Vertical Wind Turbines
Vertical wind turbines are very similar to the horizontal wind turbines that you and I are accustomed to seeing. Both use the energy produced by the wind to power a generator and gearbox. But vertical wind turbines have their own set of pros and cons.
A vertical wind turbine uses a vertical rotor shaft with the blades around it in a vertical position as well (see picture above). This design has a few key features. It keeps you from having to install a yaw because the turbine doesn't need to be pointed into the wind. This design also allows the turbine to start generating power in wind speeds as low as 6 mph the turbines make less noise than horizontal wind turbines. The main drawback of the design is the excess stress put on the blades from wind loading changes. This makes the blades more likely to fail from fatigue.
Certain designs also use guy-wires to support the turbines. These guy-wires can be mounted lower or higher, but both have their own set of issues. Mounting the guy-wires lower on the turbines causes stress on the bottom bearing causing it to wear out sooner than it should. Mounting the guy-wires higher creates strong downward thrust in gust winds.
Vertical wind turbines are difficult to mount on towers (like you see with horizontal wind turbines) and for that reason are often mounted low to the ground. This has a whole set of advantages and disadvantages.
With the wind turbines low the the ground, the generator and gear are also very low to the ground and are easily maintained. The ability to mount vertical wind turbines close the the ground is great in areas where tall structures are prohibited and in areas where the structures and terrain increase wind velocity.
Mounting the turbines low to the ground increases the chance of problems and exposes the turbines to lower wind speeds. Ground surface drag and objects reduce wind speed and cause turbulence which put the turbines at risk of pulsating torque, vibration, noise, and excessive bearing wear.
An alternative to mounting the vertical wind turbines near the ground is mounting them on the roof of a building. Many buildings are designed to help air flow over the roofs and wind turbines can use this extra wind to generate more power.