The energy powered by a wind turbine depends on multiple factors : the size of the rotor (with the blades), his effectiveness, and the wind there is in the place where the wind turbine is.
The wind turbine manufacturer always gives a graphic called "power curve" with the product. This curve shows the output power of the wind turbine depending on the wind speed it receives. This is an often complex to interpret graph, then we will give you some information to understand.
The nominal power. It is always given for a nominal speed of wind. It is the most important number of a wind turbine, but be careful about traps ! The manufacturers don't give the power of their wind turbine for the same wind speed. It is like solar panels manufacturers give us the power for a panel under sunshine, another for a panel in the shadow and another for a panel in the space. It is absurd but it is what small wind turbines manufacturers do and the standard of 11m/s is not always use. To summarize, the best wind turbine is the one which produce the most with the least amount of wind.
The speed control. A wind turbine can limit the output current to avoid being damaged. This is especially for the mast resist and the electrical wires do not burn. Strong winds contain a lot of energy (power is multiplied by 125 between 3 m/s and 15m/s). Some wind turbines stop to work (cf. Air X) and some other produce a constant power.
A wind turbine operate something like 80% of the time in one day. This represent 7000h by year and 150 000h in the life of the wind turbine, this is huge. Most of the time, the wind is calm so there is a low production. The average wind speed is more appropriate to use, they are common and contain significant energy, it is typically winds 5 to 8 m/s. The winds of 9m/s and more, make large production, but are too irregular to be able to rely on them, especially in a off grid location. When there is a wind like that, the energy will be too much. We can still enjoy it for a washing machine or something else using a lot of energy.
The wind turbine performance is an important thing to consider but when we compare it with the wind speed. A performance gain of 15% with a high-tech and heavy wind power can be done with a wind 2.5% stronger (with a higher mast for example) or a blade 4% longer !
Here are some examples of use for differents wind turbine :