Cape vulture provides inspiration for homegrown vertical-axis wind turbine

South African start-up has developed a vertical-axis wind-turbine that employs a groundbreaking morphing wing design, which seeks to mimic the movements of the Cape vulture.

A prototype of the turbine, developed by Brayfoil Technologies in collaboration with WorleyParsons, is currently being tested at the Council for Scientific and Industrial Research’s (CSIR’s) campus, in Pretoria.

The solution is the brainchild of architect and entrepreneur Robert Bray, who developed the flexible-wing concept after studying the flight of Cape Vultures and eagles during visits to the Marakele National Park, in Limpopo.

“Birds have the ability to change the shape of their wings. They are able to flare out and land on the spot, which aircraft wings can’t do. I focused on how the birds do it and then tried very hard to replicate the idea with a mechanical method,” Bray explains to Engineering News Online.

The result is a seamless wing that works without hinges, joints, panel sections or flaps.

Conscious that proving the wing design on an aircraft was out of his reach financially, Bray turned his attention to the design of a wing sail for a yacht, where he was able to prove the concept of a flexible wing.

The idea has since been patented in multiple jurisdictions internationally and Bray is convinced the applications could extended well beyond wind turbines and sails, to  the areas of aviation and automobiles.

Brayfoil will be embarking on an international road show in the coming months in a bid to attract industrial partners for the various applications and is optimistic that commercialisation may not be too far off, particularly in the yachting sector.

For the prototype wind turbine, the wings have been made from stiff, yet flexible, composite material, enabling the wing shell to change shape and create variable lift, using a simple internal mechanism. Mounted about an axis of rotation, the wings are also able to set their angle automatically and respond immediately to changes in wind direction.

The CSIR is conducting wind-tunnel testing on a turbine prototype comprising three wings attached to a rotating axis. WorleyParsons has provided the design support in the form of engineering drawings analysis and the turbine has been manufactured by Diesel Electric Services.

The initial results indicate that the design could potentially prove “disruptive” with regard to the efficiency of vertical axis wind turbines, which currently play only a minor role in a market dominated by horizontal-axis turbines.

Bray says the turbine, which is able to self-start, has a relatively small footprint and can operate at low wind speeds. He is, therefore, optimistic that it could find a niche as an urban embedded generation solution that competes with rooftop solar photovoltaic generators.

“Our simulations show that buildings have, around corners and over parapets, a 19% increase in wind speeds on average, not taking account of prevailing winds. That increase in velocity equates to a 59% increase in power – so if we take advantage of the building as a collector of wind, it could become a major source of embedded power within cities,” Bray enthuses.

Brayfoil Technologies director of strategy and operations Matthew Bray, Robert’s son, adds that the solution has none of the noise or animal mortality associated with large, high-speed turbines. In addition the turbine blades, or in this case the wings, are made from transparent materials, making the turbine far less visible.

WorleyParsons CEO Denver Dreyer reports that the company has been working closely with Brayfoil to optimise the design of the moving wing mechanism, as well as the external skin of the wing that requires flexion and morphing abilities.

Dreyer described the project as a “proudly South Africa moment”, which brought to the fore not only the calibre of South African inventors, but also its engineers, scientists and manufacturers.

“This has the potential to revolutionise the world of embedded generation forever.”