Slightly OT, regarding high-temperature superconductivity: this article [1] reports on an interesting effect that appears in some materials that are showing HTS.
A theoretical scientist is quoted there with “We probably won’t understand why the superconducting temperature in cuprates is high until we understand the strange-metal phase out of which the superconductivity emerges”. A new approach seems welcome, as it felt like progress on HTS had stalled (imo). It might finally help us to get closer to room temperature superconductors... :)
You might find the recent work on graphene superlattices [1] interesting; the video goes into a bit into what cuprates are doing and how the graphene approach might explain some of that space.
It is interesting to see that it is apparently viable - enough to not be a novelty/joke. Given materials one upgrade a stationary bicycle generator to use superconductors. Unless it became both much cheaper and much higher temperature there would be basically no reason to do so but you could. Megawatt Turbines should certainly be able to sustain it but I wonder how the math works out in terms of both performance and balance sheets.
Would be interesting to see the actual cost differential in this vs permanent magnets.
They don't go into details about the cost of fabricating the HTS, but gadolinium is less than half the cost (in oxide form) of neodymium according to the article, and it uses 1/1000th the amount.
For bigger and bigger turbines, superconductors will always win, since the material is cheaper, and chiller cost and energy loss scales with the power generated ^ (2/3), whereas the support structure needs to be both taller and stronger so scales with ^(3/2), so superconductors always ends up eventually cheaper.
Chiller cost is approximately proportional to the surface area of the generator. The power output of a generator is approximately proportional to the volume.
The mass of a generator is approximately proportional to the volume too. The support structure is proportional to the mass of the generator, times the height of the turbine (actually more than that, but we'll ignore that for now).
The height of the turbine is proportional to the square root of the wind energy collected. (turbine blades can't hit the ground)
Combine all those factors to get the power indices...
I think it’s just a publicity stunt.
There is no way that this wind turbine will be more profitable than a normal one given the pretty crazy cooling requirements.
Also I don’t really understand why they chose that kind of superconductor that apparently has to be cooled to -240 when there are other superconductors that need to be cooled to just 150K...
>There is no way that this wind turbine will be more profitable than a normal one given the pretty crazy cooling requirements.
As long as the insulation method for the superconductor is good, once it is cool, keeping it cool should use surprisingly little energy, especially compared to the output of one of these things.
>Also I don’t really understand why they chose that kind of superconductor that apparently has to be cooled to -240 when there are other superconductors that need to be cooled to just 150K...
They do the same for a lot of the SMES systems - https://en.wikipedia.org/wiki/Superconducting_magnetic_energ... - Apparently the difference in cooling costs isn't that much and there are a variety of benefits to using the low temp ones that more than offsets that cost.
I suspect that those are the sorts of question this first installation is supposed to answer. They'll certainly have models for efficiency, cost, lifetime, maintenance, etc. but they remain models and field-testing the reality is absolutely the step they appear to be taking here. This was alluded to in the article itself, where they described the cooling unit as previously untested in the relatively dirty conditions under which a wind-generator operates, as opposed the previous applications of the cooler operating in hospitals and clean lab environments.
In July there was a excellent IEEE article [1] on the potential and the difficulties of superconducting turbines. This project (Ecoswing) is mentioned there, although it seems they switched from YBCO to GdBaCuO.
Does the refrigerator still need helium? Getting rid of helium might be a bigger deal than just raising the temperature.
Edit: Thanks for the comments. Adding a note: As I understand it, in some of these materials, the transition temperature decreases when the material is in a strong magnetic field, so there's a limit to how strong a magnet can be made, and further cooling may be needed to deliver sufficient field for an application. Still, I'm excited, and hoping that the "grail" of helium free refrigeration is achieved soon, due to the tricky issue of world helium supply.
Interesting. That's around the liquid hydrogen range - still cheaper than helium, but probably not as easy to work with as nitrogen. I guess their requirements for critical field were high enough that the 77K GdBaCuO performance wasn't good enough?
It should also dissipate very quickly. There would be a brief window when it'd be dangerous, but you'd need as little wind as possible. The volumes used in these chillers are relatively small.
The (closed cycle) cooling compressor uses helium as a working fluid, but Tue quantities are usually very low. Hight temperature superconductors are usually cooled with just liquid nitrogen
I found this other document that has some information I think about this project at the end [1], which says it's conduction cooled by the cold heads. So perhaps it doesn't use either LN or liquid helium.
"Cold head" means the cold end of a cryocooler. "Conduction cooled with cold heads" means that the superconductor is in direct thermal contact with the cold end, rather than through some more complicated arrangement.
I'd be interested in a comparison of the cost and efficiency of this type of generator versus using an induction generator. Induction generators don't need magnets either.
I'm also wondering what type of generator they built. Is the superconductor in the rotor or the stator? Does it carry a DC current and, if so, is it operated in persistent mode? Or does it carry an AC current like an induction generator's rotor would?
It would seems like the superconductor works on stator and rotor like an induction generator.
Edit: looks like it's just the rotor:
Some quotes from the test:
"The EcoSwing rotor is made up of two parts which are thermally decoupled by a vacuum chamber. The part responsible for the bearing and the mechanical connection of the generator rotor is operated at ambient temperatures; the electromagnetic part of the generator rotor is designed to operate at cryogenic temperatures. This places particular requirements on the test bench: The generator has to be cooled down to 30 K (that is about -240 °C) using a closed-cycle gas cooling. While this was the first time that such a cooling system has been operated at Fraunhofer IWES, it got confirmed that this type of cooling performed very reliably."
"Sometimes less really is more: 40 per cent less weight and smaller dimensions than a comparable permanent magnet synchronous generator – these EcoSwing features are only possible thanks to superconductivity. With this solution just a fraction of the magnetically active material is required to outperform the power density of conventional generators. Since superconductors have practically no electrical resistance, the size of the conductor cross-section can be drastically reduced. This is a highly promising property for the development of future turbine generations."
Image: https://www.iwes.fraunhofer.de/en/press---media/ecoswing-sup...
Press releases and presentations say they used a direct-drive permanent-magnet generator with a full power converter and replaced the rotor. So it's most probably DC.
I wonder if superconducting induction machines would be a useful research direction. They would be strange, since the flux through any particular loop of superconductor would be a constant.
All the energy in the superconductors magnetic field is suddenly released into heat, which will make it get hot and boil off all the helium it's sitting in.
The generator will then have no magnetic field, so generate no power, and start to spin faster and faster.
Hopefully there are some breaks to stop it before this happens:
Those would be interesting indeed, as well as the transition to/from superconductivity of the rotor. I'd imagine that, when the rotor loses superconductivity, it'd becomes an insulator and the whole thing would be a rotating ceramic brick inside the fixed coils. There would be no torque to counter the wind, so it'd rotate faster, maybe fast enough to overheat the bearings.
This starts getting viable only now on a turbine scale of several Megawatts, with a very continuous workload. Scale this down to a car delivering an average of just a few kW that is driven maybe an hour or two per day and you‘ll lose all that efficiency to just cooling down the motor to -240•C and keeping it there.
I get your point about the difference of scale in power but cars routinely reach 100 kW - that's just 134HP after all. Floor the gas pedal on a mid-size sedan or a small truck and there you have it, 100kW. Good point about the load cycle.
Even that won’t use max power. The amount of energy required to move a vehicle forward at 60km/h is a fixed quantity to do with rolling resistance and drag.
There’s going to be greater loss due to friction in the engine and losses in the gearbox, probably in the single digit range? I honestly don’t know anything accurate.
It will be for a truck though - once you have 40 tonnes on your trailer, I'm almost certain the engine will have to keep producing 100kW just to keep on moving at a steady 50mph.
I assume that's why GP was talking about Tesla trucks. If a truck has two drivers it can be used for nearly a whole day - assuming the batteries could keep up.
Yes or even a Road Train with say 3 drivers on board for 24 hour use, big shortage of drivers in US apparantly.
Road train must be more feasible now, software should be able to easily steer multiple trailers with independent steering ,forward in same path as cab and for reversing which would be tricky without such.
“They require substantial quantities of rare earth metals, however, which are expensive and are mostly mined in just one country – China – which has led to worries over security of supply.“
There are other potential sources in the world, but they will not be explored until there is a clear financial benefit to exploring them. That will most likely not happen until something goes wrong with the supply in China.
China only has 1/3rd of the worlds extractable deposits. Rare earth minerals is the typical "China Bad" scare story. They reduced the amount they sold because they wanted it themselves to value-add making electronics/renewables and being the vast majority of world supply it got them a better price.
Much like many other countries on earth do. OPEC even has multiple annual meetings where they all decide to collude on restricting oil supply.
If the rest of the world was truly worried they'd subsidise the industry, as it stands most countries throw away all their rare earths in tailing dams as mining byproduct because it's not worthwhile to extract it.
In contrast to the common expectation and statements in this article - most turbines are already not using the rare earth magnet design.
Study: Substitution strategies for reducing the use of rare earths in wind turbines [1]
>According to our estimations about 23% of the global installed capacity in 2015 is based on wind turbines using [permanent magnet] technology. The remaining 77% are using conventional electromagnets generators based on magnetic steel and copper windings, both of them posing no issues about the security of material supply.
PM rotor generators have several disadvantages: they're heavy; magnetic flux fades in time, moreso under heat; inability to control the rotor's magnetic flux; probably expensive as well.
In table 3* the study summarizes 4 categories of generator.
Low speed Permanent Magnet PMSG
Low speed Excited Synchronous EESG
Mid to High speed Geared PM PMSG
High speed Geared Induction DFIG
All these types are currently competitive in large wind turbine installations, with high PM content designs getting selected in quite a minority of cases, despite modest efficiency and maintenance bonuses, even at the current top end of generator scale ~8MW.
To get beyond 10MW generators advantages of PM are desired but are also lumbered by relative heaviness besides the price of rare earths. Superconducting Magnets do seem like the way upward then, if reliable 'super-cooling' can be achieved.
You could probably pack an array of several smaller diameter dynamos within the housing of the base. Only issue is the belt/chain drive down the shaft so if one jams the others can still work.
I don't think the size of the thing is really an issue - they can always make bigger turbines. Smaller and lighter for the same power is definitely a plus, but not the big advantage the article is talking about. The real advantage of this is not having to use a tonne of rare-earth magnet and instead using only kilograms of rare earth material in the superconducting version.
[1] https://www.quantamagazine.org/universal-quantum-phenomenon-...