How much energy do wind turbines produce?

Every wind turbine has a range of wind speeds, typically around 30 to 55 mph, in which it will produce at its rated, or maximum, capacity. At slower wind speeds, the production falls off dramatically.
If the wind speed decreases by half, power production decreases by a factor of eight. On average, therefore, wind turbines do not generate near their capacity. Industry estimates project an annual output of 30-40%, but real-world experience shows that annual outputs of 15-30% of capacity are more typical.

Why only producing 30-40% Some turbines are turning more than that?

Wind turbines only generate electrical energy when they are, not shut down for maintenance, repair, or tours and the wind is between about 8 and 55 mph.

Below a wind speed of around 30 mph, however, the amount of energy generated is very small. Wind turbines produce at or above their average rate around 40% of the time. Conversely, they produce little or no power around 60% of the time.

Just because the blades are turning  85% of the time doesn’t mean it is producing any significant energy 85% of the time, that all depends on the wind, weather and temperature.

Information on Wind Turbine actual outputs: FAQ – Output.

Also see Wind Watch Wiki: EnergyCapacity factor