Hello Pierre:
It is truly interesting how far people will go in attempts to “rescue” the Savonius concept.
I just wish any of these sources could boil their reports down to something readable without taking the whole day. I mean, get to the point! I think they like to make their communications long and undecipherable in order to make it seem so complicated and confusing that people will just give up reading it and assume the “researchers” know what they are doing, and that somehow their results must be important.
“Professor Crackpot”? The third reference you supplied talks of TSR of between 4 and 5, for a Savonius(?). Did they misplace the decimal point? I’m just trying the even make any sense of it at all. How could a Savonius get above a TSR of about 1, and even at a TSR of 1, how could it be making much power, if any? Why can’t they just show a diagram and give the TSR and a power curve? What about including a few photos? One fact to note: They seem to be unable to get a Cp of much over 0.10. A better design might be possible, but likely with more moving parts, more to break, wear out, and go wrong… 
I thought that these values were very high: I have no explain.
ABSTRACT This study characterises the performance of the Savonius type vertical axis wind turbine (VAWT). The performance of the Savonius type VAWT can be characterised by power and coefficient of power. The main parameter considered for analysing the Savonius-type VAWT is the tip speed ratio (TSR). The mesh independency test and time independency test are carried out, in which the medium mesh and three degree of time step for rotation are selected. The Savonius wind turbine is analysed at various TSR ranging from 0.2 to 5.0, in which TSR is 4.4, the performance of the turbine is high. Considering 4.4 TSR as the optimum one,the analysis of the Savonius type VAWT is carried out under various wind speed ranging from 1 to 10 m/s.From the analysis, the validation between numerical analysis and theoretical analysis is carried out and the efficiency of the Savonius type VAWT is increased to 50%.
This looks to be a theoretical analysis, a sort of simulation, not measured experiments.
See the Table 3 and the Figure 7 (b) showing that Cp (power coefficient) increases with TSR, ending with high values (Cp of 0.6925 for TSR of 4.4) that are far to be known in practice, Cp of 0.6925 being even above Betz limit.
In practice as you know, Savonius turbines barely achieve TSR of 1 and Cp of 0.1.
Looks like numbers for a darrieus or gyromill, except still way too optimistic. Or, as I mentioned - a misplaced decimal point? Because a Savonius does best at around 1/10th of those numbers.
Oh well, once you are dealing with a Savonius researcher, you should expect the possibility of overoptimistic numbers and the results to make little or no sense, but this is ridiculous. That’s why I wish they could boil things down to a few simple statements that encapsulate the significant results. I don’t want to ruin my eyes, spending hours, sifting through miles of minor details.
I run out of patience for such nonsense after a while, and just retreat to my own pet description, that requires just three words, and all three words are the same word, with commas in between!
Yes. See also the second document I linked.
Page 299:
2. Wind turbine theory
As a simplest turbine, Savonius wind turbine works due to the difference of forces exert on each blade. The concave part to the wind direction caught the air wind and forces the blade to rotate around its central vertical shaft.
Page 299 just before:
The ratio of the blade tip speed to wind speed is less than unity because the returning blades on the downwind side can never travel faster than the wind. Savonius investigated the performance of thirty different model of S-rotors in the wind tunnel and open-air [5]. He reported a maximum power coefficient (Cp) of 0,31 from wind tunnel experiments while reported a maximum Cp of 0,37 from open-air tests. In the last half of century, many researchers had experimentally investigated the performances of different designs of Savonius wind turbines and obtained that the number of Cp in
the range of 0,15 to 0,35 [6-10].
“The ratio of the blade tip speed to wind speed is less than unity because the returning blades on the downwind side can never travel faster than the wind.”
This contradicts the statements in the third reference (TSR between 4 and 5) we just discussed.
Thanks Pierre
The only detail I sort of noticed was some reference to changing the windspeed, where maybe they established rotational momentum at a higher windspeed, with enough inertia to maintain the higher speed rotation, then recorded a momentary, but artificially high, TSR and Cp with their turbine still spinning fast, as they quickly lowered the windspeed.
One other knee-jerk typical “Professor Crackpot” blunder regarding Savonius machines is forcing air thru them in wind tunnels, where the size of the machine is too large in relation to the tunnel, probably saving money over hiring a larger tunnel, then enjoying the artificially-enhanced numbers that result. It never seems to occur to these idiots that there is already a standard procedure in place to measure wind turbines, and it is in a tower with and anemometer and a data logger.
But Savonius people are too dumb to even realize they should be using a tower, let alone the rest of the standard equipment. They are still working off the idea that their “urban turbine” is “responsive to winds from any direction” therefore, best placed in a backyard between houses, and, you may notice, almost ALWAYS show their prototype turbines running at a low height, even on the ground, directly adjacent to buildings, often in the parking lot of the industrial unit they are slowly going broke renting, unconnected to any load, so they can be seen to spin, and that fulfills their childish mission. They are usually happy merely to “see it spin” and even talk about the fact that “seeing it spin” is really the main thing the customer is concerned with, and they are right: All idiots, all the time, from top to bottom!
Often they have yet to even include a generator at all. Such people will bristle with anger when asked why they don’t use a generator, or record a standard power curve, or at least produce some decent output data with regard to windspeed. You may recall many such conversations in the old forum, with endless irritation and excuses from the promoter of the bad ideas.
I remember one study from Cal State Long beach, here in California, promoting a Savonius machine, which really made me realize that merely being associated with a major university did not guarantee real knowledge, clear thinking, or a quality study. Mind you, the “Cal State” system is not as academically rigorous as the “University of California” system where I studied physics and engineering, including fluid mechanics, but still very reputable, with good standards overall. Still, the researcher I remember from Cal State Long Beach was coming out as though Savonius was the big answer, based on, you guessed it, wind tunnel data. I had to laugh.
Basically, as we’ve seen over and over, people without working experience in wind energy, will usually make the same beginner errors, no matter their level of education. The problem is, the “smarter” they are, the more likely they are to assume these typical beginner “shoot-from-the-hip” impressions are correct!
Another youtube video about Harmony Savonius etc.
“How We Solved The Home Wind Turbine Problem”
How We Solved The Home Wind Turbine Problem (youtube.com)
I’ve noticed Matt Ferrel just makes videos without having any idea what he is talking about.
Like so many others…
Idiots making videos about idiots.
I can’t tell you how many of these vertical-axis turbines spinning unloaded in the parking lot of their industrial unit I’ve seen. They are all that same, all with the same false talking points
Page 3:
Rotor diameter - 270mm Height - 456mm
Rotor type - 3-Blade savonious
Blade material - Aluminium
Rated output - 10 W at 12 m/s (26 mph)
A quick calculation: area is 0.123 m², air density is assumed to be 1.2.
1/2 x 1.2 x 0.123 x 12³ = 127 W.
The rated output is specified at 10 W.
So the Cp (power coefficient) is only 0.0787, less than 0.1. It is not too much.
Another model on
In technical specifications:
- Rotor diameter: 270mm
- Rotor height: 918mm
- Rotor type: 3-Blade Savonious
- Blade material: Stainless Steel
- Rated output: 24W at 8m/s (17.8mph)
Area 0.248 m².
1/2 x 1.2 x 0.248 x 8³ = 76 W.
The Cp (power coefficient) is 0.315, which is a good value, comparable to that of very good VAWT Darrieus-type.
And yet these two turbines seem to be of the same brand, the second being higher.
And as Savonius turbines are known to be very good in very strong winds (see the curve of the 1st model), if we have a Cp of 0.3, then this can be an AWE option (with rope drive transmission), using for example shapewave® technology to ensure better rigidity ([hence efficiency] as well as lightness.
Lift by Magnus effect when the Savonius rotor is horizontal, flying like a rotating kite:
Hi Pierre:
Of course somebody should at least try it, right? I mean, why not? It would be nice to see a flying turbine that produced its own lift. Where did you find that photo? Is it “line-laundry” for kite flyers that you can buy? I’ll bet that baby can… light an LED! Or maybe a few - they take almost no power!
But I’d be careful believing ANY stated power output claims from ANY savonius-seller. This company is all over the map with regard to output. Looks like they may just be using the same exact generator for all their models, and just keep re-rating it for different models and windspeed/RPM ranges. They are charging between 1000 to over 2000 British Pounds for these. They are “made to order in 3 weeks”. Translation: they are not actually “in production”, but only built on the rare occasion anyone actually wants to buy one. Wind turbines are worth maybe a dollar per Watt of capacity. These little babies cost more like $100 per Watt!
My first impression was at least they were probably being honest about their 10-Watt output for the first model. Cuz sellers on Ebay cite thousands of Watts for similar-sized little vertical-axis plastic toys.
And there ARE use cases to be made for such small, super-robust Savonius turbines when the goal is not to make much power, but just surviving strong winds and light battery-charging or voltage maintenance for batteries. Especially if you are government-funded. I’m guessing that will be the only customers - you know, Antarctica, etc… (OPM = “other peoples’ money.”) Still, find one running anywhere. Ask to speak to a happy owner. Not saying there aren’t any, but it’s easy to SAY your little $2500 turbine can withstand 100 mph winds at 70 below zero, but can it really? Who knows.
Hi Doug,
The photo is linked to Dieppe 2000 Kite Fest, as specified on Types of Rotor Kite.
The specifications of Savonius Wind Turbines vary. Yes, it may be a generator issue.
In any case, AWE leads to drawbacks such like: efficient but heavy turbine aloft, or crosswind flygens where the small size of turbines aloft could be a limiting factor of lifespan as you mentioned (we have not data enough), or discontinuous power of reeling, not to mention the risk of crash for the crosswind AWES at the end of their moving tether, and requiring enormous protection space. …
To be attractive advantages should overcome drawbacks.
Savonius kites could have a too low efficiency but some verification would be desirable. Who knows what Magenn balloon produced? And I don’t think about a configuration like that of Magenn where the Savonius blades are settled around a cylindrical balloon, but where the blades take all the place as for a real Savonius rotor or a real rotating kite.
Why. The world cant just verify every idea?
The power is ensured by the concave blade going more or less downwind. I don’t see how the Cp could be above 0.15. But in the second example I deduced a Cp of 0.3: I have no explain of a so high Cp for a Savonius rotor.
Moreover Savonius rotors using kite technics could have a Cp still lower.
If theoretical studies are not sufficient because being divergent, some experiment would be desirable.
It’s not too difficult to show on-paper, the limited Cp of a Savonius design. Since the working surfaces are traveling downwind at half the windspeed, you can expect about 1/4 of the power one would hope for, from this downwind-traveling, power-producing side. Then subtract the power used to push the upwind-traveling side into the wind, and you are probably down to between about 1/6th and 1/8th of the power available to the swept area. That agrees with the measured Cp’s we typically see of around 0.1 or less for Savonius.
Still, any power is better than no power, and if it works and survives, there could be some use for such a configuration. And the two-blade overlap version supposedly reduces drag on the upwind-traveling side, although it also reduces the overall swept area, travel distance, and leverage from the working surfaces. Forgive my bad memory, but I’m not quite clear on whether a Savonius generates much elevating lift, in the manner of a magnus/flettner spinning cylinder, or a Sharp rotor. That’s why I asked if that photo was “line-laundry” (hanging from a kite, located above) or a free-spinning, self-elevating kite in itself. I’m guessing it was line-laundry, dependent on an elevating kite to support it. You may find you also need a kite above it, to keep it elevated.
I would point out at this point, since this AWE hype-cycle began 15 years ago, kite-flyers have naively thought spinning line-laundry would be a slam-dunk easy way to generate electricity using off-the-shelf kite-festival components. So far it has never turned out to be true. Any “real wind person” could have told them that. And I did. But that didn’t stop them from trying.
As I remember, the Magenn MARS failure made very little power - a typical “Professor Crackpot” design. After appearing on so many magazine covers and websites, including NASA, it quickly turned from the poster-child for AWE, into a complete joke (for the few people who paid attention beyond the “press-release breakthrough” stage of hype). That didn’t stop people from continuing to cite it as a great advance. I think I recently posted a link to a new video announcing this old, disproven concept as a new breakthrough! (More clickbait.) Once Professor Crackpot gets started, it’s difficult to extinguish his bad ideas from being repeatedly promoted!
The size of a large bus or more, Magenn/MARS supposedly hit about 1 kW or so? Using bicycle wheels and fan belts or something? It could have probably won a competition for the least effective wind turbine ever built, using the most material, at the highest cost, to produce the least power. No wait - that would be four (4) competitions it could have won at once.
Anyway, I will also point out, as admirable as your quick-and-dirty, “get 'er done”, low-cost experiments are, you’d probably at some point need to build a high-quality version to get any meaningful numbers beyond the typical “lighting an LED” stage of verification.
The most wacky wind generation device contest sounds like fun though…
Even on paper, it’s nowhere near satisfactory enough to continue, at least as long as I’m missing data, and then some.
AWE is a bit like looking for the five-legged sheep.
You’re likely to find the least efficient flying machines, and the worst wind turbines, all at the same time.
Hi Pierre: I say this has become “Land of the Lost”, and that has been the case for some time now, maybe from day-one. A quote from your linked-in link:
“In our journey of innovation, tools like the digital twin help us refining our kite technology and driving us towards a greener future. Join us as we pioneer advancements in renewable energy!”
How about “is driving us toward bankruptcy”?
Just sayin’…
Everyone seems to be at the point of sheer desperation, looking for some “Hail Mary” magic pill that will rescue them from the simple reality of not having anything working well enough for regular operation, no matter how the years roll on. “AI”, “3-D printing”, whatever the latest buzzwords dictate as the focus of attention, become the latest diversion, meanwhile they gave up on their main theme, pulling ships, to supposedly concentrate on generating electricity, but seem to have stopped all progress generating electricity as well. How long can anyone keep listening to this stuff, and still take it seriously?
Hi Doug, who said we take this seriously?
Are we discussing if 3D printing and AI are a thing?
Hi Tallak: Not whether either of them are for real, although if you use Microsoft’s “AI” (supposed leader of the field) you find it is no better, and no more “intelligent”, than a Google search from 20 years ago. The main reason it is suddenly grabbing the attention of the masses is the introduction of the “chat” “language” feature, so people can imagine it is “talking to them”. In fact, I’m already nauseated by “Bing”, declaring it is “Sorry to hear that” when repeating news stories about people being killed, even saying “my thoughts are with the families” - so it lies, and the lies make no sense. it is just repeating what it sees others saying. Meanwhile, the powers-that-be are scared it will flag them as “the problem”, and so are trying hard to water it down and dictate what it can say. All very sad to see.
The concept of “A.I.” (artificial idiocy?) has been around as long as I can remember, under various names such as “machine learning”, “deep learning”, etc. The thing is, if someone can’t figure out how to do wind energy, they are going to ask a system that just tries to find the answer on the internet, where much, if not most, information is wrong already? Chances are it would tell them the answer is a plastic Savonius toy turbine on Ebay that promises 4000 Watts for a hundred bucks!
And 3-D printing turns out to be great for prototyping, making dental crowns, patterns for making traditional molds, even, or so I’ve heard, jet engine blades, but it’s NOT going to save someone who purports to have the secret sauce for wind energy, when they don’t actually have any secret sauce. Either they have the secret sauce, or they don’t, and at this point, it looks like they don’t.
What they have is a lot of repetitive promotional talking points, and a track record of not getting anywhere, no matter how long they try, even to the point that it seems to be getting worse rather than better. The era of cheap (free?) money, which allowed a lot of “zombie companies” (no product, no profit) to survive by merely and endlessly “selling a dream” has passed for now, and the chickens are coming home to roost.
Wind energy has always been more of a challenge than newbies of any type imagine before they actually give it a try. When the DO try, and see that their answer was not the answer, they quickly give up. That has always been true, and the emergence of a few new trendy buzzwords does not really change anything. Most of the hype is just one more example of “the latest fad”.
Well, I think we take it somewhat seriously, or we wouldn’t even be interested enough to try anything. But it’s also good to keep a sense of humor, and be skeptical of outlandish claims, identify the repetitive symptoms of “The Professor Crackpot Syndrome”, and try not to end up as the next example!