As the source above suggests, given global wind speed average and frontal area of wind, then total Wind Power is easy to calculate.
At what lower scale is Wind no longer Wind? Is Brownian Motion Wind? Brownian molecular-scale velocities are quite high, but the path lengths are short. Lets suppose meter-scale (human-scale) turbulence to be our effective lower bound. We are considering only Planetary Wind inherently ordered to match our probable harvesting technology (from AWE at extreme-scale down to small personal devices), as Prigoginian Dissipative Systems. How much of that is there?
Here's a calculation, if someone would do the honor- Calculate the volume of the atmospheric Wind Field to 10km high, and the Wind Power in it as the cube of 10m/sec times a frontal area defined inside the Wind Field volume, like longitudinal vertical planes every 1m to 1000km, for a range of regeneration times. My head is starting to hurt. Calculating instantaneous Energy might be easiest, simply calculate Planetary Wind-Mass Kinetic-Energy at 10m/sec.
The issue of Wind Entropy is fascinating, but ontologically vague. If Information equals Thermodynamic Energy, under Shannon Equivalence, and Entropy encodes more Information than Order, then we are talking about Energy of Entropy. A Entropic System can settle into an Time-Symmetric Inverse Boltzmann Distribution, recovering Order. These are fine mind-boggling chestnuts, but the simple question here need not invoke Entropy too broadly.
What makes this Green Mathematics is applied (engineered) sustainability. Pure science ranges from opaque to transparent, but is not Green as such. We seek a mathematical peek at how the Holocene Extinction bottoms-out (cockroaches?), or if a New Golden Age is nigh. Bets, anyone?