Small wind turbine designer Hugh Piggott said he objected to Helix Wind advertising its products for rooftop installations. "The wind resource on urban rooftops is generally quite poor," Piggott wrote in a recent blog post. [A Helix turbine] is a nice ornament, but at $17,500 it's well overpriced."

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Proponents of VAWTs often say they offer certain benefits over HAWTs, although industry insiders like Gipe and Woofenden say many of those claims don't hold up to scrutiny. Gipe and Woofenden said that, contrary to VAWT marketing materials, there is no scientific evidence that they are any safer for birds or bats. (They also point out that the entire wind industry is so diminutive compared to the rest of our built environment that it poses a relatively tiny threat to wildlife.)

Morgan then started a new venture, Venger Wind, a privately held company based in Thailand. Morgan told National Geographic News he rehired a number of engineers from his old firm to develop a new version of the Savonius VAWT. In April, the company announced it has patent-pending status for its design.

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Unlike most modern wind turbine blades, the scoops do not generate lift, so they can go only as fast as the wind. That's a hindrance because, in general, the faster the blades turn, the more energy a turbine can harvest from the wind. As a result, Savonius wind turbines are said to have much lower efficiency than most horizontal axis wind turbines (HAWTs), or advanced VAWTs like the Darrieus rotor, which resembles an egg beater with its twisted blades that generate lift.

It's too early to say how much energy Venger turbines will actually produce, though physics dictates that it will be less than a similar-sized horizontal wind turbine. Zeiger said he knows the "workhorse" of the Eagles' project will be solar panels. At this installation and elsewhere, vertical wind turbines are valued as much for their ability to turn heads as to turn nature's forces into kilowatt-hours.

Both the Helix Wind design and Sauer's WindCharger are considered "Savonius-style" vertical axis turbines, named for Sigurd J. Savonius, the Finnish engineer who invented the form in 1922. The turbines have scoops, or aerofoils, arranged around a vertical shaft, and they are turned by the wind.

Zeiger said seven turbines would be placed at each end zone, where they will be highly visible. "Our goal is to show our commitment to green, but our real goal is to get fans to see how they can put this to work in their homes."

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"The turbines will contribute somewhat and are there to remind people visually that there are multiple green ways to get your energy." Zeiger added, "Just think of those blimp shots. The turbines are going to be visible."

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The failure of "rooftop” wind energy's most trumpeted start-up underscores the technology’s challenges, but believers insist vertical turbines have their place.

According to Rob Zeiger, senior vice president of communications for the Eagles, Helix's demise did not impact the team's time frame for the green project because Venger was able to step in. "We've been very pleased with the reaction from the community to build the NFL's greenest facility," Zeiger said. "Everyone wants to know when the turbines are going up," he said. (Answer: By the end of this coming season, he said).

Zeiger explained that the Eagles recently downgraded their order of turbines to 14 from as many as 80, after more careful study indicated installing them on other parts of the stadium could cause shading of the playing field, which could "interfere with catching passes."

Helix's wind turbines, seen here at the Burning Man festival in 2007, illustrate the aesthetic appeal of vertical axis wind technology, but critics of the concept say it has too many flaws to be viable.

"We've decreased its drag coefficient significantly," said Morgan. "We're going to push the Savonious to the outmost limits possible." (That will still pale in comparison to the efficiency of most HAWTs.)

Sauer Energy, which itself is $2.5 million in the red, according to filings with federal securities regulators, did not respond to a request for comment. But in a statement at the time of the purchase, Dieter Sauer, the company's chief executive, said his firm was interested in acquiring Helix's unique turbine designs and proprietary monitoring software. He added that Sauer would not assume any of Helix's liabilities. Sauer Energy has been designing its own small VAWT called the WindCharger, which has yet to be released.

The gyre ceased on May 11, when Helix Wind was forced to auction off all its assets. Another vertical wind turbine company, Sauer Energy of Newbury Park, California, purchased all that remained of Helix that same day—paying just $25,000 for hard assets and $1.5 million for the company's intellectual property, and announced plans to operate the brand as a new division.

Venger Wind has picked up some of Helix's outstanding contracts, including providing 16 turbines to Oklahoma Medical Research Foundation and 14 turbines to the Philadelphia Eagles, who will soon be mounting them as part of a $30 million plan to "green" Lincoln Financial Field. With solar panels and a biofuel cogeneration plant, the Eagles hope to generate 1 billion kilowatt-hours of clean electricity over the next two decades, making it the first team to provide all its own power locally.

Morgan criticized his former coworkers at Helix for "indiscriminately selling turbines to anyone without any feedback or guidance." He said some buyers were "interested in 'greenwashing.' " As an example, he said one client insisted on putting a turbine on the front of its building so it would be highly visible, even though prevailing winds dictated that it would perform better on the back side. "It's crazy," said Morgan. Companies buying vertical wind turbines often rush into the decision with overly optimistic expectations, "but once the romance is over," he said, "the accountants and CFOs are asking, 'What's my payback?'"

But another firm that has risen from Helix's ashes is writing the next chapter in vertical axis wind technology. Venger Wind, started by Helix founder Kenneth Morgan, whose acrimonious split from the firm ended in litigation, has now picked up some of Helix's contracts, including a high-profile installation on the Philadelphia Eagles' NFL stadium.

Morgan said Venger Wind is taking a different approach, by stressing that a site's wind regime is critical to energy production. "We won't touch many markets because there is not good wind," he said. Morgan added that he is putting his distributors through training that includes emphasis on using anemometry, the study of wind force and velocity, to study actual current patterns at prospective sites.

With graceful, sail-like blades that turned in the wind like white corkscrews, Helix Wind's vertical axis wind turbines (VAWTs) captured the imagination of bloggers and the tech press in 2007. The San Diego-based company developed a polished website and at the height of its promise, delivered two of its turbines to the Nevada desert for the annual arts and self-reliance festival, Burning Man, in 2007. The Helix turbine whirred above the vegetable-oil-fueled art cars and recycled sculptures.

The drama inside Helix's offices began long before the company's demise. In March 2010, founder Morgan settled a pair of lawsuits with the company and its then-CEO Scott Weinbrandt for $150,000. Weinbrandt declined to comment for this article.

Morgan told National Geographic News that the experience at Helix left him feeling "betrayed." He said, "It essentially destroyed the company. It almost destroyed the industry for vertical axis wind turbines. It was pretty sad."

Gipe said it is misleading for makers of VAWTs to tout their product as performing well in turbulence or having "low cut-in speeds." Turbulence robs the wind of recoverable energy, he said, and there is very little harvestable energy in low wind speeds because energy increases with wind velocity.

"Why do we keep repeating the same mistakes?" asked small wind turbine builder and author Ian Woofenden.  "No vertical axis company has survived in the marketplace for any length of time. All long-term successful wind-electric manufacturers use horizontal axis designs. This is because they work."

Morgan said he expects that customers could see a payback in five to ten years, if they have sufficient wind. (Experience shows that "if" is critical.) Morgan added that his engineers are adding computer-driven active controls to increase efficiency, something the Helix design lacked.

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When the news of Helix Wind's demise broke in April, critics of vertical axis wind turbines pounced. "I doubt there are any assets there worth anything," small wind consultant and author Paul Gipe told National Geographic News about the impending auction. Gipe and other critics argue that vertical turbines are inherently inefficient compared to the horizontal turbines that dominate the market. They say the very aspect that lends vertical turbines their appeal—their compact, "rooftop" size—further erodes their already small potential for performance, as proximity to buildings cuts down wind flow.

Woofenden added that he is "baffled" by all the recent attention given to VAWTs by venture capitalists, inventors, and the media—all ignoring the warnings of "longtime experts in the industry." He added, "Making a viable wind turbine is a very difficult job. Starting out with a flawed design and flawed assumptions virtually guarantees failure. All of this is a distraction from the real wind industry, and a waste of resources."

Although Helix Wind had received a considerable amount of positive press, the company's filings to government investment regulators told a story of financial woes. In September 2010 Helix reported $41.7 million in debt and negative cash flow.

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