And what's the source of this magical, unending source of free and clean energy? The sun. The sun warms up our planet, but because of surface irregularities and its rotation, the Earth doesn't heat uniformly. These variances in temperature also cause irregularities in air pressure, and air molecules migrate from areas of high air pressure to areas of low air pressure. This results in wind, the intensity, duration and direction of which are influenced by a number of factors including weather, vegetation, surface water and topography [source: EIA].
All of these variables add to wind's unpredictability and contribute to the concern that it could never be consistent enough to meet all of our energy needs. Some of the most predictable winds occur offshore, which, of course, adds to construction costs.