The DAWT technology is not, in itself, something new, having been developed by the then Grumman Aerospace in the 1970s as part of a US Department of Energy funded project. Eight years of wind tunnel testing puts the technology well beyond the experimental stage, says AWL. Grumman never developed it further because of problems in securing the right construction material and a redirection of research and development focus.
AWL was formed in 1994 to develop and manufacture DAWT machines, taking advantage of new key technologies which, it says, make the design commercially viable. Northrop Grumman Corporation has granted AWL exclusive worldwide rights for 40 years.
At the heart of the system is the diffuser, the shroud surrounding the turbine blade. According to the company, it "draws in wind flow from a greater stream tube area than a bare wind turbine thereby creating an area of low pressure behind the turbine blade." This increased air intake and blade lift leads to production of a far greater energy output for each wind speed compared to conventional designs.
The company adds that the DAWT produces electricity cheaper than any existing wind energy conversion system. Based on the wind speeds available at New Zealand wind farm sites, such as Baring Heads or Hau Nui, AWL says the DAWT will produce energy "well under" NZ$0.04/kWh; NZ$0.06-0.12 is the range other wind energy producers expect to achieve on the same sites. "We believe the DAWT has the capability to be a generator of electricity at lower rates than any other form of electricity generation and in the vicinity of 50% less than conventional wind power," says managing director Robin Johannink.
The company recognises that its claims are "rather radical" , but is confident that the demonstration machine will live up to its billing. To date the developers have been concentrating on technical aspects, but will be looking for international associations to "structure, fund and market" the technology. Other Grumman technology in the development is the "Max Tracker" system which "intelligently anticipates wind speed to produce the optimum electricity outputÉthrough acceleration and deceleration of the turbine shaft."
The main physical factor which delayed application of the new design was the lack of a sufficiently strong material for the diffuser and support structures. AWL has gained the use of high tensile ferro cement which, it says, has two to three times the flexural strength of steel, while being lighter and cheaper. This has made it "a key element in bringing the DAWT to commercial reality."