they are not up to speed on a technology.
With variable RPM to match the variable current speed, as we see in wind turbines, pitch control is not needed for that purpose, but is instead used for overspeed protection and sometimes fine-tuning torque as each blade transitions the gradient from high winds at high heights, to lower-speed winds nearer to the ground. Small wind turbines almost never have pitch control. When they do, it’s usually a problem and breaks down, because it involves maintenance that nobody wants to, or bothers to, perform.
I was going from their renderings, and from the renderings, you see no twist or camber, indicating that the blades likely always rotate the same direction, with a less-than-180-degree pitch range, but rather a more restricted range of +/- whatever the working pitch is. Maybe their new model moves past this early design. There must be some reason they stopped running it. Maybe they wore it out already!
As to what you say “my idea” is that “would be more hassle anyway”, well, I haven’t stated “my idea”, I just said what I had originally thought “their idea” was, which was to take the time of lull between tidal flows to allow the “ship” to re-orient itself to the new current direction. And I’m not seeing how allowing it to passively reorient itself 180 degrees is “more hassle” than including a pitch-control system. Remember, when working with steel machinery, immersed in a salt-water environment, keeping everything as simple as possible, with the fewest wear points and lowest parts count possible, is advantageous. A pitch-control system on a rotor of that size and strength is no trivial undertaking, would add cost and complexity, and of course would require maintenance.
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I agree pitch control seems like a weird place to start. But these companies tend to figure stuff out as they go, so everything is not neccessarily hopeless if they have more good ideas to compensate for misses.
I also think having production in both directions weird as it would actually take more effort to force alignment in both directions, compared to letting it rotate with the flow. So far I need to think they had a plan that caused this design choice that I would understand if I knew more details [cabling is one guess].
Seabed leasing at EMEC for tidal deployment is hugely complicated, expensive and requires a lot of analysis on seabed disturbance…
(It’s a lot easier to deploy a fishfarm there)
The issue with Orbital O2 turning round will likely be seabed anchoring given the tidal range vs depth at the location means that the chain (the huge heavy bit which lying on the sea floor and provides most of the resistance) would move across the ocean floor.
The permitting was very sensitive to ecology.
Maybe One solution to allow system rotation would be to have 2 anchors
with 1 upstream on the ebb direction
the other upstream on the flow direction
chain between the 2 anchors in a straight line
chain to the floating generator from the middle of this chain.
Sounds like a good approach, Rod. Maybe any structural way to get the anchored end of the anchor tether (cable, chain) up and off of the seafloor. Then again maybe something could catch on that structure and it would become the problem. It’s always something…
Maybe they could convert it to a fish farm! That makes power! And get a permit!
Funny how the left hand mandates clean energy while the right hand refuses to issue a permit. Can’t let cheap energy get out of hand, now can we?
But if you don’t want to close off the area for ships you need to be sure you are deep enough to not pose a danger to the ships. Even sailing vessels with keels sticking pretty far down. And that goes for both the paravane and the tether.