Alternative Types

From Wind wiki

Besides horizontal and vertical axis wind turbines, some unconventional designs have also been invented:

Airborne wind turbines

An airborne wind turbine is a design concept for a wind turbine that is supported in the air without a tower. A tether would be used to transmit energy to the ground, either mechanically or through electrical conductors. These systems would have the advantage of tapping an almost constant wind and doing so without a set of slip rings or yaw mechanism, without the expense of tower construction. The main disadvantage is that kites and 'helicopters' come down when there is insufficient wind. Also, bad weather such as lightning or thunderstorms, could temporarily suspend use of the machines, probably requiring them to be brought back down to the ground and covered. These schemes require a long power cable and, if the turbine is high enough, an aircraft exclusion zone.

Counter-rotating horizontal-axis turbines

Counter rotating turbines can be used to increase the rotation speed of the electrical generator. 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. If the turbine blades are on opposite sides of the tower, it is best that the blades at the back be smaller than the blades at the front and set to stall at a higher wind speed. This allows the generator to function at a wider wind speed range than a single-turbine generator for a given tower. To reduce sympathetic vibrations, the two turbines should turn at speeds with few common multiples, for example 7:3 speed ratio. Overall, this is a more complicated design than the single-turbine wind generator, but it taps more of the wind's energy at a wider range of wind speeds.