Intermittency and Variability of Wind Power
Wind turbines intermittently generate electricity, meaning that they do not always generate it. Intermittency complicates the process of integrating wind farms into electricity grids, and it also makes it impossible to rely on the wind for most or all of electricity unless energy storage is used.
There is a cost associated with accounting for the intermittency of wind power, which increases the cost of wind power. This is one reason an economical energy storage system would be very helpful. [Source]
Wind speeds vary, and as wind speeds increase and decrease, the power output of wind farms increases and decreases as well. Wind turbines can be used to charge energy storage systems which would then supply the right amount of electricity, at the right time, and without intermittency or variability to the electricity grid.
Some examples of energy storage systems are: batteries, supercapacitors, compressed air energy storage (CAES), flywheel energy storage, and pumped hydroelectric storage.
Frequency Variation of the Current Generated
Wind turbines at large-scale wind farms are usually designed to generate alternating current (AC). They usually contain asynchronous induction generators, rather than permanent magnet generators. The frequency of the current generated does not fluctuate with wind speed (Source: Rick Gould – A Wind Turbine Technician Instructor).