New Zealand

New Zealand

New attempt at old concept, DAWT draws dire warnings

An outlandish looking structure on farmland 100 miles south of Auckland in New Zealand represents a bid to revolutionise wind power and the energy industry, according to its developers. But wind energy experts are issuing dire warnings about the technology, the economics involved and the negative effect on the wind industry of poor publicity should the structure fail in its aims.

Despite these fears, the Vortec 7 wind turbine nonetheless performed beautifully in its initial start-up, says the company that developed the machine, Vortec Energy Ltd.

The prototype, just one third the size of the intended commercial wind turbine, is claimed to be the world's first commercial diffuser augmented wind turbine (DAWT), using a diffuser to create a suction effect downstream of the turbine to double the ambient wind speed at the rotor. It is based on a design initially investigated by Grumman Aerospace, but which has only been realisable, according to Vortec Energy, with the development of new materials.

Vortec Energy Ltd (formerly Advanced Windpower) says the diffuser will enable an augmented power extraction of six to eight times the efficiency of a conventional machine. "The key to the economic success of the Vortec lies in its ability to generate up to eight times the energy generated by a conventional wind turbine without increasing the production cost eight times," says managing director Robin Johannink.

Therein lies the crux of the matter, according to energy analysts. The 8:1 ratio is considered extremely high and critics point to tests in the late 1970s in the US and the UK that suggest a much lower ratio. In a virulent attack on the concept, Heiner Doerner of Stuttgart University warns that the design will not work. "Spend your money in Florida vacations and not on such systems," he publicly writes on The Internet. "You can never double the wind velocity, for example from ten to 20 m/s, no hope, not even in wind tunnels," he continues. "Humans cannot concentrate the natural wind." According to Doerner, the many previous investigations of the concept have revealed that, "in a complete turbulent boundary layer you can measure no effect at all with a diffuser system." He asks: "What happens if the wind direction control fails? Terrible drag forces occur, perpendicular to the tube-axis."

Aside from technical criticism, production costs for DAWTs are also said to be high. But one of the new developments enabling use of the 20-year-old concept is high-tensile ferro cement, providing a stronger, lighter alternative to steel for the diffuser and support structures, says Johannink. Furthermore, the material is also a cheaper alternative, helping the production economics. This has been challenged, however, with one source estimating that steel would be at least 5% cheaper.

Johannink admits that recent developments in the steel industry mean the company will be reconsidering its commitment to the cement approach. In particular, cost reductions in protective coatings that can last 30 years in a harsh, often coastal, environment have meant that steel has now become a viable option. Johannink says the steel and cement approaches will be closely evaluated in the next couple of months in view of the extra advantages offered by steel in terms of fabrication and speed of production. The question is not whether the technology itself will work, but whether it can provide a truly economical alternative to other forms of electricity generation, he claims.

Johannink was pleased that the early results from the machine showed the match between wind speed and generator output were within 1% of predictions, auguring well for the trial. Fifteen different wind speeds were tested and the Vortec 7 was found fundamentally to mimic wind tunnel results, a result which Johannink says they did not find surprising although others may have.

"Most traditional wind power people are of the view it won't work," he says, adding that many have based those impressions on the early work done through the 1920s and 1950s on diffuser designs. Despite the questions and scepticism, hopes for the new machine remain high, with Vortec predicting that the full-scale machines will produce electricity at about NZ$0.04/kWh.

"If Vortec 7 performs to expectation, wind power is set to become the environmentally friendly energy source that is at last competitive with all other forms of power generation. It may well produce the cheapest cost of energy for any new New Zealand generation -- and in the world context will be even more competitive," says Johannink.

The prototype has gained a great deal of interest, as well as a half-million-dollar evaluation grant from the New Zealand Foundation for Research, Science and Technology. Its performance will be evaluated by researchers from the University of Auckland and from the Crown Research Institute Industrial Research Ltd. Vortec Energy Ltd has raised NZ$5 million to complete the Vortec construction, primarily through its 100 local shareholders. It plans to make a public share offering prior to becoming a listed company and is looking to raise another $10 million to build a full-scale version.

Johannink says the company aims to build two Vortec 20 units, so named for the rotor diameter of 20 metres. They have strong interest in a site in South Australia and Johannink would like to see a Vortec 20 operating in New Zealand. What happens from here is purely a matter of commercial negotiation, he says.

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