About a year ago, I first talked about the Aeromine rooftop wind turbine and its unique “motionless” design. Now, a new rooftop turbine is hitting the scene. Norwegian company Ventum Dynamics just released its shrouded wind turbine, the VX175, to the market in February.1 It’s also deployed in the same way as the Aeromine: along the edges of large industrial and commercial buildings.2

What makes the VX175 so different, though, is the lantern-like structure wrapped around the body: a shroud. Shrouds are anything but a novel idea. Researchers have experimented with amplifying a turbine’s power output by covering the rotor for decades.3

What is new is a misunderstanding that Ventum’s approach is tethered to an even older concept: a Darwinian invention, to be specific. Well, yes, but actually no. What we’re about to dive into is more than an overview of the VX175. I always like to put these technologies into context, especially older concepts that get revived with new approaches. However, this one really threw my team and I for a loop as we learned about the origins.

How did that even happen? And how much of the VX175 is a rehash, if at all?

We’ve featured a lot of fascinating wind power designs here on the channel, from a mega-flyswatter containing multiple mini-rotors to a track with “wings” flying laps around it. But we’ve yet to cover… a covered turbine. This story isn’t just about fluid dynamics or design, though. It’s a lot more convoluted, and it starts in the 18th century. Kind of.

Before we get into that, let’s set the stage. For a variety of reasons the primary goal of wind turbine construction has pretty much always been pushing the limits of size.

However, it’s becoming less practical to build them this way, between the nail-biting logistics and the terrifying consequences of mechanical failure. While the industry changes its approach, decentralizing our power supply through smaller wind turbines also has significant benefits. One major motivator? Even if we were to perfect monolithic turbines, we still can’t fit them into most areas.

That’s where rooftop turbines can come in, and after five iterations and about six years of development, the VX175 has made its debut.4 What makes the turbine so noteworthy is immediately clear: the “shroud” that encases the rotor. In
Ventum’s words, it “accelerates the wind, allowing a greater volume of air to pass through the turbine.”2

We’ll discuss how that works later. For now, I want to focus on that burning question: what’s Charles Darwin got to do with it? Well, nothing, actually. The Darwinian windmill at hand was developed by Erasmus Darwin. That’s the English physician and notably less famous grandfather of none other than Charles Darwin.

Charles Darwin

Charles Darwin

Erasmus Darwin

Erasmus Darwin

Darwin House in Lichfield, England

Darwin House in Lichfield, England

Yep — that’s not Photoshop or a DALL-E AI generated image. What you’re looking at is a photo of a museum display showing a model of one of Erasmus’ many inventions at the Darwin House in Lichfield, England.5 And here’s a drawing of his creation. Look familiar?

Erasmus Darwin Drawing

Erasmus Darwin Drawing

Ventum Dynamic's Patent

Ventum Dynamic’s Patent

To be clear, this patent diagram is for a prior version of Ventum’s turbine, not the one that was just released to market. But even more importantly, despite the fact that the two may seem deceptively similar, there’s a lot more than eras setting them apart. No, the VX175 we know today is really a new form of this…

IMPLUX Turbine

IMPLUX Turbine

…the IMPLUX turbine, which was originally invented by engineer Varan Sureshan.6 And neither Sureshan nor the Ventum team based their work upon Darwin’s. I know this for sure because, well…we asked. As Sureshan himself said in an email interview:

“I would be lying if I said I was inspired by the Erasmus turbine, or any other turbine, as there was no internet or any search engines when I started working on some of my ideas.”

To put things into perspective, neither I nor my team had ever even heard of Erasmus until a viewer suggested I look into Ventum. In their email, they referenced a YouTube video that identified Ventum’s models as Darwin turbines. My lead writer took this information at face value and threw himself into researching 18th century history. For weeks, he prepared a sweeping, dramatic narrative about the sociopolitical woes that might explain why the shrouded windmill had effectively remained trapped in parchment…until now. Later, while scrolling through Google Images results, he stumbled across the IMPLUX and thought to himself:

“What the hell is that?”

Google Image Search

So why did I ever bring up Erasmus Darwin in the first place?

The answer is simple: because if it weren’t for the false notion that Darwin had laid the groundwork for Ventum’s new turbine, I wouldn’t be talking to you about it at all. We wanted to investigate why Ventum adapted such an old idea, and why it had been left in the dust for so long. In reality, there was no adaptation. There’s no connection between Darwin and the VX175.

To make a long story short, our confidence in the misinformation stemmed from the fact that it wasn’t just anybody comparing the VX175 to ole windmill. It was someone from an engineering background who had been studying the Darwin design for over a year. And you gotta admit…the resemblance to the older proofs of concept is a bit uncanny.

Ventum Dynamics Animation

Another element at play is that we don’t know everything. A lot of the time, we approach video topics with very little prior knowledge of the subject. This channel is as much about science communication as it is taking you with me on learning journeys. That’s why I have science and engineering advisors that help fill in the gaps. The research for this script in particular took a lot of twists and turns.

Reporter cartoon

Now, the elder Darwin did tinker with a shrouded windmill when he wasn’t busy tending to patients, writing plant romances, or designing mechanical spiders.7 But to say that the VX175 represents an evolution of one of Darwin’s many side projects simply isn’t true. The people who created the turbine weren’t aware of the comparison until a few years ago…when they watched the same videos that inspired this one. The VX175’s actual origin story is an interesting example of humans thinking alike across time, just not in the way that we had initially believed.

Hold that thought, though, because the scientific experimentation Darwin dabbled in outside his medical career is legitimately fascinating. So, for the sake of keeping things chronological (and not letting my poor writer’s research go to waste), let’s dig a little deeper into his windmill and where exactly this comparison came from. One thing that the two designs do have in common is the potential for increased power output.

Take it from the man himself, who wrote this in his 1800 book “Phytologia; or the Philosophy of Agriculture and Gardening”:

“And as the height of the tower may be made twice as great as the diameter of the fail, there is reafon to conclude that the power of this horizontal wind-fail may be conftderably greater, than if the fame fail was placed nearly vertically oppofed to the wind in the ufual manner.”8

Did you get that? Either way, according to historian Jennifer Uglow, Darwin claimed that his horizontal windmill produced a third more power than the…run-of-the-mill…vertical mills of his time.9 And like Ventum’s VX175, the windmill worked omnidirectionally, meaning it could take in winds from all angles. On its journey to the sail, wind would push through the slatted boards that made up the shell of the turbine. You get the drift.928

But that’s pretty much where a comparison to Ventum has to end. Setting aside the fact that the tech is more complex and that the applications are worlds apart, there’s a couple critical differences between the designs. First of all, the VX175, as a unit, is a new form of turbine. The novelty of Darwin’s creation was that octagonal, “smoke jack”-style tower: an air catcher. Not a turbine. Sureshan explained it like this:

“…The IMPLUX works because it is part of the group of wind turbines where there is a “static turbine” and “dynamic turbine” combination, which enables much higher power extraction well beyond the “catcher” turbine concept…Whilst increased air flow is important, it does not lead to automatic increase in power efficiency.”

On top of this, the VX175 is, like the Aeromine, entirely stationary besides the rotor.2 As Ventum’s COO, Rebekka Stumpf, described it in an email interview, one of the main objectives in designing the turbine was promoting air capture while also preventing air leakage, regardless of the wind direction. In her words, that meant “no physically closing or opening mechanisms, such as air shutters.” Meanwhile, the tower of Darwin’s windmill was composed of flaps that fluttered in the breeze.98

Well, did it work? It would seem that it did just fine, considering it was actually put to use. In 1778, Darwin’s colleague Josiah Wedgwood installed it at his pottery factory, The Etruria Works, in Staffordshire, England. There, the mill mixed clay and grinded materials like flint and enamels for a solid 14 years, until it was eventually replaced by another engine.109

However, we don’t remember grandpa Darwin as a kooky scientist for a reason. He feared for his reputation as a physician and very intentionally opted to keep his engineering pursuits to himself. I think it says a lot that he published Phytologia in 1800 and died in 1802.1081112

But while I can’t say what was going through Erasmus’ mind when he designed his windmill, there are multiple advantages to shrouds. Part of the reason why the wind industry places so much emphasis on taller and taller towers is because the higher you go, the faster the winds you can capture. The faster the winds you capture, the more power you can generate.13

The thing is, in the U.S. the majority of the country only receives average wind speeds between about 3 and 5 meters per second (or about 6 to 12 mph) when measured 10 meters off the ground.14 In Norway, Ventum’s country of origin, the windiest areas range from 5 m/s to 8 m/s at that same 10-meter mark.15

Of course, this becomes a problem in areas without much room, vertically or otherwise, to place towers that can reach for the good stuff. That’s why companies like Ventum are seeking ways to make use of the low wind speeds that are accessible from rooftops — especially in more densely populated areas like cities.

And one possible way of doing just that is by creating turbines with shrouds…or diffusers…or lenses…or ducts. Whatever you want to call it, this type of turbine is a class of its own: a DAWT, or diffuser-augmented wind turbine. Y’know, like a HAWT or a VAWT. That’s “horizontal axis wind turbine” and “vertical axis wind turbine.” I’m not trying to sound like the Cat in the Hat.

DAWT Types

“Shroud” and “duct” and “diffuser” can be used interchangeably when you’re talking physics, but I’m going to keep using “shroud” because it sounds the coolest.1617

The main idea here is power augmentation. Think about it like this: urban and residential areas have enough wind to spare, but oftentimes it’s not fast enough for turbine installations to be worth it. In other words, you wouldn’t be able to justify the costs vs. power output. What if we could somehow speed up that wind? So, in theory, shrouds have this to offer:183

  • Concentration of wind energy
  • Low exit pressure, which leads to increased airflow and faster winds
  • Avoiding what are known as tip losses, which are reductions in efficiency caused by vortices that form at the tip of turbine blades
  • Overall increased efficiency
  • Overall increased power output

Basically, shrouds increase speed — and increased speed means increased power.19 As early as 1956, studies have shown over and over again that shrouds can increase power output, and the numbers sound impressive. Figures of approximately “2 to 5 times increase in power output” get thrown around a lot in scientific literature.3 But I probably don’t have to tell you that sounding impressive is different from actually being impressive. Of the papers we reviewed, most are based upon simulations or experiments conducted in wind tunnels, which aren’t fully representative of the much more chaotic outside world.17

And as you might have already guessed, a consistent drawback is cost. From discussions that took place at the United States’ 1979 Wind Energy Innovative Systems Conference to conclusions drawn from extensive wind tunnel tests in the present day, researchers have repeatedly indicated that shrouds just aren’t economically practical.2019 However…a lot of these observations are also made within the paradigm of your typical turbine. Attaching a component that heavy and that big to an already massive tower would threaten the structural integrity. Of course it would be ludicrous to stick a shroud on one of these. But that’s not what Ventum is doing.

In any case, it seems like shrouds become trendy pretty cyclically, like jeans.17 For example, in the 1920s, inventor Dew Oliver created his “blunderbuss” ducted turbine, which might seem like a far cry from anything we’d see today…except it looks somewhat like the SheerWind INVELOX. I wouldn’t be giving you the full story if I didn’t mention that both designs were ill-fated. Oliver ended up convicted of fraud, and SheerWind filed for bankruptcy in 2017.212217

Anyway, if the superficial similarities between Darwin’s work and the VX175 didn’t already convince you that researchers have tested variations upon shrouds for a while now, I don’t know what will. But if neither the IMPLUX nor the VX175 were created with Darwin in mind, how did they come to be?

Here’s where the accurate comparisons really lie. Over the course of his engineering career, Sureshan designed systems like a hybrid rooftop solar air-conditioning unit, and took note of the bountiful supply of wind available atop buildings. So, after over 25 years of similar projects, he founded Katru Eco Energy and began developing the IMPLUX, with some of the earliest patents filed in 2005.623

Unfortunately, despite successful prototyping — including Honda’s Formula 1 team taking it for a spin — the IMPLUX never made it to the market.246 Manufacturing and installation stopped not once, not twice, but three times across three different years in three different countries.

You could say that the IMPLUX was too ahead of its time. According to Sureshan, the problems that prevented its commercialization were political, not technical. And after three attempts, it’s understandable that he and his company’s investors were hesitant to try again. So, that’s one way the IMPLUX specifically is like Darwin’s windmill. Both were long-delayed for political reasons.

Meanwhile, it seems like Ventum founder Christopher Bisset-Nilsen had basically the same lightbulb moment as Sureshan while working atop buildings in Stavanger, Norway. According to Stumpf, Bisset-Nilsen, as he installed rooftop HVAC systems, he wondered “Why are there no turbines on the roofs to power the heat pumps?” And the rest was history. 2018 marked the year of Ventum’s first patent for its V1.0, which was lovingly nicknamed the “Death Star.”4 It’s easy to see why … that’s no moon.25

Ventum Dynamics v.1.0 Design

Ventum Dynamics v.1.0 Design

Then, in 2021, Ventum approached Sureshan for guidance while testing one of its earlier versions of the turbine. And through this collaboration, the Ventum team incorporated features from the IMPLUX into the VX175, eventually acquiring the patent for the former. As Stumpf explained, the two are “basically the same machine,” except the VX175 is optimized for manufacturing. You can definitely see where Sureshan’s influence emerges on Ventum’s timeline.4

Ventum Dynamics Timeline

Ventum Dynamics Timeline

But what does this successor bring to the table? While all DAWTs have a shroud of some kind to direct airflow through the turbine, the VX175 has a specially engineered, omnidirectional shroud. This allows it to be mounted on the tops of buildings and capture energy from the turbulent airflow. The idea is to get even higher efficiencies out of higher speeds, particularly from the constantly changing, rough winds common in cities.

Here’s how Stumpf described it:

“We focus on wind acceleration that can be seen in urban environments due to wind “hitting” a wall and being redirected upwards and accelerated. We call it the edge effect…The turbine is built in a way that it can harness that upwards skewed wind and accelerate it once more inside of the turbine.”

Plus, the fact that the VX175 has no moving parts other than the rotor helps keep maintenance costs down.2 After all, it’s usually too many moving parts that gets ya.

This feature also contributes to a higher quality of life. Ventum’s turbine is pretty quiet, at least at the lower end of wind speeds. It produces noise at about 40 decibels in 6 m/s (13.4 mph) winds.2 For reference, the U.S. Environmental Protection Agency identifies 55 dB outdoors as being A-OK for human health and, you know, not wanting to bang your head into the wall repeatedly.26

According to Ventum’s website, the system amounts to these estimated values for annual energy production:

Ventum Dynamics VX175 Energy Production

Ventum Dynamics VX175 Energy Production

However, there isn’t any publicly available performance data yet. That’s a reasonable cause for skepticism, especially in the controversial world of small wind turbines. But it’s worth remembering that the more attempts engineers make, the sooner we can incorporate SWTs into our arsenal.

And it’s not like there’s no recent data on shrouded SWTs. (Or SDAWTs?) In 2020, researchers at the University of Tehran published a study comparing the levelized cost of energy (LCOE) and annual energy production (AEP) of traditional turbines vs. wind lens turbines at two sites in Iran. They found that the wind lens turbines “yielded an average decrease of 56% in LCOE and an 83% increase in AEP” on Kish Island, and “an average reduction of 59% in LCOE and a rise of 74% in AEP” in the city of Firoozkooh.27

I’ll go ahead and say the line: this is another example of picking the right tools for the right job. It ultimately doesn’t matter if this turbine isn’t as efficient as a giant HAWT, as long as the installation and operational costs are practical for bringing turbines to more populated areas. Each is meant to serve different markets. As for how well the VX175 can do that, we’ll have to wait to find out.

But will we be seeing these turbines on residential roofs anytime soon? To that, Strumpf says that single family homes have better options elsewhere. For those in apartment blocks, though, Ventum’s got you…_covered_. Alongside commercial buildings and offices, the VX175 is a good fit for apartments. The company is also in the process of releasing the VX300, a larger version of the turbine for industrial areas like warehouses and storage facilities.

In the end, if researching this video has taught me anything, it’s that it’s worth remembering the humanity behind the machines. What might seem like a technological failure could have a story more complicated under the shroud.

  1. Ventum Dynamics Unveils VX175 Wind Turbine ↩︎
  2. VX175 ↩︎
  3. A preliminary report on the design and performance of ducted windmills ↩︎
  4. The VX175 by Ventum Dynamics ↩︎
  5. Visiting Lichfield: Erasmus Darwin’s house ↩︎
  6. New omni-directional wind turbine can capture wind energy on building rooftops ↩︎
  7. Erasmus Darwin: The Leonardo da Vinci of the Midlands ↩︎
  8. Phytologia; or the philosophy of agriculture and gardening. With the theory of draining morasses and with an improved construction of the drill plough ↩︎
  9. The lunar men : the friends who made the future, 1730-1810 ↩︎
  10. Erasmus Darwin, F.R.S. (1731-1802) ↩︎
  11. Staffordshire’s Involvement with Genesis and Evolution: Keeping it in the family ↩︎
  12. Item 68 – Letter from Dr Erasmus Darwin, Staffordshire about a horizontal windmill ↩︎
  13. Wind Turbines: the Bigger, the Better ↩︎
  14. NREL: Annual Average Wind Speed at 10 Meters Above Surface Level ↩︎
  15. Norway: Mean Power Density @Height 10m ↩︎
  16. Venturi effect ↩︎
  17. Ducted or Augmented Turbines–Enflo ↩︎
  18. Shrouded wind turbines: a critical review on research and development ↩︎
  19. Wind flow through shrouded wind turbines ↩︎
  20. The science of making more torque from wind: Diffuser experiments and theory revisited. ↩︎
  21. BACK IN THE DAY: Wind machine predated iconic desert turbines ↩︎
  22. Wind-turbine startup Sheer Wind files for bankruptcy ↩︎
  23. Omni-directional wind turbine ↩︎
  24. IMPLUX Wind Power Turbine ↩︎
  25. Wind-power station for power generation ↩︎
  26. EPA Identifies Noise Levels Affecting Health and Welfare ↩︎
  27. Optimization of Power and Levelized Cost for Shrouded Small Wind Turbine ↩︎

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