A wind turbine converts the mechanical energy of flowing air into a rotational motion of the turbine. The - mechanical - energy of the rotation can used to power a mechanical device or a power generator.
Standard designs of wind turbines
Older designs use a higher number of more or less flat blades made from wood, sails on a wood structure or metal sheets. These ancient designs were used to pump water or for the milling of corn.
Modern wind turbines use three propeller-like blades. They are a contribution to make electricity available to the grid. The rotational axis of the propeller is near horizontal. At hub heights of roughly 100 meters and propeller diameters up to 100 meters these modern wind turbines need adjustable blades. They compensate for the different wind speeds during a 360 turn of the propeller. Furthermore subsystems are needed to direct the propeller into the direction where the wind comes from.
Vertical wind turbines are less prominent but valuable for smaller power generation. They have some advantages like less noise generation. And there is no need to adjust the turbine because it can be operated independantly from the main wind direction.
Typical power output
The largest wind turbines to be operated on-shore have capabilities of ca. 3 MW (= Megawatt) nominal. Good locations for wind power have a 25 percent availability of that nominal value over one years seasonal cycles. This results in a yearly output of 750 Kilowatt times 8760 hours or 6 500 000 Kilowatt hours per year. Compare that to the typical power consumption (Germany, 1 person, complete electricity demand for household, industry goods, services, public service) of 6 500 kilowatt hours per year one wind turbine can deliver the power of 1000 people.
On the other end of the scale one can find smaller systems with a nominal power output of lets say 100 watts. These systems are interesting for camping, weekend houses and smaller emergency power systems.
PROs and CONs
The main PRO is, that wind turbines can use renewable energy souces - wind is driven by the sun - and hencefore the use these energy sources is not limited in time.
But there are also different drawbacks: Modern wind turbine systems are very large installations which impact the environment, at least in terms of visibility and noise. A relatively new tendency is to install wind turbines off shore - but there the first steps have been made and there is a need to lern how these systems behave under harsh mechanical and corrosive environments. In terms of "power generation availability" wind turbines rely to the availability of wind. Large area grids allow a better duty cycle because the time pattern of wind availability is smeared using a larger area: There is a good chance that wind is available always somewhere.