Unconventional wind turbines
A second major unit type is the vertical-axis wind turbine (VAWT), with blades extending upwards, supported by a rotating framework.
The variety of designs reflects ongoing commercial, technological, and inventive interests in harvesting wind resources more efficiently and in greater volume.
Unconventional designs cover a wide gamut of innovations, including different rotor types, basic functionalities, supporting structures and form-factors.
This was the type used at Kaiser-Wilhelm-Koog, Germany, where a large experimental two-bladed unit—the GROWIAN, or Große Windkraftanlage (big wind turbine)—operated from 1983 to 1987.
Its main advantage is that it can operate in a wide range of winds and generate a higher power per unit of rotor area.
Another advantage is that the generator operates at a high rotation rate, so it doesn't require a bulky gearbox, allowing the mechanical portion to be smaller and lighter.
Power was multiplied several times using co-axial, multiple rotors in testing conducted by inventor and researcher Douglas Selsam in 2004.
The first commercially available co-axial multi-rotor turbine is the patented dual-rotor American Twin Superturbine from Selsam Innovations in California, with 2 propellers separated by 12 feet.
In 2015, Iowa State University aerospace engineers Hui Hu and Anupam Sharma were optimizing designs of multi-rotor systems, including a horizontal-axis co-axial dual-rotor model.
The spinning blade of a single rotor wind turbine causes a significant amount of tangential or rotational air flow.
[4] When the counter-rotating turbines are on the same side of the tower, the blades in front are angled forwards slightly so as to avoid hitting the rear ones.
Instead of airplane-inspired wing blades, the design takes after the Archimedean screw turbine, a helix-patterned pipe used in ancient Greece to pump water up from a deeper source.
[11] Wind turbines may be used in conjunction with a solar collector to extract energy from air heated by the sun and rising through a large vertical updraft tower.
The beam oscillates rapidly when exposed to airflow due to multiple fluid flow phenomena.
[20] Windbelt is a flexible, tensioned belt that vibrates from the passing flow of air, due to aeroelastic flutter.
Another concept uses a helium balloon with attached sails to generate pressure and drive rotation around a horizontal axis.
The turbine converts dynamic pressure or kinetic energy to mechanical rotation and thereby to electrical power using a generator.
Ridgeblade in the UK is a vertical wind turbine on its side mounted on the apex of a pitched roof.
Discovery Tower is an office building in Houston, Texas, that incorporates ten wind turbines.
The Museum of Science in Boston, Massachusetts began constructing a rooftop Wind Turbine Lab in 2009.
[38] The lab seeks to address the general lack of performance data for urban wind turbines.
An exception is the Bahrain World Trade Centre with three 225 kW wind turbines mounted between twin skyscrapers.
[41] The wind turbines themselves are generally of conventional design, while serving the unconventional roles of technology demonstration, public relations, and education.
