A wind lens is a modification made to a wind turbine to make it a more efficient way to capture wind energy. The modification is a ring structure called a "brim" or "wind lens" which surrounds the blades, diverting air away from the exhaust outflow behind the blades. The turbulence created as a result of the new configuration creates a low pressure zone behind the turbine, causing greater wind to pass through the turbine, and this, in turn, increases blade rotation and energy output. In Japan, wind lenses are being researched by the Wind Engineering Section of Kyushu University.
Their website claims:
Wind power is proportional to the wind speed cubed. If we can increase the wind speed with some mechanism by utilizing the fluid dynamic nature around a structure, namely if we can capture and concentrate the wind energy locally, the output power of a wind turbine can be increased substantially. At wind energy section of Kyushu University, a new efficient wind power turbine system has been developed. This system has a diffuser shroud at the circumference of its rotor to embody the wind energy concentration. The diffuser shroud is now named "Wind lens". To apply the wind-lens structure to a larger size turbine, we have developed a compact collection-acceleration device. There are several ongoing projects in which the wind-lens turbines are involved.