The Devil Wears a Halo: Ducted Turbine Rises from the Grave

By Paul Gipe

Flamboyant ducted wind turbine venture Ogin died a costly death in 2017, taking with it hundreds of millions in investments. The debacle tarnished the reputations of Technology Review, Arpa (DOE’s Advanced Research Projects Agency), Vice President Al Gore, and venture capital firm Kleiner Perkins all of whom had helped hype the “revolutionary” design.

The Alberta and New Zealand pension funds both lost all their investments, and Fortune magazine attributed the decline of once venerable venture capital firm Kleiner Perkins partly due to a disastrous detour into renewable energy. Ogin was one of those Kleiner Perkins investments that went sour.

Ogin was a spinoff from FloDesign, a Boston beltway tech company that began developing a ducted turbine in 2008. This was an unusually long cycle for a highly hyped “innovative” wind turbine. Most come and go within a few years. It took nearly a decade before investors finally pulled the plug on this particular high-tech gamble.


Rising from the Grave

Rising from the undeworld in 2017, some of the original promoters sought to capitalize on the technology developed at such great public and private cost to downsize the ducted wind turbine for the telecom market. The company, Halo Energy, launched with much the same hype as before.

Ducted or shrouded wind turbines are nothing new. They’ve been around almost as long as there have been windmills. Historian Robert Righter wrote of one notorious example near Palm Springs, California in the 1920s. There inventor Dew Oliver installed his “blunderbuss,” or ducted turbine, in the San Gorgonio Pass. Though Oliver claimed the turbine worked that didn’t prevent him from being sent to prison for fraud. (There should have been a lesson in that.)

The moniker, Halo Energy, refers to the double duct or shroud that surrounds the rotor, and not to any saintly pronouncements on the company’s product.

Note: Much of the research for this article was compiled more than two years ago when Halo first appeared out of the darkness. The topic has sat on my desktop since then. Despite urging from some in the trade, I couldn’t justify the time or effort necessary to put it all together. What could I say that I haven’t said many times before? Alas, sheltering-in-place has led me to a digital house cleaning and I wanted to file the Halo folder away–for good. Thus, I am posting this piece now since Halo’s web site still exists.

As with FloDesign and Ogin, Halo’s promoters stressed the supposed higher efficiency of their device over that of conventional wind turbines–as though that’s the only weakness holding back the small wind turbine market is rotor efficiency. That’s hardly the case, but it does make good copy for the tech press.

Halo claimed “our wind turbines have best-in-class performance and the lowest achievable cost of electricity.” Like so many other erstwhile manufacturers of new wind turbines that disappear after a few years of glowing press, Halo had no data at the time on which to make such claims. It had not produced, sold, or operated any of its wind turbines. How could the company then claim that its device produced electricity at lower cost than competing products when it hadn’t sold or operated any of its design?

Ogin Breakthrough?

Halo goes on to say it was “leveraging the significant advancements made by Ogin in shrouded turbine technology” and would apply “the aerodynamic breakthroughs of Ogin’s technology to our small turbine platform.”

Ogin did develop a ducted wind turbine, fielding two prototypes, and installing a group of test turbines in the San Gorgonio Pass before it folded. However, Halo is promoting a far different turbine, one considerably smaller, and one for an entirely different application. Thus, whatever field experience Ogin gained may not be directly applicable to Halo’s derivative.

There were no breakthroughs at Ogin-FloDesign. There were advancements in ducted rotor performance according to those who worked at Ogin. The company’s chief designer claims their turbine achieved the highest performance of any wind turbine rotor in history–ducted or otherwise. This wasn’t a breakthrough, it was a point on a continuum of steady improvement in wind turbine rotor performance since Poul la Cour, the Danish Edison, tested his first turbine in a crude wind tunnel in the late 19th century. An achievement, yes. Breakthrough? No.

Before its demise, Ogin said that it had obtained third-party verification of the power curve for its 150 kW OE20d design. It published a chart of electrical power coefficient for its investors showing the OE20e design achieving an efficiency near 55% relative to the nearly 50% efficiency of conventional large wind turbines and a little more than the 40% efficiency for household-size turbines. The chart is misleading. Remember, it’s for investors.

This is subtle so bear with me. Ogin field tested the OE20d design. The OE20d design achieved a performance of about 48%. This is comparable to that of large conventional wind turbines labeled Enercon and GE on the Ogin chart. They never built the OE20e. They ran computer models for the OE20e. The outsize performance of the OE20e never occurred. It’s only on paper.

In the world of wind energy, the performance of the OE20d at 48% is remarkable for its size. Still, it isn’t a breakthrough. And it completely ignores whether there is sufficient value in improved efficiency to justify the cost and disadvantages of the ducted design over that of conventional wind turbines.

Wind turbines are not race cars. They don’t run a few laps and then head for the garage. Their job is to produce clean electricity for a very long time. They’re best when their electricity is cheaper than that of competing energy sources. They don’t have to be the most efficient design to do that. It helps, but it’s not essential. The cost and reliability of the wind turbine are far more important than efficiency in delivering low-cost electricity.

Proven Design?

Halo’s web site goes on to claim that their design is “proven technology.” Yet the site does not explain how the technology was proven. This may be in reference to the work of Ogin. However, that was a different, much larger, turbine built by a different company. There’s no evidence that the Halo design has been “proven” by anyone.

That’s not the end of the hyperbole. Halo claims it produces “the world’s most efficient small-scale wind turbines.” There was no proof of this statement that I could find. There was no evidence that they were even producing when turbines when the web site was first created several years ago. And today’s web site makes no mention of actual turbines in the field delivering electricity.

The company claims that “turbine performance has been validated using data collected in 2018 from Halo Energy’s test wind turbine in Massachusetts” and includes a video of a ducted turbine spinning somewhere in an urban setting. There’s no audio dialogue so we don’t know if it’s generating electricity or simply spinning in the wind. Again, there’s no reference to any published data on this example, no chart of electricity being produced, just a video of something spinning in the wind.

Unfortunately, the company has issued no press releases since the spring of 2019 when Halo announced that they planned to install a turbine for certification testing in Kern County, California. The test turbine was to be part of a small production run of ten units. Some of these ten were planned for a Cannabis operation somewhere in California. (Cannabis and hemp are big business in the state.)

There is at least one ducted turbine in Kern County. Ogin had installed a prototype of its second generation design in California’s Antelope Valley in 2014. That device was located in Kern County and is still standing, derelict, since the company dissolved in 2017.

There are no Halo turbines listed by the Small Wind Certification Council as certified or as applicants for certification. A Google search turned up no Halo Energy turbine being tested for certification.

Halo further asserts that their “proprietary shroud design” is backed by ten years and $200 million in research & development. That’s probably true. The company’s founders spent ten years and at least $200 million of other people’s money and it appears that –Ogin or Halo–still don’t have a product to show for it.

Shrouds are a Drag

One of the principle drawbacks of ducted turbines, apart from the cost of the shroud, is what to do with the shroud in high winds. Halo’s design has no high-wind cut-off. There is no cut-out wind speed. Naive consumers may think that’s a good idea as they mistakenly believe that the wind turbine will generate a lot more electricity if it doesn’t turn off in high winds. But experienced wind hands head for the hills when they see such statements. It’s a tip off that trouble lies ahead.

The power in the wind increases exponentially with wind speed. In high winds, the drag forces trying to tear the wind turbine apart are tremendous. Experienced wind turbine designers try to reduce these forces by regulating the wind turbine or shutting it off entirely.

Halo’s device, unfortunately, depends upon “passive stall regulation” to control rotor power in high winds–a method abandoned by the wind turbine industry at least two decades ago. And without a way to furl or turn the shroud out of the wind, the shroud creates enormous drag on the structure holding it in high winds. This remains a fundamental disadvantage to shrouded or ducted wind turbines–what to do with the shroud when hurricane force winds are trying to tear it off the tower. This also leads to higher structural costs in the tower and foundation as it must prevent the shroud and rotor from toppling the tower or breaking it in two.

The good news for Halo is that the abandoned Ogin turbine in Kern County has yet to fall down or be ripped apart by the notorious winds of the Antelope Valley. So there’s something to be said for the original tower and foundation design.

Do the Numbers Stack Up?

Now, let’s look at some numbers.

Halo says it’s fielding a ducted turbine with a shroud diameter of 3.7 meters (12 feet), giving it a swept are just shy of 11 square meters. They are rating the turbine at 6 kW in a wind speed of 12 m/s (27 mph). This is three times the rated power (2 kW) of conventional wind turbines the same size as the shroud. Keep in mind they haven’t shown this as a fact. This is only a claim until verified by a third party.

This puts Halo’s ducted turbine among the larger of the small ducted turbines developed in the past two decades. It’s one-tenth the size of the infamous Vortec 7 installed in New Zealand during the late 1990s.

Notably, Halo’s design is tiny compared to its progenitor, Ogin’s 19.5 meter diameter shrouded turbine rated at 100 kW. Halo’s shroud intercepts only 4% of the wind stream of Ogin’s design.

In wind energy, the size of the rotor (the spinning part) and the shroud affect aerodynamic performance. Smaller turbines have inherently poorer performance than their larger brethren. That Halo’s shroud is so much smaller than Ogin’s suggests that the Halo 6 kW will likely have poorer performance than Ogin’s commercial-scale machine. It also suggests that data for Ogin’s performance in the field is not applicable to Halo’s design.

To Halo’s credit, their claims are not as outlandish as previous ducted turbine promoters. In comparison to the French Eléna Energie, Halo is quite holy. And nearly everyone wears a halo compared to the otherworldly claims of Vortec’s outside performance.

Again, note that all of these are claims. None of these turbines have ever delivered on their promises.

Ogin came the closest. They actually tested turbines in the field. Their later performance claims are not beyond the pale like the other examples. The estimate in the table was gleaned from their web site late in their program where they said their wind turbine would produce 100 kW. This puts Ogin’s design right within the range of modern large wind turbines.

In a late report to investors, Ogin referred to their design as 150 kW. According to observers in the field, the Ogin turbine was capable of 150 kW.

Unfortunately, without a published certification report or test data, we have no way of knowing whether its “peak power” was 150 kW or whether the turbine produced 150 kW at or near its “rated speed.” Most wind turbines–ducted or otherwise–produce more than their “rated power,” but this is not a reliable gauge of how much electricity the turbine will generate over a period of time. Promoters often play on the confusion among the public and investors over the difference between rated and peak power. Investors, for example, when they hear 150 kW peak power, think 150 kW rated power not knowing that they’re being hoodwinked. However, observers noted that Ogin’s turbine in the field delivered 150 kW at 14 m/s from a slightly larger turbine than what I interpreted from their web site.

Ogin wouldn’t talk–at least to me. The only information I could find was posted publicly on their web site. Thus, we have two versions of the Ogin turbine: the one derived from their web site, and one from observers who actually saw the real thing.

Intertek tested Ogin’s OE20d for design conformity in Intertek’s Wind Turbine Certification Program. So we do know that Intertek tested the turbine. Their report, like so much about Ogin, is not public.

Even with the higher power of 150 kW than that touted on the web site, Ogin’s performance estimates are within the range expected for large wind turbines.

Halo’s claimed performance far exceeds that of Ogin’s later estimates, the latter likely reflected results from Intertek’s certification tests. Halo forecasts that the yield in W/m² for their 6 kW turbine would be 17% greater than that from Ogin’s model OE20d (558 vs 476 W/m²) despite being a fraction of its size. This is highly unlikely.

Similarly, Halo’s claim that their turbine is nearly twice as efficient, 53%, as that of Ogin’s OE20d, 28%, at their relative rated wind speeds is hard to fathom. This is especially true when you consider that Ogin had already spent upwards of $200 million on development and had paid for a full certification test. If you were a betting person, you’d bet on someone who had already done all their homework and had been tested by a third party, not on the claims of an untested newcomer.

In short, Halo’s performance claims are two to three times that of actual wind turbines that have been tested by third parties.

It doesn’t get any better when we look at the mass of the shroud that Halo wraps around the wind turbine. Tower-top mass is a surrogate for the materials invested in a wind turbine and hence its cost. If the turbine includes a lot of mass, that is, material, relative to its size than other turbines, it will likely be more expensive. And Halo comes in with a whopping two to three times the relative mass of other small wind turbines. Unless it can deliver on its unlikely performance claims, it will be difficult for it to compete with other small turbines on the basis of cost.

And in all of this discussion we’ve avoided the big bugbear: solar. Halo is targeting telecom where solar dominates. Solar is so cheap and so reliable that it has effectively killed the small turbine industry worldwide–shrouds or not.

It will take divine intervention for Halo to live up to its performance and cost claims and beat solar–a technology that gets its energy directly from the heavens.

Shrouds haven’t worked in wind energy. They are best left in the crypt.

  • For some background, see FloDesign-Ogin Some Brief Comments.
  • For more on ducted turbines, see Ducted Wind Turbines and Ducted or Augmented Turbines–Enflo.
  • For photos of some shrouded wind turbines, see Ducted Wind Turbines (DAWTs) (photos).